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Default rec.audio.car FREQUENTLY ASKED QUESTIONS (caution, this is HUGE)

This used to get published here every month (but I haven't seen it
published lately). Based on some of the questions we've been getting of
late, I thought it might help many people if I were to publish this. I
would STRONGLY ADVISE those new to car audio to make a print out or to save
this document as it can be a life-saver. Enjoy.
rec.audio.car Frequently Asked Questions
****************************************

$Revision: 4.55 $
August 2005

This is the FAQ list for the Usenet newsgroup rec.audio.car, maintained
by Ian D. Bjorhovde , with contributions from
many other people (see Section 8). The contents of this document are
based on the contributors' opinions; neither the contributors nor the
FAQ maintainer accept any responsibility or liability for any damages
brought about by the information contained herein.

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If you have suggestions for improvements to this document, or if you
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following each question.

This document is posted once per month to the Usenet newsgroups
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anonymous FTP from:

`ftp://rtfm.mit.edu/pub/usenet/rec.audio.car/FAQ/'

It is also available on the World Wide Web (WWW) and can be accessed
using the URL

`http://www.mobileaudio.com/rac-faq/'

If you do not have access to FTP or a WWW client (such as Mozilla or
Internet Explorer) and cannot find the FAQ on any of the aforementioned
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with the following three lines in the
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`send usenet/rec.audio.car/FAQ/part1'
`send usenet/rec.audio.car/FAQ/part2'
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Changes to this document are listed in the last section. *Note
Changes::.


Table of Contents
*****************

1 Definitions
1.1 What do all of those acronyms mean?
1.2 What is meant by "frequency response?"
1.3 What is a "soundstage?" What is an "image?"
1.4 What is meant by "anechoic?"
2 Electrical
2.1 My speakers make this high-pitched whine which matches the
engine's RPMs. What is it, and how can I get rid of it?
2.1.1 Level 1: Check out the Amplifier(s)
2.1.2 Level 2: Reduce the System
2.1.3 Level 3: Move the Head Unit
2.1.4 Level 4: Testing the Car
2.1.5 Level 5: Adding Signal Processors
2.1.6 Level 6: Processor Isolation Tests
2.2 My system "pops" when I turn it off. What is happening and
how can I get rid of it?
2.3 What is the best power wire to use?
2.4 What is the best speaker wire to use?
2.5 I heard that I should run my power wire directly to my car's
battery. Why should I bother, and how do I do it?
2.6 Should I do the same thing with my ground wire, then?
2.7 Sometimes when I step out of my car, I get a really bad
shock. What is wrong with my system?
2.8 When my car is running and I have the music turned up loud,
my headlights dim with the music. Do I need a new battery or
a new alternator?
2.9 2.9 What is a "stiffening capacitor", and how does it work?
2.9.1 Do I need a capacitor?
2.9.2 Can I just upgrade my headlight wiring instead?
2.9.3 Will the dimming go away if I upgrade the amplifier power/ground
wiring?
2.9.4 What do I look for when buying a capacitor?
2.9.5 How do I install a capacitor?
2.9.6 I have more than one amp in my audio system. Which one
should I have the capacitor run?
2.9.7 Will my bass response improve by adding a capacitor?
2.10 When should I upgrade my battery or add a second battery?
3 Components
3.1 What do all of those specifications on speakers mean?
3.2 Are component/separates any better than fullrange or coaxials?
3.3 What are some good (and bad) brands of speakers?
3.4 What do all of those specifications on amplifiers mean?
3.5 What does "bridging an amp" mean?
3.5.1 Why should I bridge my amp?
3.5.2 Why shouldn't I bridge my amp?
3.5.3 What happens when an amp is bridged?
3.5.4 Does bridging an amp would halve the impedance of the
speakers?
3.5.5 Can I bridge my 4 channel head unit?
3.6 What is "mixed-mono?" Can my amp do it?
3.7 What does "two ohm stable" mean? What is a "high-current"
amplifier?
3.8 Should I buy a two or four (or more) channel amplifier?
3.9 What are some good (and bad) brands of amplifiers?
3.10 What is a crossover? Why would I need one?
3.11 Should I get an active or a passive crossover?
3.12 Should I buy an equalizer?
3.13 What are some good (and bad) brands of equalizers?
3.14 What do all of those specifications on tape deck head units
mean?
3.15 What are features to look for in a tape deck?
3.16 What are some good (and bad) brands of tape decks?
3.17 What are features to look for in a CD head unit?
3.18 Should I buy a detachable faceplate or pullout CD player?
3.19 What are some good (and bad) brands of CD head units?
3.20 Can I use my portable CD player in my car? Won't it skip
a lot?
3.21 What's that weird motor noise I get with my portable CD
player?
3.22 What are some good (and bad) brands of portable CD players?
3.23 What's in store for car audio with respect to MD, DAT and
DCC?
3.24 Are those FM modulator CD changers any good? What are my
other options?
3.25 What kind of changer will work with my factory head unit?
3.26 What are some good (and bad) brands of CD changers?
3.27 Why do I need a center channel in my car, and how do I
do it?
3.28 Should I buy a sound field processor?
3.29 What are some good (and bad) brands of signal processors?
3.30 I keep hearing that speakers for Company X are made by
Company Y. What's the deal?
3.31 What is a Line Driver? Do I need one?
3.32 Can I play MP3 files in my car?
4 Subwoofers
4.1 What are "Thiele/Small parameters?"
4.2 How does speaker sensitivity affect real world SPL? Will
a higher sensitivity give me a larger SPL?
4.3 What are the enclosure types available?
4.4 Which enclosure type is right for me?
4.4.1 Infinite Baffle ("free-air")
4.4.2 Sealed Box
4.4.3 Ported Box
4.4.4 Bandpass Box
4.5 How do I build an enclosure?
4.6 MDF for Dummies
4.6.1 What is MDF?
4.6.2 Where can I get MDF?
4.6.3 What type of saw blade works best when cutting MDF?
4.6.4 What type of router bits work well with MDF?
4.7 What driver should I use?
4.8 Is there any computer software available to help me choose
an enclosure and a driver?
4.9 What is an "aperiodic membrane?"
4.10 Can I use my subs in the winter?
4.11 How can I carpet my enclosure?
4.12 Are large magnets always better than small magnets?
4.13 I know the box volume required for my subwoofer, but what
are the best dimensions for my enclosure?
5 Installation
5.1 Where should I buy the components I want?
5.2 What mail-order companies are out there?
5.3 What tools should I have in order to do a good installation?
5.4 Where should I mount my speakers?
5.5 What is "rear fill", and how do I effectively use it?
5.6 How do I set the gains on my amp?
5.7 How do I select proper crossover points and slopes?
5.8 How do I flatten my system's frequency response curve?
5.9 How do I wire speakers "in series" and "in parallel?"
5.10 Are there any alternatives for Dynamat? It's too expensive!
5.11 How many devices can I attach to my remote turn-on lead?
5.12 How do I wire a relay in my system?
5.13 How do I design my own passive crossovers?
5.14 How do I build my own passive crossovers?
5.15 Can I split the single pre-amp output from my head unit
to drive two amplifiers with a Y-cable?
5.16 How do I turn a stereo signal into a mono signal
5.17 How do I determine a speaker's polarity?
5.18 How can I use an oscilloscope to set the gains in my system?
5.19 Why are kickpanels such a popular location for mounting
speakers?
5.20 How can I build custom kickpanels?
5.21 What's worse for a speaker, too much or too little power?
5.22 Why is distortion harmful to my speakers?
5.23 What tools do I need to cut Plexiglas?
5.24 Are there any other special requirements for working with
Plexiglas?
6 Competition
6.1 What is IASCA, and how do I get involved?
6.2 What is USAC, and how do I get involved?
6.3 What are the competitions like?
6.4 Should I compete?
6.5 What class am I in?
6.6 Where can I find out when these Sound-Offs are?
6.7 How do I get sponsored by a manufacturer?
7 Literature
7.1 What magazines are good for car audio enthusiasts?
7.2 Are there any newsletters I can read?
7.3 What books can I read?
7.4 Can I contact any manufacturers on-line?
8 Credits
9 Changes


1 Definitions
********************

This section contains background information which defines some of the
acronyms and terminology commonly used in the car audio world.
Understanding these definitions is important in order to understand the
other sections of this document.


1.1 What do all of those acronyms mean? [JSC,MZ]
================================================== =====

`A' is for "amperes", which is a measurement of current equal to one
coulomb of charge per second. You usually speak of positive current -
current which flows from the more positive potential to the more
negative potential, with respect to some reference point (usually
ground, which is designated as zero potential). The electrons in a
circuit flow in the opposite direction as the current itself. Ampere
is commonly abbreviated as "amp", not to be confused with amplifiers, of
course, which are also commonly abbreviated "amp". In computation, the
abbreviation for amps is commonly "I".

`V' is for "volts", which is a measurement of electric potential.
Voltages don't "go" or "move", they simply exist as a measurement (like
saying that there is one mile between you and some other point).

`DC' is for "direct current", which is a type of circuit. In a DC
circuit, all of the current always flows in one direction, and so it is
important to understand which points are at a high potential and which
points are at a low potential. For example, cars are typically 12VDC
(twelve volts direct current) systems, and it is important to keep
track of which wires in a circuit are attached to the +12V (positive
twelve volts) lead of the battery, and which wires are attached to the
ground (or "negative") lead of the battery. In reality, car batteries
tend to have a potential difference of slightly higher than 12V, and
the charging system can produce upwards of 14.5V when the engine is
running.

`AC' is for "alternating current", which is a type of circuit in which
the voltage potential fluctuates so that current can flow in either
direction through the circuit. In an AC circuit, it is typically not
as important to keep track of which lead is which, which is why you can
plug household appliances into an outlet the "wrong way" and still have
a functioning device. The speaker portions of an audio system comprise
an AC circuit. In certain situations, it is indeed important to
understand which lead is "positive" and which lead is "negative"
(although these are just reference terms and not technically correct).
See below for examples. The voltage of an AC circuit is usually given
as the RMS (root mean square) voltage, which, for sinusoidal waves, is
simply the peak voltage divided by the square root of two.

`W' is for "watts", a measurement of electrical power. One watt is
equal to one volt times one amp, or one joule of energy per second. In
a DC circuit, the power is calculated as the voltage times the current
(P=V x I). In an AC circuit, the average power is calculated as the
RMS voltage times the RMS current (Prms=Vrms x Irms).

`Hz' is for "hertz", a measurement of frequency. One hertz is equal to
one inverse second (1/s); that is, one cycle per second, where a cycle
is the duration between similar portions of a wave (between two peaks,
for instance). Frequency can describe both electrical circuits and
sound waves, and sometimes both. For example, if an electrical signal
in a speaker circuit is going through one thousand cycles per second
(1000Hz, or 1kHz), the speaker will resonate at 1kHz, producing a 1kHz
sound wave. The standard range of human hearing is "twenty to twenty",
or 20Hz-20kHz, which is three decades (three tenfold changes in
frequency) or a little under ten octaves (ten twofold changes in
frequency).

`dB' is for "decibel", and is a measurement for power ratios. To
measure dB, you must always measure with respect to something else.
The formula for determining these ratios is P=10^(dB/10), which can be
rewritten as dB=10log(P). For example, to gain 3dB of output compared
to your current output, you must change your current power by a factor
of 10^(3/10) = 10^0.3 = 2.00 (that is, double your power). The other
way around, if you triple your power (say, from 20W to 60W) and want to
know the corresponding change in dB, it is dB=10log(60/20)=4.77 (that
is, an increase of 4.77dB). If you know your logarithms, you know that
a negative number simply inverts your answer, so that 3dB corresponding
to double power is the same as -3dB corresponding to half power. There
are several other dB formulas; for instance, the voltage measurement is
dB=20log(V). For example, a doubling of voltage produces 20log2 =
6.0dB more output, which makes sense since power is proportional to the
square of voltage, so a doubling in voltage produces a quadrupling in
power.

`SPL' is for "sound pressure level" and is similar to dB. SPL
measurements are also ratios, but are always measured relative to a
constant. This constant is 0dB which is defined as the smallest level
of sound pressure that the human ear can detect. 0dB is equal to
10^-12 (ten to the negative twelfth power) W/m^2 (watts per square
meter). As such, when a speaker is rated to produce 92dB at 1m when
given 1W (92dB/Wm), you know that they mean that it is 92dB louder than
10^-12W/m^2. You also know than if you double the power (from 1W to
2W), you add 3dB, so it will produce 95dB at 1m with 2W, 98dB at 1m with
4W, 101dB at 1m with 8W, etc.

`THD' is for "total harmonic distortion", and is a measure of the how
much a certain device may distort a signal. These figures are usually
given as percentages. It is believed that THD figures below
approximately 0.1% are inaudible. However, it should be realized that
distortion adds, so that if a head unit, equalizer, signal processor,
crossover, amplifier and speaker are all rated at "no greater than
0.1%THD", together, they could produce 0.6%THD, which could be
noticeable in the output.

An "Ohm" is a measure of resistance and impedance, which tells you how
much a device will resist the flow of current in a circuit. For
example, if the same signal at the same voltage is sent into two
speakers - one of which is nominally rated at 4 ohms of impedance, the
other at 8 ohms impedance - twice as much current will flow through the
4 ohm speaker as the 8 ohm speaker, which requires twice as much power,
since power is proportional to current.

`PSRR' is the "Power supply rejection ratio". This is a spec sometimes
provided with amplifiers, but is not exclusive to amplifiers. It
refers to the propensity for an AC signal present at the output of the
power supply to appear somewhere in the signal path. A poor PSRR often
leads to an increase in noise, distortion, and crosstalk.

`BJT' is short for "Bipolar junction transistor". It is a very common
type of transistor that is found in a multitude of circuits. Often
times, amplifier manufacturers will specify that a certain amplifier
utilizes a BJT output stage. This simply means that the major
current-carrying output devices (the output transistors) are of the BJT
variety rather than FET. Regardless of output device type, most
discrete amplifiers will incorporate many BJTs throughout the entire
amplifier.

Many people do not realize that `MOSFET' is an acronym, but it stands
for "Metal oxide semiconductor field-effect transistor". It is another
common type of transistor, but of the FET class. This type of
transistor operates in a different manner than BJTs. There's much
debate about which type of transistor is more suitable for car audio
amplifiers, but in the end it becomes a matter of personal preference
for the designer. It's important to note that neither design has an
inherent benefit in terms of sound quality. However, properly
constructed MOSFET output stages are sometimes more durable and immune
to damage produced by device failure or poor output protection
circuitry, whereas BJT output stages can sometimes be slightly more
efficient and cheaper. But both of these statements depend even moreso
on the circuit design and the transistor used.

`RMS' is the abbreviation for "root mean-square". It is usually
associated with power measurements, and refers to a calculation that
consists of the following procedu 1) square the waveform; 2) take
the mean of the result; 3) take the square root of this number. If the
waveform is a sine wave, the RMS value is .707 times the peak value.
If the waveform is a square wave, the RMS value is equal to the peak
value. Importantly, the RMS voltage of a signal multiplied by the RMS
current of a signal will yield the signal's average power. Sometimes,
average power is erroneously referred to by manufacturers and hobbyists
alike as "RMS power". "RMS power" would require calculating the root
mean-square value of a power waveform, which ends up yielding a
different result than average power, but it's become almost an industry
standard.

`DCR' is the "DC resistance" of a speaker driver (it is sometimes
referred to as `RE'). This number is typically lower than the nominal
impedance provided by the manufacturer. It specifies the resistive
component of the speaker's impedance characteristic at a given
temperature. Sometimes it's useful to estimate a speaker's impedance
by measuring its DCR value with a simple ohmmeter. Typical DCR values
for 4 ohm speakers are on the order of 3.2 to 3.5 ohms, and for 8 ohm
speakers, usually over 5.5 ohms.

`Q' is typically known as "quality factor", and tends to refer to the
rolloff behavior of a filter or group of filters. Values of Q are
intimately related to the breadth of bandpass rolloff (eg. in
equalizers), degree of overlap between filters, filter alignment, or
loudspeaker/enclosure interaction. In general, the higher the Q, the
narrower the passband, greater the overlap, or steeper the slope
(depending on what the Q is referring to).


1.2 What is meant by "frequency response?" [JSC]
================================================== =====

The frequency response of a device is the range of frequencies over
which that device can perform in some fashion. The action is specific
to the device in question. For example, the frequency response of the
human ear is around 20Hz-20kHz, which is the range of frequencies which
can be resolved by the eardrum. The frequency response of an amplifier
may be 50Hz-40kHz, and that of a certain speaker may be 120Hz-17kHz.
In the car audio world, frequency responses should usually be given
with a power ratio range as well, such as (in the case of the speaker)
120Hz-17kHz +/-3dB. What this means is that given an input signal
anywhere from 120Hz to 17kHz, the output signal is guaranteed to be
within an "envelope" that is 6dB tall. Typically the extreme ends of
the frequency range are the hardest to reproduce, so in this example,
the 120Hz and 17kHz points may be referred to as the "-3dB points" of
the amplifier. When no dB range is given with a frequency response
specification, it can sometimes be assumed to be +/-3dB.


1.3 What is a "soundstage?" What is an "image?" [CD]
================================================== =========

The "soundstage" is the position (front/back and high/low) that the
music appears to be coming from, as well as the depth of the stage. A
car with speakers only in the front will likely have a forward
soundstage, but may not have enough rear fill to make the music seem
live. A car with both front and rear speakers may have anything from a
forward to a rear soundstage, with an accompanying fill from the softer
drivers depending on the relative power levels and the frequencies
reproduced. The high/low position of the soundstage is generally only
obvious in a car with a forward soundstage. The music may seem to be
originating in the footwells, the dash, or out on the hood, depending
on how the drivers interact with the environment.

The "stereo image" is the width and definition of the soundstage.
Instruments should appear to be coming from their correct positions,
relative to the recording. The position of the instruments should be
solid and easily identifiable, not changing with varying frequencies.
A car can image perfectly with only a center-mounted mono speaker, but
the stereo placement of the music will be absent.


1.4 What is meant by "anechoic?" [JSC]
=============================================

"Anechoic" means not echoing. It usually refers to a style of
measuring a speaker's output which attempts to eliminate echoes (or
"reflections") of the speaker's output back to the measurement area,
which could alter the measurement (positively or negatively).


2 Electrical
*******************

This section describes various problems and concepts which are closely
related to electronics.


2.1 My speakers make this high-pitched whine which matches the
engine's RPMs. What is it, and how can I get rid of it? [IDB]
================================================== ===================

The answer to this section was generously provided by David Navone of
Autosound 2000. The material in these instructions was adapted from
the Autosound 2000 Troubleshooting Flow Chart by Ian Bjorhovde with the
permission of Autosound 2000. For more information about Autosound
2000, (see Section 7).

This is a set of instructions to debug a stereo installation if there
is any noise present after it is completed. Follow each step
carefully! If you have more than one amplifier, repeat level one for
each amp to be sure that none of them are responsible for the noise.


2.1.1 Level 1: Check out the Amplifier(s)
------------------------------------------------

After you have determined that there is noise in the system, determine
if the amplifier is causing the noise. To do this, mute the signal at
the inputs to the amp by using shorting plugs. If there is no noise,
then the amp is fine, and you can proceed to level 2. However, if
there is noise, then use a test speaker at the amp's output. If this
stops the noise, then the problem is originating in the speaker wiring,
or the passive crossovers. Check to make sure that none of these are
shorting with the body of the car, and start again at level 1. If
noise is still present when using the test speaker, then there may be a
problem with the power supply on the amp. Try connecting an isolated
power supply - if this does not get rid of the noise, then there is
something seriously wrong with the amp, and it should be replaced. If
the noise goes away, then there may be a problem with power supply
filtering or isolation. This can be fixed by changing the amp's ground
point or b adding external supply filtering.


2.1.2 Level 2: Reduce the System
---------------------------------------

The amps have been determined to be noise free. If you have any
processors between the head unit and the amps, disconnect them and
connect the head unit directly to the amp. If this gets rid of the
noise, then one (or more) of the processors must be at fault, so
proceed to level 5. Otherwise, try running the signal cables over a
number of different routes. If you are able to find one that does not
produce any noise, permanently route the cables in the same manner, and
proceed to level 5. If not, then you must isolate the head unit from
the car's chassis (except for its ground!) - don't forget to disconnect
the antenna, since it is also grounded to the car. If isolating
the head unit does not solve the problem, the move the grounding point
of the head unit. Hopefully the noise will be gone, and you can
install the head unit with a quiet ground and proceed to level 5,
otherwise go on to level 3.


2.1.3 Level 3: Move the Head Unit
----------------------------------------

The amplifiers are fine, but moving both the ground for the head unit
and the signal cables does not solve the noise problem. Take the unit
completely out of the dash, and put it on either the seat or carpet,
and run new signal cables to the input of the amp. If this solves the
problem, re-install the head unit, one step at a time and skip to level
5. But if the noise persists, then move the head unit as close to the
amp as possible and use the shortest possible signal cables. This will
verify that the original signal cables are not causing the problem -
assuming the noise is gone, reinstall the head unit one step at a time
and go to level 5. Otherwise, there may be a problem with the power
filtering for the head unit. As with the amps, power the head unit
with an isolated power supply (again making sure that the head unit
isn't touching the car's chassis at all). If the noise goes away, you
can add power supply filtering or an isolated power supply; go to
level 2. But if the isolated power supply does not solve the problem,
then you can either replace the head unit and go to level 2, or check
the car's electrical system in level 4.


2.1.4 Level 4: Testing the Car
-------------------------------------

There does not seem to be a problem with either the head unit or the
amplifier, and the car's charging system is suspect. To see if this is
the case, we can use a system in a car that is already known to be
"quiet." Bring both cars together as if you were going to jump one,
and use jumper cables to connect the two batteries. Start the engine
of the car with the noise problem, and listen to the "quiet" car's
system. If the noise does not go away, there is a SERIOUS problem with
your car's electrical system (possibly a bad alternator). Have a
qualified mechanic check the charging system out. If there is no noise
in the "quiet" car, then the "noisy" car's charging system is
definitely quiet, so continue with level 5.


2.1.5 Level 5: Adding Signal Processors
-----------------------------------------------

We have proven that the amplifiers are good, the head unit is good, and
the car's electrical system is good. Now we need to reconnect each
signal processor. Repeat this level for each signal processor used in
your system; if you have added all of your signal processors, and
there is no longer any noise, CONGRATULATIONS! You've removed the
noise from your system! Connect the signal processor. If there
isn't any noise, then go on to the next signal processor. Otherwise,
try re-routing the signal cables. If this cures the problem, the route
them permanently over the quiet path, and install the next processor.
If not, then isolate the processor from the car's chassis except for a
single grounding point. If this works, then permanently isolate the
processor, and move on to the next processor. If isolation does not
help, then advance to level 6.


2.1.6 Level 6: Processor Isolation Tests
------------------------------------------------

Now, noise enters the system when one particular processor is
installed, but regrounding it does not help. Move the processor very
close to the amp, and check for noise again. If there isn't any, then
re-install the processor, carefully routing the cables to ensure no
noise, and continue at level 5 with the next processor. Otherwise, use
an isolated power supply to power the processor, making sure that no
part of the processor is touching the car's chassis. If this solves
the problem, the consider permanently installing an isolated power
supply or possibly a 1:1 transformer, and go to level 5 with the next
processor. Otherwise, separate the processor and isolated power supply
from the car by many feet and re- test. If there is still noise, then
there is a serious problem with the processor's design. Get a
different processor, and continue at level 5 with it. If separating
the power supply and processor from the car does solve the noise
problem, then either the processor is damaged, or your tests were
inaccurate. Repeat level 5.


2.2 My system "pops" when I turn it off. What is happening and
how can I get rid of it? [JD]
================================================== ===================

This kind of problem is often caused by transients in the signal
processor as it powers down finding their way into the signal path,
which the amplifier then transmits to the speakers.

Usually this can be solved by adding a little turn-off delay to the
processor. This allows the processor to stay powered on for a short
time after the amplifiers have powered down, thus preventing the pop.

Many components sold today (such as crossovers, equalizers, etc) have
delays built-in. Read your manual to see if it is possible to set this
delay on your piece of equipment or be sure to look for this feature
during your next car audio purchase.

If your processor does not have this feature, you can build your own
delay circuit with a diode and a capacitor. Add a 1N4004 diode in
series with the processor's turn-on lead, striped side towards the EQ.
Then add a capacitor in parallel, the (+) side of the cap connects to
the striped (processor) side of the diode, the (-) side of the cap goes
to ground (not the radio or EQ chassis - connect to the car chassis).

Experimenting with the cap value will give you the right amount of delay
before the EQ shuts off. You don't want it too long, just long enough to
make sure the amp is off before the EQ powers down. 220 - 1000 uF is
about right, and make sure the cap is a polarized electrolytic, 16V or
higher. Also keep in mind that the diode will introduce a 0.7V drop on
the remote wire, which can cause the processor to power down before the
rest of the system.


2.3 What is the best power wire to use? [JSC]
================================================== ==

There is much debate over the benefit of certain wiring schemes
(oxygen-free, multistranded, braided, twisted, air core, you name it).
However, most people do agree that the most important factor in
selecting power wire is to use the proper size. Wire is generally
rated in size by American Wire Gauge, abbreviated AWG, or commonly just
"gauge". To determine the correct wire size for your application, you
should first determine the maximum current flow through the cable
(looking at the amplifier's fuse is a relatively simple and conservative
way to do this). Then determine the length of the cable that your will
use, and consult the following chart, taken from the IASCA handbook
(see Section 6.1),

Length of run (in feet)
Current 0-4 4-7 7-10 10-13 13-16 16-19 19-22 22-28

0-20A 14 12 12 10 10 8 8 8
20-35A 12 10 8 8 6 6 6 4
35-50A 10 8 8 6 6 4 4 4
50-65A 8 8 6 4 4 4 4 2
65-85A 6 6 4 4 2 2 2 0
85-105A 6 6 4 2 2 2 2 0
105-125A 4 4 4 2 2 0 0 0
125-150A 2 2 2 2 0 0 0 00

If aluminum wire is used instead of copper wire, the next larger size
(smaller number) should be used. You should also consider the
installation demands: will you need to run the wire around corners or
through doors or into the engine compartment? These sorts of problems
in the car audio application require some special care in cable
selection. You will want to have cable that is flexible; it should
have thick insulation as well, and not melt at low temperatures. You
don't want to install wire that is rigid and prone to cracks and cuts,
or else the results could literally be explosive.


2.4 What is the best speaker wire to use? [JSC, JW]
================================================== ========

Again, there is much debate over the benefit of the various schemes
that are being used by different manufacturers. In general, however,
you will probably want to upgrade your speaker wire from the factory
~20 gauge to something bigger when you upgrade your amplifiers and
speakers. In most cases, 16 or 18 gauge should be sufficient, with the
possible exception of high-power subwoofers. According to an example by
Jerry Williamson, using 18 gauge instead of 12 gauge would only result
in a power loss of 0.1dB, which is essentially undetectable by humans.
Thus, other factors play more important roles in the selection of
speaker wire. One issue is that different wires will have different
line capacitances, which could cause the wire to act as a low pass
filter. Generally, however, the capacitances involved are so small that
this is not a significant problem. Be sure to heed the warnings above
regarding cable flexibility and insulation, especially when running
wire into doors and other areas with an abundance of sharp metal.


2.5 I heard that I should run my power wire directly to my car's
battery. Why should I bother, and how do I do it? [JSC]
================================================== =====================

For some components, like head units and equalizers, it's acceptable to
use the stock wiring for power. However, amplifiers generally require
large amounts of power, and accordingly will draw large amounts of
current. The factory wiring in most cars is not designed to handle
large amounts of current, and most wires have 10-20A fuses on them.
Thus, you will almost always want to run the power line for your
amplifier directly to the positive terminal of the battery. This could
require drilling a hole through the car's firewall, or at least
spending time hunting for an existing hole (the steering column is a
good place to start looking). Always remember to place a fuse on your
wire as near to the battery as possible! For various reasons, such as
an accident or simple wear and tear, your wire's insulation may
eventually crack, which could allow the conducting wire to make contact
with the chassis of the car and short the battery through this wire,
which could lead to a serious fire. The closer you place a fuse to the
battery, the more protected you are. Also, when running wire through
areas with sharp metal corners, it is a good idea to use rubber
grommets to provide extra protection against tearing through your
wire's insulation.


2.6 Should I do the same thing with my ground wire, then? [JSC,
IDB]
================================================== =====================

No. In almost every case, the best thing to do is to ground your
amplifier to a point that is attached to the chassis of the car and is
as close to the amplifier as possible. The ground wire should not need
to be more than about eighteen inches long, and should be at least as
large as the power wire. The point to which you make your ground
connection should be an unpainted piece of bare metal.

Some cars (Audi, Porsche) have galvanized bodies, and in these cars,
you must find one of the manufacturers' grounding points or else some
noise can result.


2.7 Sometimes when I step out of my car, I get a really bad shock.
What is wrong with my system? [IDB]
================================================== =======================

Nothing. This is caused by static buildup by rubbing against the seats,
floor mats, etc., just like walking across a carpet in a home. You can
avoid this shock by touching something metal on your car _before_ you
put your foot on the ground.


2.8 When my car is running and I have the music turned up loud,
my headlights dim with the music. Do I need a new battery or
a new alternator? [CD, MO]
================================================== =======================

The headlights will dim because of a momentary drop in the voltage
level that is available to power the vehicle's accessories, including
the headlights, amplifiers, the engine, etc. This voltage drop can be
caused by a very large current demand by an accessory, such as an
amplifier trying to reproduce a loud bass note.

The first thing to do is to get your battery and alternator checked for
proper functioning. A failing battery can place undesirable loads on
the alternator, leaving less power for your system.

If the power system appears to be working correctly, an improved
alternator may be required for the large current demands of the audio
system. When upgrading an alternator, be careful in your purchase, for
there are some potential problems. An alternator which advertises a
certain output level may only achieve that output at very high engine
RPM ranges, for instance. Also, the new alternator must be adjusted to
provide an output voltage within a reasonable range in terms of the
voltage regulator.

If you find your car will not start after playing the stereo for long
periods of time with the engine off, and the present battery is in good
working order, then another, paralleled battery could prevent this
embarrassing problem.


2.9 What is a "stiffening capacitor", and how does it work? [JSC]
================================================== =======================

"Stiffening Capacitor" (note capitals) is a trademark of Autosound
2000. However, "stiffening capacitor" (note lowercase), as a generic
term, refers to a large capacitor (several thousand microfarads or
greater) placed in parallel with an amplifier. The purpose of doing so
is to provide a sort of reserve power source from which the amplifier
can rapidly draw power when it needs it (such as during a deep bass
note). The electrical theory is that when the amplifier attempts to
draw a large amount of current, not only will the battery be relatively
slow to respond, but the voltage at the amplifier will be a little lower
than the voltage at the battery itself (this is called "line drop"). A
capacitor at the amplifier which is charged to the battery voltage will
try to stabilize the voltage level at the amplifier, dumping current
into the amplifier. Another way to think about it is that a capacitor
in parallel with a load acts as a low pass filter (see Section 3.10),
and the voltage level dropping at the amplifier will appear as an AC
waveform superimposed upon a DC "wave". The capacitor, then, will try
to filter out this AC wave, leaving the pure DC which the amplifier
requires.

The following sections provide more detail about when and why to use a
stiffening capacitor.


2.9.1 Do I need a capacitor? [MZ]
-----------------------------------------

Before installation, it's often difficult to predict whether or not a
capacitor will be beneficial to you. It's generally best to install
the audio equipment prior to making the determination, so that you can
address which symptoms need to be remedied and assess the severity of
the symptoms. This will not only help you decide whether or not you
need a capacitor, but also how much capacitance would be beneficial.

The most common symptom in need of added capacitance is headlight
dimming (and sometimes dimming of the interior/dash lights). It's
caused by a drop in system voltage associated with excessive current
draw. While there may indeed be several loads drawing substantial
amounts of current from the electrical system (eg. heat, AC, and so
forth), it's usually the transient draws that best manifest themselves
in noticeable dimming. This is partly because our visual systems are
most sensitive to detecting rapidly changing intensity levels rather
than steady absolute differences.

Once you've assessed whether or not the dimming is noticeable (and
sufficiently annoying), you must decide whether a capacitor is
warranted or if you'd be better served by upgrading the alternator.
After initially having your alternator and battery checked out (some
places will do this for free), the choice should be based on the
severity of the dimming.

A commonly-used estimate for determining the appropriate size capacitor
is 1F/kW (one farad per kilowatt). For example, a system running at
300W would need a 0.3F (or 300,000uF) capacitor. However, there are
several variables at play here, including the capabilities of the
vehicle's electrical system (which generally varies from idle to higher
RPMs), the efficiency of the amplifiers, and the listening habits of
the user (ie. the tone controls and the type of music). These factors
should all be considered when making the determination. Moreover, the
voltage drop can be so severe that added capacitance is nothing more
than a band-aid. That is, even several Farads of capacitance would not
be able to sustain the voltage for as long as the drop persists. This
is when an alternator upgrade may be in order.


2.9.2 Can I just upgrade my headlight wiring instead? [MZ]
------------------------------------------------------------------

Although headlight wiring upgrades can often be beneficial for
achieving a higher steady-state illumination, it will not improve the
dimming situation. Since the headlights are not the cause of the
voltage fluctuations that are producing the dimming, upgrading the
wiring will not fix the problem. The voltage fluctuation is present at
the battery terminals, so it will be transmitted to the headlights
regardless of how the headlights are wired. If you think of the
fluctuation as an AC signal, then it becomes readily apparent that this
circuit can be represented by an AC signal in a voltage divider.
Decreasing the resistance in series with the load by upgrading the
headlight wiring actually serves to slightly enhance the AC signal at
the headlight's terminals. In other words, the dimming effect could
become even worse by upgrading the headlight wiring!


2.9.3 Will the dimming go away if I upgrade the amplifier power/ground
wiring? [MZ]
-----------------------------------------------------------------------------

A common myth in the car audio community is that upgrading the power or
ground wire to the amplifier will result in the amplifier drawing less
current and therefore decreasing the voltage fluctuation. While the
logic is sound, the premise is not. Most amplifiers on the market have
semi-regulated supplies which don't maintain a steady power output at a
range of supply voltages. This is reflected in the power ratings
provided by many manufacturers; some provide ratings for their
amplifiers at two different voltages, and the lower voltage almost
always causes the amp to deliver less power. In general, the
difference in power output tends to correspond well with the supply
voltage such that the current draw remains roughly constant (assuming
somewhat similar efficiency). Consequently, upgrading the power/ground
wiring, which serves to increase the voltage at the amplifier's
terminals, will not reduce headlight dimming.


2.9.4 What do I look for when buying a capacitor? [MZ]
--------------------------------------------------------------

The single most important attribute is the capacitance value (expressed
in Farads). Put simply, more is better. Another important
consideration is to make sure the maximum voltage rating of the
capacitor safely exceeds the operating voltage of your vehicle's
electrical system. In addition, ESR and ESL values may be provided
with some capacitors to essentially indicate the amount of voltage drop
that occurs when a capacitor is delivering current. Smaller values are
better in this regard.


2.9.5 How do I install a capacitor? [MZ]
------------------------------------------------

If you conclude that your best course of action is to install a
capacitor, it should be installed in parallel with the amplifier and,
generally speaking, should be wired with approximately the same gauge
wire used for a single amplifier (usually 8 ga. is sufficient even for
rather large capacitors).

Before permanently installing it, it must be charged. Failure to do so
could lead to blown fuses and lots of sparks! Some capacitors come
with charging resistors. If yours does not, you can simply buy an
automotive bulb and wire it in series with the capacitor's + lead while
the capacitor is grounded. The bulb will continue to dim until the
capacitor is fully charged. Once the capacitor is charged, it should
be treated as you would a car battery; caution must be used to be sure
not to short the terminals.

The final step is to permanently install it into the car. There's been
much debate about where to install the capacitor. It's been argued
that the placement is important because it requires shorter wire
lengths. While this is true, there has never been any evidence
supporting the notion that it should be installed as close
(electrically) to the amplifier as possible. In fact, electrical
theory demonstrates that it's more effective at quenching the dimming
effects by installing it as close to the device exhibiting the symptom
(ie. the headlights) rather than the device that's drawing the bulk of
the current (ie. the amplifiers). However, the benefit to doing so is
negligible. Therefore, hooking it directly to the battery, the
amplifier terminals, or the distribution block are equally valid
solutions as long as the mounting location is safe, the wire lengths
are reasonably short, and there's an adequate ground present.


2.9.6 I have more than one amp in my audio system. Which one
should I have the capacitor run? [MZ]
-------------------------------------------------------------------

The amplifiers are all connected in one way or another to the battery.
In fact, unless you're running separate power wires to each amplifier
all the way from the battery, they're usually connected at a more
proximal site (a distribution block, for example). The effects of the
capacitor are felt by the entire electrical system, including the
amplifiers. Therefore, you cannot selectively dedicate a capacitor to
a specific amplifier.


2.9.7 Will my bass response improve by adding a capacitor? [MZ]
----------------------------------------------------------------------

A capacitor serves to smooth the voltage fluctuations associated with
transient current draw. As a result, the supply voltage presented to
the amp during peak demands tends to be slightly higher than without
the capacitor. For most amplifiers, this will increase the power
output of the amplifier during transients. The degree to which it
increases, however, typically leads to an inaudible improvement.

To illustrate, if you consider an amplifier that delivers 100 watts at
14v and 80 watts at 12v (these numbers are somewhat typical), the
difference in output from the speaker will be at best 1 dB when the
supply voltage fluctuates from 14v to 12v. However, when you take into
account the fact that no practical amount of capacitance can completely
eliminate this voltage drop during transients, the difference in output
becomes even less pronounced. Further, if you take into account other
factors such as loudspeaker power compression (discussed elsewhere in
the FAQ), the equivalent series impedance of the capacitor, the length
of the transient, and the human's decreased ability to perceive
differences in intensity for shorter intervals, this difference in
output becomes negligible.


2.10 When should I upgrade my battery or add a second battery? [IDB]
================================================== ====================

The battery is most important when the engine is turned off, because it
supplies all of power to the audio system. The stock battery in your
car may not be up to the task of running a stereo with multiple (or
large) amplifiers if it can't supply enough current to the amplifiers.
Upgrading your current battery to a larger model may help solve the
problem because batteries like the Optima 800 offer a larger number of
cold cranking amps.

Generally, adding a second battery is great if you want to listen to
your stereo with the car turned off (and be able to start the car again
later!). This is accomplished using a dual-battery isolator: a device
which allows the second battery to be charged by the alternator, but
prevents the amplifiers that are connected to the second battery from
drawing any power from the main battery. Installing a second battery
may be done instead of upgrading the main battery.


--
ian d bjorhovde -
internet mobile audio -
http://mobileaudio.com 3
Components
*******************

This section describes various components that you can have in a car
audio system, along with common specifications, desirable features,
some of the best and worst brands, and so on.

Be aware that there is no standardized testing mechanism in place for
rating car audio products. As such, manufacturers are open to
exaggerating, "fudging", or just plain lying when it comes to rating
their own products.


3.1 What do all of those specifications on speakers mean? [JSC,
CD]
================================================== ====================

"Input sensitivity" is the SPL the driver will produce given one watt
of power as measured from one meter away given some input frequency
(usually 1kHz unless otherwise noted on the speaker). Typical
sensitivities for car audio speakers are around 90dB/Wm. Some
subwoofers and piezo horns claim over 100dB/Wm. However, some
manufacturers do not use true 1W tests, especially on low impedance
subwoofers. Rather, they use a constant voltage test which produces
more impressive sensitivity ratings.

"Frequency response" in a speaker refers to the range of frequencies
which the speaker can reproduce within a certain power range, usually
+/-3dB.

"Impedance" is the impedance of the driver (see Section 1.1), typically
4 ohms, although some subwoofers are 8 ohms, some stock Delco speakers
are 10 ohms, and some stock Japanese imports are 6 ohms.

"Nominal power handling" is the continuous power handling of the
driver. This figure tells you how much power you can put into the
driver for very long periods of time without having to worry about
breaking the suspension, overheating the voice coil, or other nasty
things.

"Peak power handling" is the maximum power handling of the driver.
This figure tells you how much power you can put into the driver for
very brief periods of time without having to worry about destroying it.


3.2 Are component/separates any better than fullrange or coaxials?
[JSC, DK]
================================================== =======================

Usually, yes. Using separates allows you to position the drivers
independently and more carefully, which will give you greater control
over your imaging. For best results, try to keep the mid and tweeter
as close together as possible - this will make the two drivers act more
like a single point source (which is ideal).

For rear fill applications, however, coaxial speakers will perform
fine, as imaging is not a primary concern. However, it is very common
to use a low pass crossover with the rear speakers (at 2500 Hz) since
rear-fill is intended to produce "ambiance," and high frequencies (
2500 Hz) can confuse the soundstage, making it appear that music is
originating behind you.


3.3 What are some good (and bad) brands of speakers? [JSC]
================================================== ===============

People will emotionally defend their particular brand of speakers, so
asking what the "best" is is not a good idea. Besides, the best
speaker is the one which suits the application the best. In general,
however, various people have claimed excellent experiences with such
brands as Boston Acoustics, MB Quart, a/d/s/, and Polk. Also, most
people agree that you should avoid brands like Sparkomatic and Kraco at
all costs.


3.4 What do all of those specifications on amplifiers mean? [JSC,
BG]
================================================== ======================

"Frequency response" refers to the range of frequencies which the
amplifier can reproduce within a certain power range, usually +/-3dB.

"Continuous power output" is the power output of the amplifier into one
channel into a certain load (usually four ohms) below a certain
distortion level (usually at most 1%THD) at a certain frequency
(usually 1kHz). A complete power specification should include all of
this information, e.g. "20W/ch into 4 ohms at 0.03%THD at 1kHz"
although this can also be stated as (and be assumed equivalent to)
"20W/ch at 0.03%THD". The amplifier should also be able to sustain
this power level for long periods of time without difficulties such as
overheating.

"Peak power output" is the power output of the amplifier into one
channel into a certain load (usually four ohms) below a certain
distortion level (usually much higher than the continuous rating level)
at a certain frequency (usually 1kHz). A complete power specification
should include all of this information, e.g. "35W/ch into 4 ohms at
10.0%THD at 1kHz" although this can also be stated as (and be assumed
equivalent to) "35Wch at 10.0%THD". Consumer warning: some
manufacturers will state the "peak power output" rating by including
the amount of power which can be drawn from "headroom", which means
power supply capacitors. They usually will not tell you this in the
specification, however; indeed, they tend to prominently display the
figure in big, bold letters on the front of the box, such as "MAXIMUM
200W PER CHANNEL!!!" when the continuous rating is 15W/ch and the unit
has a 5A fuse.

"Damping factor" represents the ratio of the load being driven (that
is, the speaker - usually four ohms) to the output impedance of the
amplifier (that is, the output impedance of the transistors which drive
the speakers). The lower the output impedance, the higher the damping
factor. Higher damping factors indicate a greater ability to help
control the motion of the cone of the speaker which is being driven.
When this motion is tightly controlled, a greater transient response is
evident in the system, which most people refer to as a "tight" or
"crisp" sound. Damping factors above 100 are generally regarded as
good.

"Signal to Noise" or "S/N" is the ratio, usually expressed in decibels,
of the amount of true amplified output of the amplifier to the amount
of extraneous noise injected into the signal. S/N ratios above 90 to
95dB are generally regarded as good.


3.5 What does "bridging an amp" mean? [MHa]
==================================================

"Bridging" refers to taking two channels of an amplifier and combining
them to turn the amplifier into a one channel amplifier.


3.5.1 Why should I bridge my amp?
----------------------------------------

For increased power. If your amp can handle the load, it will put out
more power through a bridged channel than it would into through a
non-bridged channel. Theoretically, a "perfect" amplifier that puts
out X watts into Y impedance into each of two channels will put out 4X
watts into Y impedance into one bridged channel. Be aware that some
amps more closely approximate that perfect amp than others, and some
manufacturers build current limiters into their amps to allow them to
remain stable into difficult loads at the expense of power gains.


3.5.2 Why shouldn't I bridge my amp?
-------------------------------------------

There are several reasons: you might need those extra channels; your
amp might not be stable into the load your speakers present if the amp
is bridged; you might be a hyper-perfectionist that can't stand the
thought of an small increase in distortion; or perhaps you just don't
need more power. Car audio power is relatively cheap, and if you are
not trying to make a mega-gonzo system, you may not need to double your
power.


3.5.3 What happens when an amp is bridged?
-------------------------------------------------

Basically, one channel's signal is inverted, and then the two channels
are combined to form one channel with twice the voltage of either of
the original channels.

Ohm's Law for Alternating Current states that I = V/Z where I is
current, V is voltage, and Z is impedance. We also know that P = IV,
where P is power. If we use Ohm's Law and substitute into the power
equation, we get P = V(V/Z), which can be rewritten as P = (V^2)/Z.
Therefore, power is the square of voltage divided by impedance.

Now, why do we care about all that? Because it explains precisely what
happens when an amp is bridged. I'll give a practical example and
explain the theoretical basis of that example.

Imagine you have a two-channel amp that puts out 50 watts into each
channel when driven into a load of 4 ohms per channel. Since we know P
and Z, we can plug these numbers back into our power equation and find
V. 50 = V^2/4 - V = sqrt(200). So, we're seeing a voltage of 14.1
volts across each channel.

Now, imagine we bridge this amp, and use it to push just one of those 4
ohms loads. When the amp is bridged, the voltage is doubled. Since we
know the voltage (2*14.1 volts), and the impedance (4 ohms), we can
calculate power. Remember that P = V*V/Z. That means P = (28.2)^2/4,
which is 198.1 watts. It should be clear by now that the new power is
approximately 200 watts - quadruple the power of a single, unbridged
channel!

You can probably see that should be the case, especially if you look
back at the power equation. Since P = V*V/Z, if you double V, you
quadruple power, since V is squared in the power equation.

Now, all this assumes the amp is stable into 4 ohms mono. The mono
channel is putting out four times as much power as a single unbridged
channel, so it must be putting out twice as much as the two single
channels combined. Since the voltage on the supply side of the amp is
dependent on the car's electrical system, it doesn't change (OK, the
increased current might cause a voltage *drop*, but let's not worry
about that now). Looking at the first power equation, at the supply
side of the amp, we see P = IV. Now, when we bridged the amp, we
doubled the power, but the input voltage stayed the same. So, if we
hold V constant, the only way to double the power is to double the
current.

That means the amp is now drawing twice as much current when it's
running at a given impedance mono than it would be running two stereo
channels at the same impedance. There are only two ways the amp can do
that - it can simply draw more through it's circuits, and dissipate the
extra heat, or it can utilize a current limiter, to prevent the
increase in current. Of course, using the current limiter means you
don't get the power gains, either! So, if the amp can't handle the
extra current, and it doesn't limit the current in some way, kiss it
goodbye. For that reason, an amp is typically considered mono stable
into twice the impedance it is considered stereo stable.


3.5.4 Does bridging an amp would halve the impedance of the speakers?
----------------------------------------------------------------------------

Impedance is a characteristic of the speakers. The speakers don't give
a flip how the amp is configured: they have a given impedance curve,
and that's that. It should be clear that when you bridge an amp, you
are changing *the amp*. The speaker's impedance is *not* a function of
the amp, but the amp's tolerance to a given impedance depends
completely on the way the amp is configured. If you'll remember from
section 4, an amp bridged into a given impedance draws twice as much
current as it would if it were driving two separate channels, each at
that impedance. So, a four ohm speaker stays a four ohm speaker, if
it's hooked to one channel, a bridged channel, a toaster, or the wall
socket. But, it is more stressful for the amp to drive any impedance
bridged than unbridged.

So, why do people talk about the impedance halving? Well, it's a
simple model that isn't correct but is easy to explain to people who
don't know what's really going on. It goes like this: When you bridge
the amp, each channel is "seeing" half the load presented to the amp.
So, if you bridge an amp to 4 ohms, each channel "sees" 2 ohms.
Therefore, each channel puts out twice as much power, and the combined
output is quadruple a single channel at 4 ohms.

Why is that still wrong? Because each channel isn't really used as a
single channel. You've used part of one channel, and an inverted part
of another channel to create a totally new channel, the bridged
channel. Also, there's no way for a channel to "see" only part of a
circuit. If it's "seeing" half the speaker, it's "seeing" it all.

Second, it makes it awkward if people believe that the impedance is
really, literally, changing. If you use that model, is it safe to run
a 4 ohm mono stable amp into a 4 ohm speaker? It should be, but we
just said the impedance halves, so that's now a 2 ohm speaker, and you
can't use it. That's wrong, and confusing, and it makes people think
they can't do things they really can.


3.5.5 3.5.5 Can I bridge my 4 channel head unit?
-------------------------------------------------

Generally, NO. Unless the manuals that came with your head unit
specifically state that your head unit can be bridged, then do NOT
attempt it - this could destroy the head unit's internal amplifier, and
possibly void your warranty.


3.6 What is "mixed-mono?" Can my amp do it? [JSC, IDB]
================================================== ===========

Some amplifiers which are both bridgeable and able to drive low
impedance loads also allow you to use "mixed-mono" mode. This involves
driving a pair of speakers in stereo mode as well as simultaneously
driving a single speaker in bridged mono mode off of ONE pair of the
amp's channels.

To do this, you connect the mono speaker (typically a subwoofer) to the
amp as you normally would in bridged mode, and then connect the left
and right stereo speakers to the left and right stereo channels,
respectively.

However, for this to work, the amplifier must actually use both input
channels in bridged mode. Many amplifiers, when placed in bridged
mode, will simply "copy" and invert either the left or the right
channel. This practice ensures high output to the mono speaker, but
eliminates the possibility of mixed mono since you lose one channel.

It is VERY important to use passive crossovers when configuring your
amplifier in mixed-mono mode in order to keep from overloading the amp.
The reason almost all new amplifiers are able to run in mixed-mono
mode (even if they are only 2-ohm stable) is that the impedance seen by
each channel of the amplifier is the same across the entire frequency
spectrum when using passive crossovers. Here's how it works: Take a
typical 2-channel amplifier that is stable to 2 ohms (stereo) or 4 ohms
(mono). When the subwoofer is connected with a low-pass crossover (at
100Hz, for example) then the amplifier "sees" a 2 ohm load on each of
its channels (see 3.5) from 100Hz and down. When the full range
speakers are connected with a high-pass crossover (at 125Hz, for
example), the amplifier "sees" a 4 ohm load on each of its channels from
125Hz and up. The passive crossovers prevent the amplifier from seeing
more than one speaker on either channel at any given frequency. Of
course, between the two crossover points the amp DOES see more than one
speaker (and therefore the load on the amp dips to 1.33 ohms when using
4 ohms speakers).

A graph of impedance vs frequency for ONE channel of an amplifier would
look similar to this when using 3 4-ohm speakers and crossover points
at 100Hz(LP) and 200Hz (HP):

+-----------------------------------------------------------+
| ****************************************| 4
| * |
| * |
|************* * | 2
| * * |
| * |
| | 1
| |
| |
+^-----^-----^-----^-----^-----^-----^-----^-----^-----^---^+ 0
25 50 100 200 400 800 1.6K 3.15K 6.3K 12.5K 20K


3.7 What does "two ohm stable" mean? What is a "high-current"
amplifier? [JSC]
================================================== ==================

An X-ohm stable amplifier is an amp which is able to continuously power
loads of X ohms per channel without encountering difficulties such as
overheating. Almost all car amplifiers are at least four ohm stable.
Some are two ohm stable, which means that you could run a pair of four
ohm speakers in parallel on each channel of the amplifier, and each
channel of the amp would "see" two ohms. Some amps are referred to as
"high-current", which is a buzzword which indicates that the amp is
able to deliver very large (relatively) amounts of current, which
usually means that it is stable at very low load impedances, such as
1/4 or 1/2 of an ohm. Note that the minimum load rating (such as "two
ohm stable") is a stereo (per channel) rating. In bridged mode, the
total stability is the sum of the individual channels' stability *Note
Bridging::.


3.8 Should I buy a two or four (or more) channel amplifier? [JSC]
================================================== ======================

If you only have one line-level set of outputs available, and wish to
power two sets of speakers from a single amplifier, you may be able to
save money by purchasing a two channel amplifier which is stable to two
ohms rather than spending the extra money for a four channel amp. If
you do this, however, you will be unable to fade between the two sets
of speakers (without additional hardware), and the damping factor of the
amplifier will effectively be cut in half. Also, the amp may run hot
and require fans to prevent overheating. If you have the money, a four
channel amp would be a better choice. You would need to add a dual-amp
balancer in order to maintain fader capability, however, but it is more
efficient than building a fader for a two channel amp. If you wish to
power a subwoofer or additional speakers as well, you may want to
purchase a five or six channel amp.


3.9 What are some good (and bad) brands of amplifiers? [JSC, IDB]
================================================== ======================

As with speakers, people emotionally defend their amplifier, so
choosing the best is difficult. However, some brands stand out as
being consistently good while others are consistently bad. Among the
good are HiFonics, Phoenix Gold, a/d/s/, and Precision Power.

Generally, "good" amplifiers tend to cost more (in money/watt) than
"bad" amplifiers. So when you see an amp advertising 300W for only
$100, and are comparing an amp with 50W for $300, you will usually find
that the 50W/$300 amp will be of much higher quality than the 300W/$100
amp.


3.10 What is a crossover? Why would I need one? [JSC]
================================================== ==========

A crossover is a device which filters signals based on frequency. A
"high pass" crossover is a filter which allows frequencies above a
certain point to pass unfiltered; those below that same point still get
through, but are attenuated according to the crossover slope. A "low
pass" crossover is just the opposite: the lows pass through, but the
highs are attenuated. A "band pass" crossover is a filter that allows a
certain range of frequencies to pass through while attenuating those
above and below that range.

There are passive crossovers, which are collections of purely passive
(non-powered) devices - mainly capacitors and inductors and sometimes
resistors. There are also active crossovers which are powered
electrical devices. Passive crossovers are typically placed between
the amplifier and the speakers, while active crossovers are typically
placed between the head unit and the amplifier. There are a few
passive crossovers on the market which are intended for pre-amp use
(between the head unit and the amplifier), but the cutoff frequencies
(also known as the "crossover point", defined below) of these devices
are not typically well-defined since they depend on the input impedance
of the amplifier, which varies from amplifier to amplifier.

There are many reasons for using crossovers. One is to filter out deep
bass from relatively small drivers. Another is to split the signal in
a multi-driver speaker so that the woofer gets the bass, the midrange
gets the mids, and the tweeter gets the highs.

Crossovers are categorized by their order and their crossover point.
The "order" of the crossover indicates how steep the attenuation slope
is. A first order crossover "rolls off" the signal at -6dB/octave
(that is, quarter power per doubling or halving in frequency). A
second order crossover has a slope of -12dB/octave; third order is
-18dB/octave; etc. The "crossover point" is generally the frequency at
which the -3dB point of the attenuation slope occurs. Thus, a first
order high pass crossover at 200Hz is -3dB down at 200Hz, -9dB down at
100Hz, -15dB down at 50Hz, etc.

It should be noted that the slope (rolloff) of a crossover, as defined
above, is only an approximation. This issue will be clarified in
future revisions of this document.

The expected impedance of a passive crossover is important as well. A
crossover which is designed as -6dB/octave at 200Hz high pass with a 4
ohm driver will not have the same crossover frequency with a driver
which is not 4 ohms. With crossovers of order higher than one, using
the wrong impedance driver will wreak havoc with the frequency
response. Don't do it.


3.11 Should I get an active or a passive crossover? [JSC, JR]
================================================== ==================

Active crossovers are more efficient than passive crossovers. A
typical "insertion loss" (power loss due to use) of a passive crossover
is around 0.5dB. Active crossovers have much lower insertion losses,
if they have any loss at all, since the losses can effectively be
negated by adjusting the amplifier gain. Also, with some active
crossovers, you can continuously vary not only the crossover point, but
also the slope. Thus, if you wanted to, with some active crossovers
you could create a high pass filter at 112.3Hz at -18dB/octave, or
other such things.

However, active crossovers have their disadvantages as well. An active
crossover may very well cost more than an equivalent number of passive
crossovers. Also, since the active crossover has separate outputs for
each frequency band that you desire, you will need to have separate
amplifiers for each frequency range. Furthermore, since an active
crossover is by definition a powered device, the use of one will raise
a system's noise floor, while passive crossovers do not insert any
additional noise into a system.

Many people find it advantageous to use both active and passive
crossovers. Often, a separate amp is dedicated to the subwoofers, to
give them as much power as possible. The other amplifier is used to
power the mids and tweeters. In this scheme, an active crossover is
used to send only the sub-bass frequencies to the sub amp, and the
other frequencies to the other amp. The passive crossovers are used to
send the correct frequencies to the individual speakers (e.g., mids and
tweeters).

Thus, if you have extra money to spend on an active crossover and
separate amplifiers, and are willing to deal with the slightly more
complex installation and possible noise problems, an active crossover
is probably the way to go. However, if you are on a budget and can
find a passive crossover with the characteristics you desire, go with a
passive.


3.12 Should I buy an equalizer? [JSC]
============================================

Equalizers are normally used to fine-tune a system, and should be
treated as such. Equalizers should not be purchased to boost one band
12dB and to cut another band 12dB and so on - excessive equalization is
indicative of more serious system problems that should not simply be
masked with an EQ. However, if you need to do some minor tweaking, an
EQ can be a valuable tool. Additionally, some EQs have spectrum
analyzers built in, which makes for some extra flash in a system.
There are two main kinds of EQs available today: dash and trunk. Dash
EQs are designed to be installed in the passenger compartment of a car,
near the head unit. They typically have the adjustments for anywhere
from five to eleven (sometimes more) bands on the front panel. Trunk
EQs are designed to be adjusted once and then stashed away. These
types of EQs usually have many bands (sometimes as many as thirty).
Both types sometimes also have crossovers built in.


3.13 What are some good (and bad) brands of equalizers? [HK]
================================================== =================

Generally, companies that produce 1/3 octave (30 band) and 2/3 octave
(15 band) equalizers are good. These include AudioControl, USD, Rane,
Phoenix Gold. Most people try to stay away from equalizers that
contain a "booster;" these are made by Kraco, Urban Audio Works and
others.


3.14 What do all of those specifications on tape deck head units
mean?
================================================== =====================


3.15 What are features to look for in a tape deck?
================================================== =======


3.16 What are some good (and bad) brands of tape decks?
================================================== ============


3.17 What are features to look for in a CD head unit?
================================================== ==========


3.18 Should I buy a detachable faceplate or pullout CD player? [IDB]
================================================== ===================

It is getting difficult to find pullout CD players any more, since
detachable faceplates are much more convenient to carry around.
However, there is the obvious trade off - it is still possible to steal
the chassis for the detachable face unit, when that is not possible
with a pullout. Although some companies will advertise that it is very
difficult to get replacement faces without the original receipt,
thieves can still get the faceplates.

Some companies, such as Eclipse, are starting to offer alternative
methods for preventing theft. Some Eclipse decks now offer ESN
(Eclipse Security Network), where the owner chooses a "key" CD that
must be inserted to "revive" the deck should it lose power. The entire
deck stays in the dash, with nothing to carry around; this expands on
the trend towards convenience while offering the owner peace of mind.


3.19 What are some good (and bad) brands of CD head units? [HK]
================================================== ====================

Generally, Alpine, Clarion, Eclipse, McIntosh, Phillips and Pioneer are
considered to produce good quality CD head units. They all have their
problems, but these brands seem to be common and relatively
problem-free.

Bad brands include Kraco, Radio Shack, Rockwood and other "bargain"
brands.


3.20 Can I use my portable CD player in my car? Won't it skip
a lot? [JSC]
================================================== ====================

You can use any portable CD player in a car provided that you have
either an amplifier with line level inputs (preferred) or a tape deck.
If you have the former, you can simply buy a 1/8" headphone jack to RCA
jack adapter and plug your CD player directly into your amplifier. If
you have the latter, you can purchase a 1/8" headphone jack to cassette
adapter and play CDs through your tape deck. The cassette adapters
tend to be far more convenient; however, there is a significant
tradeoff: by using cassette adapters, you limit your sound to the
frequency response of the tape head, which is sometimes as much as an
entire order of magnitude worse than the raw digital material encoded
onto the CD itself.

Portable CD players which were not designed for automotive use will
tend to skip frequently when used in a car (relatively). CD players
that are specially designed for automotive use, such as the Sony Car
Discman, tend to include extra dampening to allow the laser to "float"
across the bumps and jolts of a road. Some people have indicated
success with using regular portable CD players in a car when they place
the CD player on a cushion, such as a thick shirt or even on their
thighs.


3.21 What's that weird motor noise I get with my portable CD
player? [JSC]
================================================== ====================

Many people report problems while playing CDs from a portable CD player
into their car audio systems. The problem, stated very simply, has to
do with the stepping of the motor requiring a varying amount of current
and non-isolated power and audio signal grounds. Using a liberal
application of capacitors and inductors, this voltage variance can be
restricted to a window of 8.990 to 9.005V for a 9V CD player, yet even
the swing between these two levels is enough to cause annoyingly loud
noise on the outputs. It has been reported that this entire problem
can be solved by using a true DC-DC inverter at the power input to the
CD player.


3.22 What are some good (and bad) brands of portable CD players?
================================================== =====================


3.23 What's in store for car audio with respect to MD, DAT and
DCC? [HK]
================================================== =====================

MiniDisc (MD) seems to have a better future than Digital Audio Tape
(DAT) or Digital Compact Cassette (DCC) which don't seem to have appeal
to the public. Ease of use seems to be an important factor and the CD
formats allows direct access to musical tracks at an instant. Although
MD doesn't match the sound quality of the standard CDs it will probably
be popular since the players have a buffer to eliminate skipping. DAT
will remain as a media for ProAudio for recording purposes before
pressing CDs.


3.24 Are those FM modulator CD changers any good? What are my
other options? [PW, JGr]
================================================== =====================

Almost all manufacturers offer an FM modulator for their changers. As
with all equipment, some are good and some are not. A person thinking
about using an FM modulator must take into consideration that the sound
quality will only be as good as the tuner in your head unit. Also, FM
is limited in its frequency response. There is usually a noticeable
loss of the high frequencies, due to the nature of transmitting via FM.

If you do not want to use an FM Modulated CD changer, some
manufacturers make controllers for changers that feature line-level
(RCA) outputs. This allows you to connect the changer directly to an
amplifier, bypassing the stock system altogether. Some models offer
line-level inputs, allowing you to connect the stock system to the
changer (so you can continue to use your radio/tape). Clarion, Sony,
and Kenwood make such units.

Your third option is to use the aftermarket changer that corresponds to
the stock unit in your car. Not all cars have this option, but it is
becoming easier. (see Section 3.25).


3.25 What kind of changer will work with my factory head unit? [PO]
================================================== =====================

Many factory head units these days have the ability to control a
remotely mounted cd changer. Generally, the head will have a button
labeled "CD" to switch sources to the external changer. In this mode
either the radio preset buttons and/or the tuner up/down buttons will
control which CD and/or track is playing. Check your car's manual to
make sure your head can control a changer and how the buttons work.

Once you know your head can control a changer, you wonder "What kind of
changer will work with my factory head unit?" Of course, the one the
dealer wants to sell you will work. However, the dealer makes lots of
money selling you a changer, and there are often other after-market
solutions, usually involving an adapter cable and a name-brand changer.
The dealer will tell you that their solution is better and that's why it
costs so much more (often more than twice as much as an aftermarket
solution).

The car manufacturers are constantly changing the interfaces between
their heads and changers, in an effort to get you to buy their solution.
However, the after-market is constantly reverse-engineering the
interfaces and providing alternative solutions for the cost-conscious
consumer.

Two companies that make such adapters are Precision Interface
Electronics (or PIE, `http://www.pie.net') and Peripheral Interface
Components (`http://www.stinger-aamp.com/peripheral/s-ind.htm'). Check
their web sites to see if there's an adapter for your car's factory
head. They also list which changer(s) will work with their adapters.

For example, many of Honda's late-model heads were made for them by
Alpine, so the OEM changer you'd pay your friendly Honda dealer ~$700
for is essentially the same as Alpine's changers. The only difference
is the interface wiring, where they swapped two pins, specifically so
you'd have to get it from the dealer. (If you're interested in the
details, see
`http://integra.cyberglobe.net/caraudio/diagrams/DIN.html'). The
after-market adapters for this head simply swap the pins back, so you
can use the regular Alpine changer, which can be bought for ~$300.

Once you know which adapter/changer combo will work, you can get it from
your local car audio dealer or favorite mail order place. The advantage
of getting it from a local dealer is that they'll be able to install it
for you. However, if you have the time and are at all mechanically
inclined, you should readily be able to install it yourself.


3.26 What are some good (and bad) brands of CD changers?
================================================== =============

You will find that those companies who make high-quality in-dash CD
players will also make good CD changers. (see Section 3.19), for
a list.


3.27 Why do I need a center channel in my car, and how do I do it?
[HK, JSC]
================================================== ===================

If a proper center image isn't achievable via a two channel
configuration, installation of a center channel can help. Since the
majority of recordings are done in two channel, a two channel system
designed correctly should be able to reproduce a center image which was
captured during recording. A center channel is not simply a summation
of the left and right channels, like bridging an amplifier; rather, it
is an extraction of common signals from the left and right channels.
This usually means the lead vocals, and perhaps one or two instruments.
These signals will then be localized to the center of the stage,
instead of perhaps drifting between the left center and right center of
the stage. A signal processor is usually required in order to properly
create a center channel image. The image should then be sent to a
driver in the physical center of the front of the car, at an
amplification level somewhat lower than the rest of the speakers. The
correct frequency range and power levels will depend on the particular
installation, though a good starting point is perhaps a pass band of
250-3000Hz at an amplification level of half the power of the main
speakers (3dB down).


3.28 Should I buy a sound field processor? [DK]
=================================================

Sound field processors (also known as DSPs) are fun toys to play with,
and can have some use, but it is generally good to keep the KISS
principle in mind: Keep It Simple, Stupid.

The fewer signal processors (this includes equalizers, and active
crossovers) that are in your system, the less chance there will be for
noise to enter your system. You'll also save money, have a lower noise
floor. Surround sound processors and bass regenerators are nothing
more than bells and whistles and are totally superfluous in a properly
designed system.


3.29 What are some good (and bad) brands of signal processors? [IDB]
================================================== ====================

If you do decide to buy a signal processor, try to stick with reputable
brands like: AudioControl, Clark, Crystal-Line, Phoenix Gold, Rane or
Clarion. Try to stay away from brands such as Petras, Urban Audio
Works and Kraco.


3.30 I keep hearing that speakers for Company X are made by Company
Y. What's the deal? [IDB, DK]
================================================== ========================

Many of the speakers you've ever purchased or ever will purchase have
been assembled in plants "along side" speakers from other
manufacturers, but that does NOT imply in any way, shape or form
whatsoever that the two brands are even VAGUELY similar. This is often
done in order to reduce costs because purchasing your own gaussing
stations and mass producing your own drivers takes a LOT of money to
implement.


3.31 What is a Line Driver? Do I need one? [LC,IDB]
================================================== =========

A line driver is a device that amplifies a signal, such as the low-level
signal output from a head unit. Line drivers are made to amplify the
line level signal to as much as 10 volts or higher. This, of course, is
useless unless the receiving end can handle 10 volts as input. To solve
this problem, there are line receivers which bring the line level
voltage down from 10 volts or more to about 1 volt. Usually, the line
driver and receiver are placed as close to the sending signal source and
destination as possible, to minimize noise pick up.

The automobile is an inherently noisy electrical environment. So RCA
cables may pick up noise as it makes its way to the amplifier. Note
that noise here refers to the induced noise, not ground loop noise such
as engine whine. A simple way to fight against this noise is to make
the signal level carried in the RCA cable very high, thus increasing the
signal's resistance to induced noise and resulting in a higher signal to
noise ratio at the destination of the RCA cable. Most head units
produce a fairly low output voltage ( 1.5 V), although recently high
end head units advertise 4 volt or higher output, and won't usually need
a line driver.

The line driver will increase dynamic range in certain cases where
excessive noise is masking the lower level signals. However, a line
driver will not increase the dynamic range when used in a system with
little noise to begin with.

There is some truth to the claim that a line driver will let you play
your stereo louder since there are cases where the amplifier still
doesn't play at its full potential even when its gain is turned all the
way up and the volume on the head unit is maxed out. Adding a line
driver here will allow you to turn down the gain on the amp while using
a lower volume setting on the head unit.

But before you jump in with both feet, remember that all electronics
has their own inherent noise. Thus if you don't have a serious case of
induced noise, a line driver will do little good since it might add
enough noise to offset what little noise it "takes away."

The line driver is a patch to the noise problem rather than a fix so it
is still not the ultimate solution. My personal experience has shown
to ME that a properly installed system with none-malfunctioning
components will have little noise, even if you use low grade components
such as those made by the less desirable manufactures. Also, a lot of
crossovers and EQ units have rather high low-level output signals.
Some times as high as 8 volts. So be sure to take this into
consideration.


3.32 Can I play MP3 files in my car? [AK]
================================================

In a few short years several products have hit the mainstream which
enable consumers to use digital music files instead of relying on fixed
media like tapes and CDs. The most popular format is MPEG Layer 3 or
simply MP3. Most aftermarket manufacturers produce at least one
product which will allow you to play MP3 files that have been copied to
a CD-R or CD-R/W, and to do so without converting the MP3 files into CD
Audio format. Some of these units will also play other formats, such
as WMA (Window Media Audio), or Ogg Vorbis.

Another option which is often less expensive is to use a portable music
player such as Apple's iPod or the Creative Nomad, and to use an
inexpensive FM modulator to broadcast the player's audio output over FM
radio. Then, you simply tune your headunit to the proper FM station to
listen to your music. The downside of this is that your overall sound
quality is limited not by the encoding of the file, but by the
capability of FM radio, which is significantly less than audiophile
quality.


--
ian d bjorhovde -
internet mobile audio -
http://mobileaudio.com 4
Subwoofers
*******************

This section describes some elements necessary for understanding
subwoofers - how they operate, how to build proper enclosures, how to
pick the right driver for you, and how to have a computer do some of
the work for you.


4.1 What are "Thiele/Small parameters?" [CD, RDP]
================================================== ======

These are a group of parameters outlined by A. N. Thiele, and later R.
H. Small, which can completely describe the electrical and mechanical
characteristics of a mid and low frequency driver operating in its
pistonic region. These parameters are crucial for designing a quality
subwoofer enclosure, be it for reference quality reproduction or for
booming.

`Fs'
Driver free air resonance, in Hz. This is the point at which
driver impedance is maximum.

`Fc'
System resonance (usually for sealed box systems), in Hz

`Fb'
Enclosure resonance (usually for reflex systems), in Hz

`F3'
-3 dB cutoff frequency, in Hz

`Vas'
"Equivalent volume of compliance", this is a volume of air whose
compliance is the same as a driver's acoustical compliance Cms
(q.v.), in cubic meters

`D'
Effective diameter of driver, in meters

`Sd'
Effective piston radiating area of driver in square meters

`Xmax'
Maximum peak linear excursion of driver, in meters

`Vd'
Maximum linear volume of displacement of the driver (product of Sd
times Xmax), in cubic meters.

`Re'
Driver DC resistance (voice coil, mainly), in ohms

`Rg'
Amplifier source resistance (includes leads, crossover, etc.), in
ohms

`Qms'
The driver's Q at resonance (Fs), due to mechanical losses;
dimensionless

`Qes'
The driver's Q at resonance (Fs), due to electrical losses;
dimensionless

`Qts'
The driver's Q at resonance (Fs), due to all losses; dimensionless

`Qmc'
The system's Q at resonance (Fc), due to mechanical losses;
dimensionless

`Qec'
The system's Q at resonance (Fc), due to electrical losses;
dimensionless

`Qtc'
The system's Q at resonance (Fc), due to all losses; dimensionless

`Ql'
The system's Q at Fb, due to leakage losses; dimensionless

`Qa'
The system's Q at Fb, due to absorption losses; dimensionless

`Qp'
The system's Q at Fb, due to port losses (turbulence, viscosity,
etc.); dimensionless

`n0'
The reference efficiency of the system (eta sub 0) dimensionless,
usually expressed as a percentage

`Cms'
The driver's mechanical compliance (reciprocal of stiffness), in
m/N

`Mms'
The driver's effective mechanical mass (including air load), in kg

`Rms'
The driver's mechanical losses, in kg/s

`Cas'
Acoustical equivalent of Cms

`Mas'
Acoustical equivalent of Mms

`Ras'
Acoustical equivalent of Rms

`Cmes'
The electrical capacitive equivalent of Mms, in farads

`Lces'
The electrical inductive equivalent of Cms, in henries

`Res'
The electrical resistive equivalent of Rms, in ohms

`B'
Magnetic flux density in gap, in Tesla

`l'
Length of wire immersed in magnetic field, in meters

`Bl'
Electro-magnetic force factor, can be expressed in Tesla-meters or,
preferably, in meters/Newton

`Pa'
Acoustical power

`Pe'
Electrical power

`c'
Propagation velocity of sound at STP, approx. 342 m/s

`p'
Density of air at STP 1.18 kg/m^3 (rho)


4.2 How does speaker sensitivity affect real world SPL? Will
a higher sensitivity give me a larger SPL? [MS]
================================================== =================

When it comes to mids and highs, efficiency (sensitivity) is a fairly
good indicator of output differences at the same power level. When it
comes to subwoofer performance, the driver's sensitivity is irrelevant
unless you are also specifying a box volume.

An efficient sub requires a larger box to achieve equivalent extension
to a less efficient sub. In a small box, the less efficient sub will
actually be LOUDER at low frequencies at the SAME POWER as the more
efficient sub.

Linear excursion is a very good indicator of ultimate output capability
(given sufficient power to drive the speaker to that point.) To make
sound you must move air; therefore, the more air you move, the more
sound you make. When comparing two speakers of equal surface area, the
one with greater excursion capability will play louder given sufficient
power.


4.3 What are the enclosure types available? [JLD, JG]
================================================== ==========

Only the order of the enclosure itself is shown here. The addition of
a crossover network increases the order of the system by the order of
the crossover. Example: If a First-Order, 6dB/Oct. crossover (single
inductor in series with the speaker) is used with a Fourth Order
enclosure, the total system is a fifth order. Note: Air volumes and
ratios shown here may not be to scale. This is designed to provide
order information only.

First Order
Infinite-Baffle or Free-Air

|
|
/
/
||
||
\
\
|
|


Second Order Second Order
Acoustic- or Air-Suspension Isobaric* Acoustic-Suspension
or Sealed (Compound Loaded)
_______________________ _______________________
| | | _____|
| / | / /
| / | / /
| || | || ||
| || | || ||
| \ | \ \
| \ | \____\
|_______________________| |_______________________|


Fourth Order Fourth Order Fourth Order
Bass-Reflex or Passive Radiator Isobaric*
Vented or Ported Bass-Reflex Bass-Reflex
_______________ _______________ _______________
| | | | | ____ |
| / | / | / /
| / | / | / /
| || | || | || ||
| || | || | || ||
| \ | \ | \ \
| \ | \ | \____\
| | | | | |
| | | / | |
| | | / | |
| ____| | | | ____|
| | | |
| ____ | \ | ____
| | | \ | |
|_______________| |_______________| |_______________|


Fourth Order Fourth Order
Single-Reflex Bandpass Isobaric* Single-Reflex Bandpass
_________________ ____ _______________________ ____
| | | | | | | | | |
| / | | | | / \ | | |
| / | | / \ |
| || | | || || |
| || | | || || |
| \ | | \ / |
| \ | | \ / |
|_________|_______________| |_______________|_______________|


Fourth Order Fourth Order
Three Chamber Three Chamber Isobaric*
Single-Reflex Bandpass Single-Reflex Bandpass
____________ ____________ ______________ ______________
| | | | | | | | | | | |
| / | | \ | | / \ | | / \ |
| / \ | | / \ / \ |
| || || | | || || || || |
| || || | | || || || || |
| \ / | | \ / \ / |
| \ / | | \ / \ / |
|______|_____________|______| |_______|_______________|_______|


Fifth Order = Fourth Order Enclosure + First Order Crossover
= Third Order Enclosure + Second Order Crossover, etc.


Sixth Order Sixth Order
Dual-Reflex Bandpass Isobaric* Dual-Reflex Bandpass
____ _____________ ____ ____ ____________ ____
| | | | | | | | | | | | | |
| | | / | | | | | | / \ | | |
| | | / | | | | / \ |
| || | | || || |
| || | | || || |
| \ | | \ / |
| \ | | \ / |
|_______________|_____________| |______________|_____________|

Sixth Order
Three Chamber Quasi-Sixth Order
Dual-Reflex Bandpass Series-Tuned Bandpass
_ _________ _________ _ _________________ ____
| | | | | | | | | | | | | | |
| | | / | | \ | | | | / | | |
| / \ | | / |
| || || | | || |
| || || | | || |
| \ / | | \ |
| \ / | | \ |
|________|_____________|________| | ____| |
| |
| ____ |
| | |
|___________|_____________|


Seventh Order = Sixth Order Enclosure + First Order Crossover, etc.

Quasi-Eighth Order
Series-Tuned Dual-Reflex Eighth Order
Bandpass Triple-Reflex Bandpass
_ _______________ _ ____________ _____________
| | | | | | | | | | |
| | | / | | | | | | |
| / | | |
| || | | |
| || | | |
| \ | |____ _____________ ____|
| \ | | | | | | | |
| ____| | | | | / | | |
| | | / |
| ____ | | || |
|_____________|___________| | || |
| \ |
| \ |
|______________|______________|


* Isobaric or Coupled Pair (Iso-group) Variations:

A variety of configurations may be used in the isobaric loading
of any order enclosure. Physical and acoustic restrictions may
make one loading configuration preferable to another in a
particular enclosure.

Composite or Push-Pull Compound or Piggy-Back
or Face-to-Face Loading or Tunnel Loading
_________________ ___________________________
| | | ____|
| / \ | / /
| / \ | / /
| || || | || ||
| || || | || ||
| \ / | \ \
| \ / | \___\
|_________________| |___________________________|

Back-to-Back Loading Planar Loading
_________________________ ___________________________
| _________| | | |
| \ / | / |
| \ / | / |
| || || | || |
| || || | || |
| / \ | \ |
| /_______\ | \ |
|_________________________| |________________________| |
| |
/ |
/ |
|| |
|| |
\ |
indicates direction of \ |
simultaneous cone movement. |__|



4.4 Which enclosure type is right for me? [IDB, DK]
================================================== ========

This answer is not designed to tell you exactly what kind of enclosure
to build, but rather to give an idea of the advantages and
disadvantages to the simple configurations (Infinite baffle [1st
order], Sealed [2nd order], Ported [4th order] and basic bandpass).
Building and designing more complicated systems (order 4) is not for
the light at heart.


4.4.1 Infinite Baffle ("free-air")
-----------------------------------------

* Advantages...
- No box necessary!

- This means it's usually cheaper to design and implement
in your system

* Disadvantages...
- Requires that a good seal be obtained between front and
rear of driver. In a car, this can be quite difficult and
may require the installer to remove trim panels to plug any
holes that would let energy "bleed through".

- The responsibility for damping cone motion rests solely
on the driver's suspension. As fatigue sets in, this becomes
a critical issue in infinite baffle set-ups.

- Less efficient in the sub-bass region than above
mentioned enclosures.

- Potentially more expensive drivers than good boxable
woofer - The suspension must be extremely hearty and
long-lasting to withstand high power applications.


4.4.2 Sealed Box
-----------------------

* Advantages...
- Small enclosure volumes

- Shallow (12 dB/Octave) roll off on low end

- Excellent power handling at extremely low frequencies

- Excellent transient response/ group delay
characteristics

- Easy to build and design

- Forgiving of design and construction errors

* Disadvantages...
- Not particularly efficient

- Marginal power handling in upper bass frequencies

- Increased distortion in upper bass over ported design

- When using high power and small box, magnet structure
is not in an ideal cooling environment


4.4.3 Ported Box
-----------------------

* Advantages...
- 3-4 dB more efficient overall than sealed design

- Handles upper bass frequencies better with less
distortion

- Magnet is in good cooling environment

- When properly designed, a ported box will slaughter a
sealed in terms of low frequency extension

* Disadvantages...
- Size (not so critical outside the mobile environment)

- Woofer unloads below Fb

- More difficult to design/ can result in boomy, nasty
sounding bass if misaligned


4.4.4 Bandpass Box
-------------------------

* Advantages...
- When properly designed and implemented, can provide
superior LF extension and efficiency.

- Cone motion is controlled more and therefore mechanical
power handling is increased.

- Cones are physically protected from contents of trunk
flying around.

- Output is easily channeled directly into the interior
of sedans.

* Disadvantages...
- Difficult to build (not recommended for newbie's), and
very sensitive to misalignment due to calculation or
construction errors.

- Their characteristic filtering often masks any
distortion that occurs as a result of amplifier clipping or
overexcursion and thus will give the user no warning that the
driver is over-stressed and about to fail.

- Need substantial mid-bass reinforcement to make up for
narrow bandwidths in efficient alignments.

- Transient response is largely dependent upon the
alignment chosen....wider bandwidths will result in sloppier
performance, narrower bandwidths (and thus higher effiencies)
result in better transient performance.

- They can oft times be quite large.


4.5 How do I build an enclosure? [AO]
============================================

These instructions are for building a first order (sealed) subwoofer
enclosure. Building ported or bandpass boxes is more difficult, and
those designs are less forgiving of mistakes. These instructions apply
for all box designs, but be sure of the measurements before you make
your cut. Building your own enclosure can save you a lot of money, but
only if you don't need to buy all of your materials twice because of
mistakes!

You will need:

*Wood*
I only use MDF (see Section 4.6), but others have reported
success using other hardwoods like birch and oak. Do not use
plywood - it's far to flexible and porous. Use a minimum of 3/4"
wood - flexing sub enclosures lose precious energy!

*Screws*
For one inch wood use #8 2 inch wood screws. For 3/4 inch wood use
#8 1 3/4 inch screws. Double grip Drywall screws also work well.

*Adhesive*
I use "Liquid Nails" which comes in a caulk tube or a bucket, but
any paste type of adhesive will work. Spray adhesives will not
work.

*Silicone sealant*
White, brown, clear, caulk tube, or squeeze bottle, it doesn't
matter. Make sure you don't get silicone lubricant (which comes
in a spray can)!

*Terminals/Terminal Cup*
To allow easy connections from your amp.

Besides these materials you will need several tools:

*Table saw or radial arm saw*
I use a radial arm saw, just because it's a little easier and
accurate, but a table saw will work also. You can use a circular
saw, but be very careful to make your cuts straight.

*Jig saw*
For cutting your speaker hole.

*Drill*
You will also need a 1/8" drill bit, a screwdriver bit, and a
countersinking bit.

*Pencil*
To mark your cuts, make notes, etc.

*Measuring tape*

*Safety Goggles*

*Face Mask*
Breathing MDF dust has not been proven to cause health-related
problems, but hang around with with a few installers at your local
shop for an afternoon and you'll see why you need a face mask. :-)

Start by marking the cuts you need to make on your wood. Double check
your math, and your measurements.

Use the table or radial arm saw to cut your wood. When you're done you
should have six pieces of wood which fit together tightly to form a box.

At this point you will need to trace the cut out for your subwoofer onto
the front of the box. Remember that if you have a 10 inch subwoofer you
do NOT want a 10 inch cutout. The 10 inch measurement is from the
outside of the mounting ring. The actual cutout diameter should be with
your instructions. Transfer the proper sized circle onto the sub box
and cut it out with the jig saw. If you have trouble starting cuts with
a jig saw, drill a 1/2" hole in the wood inside the circle. You can
drop your blade into the hole and then cut out to the edge of the circle
and around.

After you have cut out your mounting hole you will need to cut out a
square on one of the sides for your terminal cup. Transfer the proper
size rectangle onto the wood and cut it out with the jig saw.

Now you are ready to start assembling the enclosure. Choose one of the
ends, and one of the sides. Apply a bead of adhesive along the edge of
the end piece. Affix it to the edge of the bottom piece. Flip it over
(have a friend hold the other end and hold the end in place,) and screw
the edge to the end. Use one screw at each corner and then one more
screw about every 8 inches. Drill a pilot hole with your 1/8" drill
bit, then drill a countersink with your countersinking bit. Finally,
drive the screw in. Make sure that you don't strip the hole.

Repeat the above procedure with the other end. You should now have the
two ends connected to one side. Affix the other three sides the same
way.

Finally, you'll want to seal the insides of the box with silicone. Apply
a bead of silicone across all the inside edges and around the terminal
strip.

Allow the box to dry over night and then place your speaker into the
hole. Screw it down and you're done!


4.6 MDF for Dummies [IDB]
================================

Since MDF (Medium Density Fiberboard) is used so frequently in building
subwoofer enclosures and other projects, this section provides some more
detailed information.


4.6.1 What is MDF? [PS]
------------------------------

MDF (Medium Density Fiberboard) is a hardboard product comprised of hot
compressed wood fibers glued together. The color of this material can
vary from light to dark brown depending on the brand of manufacturer.
Particle Board or Flakeboard consist mostly of recycled wood chips. The
size of the wood chips used varies which means that the coarser the wood
chips reduces the structural density of the material.


4.6.2 Where can I get MDF? [PS]
--------------------------------------

Wholesale distributors of lumber products. Home Improvement Centers,
such as Home Depot or Home Base, and Lumber Yards may or may not stock
MDF products, but they will be able to order it for you. Contact
woodworking or cabinet making shops in your area, ask them where to get
it or if it may be possible to buy the material from their business.


4.6.3 What type of saw blade works best when cutting MDF? [PS]
---------------------------------------------------------------------

If you're using a circular saw, a good 40 tooth carbide tipped blade
works best. If you're using a table saw, a 50/60 tooth carbide tipped
combination or ripping blade will provide smooth cuts.


4.6.4 What type of router bits work well with MDF? [PS]
--------------------------------------------------------------

As far as router bits go, use only two flute carbide bits and make
several passes as opposed to one single pass. If possible, trace the
outline of what you intend to router and remove the majority of the
material with a jigsaw which will reduce the amount of material being
removed and will put less strain on the router as well, not to mention,
this will all reduce the amount of MDF dust.


4.7 What driver should I use?
====================================


4.8 Is there any computer software available to help me choose
an enclosure and a driver? [JSC, MH, DK]
================================================== ===================

Various enclosure design software is available via ftp from

`ftp://ftp.uu.net/usenet/rec.audio.high-end/Software/'.

The most popular program there is Perfect Box, which is in the file
`perf.uu' (or `perf.zip').

Note that NO program can tell you what enclosure is best for YOUR car!
The program does not take into consideration your space limitations,
the type of car you drive, the type and number of mid-bass drivers you
use, your musical preferences and the goals you have for your system.
Many people follow (blindly) what a computer program says is "optimal,"
and end up unhappy with the results. Therefore, it is always a good
idea to discuss a design you think looks good with a qualified
installer or (even better) with the manufacturer.

For an overview of many programs and devices available for enclosure
design, obtain the file `sahfsd01.doc' at the ftp.uu.net archive. The
filename stands for "Software and Hardware for Speaker Design", and was
added to the archive in June 1994 by an anonymous contributor.


4.9 What is an "aperiodic membrane?" [CD, DK]
================================================== ==

An "aperiodic membrane" is one part of a type of subwoofer enclosure.
It is an air-permeable sheet which has frequency-dependent acoustical
resistance properties. The original design goes back to Naim, for use
in home systems, but has been applied by several individuals and
companies in car audio.

The completed system will be aperiodic, which means it will prove to be
over-damped with a Q well below 0.7. In contrast, the most commonly
used sealed enclosures have Qtc's in the range of 0.8 to 1.1 which are
considered, by definition, to be underdamped. When improperly used, a
high-Q system may have poor transient response, nasty peaks in
frequency response, and high rates of roll-off. Aperiodic systems will
feature excellent Aperiodic systems are characterized by better
transient response, flatter frequency response and somewhat extended
low frequency response.

Another benefit of the system is that you can pretty much choose
whichever driver you'd like to use, as long as they are big. The
Thiele/Small parameters (which would normally determine what kind of
box would be used) are taken into consideration by the membrane
designers so that the response is extended and overdamped, regardless
of the characteristics of the driver.

Physically, the aperiodic membrane isn't for every car. It requires
sealing the trunk from the passenger compartment in an air-tight
manner, as well as sealing the trunk from the outside for best results.
The drivers are then mounted into the baffle between the passenger
compartment and the trunk, as would be standard in an
infinite-baffle/free-air set-up. The aperiodic membrane is then placed
either in front of the driver or behind the driver, depending on the
type. When mounting behind the driver, the membrane is used as the
rear-wall of a very small box which the driver sits in (as in Richard
Clark's infamous Buick Grand National). So, in short, it's not
suitable for trucks, jeeps, R/V's, or hatchbacks.

You should probably only get an aperiodic membrane if you've got money
to burn, lots of amplifier power, some big subs, a sedan, a desire for
trunk space, and no wish to boom. If your tastes lean towards
bass-heavy booming, as opposed to well-recorded acoustic instruments,
you're not going to be pleased with the result.


4.10 Can I use my subs in the winter? [MS]
=================================================

The following applies to all speakers in extremely cold conditions, but
the question most often occurs in reference to subwoofers.

The suspension of the speakers will stiffen considerably at very cold
temperatures (lower than 30 degrees F). So will certain cone materials
which may become more brittle.

If a very cold speaker is played very hard there is a small potential
for damage because more stress is placed on the cone's neck. The
likelihood of damage is minimal for well-constructed and well-designed
automotive speakers, however.

Thermally, the danger is minimal because the ambient temperature and
the coil temperature are so low that it is highly unlikely that a coil
will overheat and burn, despite limited movement and ventilation.

At temperatures between +20 degrees F and 0 degrees F, it is a good idea
to play the system at a moderate level until the car's heater has warmed
the vehicle interior. As the speakers warm up, they will play louder
and lower signifying that their suspensions are warming up and returning
to nominal compliance.

If the temperature is extremely cold (less than 0 degrees F), you should
avoid playing the system at all until the vehicle interior is warm.
This is to avoid stress fractures in the surround material (especially
with rubber surrounds).


4.11 How can I carpet my enclosure? [AO]
===============================================

What you will need:

* Adhesive (3M Super 77 or Super 90 is excellent.)

* Carpet.

* A good sharp pair of scissors.

* A razor sharp utility knife. Buy a BOX of blades, they go dull
fast.

* Solvent to clean up excess adhesive.

Before you start, find a large, clean, flat surface on which to set the
box as you carpet it. Start by unrolling the carpet onto the surface,
smoothing it out so that its flat, and setting the box on top of it
edgewise. Also, make sure that you remove the speaker, any ports and
terminal cups from the box.

The instructions on how to carpet the box are as follows:

1. Place the box such that it is centered on the carpet lengthwise,
and one edge of the box is about one inch from the edge of the
carpet.

2. Roll the box back so that the side of the box that was previously
done faces forward, and the carpet beneath it is exposed. Coat
both the box and carpet with adhesive, but do NOT apply the carpet
to the box - the adhesive needs a few minutes to set up (follow
the instructions from your adhesive to find out how long you
should wait).

3. After the adhesive has set up, roll the box back into position.
Wait a few more minutes for the adhesive to bond.

4. Now coat the side of the box adjacent to the remaining carpet (the
side facing backwards) and the carpet next to it with adhesive,
let the adhesive set up, and roll the side you just coated onto
the coated carpet. Repeat this until three sides of the box are
carpeted.

5. Before carpeting the next side, the 1 inch of carpet sticking over
the edge must be removed. To do this, rotate the box so that the
first side that was carpeted is up. Pull the carpet sticking over
the edge down towards the uncarpeted edge and cut it off with the
knife, flush with the uncarpeted side of the box. You will have to
run the knife nearly parallel to the uncarpeted side to get a
perfect cut.

6. This done, spray the remaining side and carpet, and roll the box
onto it. Shear off the remaining carpet sticking out from all
edges with the scissors leaving a 1 inch border everywhere.

7. Clean up the ends of the box so that the carpet is flush with the
sides of the box as in step 4.

8. Next cut off the remaining 1 inch flap of carpet (located at the
point where you began carpeting). This is the tricky part, as you
don't want to be able to see this seam. Again, pull the flap down
over the edge of the box, but this time cut it at roughly a 45
degree angle. If you are successful you shouldn't be able to see
the wood under the seam, but will probably see the white of the
adhesive and the back of the carpet.

9. Soak some of the solvent onto a rag and use this to scrub the edge
you just cut off. It should dissolve the adhesive and the carpet
backing somewhat, causing the carpet on the edge to become fuzzy.
Keep scrubbing the edge until you can no longer see the seam.

10. Now carpet the ends of the box. Cut two pieces of carpet slightly
larger than the ends of the box and lay one of them flat on the
surface. Spray the carpet and one end of the box with adhesive,
and set the end of the box on the carpet, so the box stands on end.

11. After the adhesive has dried sufficiently cut off the remaining
border of the carpet as in 7 and 8.

12. Repeat step 9 and 10 for the other end of the box.

Congratulations! You've just carpeted your box!


4.12 Are large magnets always better than small magnets? [ST]
================================================== ==================

Magnet *size* is meaningless!

Every speaker will have an optimal BL ((see Section 4.1),) product,
the field strength in the air gap multiplied by the length of the voice
coil wire in the field.

If the BL product is too low, the speaker is electrically not very well
damped (which will result in a woofer with a high Qts). A bump in
frequency response and a level drop in midband efficiency may be the
result. If the BL product is too high, the speaker is electrically
overdamped (Low Qts woofer). A very high midband efficiency, but the
driver starts to roll of early.

An high BL product can be achieved in a number of ways: increase field
strength; or increase wire length in magnetic gap.

The increase in field strength is limited; so some manufacturers use
very thin wire for the voice coil, as such they can achieve a high BL
product with a low field strength (cheap magnet). Or they use an 8 layer
voice coil... needless to say that electrical power handling will
decrease enormously.

Long stroke woofers, having only a part of the voice coil in the air
gap, need a very high field strength to achieve a high BL product. Often
this means a big magnet as well...

Use magnet size as an indication, but as nothing more than that.


4.13 I know the box volume required for my subwoofer, but what
are the best dimensions for my enclosure? [IDB]
================================================== ===================

The specific dimensions of a subwoofer enclosure aren't really
important. Once you know the appropriate volume of the box, and you
know where in your car you want to install it, you will have some idea
of the restrictions in the dimensions. For example, if the distance
between the floor of your trunk and the bottom of the rear deck is 16",
then you probably shouldn't make your box any taller than 16".
Likewise, if width of the trunk (between the wheel wells is 38", then
you've got that much space to work with.

You can also infer some other information about your box, from the
speaker specifications (for a PPI PC10):

Mounting Depth: 4.5625"
Speaker Displacement: .032 ft^3

Here is an ASCII drawing of a subwoofer enclosure to help illustrate a
few things:


|--- L ---|
__________ ___
/ /| |
/ + / | | + = Center of speaker
/ x / | D x = center of port
/_________/ | |
| | | _|_ W = Width of box
| | / / L = Length of box
| | / W D = Depth of box
|_________|/ _/_

Because of the speaker's mounting depth, you know that the box MUST be
at 5.5" deep (it's always good to leave at least 1" of space behind the
speaker, but leave more if you can). If you use a straight port (3"
diameter PVC) then the box will need to be at least 13" deep (leaving 2
inches between the end of the port and the back of other side of the
enclosure), assuming that your port will reside completely within the
enclosure. If you use Flex-Port or choose to have a portion of the
port extending outside of the enclosure, you can make the box less deep.

We also know that with a 10" woofer, the length and width should both
be a minimum of 12" (leave 1" on either side of the woofer). Obviously
both dimensions can't be 12" otherwise we can't put the port on the
same face as the speaker.

With volume, remember a couple of things. Recommended volume is the Net
Internal volume. Both the speaker and the port will displace volume
from the box - this means that you MUST account for these (i.e., make
the interior volume of the box larger than the recommended value). In
this case, you know the following:

Required Volume: 1.25 ft^3
Speaker Displacement: 0.032 ft^3
Port Displacement: ??

3" (interior diameter) PVC will usually have an exterior diameter of
3.5" (0.25" wall thickness). Volume of a cylinder = pi*r^2*h, where r
= 1.75" and h=12.25" (13" port length - 0.75" for the thickness of the
MDF). Therefore the port displacement is: 117.9 in^3 or 0.068 ft^3
(1728 in^3 = 1 ft^3).

Required Volume: 1.25 ft^3
Speaker Displacement: 0.032 ft^3
Port Displacement: 0.068 ft^3

TOTAL INTERIOR VOLUME: 1.35 ft^3 or 2332.8 in^3

Now, to calculate the dimensions of the box: For a rectangular box, L
x W x D = Volume.

If we know that the minimum interior depth is 15" (because the port is
13" and you should leave 2" between the port and the wall of the
enclosure), we can say,

L x W x 15" = 2332.8 in^3 or
L x W = 155.52 in^2

Since we know that L must be at least 12" (since the speaker is 10" in
diameter), we can continue:

12" x W = 155.52 in^2
W = 12.96"

So, we have determined that the interior dimensions of the box must be
12" x 12.96" x 15". Obviously this can't work, since there is nowhere
to put the port! You will either have to have the port extend outside
of the enclosure, or use flex-port. Keep in mind that if you have part
of the port "sticking out" of the enclosure, the Port Displacement will
also change!!.

For simplicity, (in this example) let's use flex-port. This will let
you decrease the thickness of your box to about 6". So,

L x W x 6" = 2332.8 in^3
L x W = 388.8 in^2
12" x W = 388.8 in^2
W = 32.4"

This is a little more reasonable. This will be a flat, wide box.
Again, keep in mind that these are internal dimensions. If you use
3/4" MDF (and you should) to build the enclosure, this will add 1.5" to
each of these figures for the external dimensions. e.g.:

13.5" x 33.9" x 7.5"

Remember, the 6" depth and 12" length are just the minimum values, you
can alter them if, for example, you don't have enough space between your
wheel wells for a 34" box. If you only have, say, 28", then:

maximum external width = 28"
maximum internal width = 26.5"

L x W x D = 2332.8 in^3
L x 26.5" x 6" = 2332.8 in^3
L = 14.7" (internal)

Got it? It can be a pain, but that's part of the fun in building a
speaker enclosure.


--
ian d bjorhovde -
internet mobile audio -
http://mobileaudio.com 5
Installation
*********************

This section describes how to do what you want once you know
what it is you want to do.


5.1 Where should I buy the components I want? [JSC]
================================================== ========

Most of the time, you will either buy from a local dealer, or from a
mail-order house. Buying from a local dealer can be good because you
get to deal directly with a person: you can show them your car, ask
specific questions, haggle prices, get quick service when there are
problems, get deals on installation, etc. But there can also be
advantages to buying mail-order: generally cheaper prices, sometimes
better service, etc. In either case, you should always check prices
before you buy, inquire about warranty service, and ask about trial
periods.


5.2 What mail-order companies are out there? [JSC, JM, MM, IDB]
================================================== ====================

*Crutchfield* - 800/955-3000
1 Crutchfield Park, Charlottesville, VA 22906 USA

* Advantages:
- Great customer service

- Generally knowledgeable sales and tech support personnel

- Custom mounting kits, wiring harnesses, etc. free of
charge.

* Disadvantages:
- limited product line

- generally higher prices than local shops

*J.C. Whitney* - 312/431-6102
1917-19 Archer Avenue, P.O. Box 8410, Chicago, IL 60680 USA

* Advantages:
- Lots of "miscellaneous" items

- 10kW amps for $19.99

* Disadvantages:
- 10kW amps that really only put out 1mW and break after first
10 minutes of use.

*Parts Express* - 800/338-0531
340 E. First St., Dayton, OH 45402 USA

* Advantages:
- Large selection of electronics supplies at respectable prices.

- Showroom prices said to be better than catalog prices.

* Disadvantages:
- Also carries some of the same quality-level components as
J.C. Whitney.

*Classic Research/Z-Box* - 520/571-0171
5070 E. 22nd St., Tucson, AZ 85711 USA

* Advantages:
- Creates custom door panels with car audio in mind.

* Disadvantages:
- Only services expensive sports and luxury cars.

*MCM Electronics* - 800/543-4330
650 Congress Park Drive, Centerville, OH 45459-4072 USA

* Advantages:
- Sells lots of decently priced trinkets (fuses, fuse holders,
wire, etc.)

- Has excellent service and available technical support.

* Disadvantages:
- ?

There are many other mail-order houses that can be found in the back of
magazines, such as S.B.H. Enterprises, Speed and Sound and Smile
Electronics, but people seem to have mixed feelings about these
companies. The prices are very low, often due to the fact that these
companies are not factory authorized - this means that there could be
problems getting the unit serviced by the manufacturer should it break.
To get around this, these mail order houses will often provide their
own service departments, to repair defective units. Generally, it is
advised to be careful when dealing with any mail order companies, to
protect yourself.

There are also a number advertisements for mail order houses (such as
Apex Audio & Electronics or Insider's Audio) that offer special deals
or free equipment if you buy their expensive catalog or pay a
membership fee. While these ads may be enticing, keep in mind that
they are often *too good to be true*! Usually you have to buy a large
amount of equipment before you qualify for the "bonus" or the prices
are very high for most equipment.


5.3 What tools should I have in order to do a good installation?
[JSC]
================================================== =====================

*Electrical tape*
Make sure you get some that can withstand extreme temperature
ranges.

*Wire cutters/strippers and crimpers*
Get a big pair with stripper holes precut for individual wire
sizes.

*Angled screwdrivers*
Makes taking dash and rear deck speakers out a lot easier.

*Multiple size screwdrivers, both flathead and Phillips.*
Magnetic screwdrivers can be a big help when trying to get screws
into (or out of) tight spaces.

*Various wrenches, pliers, and socket sets*
The specific sizes you need will depend on your vehicle.

*Metal drill and saw*
You'll need these if you need to modify your vehicle for new
speaker cutouts or to accommodate a new head unit.

*Hot glue gun*
Good for putting carpeting or door panel trim back in place after
modifications.

*Razor knife*
Helps for detailed modifications of door panels or carpeting,
especially when installing new speakers.

*Wire*
(see Section 2.3).

*Soldering Iron*
Makes excellent connections, but can be messy if not careful.

*Shrink wrap or flex tubing*
Good for protecting wire, especially in the engine compartment.

*Multimeter*
Helps to diagnose installations.

*Extra hardware*
Screws, nuts, bolts, connectors, etc.

*Fuse puller and extra fuses.*
In addition to the fuses for your stereo system, check your car's
fusebox to find the various sizes you'll need. Also, you can use
needle-nosed pliers to pull fuses.

*Wire ties*
Helps to tuck wire away in otherwise exposed areas.

*Small light source*
A flashlight will do - you just want something that you can poke
around the innards of your car with.

*Tape measure*


5.4 Where should I mount my speakers?
============================================


5.5 What is "rear fill", and how do I effectively use it? [HK,
JSC]
================================================== ===================

"Rear fill" refers to the presence of depth and ambiance in music. A
properly designed system using two channels will reproduce original
rear fill on the source without rear high frequency drivers. Since
recordings are made in two channels, that is all you will need to
reproduce it. What is captured at the recording session (coincident
pair mics, Blumlein mic patterns, etc.) by a two channel mic array will
capture the so called rear fill or ambiance. Many of the winning IASCA
vehicles have no rear high frequency drivers. Also a lot of this has
to do with system tuning. If rear high frequency drivers are added,
however, the power level of the rear fill speakers should be lower than
that of the front speakers, or else you will lose your front-primary
staging, which is not what you want (when was the last time you went to
a concert and stood backwards?). The proper amount of amplification
for rear fill speakers is the point where you can just barely detect
their presence while sitting in the front seat. Separates are not a
requirement for rear fill; in fact, you may be better of with a pair of
coaxial speakers, as separates may throw off your staging.


5.6 How do I set the gains on my amp? [JSC]
==================================================

The best way to do this is with a test tone and an oscilloscope (*Note
Oscilloscope::.) Since most people have neither item, the following
will work approximately as well.

1. Disconnect all signal inputs to the amp

2. Turn all sensitivity adjustments as low as possible

3. Turn head unit on to around 90% volume (not 100% or else
you'll have head unit distortion in there - unless you've got
a good head unit) with some music with which you're familiar,
and with EQ controls set to normal listening positions

4. Plug in one channel's input to the amp

5. Slowly turn that channel's gain up until you just start to
notice distortion on the output

6. Turn it down just a wee little bit

7. Disconnect current input

8. Repeat steps 4-7 with each input on your amp

9. Turn off head unit

10. Plug in all amp inputs, and you're done

If by some chance you do have an oscilloscope (and preferably a test
disc), you do essentially the same thing as above, except that you stop
turning the gains up when you see clipping on the outputs of the
amplifier.

Note that if you are paralleling multiple speakers on a single amp
output, you need to set the gains with all of the speakers in place,
since they will be affecting the power and distortion characteristics
of the channel as a whole.


5.7 How do I select proper crossover points and slopes? [DK]
================================================== =================

Basically, this requires a degree of patience. The subwoofer should be
started off at about 100Hz and adjusted until you are happy with the
sound. Keep in mind that the higher the crossover point, the more
power the driver on the high-pass will be able to handle but raising
excessively may cause the low-pass driver to sound raspy or unnatural.
The idea here is to first make rough selections to protect the drivers
and then to fine tune crossover point selections to achieve optimum
fidelity. It's all a matter of what sounds good to you after that, but
remember that even *minute* changes in crossover frequency can make
dramatic differences in the way your system sounds and images.

As a rule, subs should be crossed over no higher than 120Hz, a 6 1/2
mid should be able to handle about 90 Hz, a 5 1/4" should be okay with
about 100Hz, a 4" - about 500Hz, and tweeters vary from about
3500-5000Hz. These points all assume the use of a 12dB/octave
crossover ... if you have a steeper roll-off a lower crossover point
may be chosen. Remember, these are not hard and fast rules but rather
a rule of thumb to help you get started (and so you don't blow up all
your speakers when you are setting your gains!).


5.8 How do I flatten my system's frequency response curve? [IDB,
DK]
================================================== =====================

First, you'll need a good quality equalizer - either a 2/3 octave
(15-band) or 1/3 ocatve (30 band) equalizer or a quasi- parametric
equalizer such as PPI's PAR 224 that allows you to choose the center
frequency and bandwidth (Q) of each knob on the EQ. This will allow
adjustments to very specific frequency ranges. Next, you'll need to
get a hold of an RTA (Real Time Analyzer), which is an expensive piece
of equipment that good shops will usually have. The shops can then
equalize the system by making a measurement with the RTA, and varying
the levels on the equalizer in order to make the overall response curve
flat.

Unfortunately, most shops will not do this for free, since proper
equalization can take anywhere from a half hour to many many hours.

Another method involves buying an SPL meter (available from Radio Shack
for between $32 and $60) and a test disc (Autosound 2000 makes one that
runs about $25) that plays discreet frequency ranges - in 1/3 octave
groups. Then, moving through the range of frequencies, SPL
measurements can be taken at each range, and you can plot out a
"response" curve. You'll be able to see what frequency ranges need to
be boosted and which need to be cut. This process will be time
consuming (more so than an RTA, which can analyze the entire frequency
spectrum simultaneously), but should be much less expensive than having
it professionally done.

One last note: While a smooth curve will get the most points at an
auto sound competition, you must NOT rely only on the RTA to tell you
what sounds good. Use the RTA to get a good start, and then use your
(better, use someone experienced in tuning systems) ears to do the
fine-tuning.


5.9 How do I wire speakers "in series" and "in parallel?" [IDB]
================================================== =====================

Wiring speakers in series involves connecting at least two speakers so
that the first speaker's positive lead is connected to the amplifier's
positive terminal, and the negative lead is connected to the positive
lead of the second speaker. If there is a third speaker, its positive
lead will be connected to the second speaker's negative lead ... and so
on. The last speaker in the chain will have its negative lead
connected to the amplifier's negative terminal.

Speakers that are wired in parallel are all connected to the positive
and negative terminals of the amplifier. So, when two speakers are
wired in parallel, you'll connect each speaker's positive lead to the
amplifier's positive terminal, and you'll connect each speaker's
negative lead to the amplifier's negative terminal.

Be careful when wiring multiple speakers in parallel or series so that
you do not exceed your amplifier's rating. To calculate the effective
impedance of a number of speakers, use the following formulas:

Series Connections:
Z(t) = Z(1) + Z(2) + Z(3) + ... + Z(n)

That is, add up all of the impedances for each speaker to
get the total impedance. For example, with 3 4-ohm speaker
in series, the total impedance is 4 + 4 + 4 = 12 ohms.

Parallel Connections:
1/Z(t) = 1/Z(1) + 1/Z(2) + 1/Z(3) + ... + 1/Z(n)

That is, add up the inverse of the impedance of each
speaker and invert the sum to get the total impedance. For
example, with 3 4-ohm speakers in parallel, the total
impedance is 1 / ( 1/4 + 1/4 + 1/4) = 1 / (3/4) = 1.33 ohms.


5.10 Are there any alternatives for Dynamat? It's too expensive!
[MM, PK]
================================================== =====================

In this question, "Dynamat" refers to all commercial products that are
marketed expressly for reducing ambient noise in the car. Dynamat,
Stinger RoadKill, _et al._ all have similar pricing, so this question
is intended to give non-standard options.

There is a material known as "Ice Guard," which is used by roofing
contractors. It is similar to Dynamat, both in thickness and density.
It is self-adhesive on one side, and seems to work very well.
Unfortunately, it is sold only in large quantities (225 ft^2 rolls),
and runs about $70 for this much. Perhaps a few people could get
together for a roll, or it might be possible to get scraps from a
roofing contractor.

MCM Electronics (see Section 5.2), sells a product called
"Sound Deadening Pads" (part #60-2010) which cost $0.90 for each 10" x
10" square.


5.11 How many devices can I attach to my remote turn-on lead?
[IDB]
================================================== =====================

The remote turn-on lead that most head units will not provide very much
current (usually 250-300mA), so there is a limit to the number of
components you can activate with it. Generally, it is safe to hook up
two devices to the lead without having to worry about problems.
However, if you'll be activating more components, then you should
probably use a relay.


5.12 How do I wire a relay in my system? [IDB]
================================================== ===

There are two types of relays that are commonly used in 12-volt
automotive applications: Single-pole Double Throw (SPDT) relays, which
have 5 pins, and Single Pole, Single Throw (SPST) relays, which have 4
pins. Depending on the application, you can use either of these; for
remote turn-on leads (see Section 5.11), an SPST relay is fine,
SPDT relays are often used in alarm installations. Make sure that you
get a 12-volt relay - this specifies the voltage required to make the
relay "switch."

The connections on the two types of relays look like this:

SPST SPDT
===================== =====================
(87) (87)
+---------+ +---------+
| --- | | --- |
| | | |
(86) | | | | (85) (86) | | --- | | (87a - center)
| | | | (85 - right)
| | | | | |
+---------+ +---------+
(30) (30)

Pins 85 and 86 connect to the coil which causes the relay to switch.
On both relays, pins 30 and 87 are normally disconnected. When the
relay is activated (switched) pin 30 and 87 are then in contact. The
difference with the SPDT relay is that in the "normal" state, pins 30
and 87a are in contact.

To hook up a relay (either kind) for a remote turn on, make the
following connections:

*Pin 30*
+12 Volts (Battery +)

*Pin 87*
Amplifiers' remote turn-on terminal

*Pin 86*
Head unit remote turn-on lead

*Pin 85*
Ground

*Pin 87a*
No connection (SPDT only)


5.13 How do I design my own passive crossovers? [JSC, JR]
================================================== ==============

A "first order high pass crossover" is simply a capacitor placed inline
with the driver. A "first order low pass crossover" is an inductor
inline with the driver. These roles can be reversed under certain
circumstances: a capacitor in parallel with a driver will act as a low
pass filter, while an inductor in parallel with a driver will act as a
high pass filter. However, a parallel device should not be the first
element in a set; for example, using only a capacitor in parallel to a
driver will cause the amplifier to see a short circuit above the cutoff
frequency. Thus, a series device should always be the first element in
a crossover.

When like combinations are used, the order increases: a capacitor in
series followed by an inductor in parallel is a "second order high pass
crossover". An inductor in series followed by a capacitor in parallel
is a "second order low pass crossover".

To calculate the correct values of capacitors and inductors to use, you
need to know the nominal impedance Z of the circuit in ohms and the
desired crossover point F in hertz. The needed capacitance in farads
is then 1/(2 * pi * f * Z). The needed inductance in henries is Z/(2 *
pi * f). For example, if the desired crossover point is 200Hz for a 4
ohm driver, you need a 198.9 x 10^-6 F (or 199uF) capacitor for a high
pass first order filter, or a 3.18 x 10^-3 H (or 3.18mH) inductor for a
low pass first order filter.

To build a second order passive crossover, calculate the same initial
values for the capacitance and inductance, and then decide whether you
want a Linkwitz-Riley, Butterworth, or Bessel filter. An L-R filter
matches the attenuation slopes so that both -3dB points are at the same
frequency, so that the system response is flat at the crossover
frequency. A Butterworth filter matches the slopes so that there is a
peak at the crossover frequency, and a Bessel filter is in between the
two. For an L-R filter, halve the capacitance and double the
inductance. For a Butterworth filter, multiply the capacitance by
1/sqrt(2) and the inductance by sqrt(2). For a Bessel filter, multiply
the capacitance by 1/sqrt(3) and the inductance by sqrt(3).

You should realize, too, that crossovers induce a phase shift in the
signal of 90 degrees per order. In a second order filter, then, this
can be corrected by simply reversing the polarity of one of the
drivers, since they would otherwise be 180 degrees out of phase with
respect to each other. In any case with any crossover, though, you
should always experiment with the polarity of the drivers to achieve
the best total system response.

One other thing to consider when designing passive crossovers is the
fact that most passive crossovers are designed based on the speakers'
nominal impedance. This value is NOT constant, as it varies with
frequency. Therefore, the crossover will not work as it has been
designed. To combat this problem, a Zobel circuit (also known as an
"Impedance Stabilization Network") should be used. This consists of a
capacitor and resistor in series with one another, in parallel with the
speaker, e.g.,

________ __
+ o----| |----o-----o + | | /
INPUT | Xover | R1 | |/
| | C1 | |\
- o----|________|----o-----o - |__| \

To calculate these values, R1 = Re (in ohms) x 1.25, and C1 = (Lces in
henries / Re^2) * 10^6. See 4.1 for definitions of Re and Lces. R1
will be in ohms, and C1 will be in uF (micro- farads). As an example,
an Orion XTR10 single voice coil woofer has Re = 3.67 ohms and Lces =
0.78 mH. So, R1 = 3.67 * 1.25 = 4.6 ohms. C1 = ( 7.8E-4 / 3.67^2 ) *
10^6 = 57.9 uF (be careful with units - 0.78 mH = 7.8E-4 H)

As with the definition of crossover slopes, the above definition of the
phase shift associated with a crossover is also an approximation. This
will be addressed in future revisions of this document.


5.14 How do I build my own passive crossovers? [JSC]
================================================== =========

This section assumes that you have a basic understanding of how to
solder, so the actual assembly of the crossover is not discussed.
Rather, tips on choosing the proper types of capacitors and inductors
are given here.

To obtain low insertion losses, the inductors should have very low
resistance, perhaps as low as 0.1 to 0.2 ohms.

Also, be sure to select capacitors with proper voltage ratings. The
maximum voltage in the circuit will be less than the square root of the
product of the maximum power in the circuit and the nominal impedance
of the driver. For example, a 4 ohm woofer being given 100W peak will
see a maximum voltage of sqrt(100*4) = sqrt(400) = 20V. Make sure that
the capacitors are bipolar, too, since speaker signals are AC signals.
If you cannot find bipolar capacitors, you can use two polar capacitors
in parallel and in opposite polarity (+ to - and - to +). However,
there are some possible problems with this approach: the forward
voltage rating will probably not be equal to the reverse voltage
rating, and there could be a reverse capacitance as well. Both
problems could adversely affect your circuit if you decide to use
opposite polarity capacitors in parallel.


5.15 Can I split the single pre-amp output from my head unit
to drive two amplifiers with a Y-cable? [IDB]
================================================== =================

[This section was written by someone who wishes to remain anonymous,
but I will field any questions on the subject -IDB]

Yes. When two loads are connected in parallel (such as with a Y-cable)
they get the same voltage as each other. They do NOT get the same
voltage as if only one load was connected because the head-unit has an
internal resistance (typically around 600 ohms). So, given that the
amp has a typical input impedance of around 10k ohms then we get
something like this:

----------------------------- ----------------------------
HEAD UNIT ________ | | AMP |
______| |_________Vamp___________ |
| | R(head)| | | | | _ |
__|__ |________| | | __|___ |__| - _ |
/ \ | | | | | -___|__
| Vi | | | |R(amp)| | _- |
\_____/ | | |______| __| _- |
|_______________________________|________| - |
| | |
----------------------------- ----------------------------

for the single amp situation. Please realize that the R(head) and
R(amp) are internal to the head unit and amplifier and in fact are not
deliberately added resistors but are characteristic of the real world
circuits (non-ideal) in the head-unit and amplifier (and eq's, etc.).
These numbers are typical, check your specific equipment for its
particular specs. the worst case situation is a high source output
impedance and low load input impedance.

So, assuming a typical head unit and single amp the voltage seen at the
amp (Vamp) is given by (Ohms law/Kirkov's law/1st year EE/high school
electronics technology class/etc.):

R(amp)
Vamp1 = Vi * ------------------
R(amp) + R(head)

Vamp1 = Vi * 0.94

Now, putting two amps in parallel from the original signal, R(amp) is
effectively halved while R(head) is unchanged. Using the same voltage
divider formula we get:

10000/2
Vamp2 = Vi * ---------------------
10000/2 + 600

Vamp2 = Vi * 0.89

So, for an Alpine 4V preout, Vi in the diagram (the open circuit head
unit line level output) is 4V. Thus Vamp1 = 3.76V and Vamp2 = 3.56V.
With two amplifiers' inputs connected in parallel, the voltage is
reduced from 3.76V to 3.56V or approximately 5%, not a big deal.

If you had a more typical 1V preout you would get Vamp1 = 0.95V and
Vamp2 = .89V, also not a noticeable drop.

This is also why this is slightly more susceptible to noise than a
direct one-to-one connection. If the noise level inserted due to
cabling was 0.1V per cable then the noise level in the signal reaching
each of the two amps would be a slightly higher percent of the signal
level but not doubled. (this is also why the 4V head unit is favored
over the 1V unit for noise immunity: 0.1V noise / 3.76V or 3% is much
less than 0.1V noise / 0.95V or 10% even in a one to one connection).


5.16 How do I turn a stereo signal into a mono signal [BW]
================================================== ===============

Creating a mono signal is often necessary when you are powering a
subwoofer by bridging the amplifier. Many people do not realize that
bridging an amplifier does not always provide a mono signal - many
amplifiers will simply use only one input channel, which means that the
subwoofer won't be receiving the full signal.

Some amplifiers have a switch that will allow you to combine the left
and right channels into a mono signal. Some signal processors and head
units provide a subwoofer-out channel that can be switched between
stereo and mono.

If you don't have this feature on any of your equipment, you will need
to provide a mono signal to the amplifier. The common thought is to use
a Y-adapter to "combine" the left and right channels. However, by
using a Y-adapter, you are actually summing the line voltages and
directly shorting the left and right channels at the head unit, which
could cause problems.

The correct way to create a mono signal is to cut off the ends of the
RCA cables, combine the signal grounds (the outer shield), and then use
a 1 kOhm (1/4 watt, 5% tolerance) resistor to each of the center
conductors. Solder and insulate the resistors so that you don't short
them prematurely, and then connect the two resistors together. Connect
the summed signal ground to the shield of the new RCA plug, and the
summed center conductor to the center pin of the RCA plug.


5.17 5.17 How do I determine a speaker's polarity? [IDB]
================================================== ========

If you have a speaker and the terminals are no longer marked, you can do
a simple test to determine which terminal is positive (+) and which is
negative (-). This test is useful for midrange/midbass/subwoofers, but
not for tweeters.

Use a 1.5V battery (AA, C, D) and connect the (+) terminal on the
battery to one terminal of the speaker, and connect the (-) terminal to
the other terminal of the speaker.

If the cone moves OUT, then the battery is connected "properly," i.
e., the (+) terminal of the battery is connected to the (+) terminal of
the speaker, and the (-) terminal of the battery is connected to the
(-) terminal of the speaker.

If, however, the cone moves IN, the battery has been connected
"backwards," i. e., the (+) terminal of the battery is connected to the
(-) terminal of the speaker, and the (-) terminal of the battery is
connected to the (+) terminal of the speaker.


5.18 How can I use an oscilloscope to set the gains in my system?
[AO]
================================================== ======================

This section assumes you are already familiar with your oscilloscope and
will not go into setting it up. If you haven't already, spend a few
minutes with your scope's manual.

You'll need a test disc with a variety of test tones. I use the official
IASCA test disc, but there are some of the "Bass Discs" that have test
tones as well. You do NOT want to use sweeps, only pure tones. There is
an AutoSound 2000 disc (#101?) which has a signal which is unclipped for
20 seconds, clipped for 5, and then unclipped for the last 5 seconds. I
have never used the AutoSound 2000 discs, but know them to have
excellent recommendations (as well as all the test tones you could ever
need). Viewing this track on your scope's display could be useful if
you've never seen clipping on an oscilloscope display before.

You start by finding the clipping level of your head unit. Many of the
better head units will not clip the pre-amp outputs, even at full
volume, but it's always better safe than sorry. Disconnect the RCA's
from your head unit. Pop in your test disc and skip to the track with a
1 KHz tone. If your CD player has a repeat function, set it to repeat
just this track. That way you won't have to skip back at the end of the
tone. Set your bass, treble, fader, and balance all to center. Turn the
volume all the way up. Probe your right and left front (and rear if you
have them) one at a time. Your scope should show a wave, either a sine
wave or a clipped sine wave. If you have a standard pure sine wave then
all is good, and you're ready to proceed. If you have a clipped wave
then you need to turn down the volume, one click at a time until you
see a perfect sine wave on your scope's display. Remember this point, as
this is the highest you can EVER turn up your head unit. After you set
the level for one of your outputs the rest should be the same, but check
them all just to be sure. The results will be the same if you leave the
RCA's plugged into the head unit and disconnect them at the other end
(from your amp/EQ/processor/whatever) but unless you have a remote
control you'll be running back and forth to change the volume.

If your head unit has subwoofer pre-amp outputs you'll need to test them
using a different tone. I usually test subwoofer outputs at a level
midway between the crossover points. For example, if your subwoofer
outputs are crossed over at 80Hz then you would want to use a 40Hz test
tone. Other than that the procedure for testing subwoofer pre-outputs is
the same as testing front or rear outputs.

Once you've found the clipping level of your head unit it's time to
proceed down the signal chain. If you are using an EQ, preamp, DSP, or
other processor (NOT including crossovers) test them next. Leave your EQ
set the way you usually use it. Hook up the processor and probe all the
outputs of your processors in the same method as you did your head
unit. You should probe each of the outputs using tones that match the
bands of your EQ. For example, if you have a 9 band EQ with bands at
50/100/200/400/800/1.5k/3k/6k/12kHz you would probe your EQ 9 times,
once with a 50 Hz test tone, once with a 100 Hz test tone, and so on. If
your EQ also includes a crossover you'll need to follow the crossover
procedure. If any of these processors are clipping you will probably
need to turn down your head unit's volume control or make any
adjustments on that unit that you can. For example, if you are testing
an EQ and you have any bands excessively boosted, try bringing down
that band first. That may be causing your clipping.

To test your crossover you need to probe each output using a test tone
that is midway between the high and low pass. For example, a channel
which is crossed over between 100 Hz and 20 KHz (like a front channel)
would be tested at 9950 Hz. Since you'll be hard pressed to find a 9975
Hz test tone on your CD use the 10Khz tone. For a rear channel crossed
over with a lowpass of 3500 Hz you would use a 1750 Hz tone. As you
again would have problems finding a 1750 Hz tone on a CD use a 2 KHz
tone. For a subwoofer channel lowpassed at 70 Hz you would use a 35 Hz
tone. This one you may find on your CD, if not use 30 Hz or 40 Hz.

Assuming your crossover has level settings you will want to turn the
level for whatever channel you're testing all the way up and probe the
output. Assuming the output is clipping, back the level down slowly
until you see a perfect wave on your scope.

Now it's time to check your amp's outputs. Hook up your amps and play
the same test tones you were using on the crossover. Disconnect the
speakers and then turn the gains all the way up. Probe the first
channel's output. Adjust the gain the same way you did your crossover.
Back the gain down slowly until your wave isn't clipping anymore.

Voila! You are done. You have just effectively eliminated clipping from
your system. If you turn your bass or treble up, or boost up a channel
on your EQ you may introduce some clipping. After major EQ work you may
want to redo this procedure, starting at the EQ.


5.19 Why are kickpanels such a popular location for mounting
speakers? [ES]
================================================== ======================

There is a lot more to mounting speakers in the kick panels than just
equalizing the path length difference (PLD). Two of which a on-axis
response, and angling for pattern control. On-axis response refers to
the fact that most speakers sound best when listened to on-axis, or as
close to on-axis as possible. Second, after mounting your speakers in
the kick panels you can then angle the speakers to take advantage of
their off-axis response to use output level to overcome any PLD that is
still present. The pattern control I am mentioning is one of the ways a
horn loaded compression driver works very well, they not only use
amplitude to overcome any PLD that is still present they minimize early
reflections that can destroy imaging staging and spectral balance.

PLD can be improved more than marginally when you consider the stock
locations in a lot of vehicles, or the locations most installers choose.
Measure the PLD between tweeters when mounted high in the dash or at the
front corner at the top of the door and you will notice its probably on
the order of 24". This mounting setup requires a lot of amplitude
adjustment to correct the problems induced by this difference. The
nearer tweeter is out phase from the opposite side and is arriving much
sooner and with much greater amplitude due to the fact is not as far
away. When all these factors are added together, it is very difficult
for even the most flexible DSP unit to correct. On top of that, not
many people or installers have access to the necessary tools to properly
set up time delays using a DSP - TEF, MLSSA or other very expensive
time domain measuring equipment are required to do the job properly.

There will always be trade offs involved and deciding which trade offs
to take can be very hard. A small dropout due to phase cancellation will
probably not be noticed by most people but most people will quickly
notice when a vehicle is not imaging properly, and if you can move the
problem to higher frequency where we determine localization more from
amplitude rather than phase differences, it will be much easier to deal
with. Also, if you minimize the time/phase difference it will be much
easier to correct with amplitude.

Some people complain that kickpanel mounting gives a low sound stage.
However, keep in mind that when any stereo system is imaging properly
the point sources can no longer be localized. When our brains can no
longer localize the point sources it will then hear things at eye level.


5.20 How can I build custom kickpanels? [MB]
================================================== =

Building custom kickpanels for your car is a fairly advanced task, and
requires knowledge (and experience) in working with fiberglass. Auto
Sound & Security published an article in the August 1996 issue that
covered the basics of working with fiberglass.

This is kick panels in a nutshell. It takes about 2 days to do this
right, although it is possible to do overnight (a LONG night) in one
vehicle.

Step 1: Cover base area with plastic & duct tape.

Step 2: Lay fiberglass over the entire area. Don't worry about getting
the pieces cut to the exact size and shape, you will trim them later.

Step 3: Build the baffles for your speakers.

Step 4: After the fiberglass has cured, set the baffles (with the
speakers properly mounted into the panels and use a backstrap to secure
the baffle to the panels. Now, spend some time listening to the car and
aim the baffles until you get the best image and stage in the car.
Note: Take your time aiming the speakers - once you fix the baffles,
you won't be able to readjust the speakers. You may want to spend a few
days listening to different positions to determine what sounds best.

Step 5: Remove the speakers from the baffle and fill from behind with
self-expanding insulation foam. This will allow you to mold the baffle
into the rest of the car.

Step 6: After the foam has hardened, sand it to the shape you want the
panel to have.

Step 7: Lay fiberglass over the foam to form the top panel of the kick
panel.

Step 8: After the fiberglass has hardened, sand the surface smooth.
This may require the use of a little bondo to get things perfect.

Step 9: Remove the foam by grinding it out from the inside of the
kickpanel.

Step 10: Cover the panels with carpet, vinyl, leather, fleckstone or
other substance of your choice.

Step 11: Install the kick panels in the car.

Step 12: Install the speakers in the panels.

Step 13: Make speaker baffles from Plexiglas, and grilles.

Step 14: Enjoy.


5.21 What's worse for a speaker, too much or too little power? [IDB]
================================================== ====================

Problems occur (in everyday operation) when distortion is fed to a
speaker. This occurs MUCH more often when you are dealing with an
underpowered system - typically the owner will turn up the volume too
much or set the amplifier gains too high to try and get more volume
from the system. These introduce distortion to the signal - this will
destroy *any* speaker. ((see Section 5.22).)

When a speaker is overpowered, however, it is not nearly as common to
have these kind of problems, so speakers aren't blown as much. Of
course, it is certainly possible to destroy a speaker (thermally) by
overpowering it, but you'll have a pretty hard time doing this on your
own, especially with standard car audio amplifiers.


5.22 Why is distortion harmful to my speakers? [RK]
================================================== ========

Distortion is hard on speakers for two reasons.

Reason 1: Distortion causes the power spectrum to shift upwards in
frequency. A bass note, when distorted, will have lots of high
frequency energy. This will cause mid-ranges and tweeters to fry, if
the amplifier is operating full range. It doesn't harm woofers,
necessarily.

Reason 2: Distortion causes the average power to be much higher.
Typically, a music signal that never clips has an average power level of
1/4 the peak power level for even the most compressed speed metal or
pop. More dynamic music will be 1/8 the peak level or less on average.
When you clip the amp hard, the average output moves up to the
full-rated output of the amp or more. The peak to average ratio can be
less than 2 to 1, with the peaks being at double the rated power of the
amp, and the average being at the rated power of the amp or higher.

Thermally, the speaker can handle the average power being 1/4 the rated
power of the amp (little to no clipping), but it will have a much harder
time with the average power being the amp's rated power or more (massive
clipping). As you might expect, this is pretty hard on the amp, too.

For transients, most speakers can handle a ton of power. But for long
term signals, the power handling is much less.


5.23 What tools do I need to cut Plexiglas? [PS]
================================================== =====

A good quality Carbide Tipped Triple Chip saw blade is preferred when
cutting Plexiglas. This reduces the amount of chipout on the opposite
side of the material and produces a smooth edge.

A Router can be used to cut Plexiglas as well. The Router should be at
least 1.5 HP or better and with changeable collets for a 0.5" Shank
quality 2 flute Carbide bit. This reduces the vibration and chattering
when cutting and will produce a more smooth edge.

Since Plexiglas is an acrylic plastic (polymer), heat generated by the
saw blade or router bit when cutting will melt the material and create a
glazed imperfection viewed from the face if you do not maintain a steady
rate of cut. It is best that when cutting you do a rough cut first,
then do the finished size cut to reduce stress on the cutting blade and
equipment.


5.24 Are there any other special requirements for working with
Plexiglas? [PS]
================================================== ===================

Check the protective paper covering for any rips, tears or folding at
the time of purchase. In most cases if visual inspection is not done
at the place of purchase, it's very difficult to prove product defects
or damage done by the seller.

Inspect all surfaces that will come into contact to reduce tearing and
scratching of the protective paper covering and the Plexiglas finish.
Make sure that the protective paper covering remains in place until all
machining and milling tasks are finished.

6 Competition
********************

This section describes the competition branch of the car audio world -
what it is, and how to get involved.


6.1 What is IASCA, and how do I get involved? [JSC, HK, IDB]
================================================== =================

IASCA is the International Auto Sound Challenge Association, a
sanctioning body for car audio competitions held throughout the world.
Competitors earn points at each competition, and those that perform the
best each year can advance to the finals. Prizes (trophies, ribbons,
and sometimes cash) are usually given out to the top competitors in
each class at every competition.

IASCA memberships can be purchased at your local car audio retailer, if
they are an IASCA member. You can call IASCA at 602/437-4678 to get a
list of IASCA shops in your area.


6.2 What is USAC, and how do I get involved? [HK]
================================================== ======

USAC is another sanctioning body, similar to IASCA. However, USAC
places greater emphasis on SPL measurements than IASCA.


6.3 What are the competitions like? [HK, CD, IDB]
================================================== ======

[HK writes:]

They are much like loud car shows: a lot of cars parked with their
hoods/doors/trunks open showing their audio systems. There are two
types of judging styles: 1) drive through - where competitors drive
their own vehicles to judging stations to be judged, and 2)
walk-arounds - where the teams of judges will walk around the event
site and judge vehicles that fit within their judging assignments.
Typically SPL is done first with the mic stand in the driver's seat and
the competitor in the passenger side adjusting only the volume.
Hearing protection must be worn. After SPL measurements are completed,
RTA measurements are performed by playing pink noise. When the volume
level is within the specified "window" around 90db-110db, the RTA judge
will signal you out, and at that point you must exit the vehicle for
the actual scoring measurements. The next area for judging should be
sound quality where two judges will sit in your car and judge the sound
quality based on IASCA's reference CD/tape. The next area is
installation judging where the competitor has 5 minutes to explain and
show the installation of his/her vehicle. It is very useful to have a
picture book/album of photos of the installation that may not be
visible to prove that items not visible do exist. When that is
completed, the competitor can park the vehicle and show spectators the
vehicle. These procedures may differ from show to show, and at the
regional/final levels they are very strict in what can and can't be
done, e.g. a judge will make sure no adjustments are made after SPL
until after sound quality judging is over, ear protection, etc.

[CD writes:]

Most involve a lot of waiting around. Thus, they are perfect for
meeting other people interested in car audio, and seeing some
installations which may give you some ideas. They're also perfect for
listening to some cars that sound a lot better and a lot worse than
your own. In IASCA competition, the cars are judged on:

* Installation Quality (187 pts possible)

- Wiring (40 pts)

- Source Units (15 pts)

- Amplifiers (25 pts)

- Speakers (25 pts)

- Other Devices (25 pts)

- Overall Creativity (30 pts)

- Attention to Show Details (20 pts)

- Security and Convenience Features (7 pts)

* Sound Quality (248 pts possible)
- Tonal Accuracy and Spectral Balance (100 pts)

- Soundstage and Ambiance (65 pts)

- Imaging (50 pts)

- Sound Linearity (30 pts)

- Ergonomics (+/- 3 pts)

- Noise Adjustment (up to -20 pts)

* Frequency Response - RTA (40 pts maximum)

* Sound Pressure Level - SPL (1 point per dB)


6.4 Should I compete? [CD]
=================================

You should compete if:

a. You have an okay sounding stereo

b. You have an okay installation (i.e. no amps/changers sliding
around in the trunk)

c. You'd like some pros to comment on your system

d. Your feelings won't get hurt if you don't get first place

e. You've been to a contest and talked to competitors about it

f. You've read the rule book

g. You've listened to a test disc in your car, and understand
what the sound quality judges are listening for

You can compete even if you don't do all of the above, but the
recommendations will help you understand and gain the most from
competing.


6.5 What class am I in? [HK, JSC]
========================================

This section is mainly geared toward IASCA.

[HK,JSC write:]

There are three classes: novice, amateur, and pro. The novice class is
intended to be an unintimidating level where beginners can start out;
however, a competitor may only be in the novice class for one year, at
which time he is automatically moved to the amateur class. Most
competitors stay in the amateur class indefinitely, unless they become
affiliated with a car audio shop or manufacturer, at which point they
are moved into the pro class.

[CD writes:]

Are you or were you employed by a car audio manufacturer or dealer?

_Yes:_
You compete in pro

_No:_
Is this your first year of competing?

_Yes:_
You compete in novice for the first year

_No:_
You compete in amateur

Note that modifying your amplifiers, buying your equipment below
retail, or being sponsored by a manufacturer or dealer will get you
kicked into pro.

Also note that any home built active gear in the signal path (e.g.
custom built equalizers, crossovers, or noise gates) will get you
kicked out of novice.

Once you know what group you are, you next need to know what power
category you are in. Add up the 4-ohm non-bridged rating of all your
amplifiers, including your head unit if your head unit is powering
speakers (rather than exclusively feeding amplifiers). Then, find the
category you fit into:

Novice 1-150 151-300 301-600 601+
Amateur 1-150 151-300 301-600 601+
Pro 1-150 151-300 301-600 601+
Expert 1-600 601+

Thus, if you had a Rockford Punch 4040 (20Wx4) and a Punch 60ix
(30Wx2), with a head unit that put out 6Wx2 (powering, perhaps, a
center channel) you're in the 151-300 class. It does not matter if
your amps are bridged down to .002 ohms; it's only the 4ohm rating that
counts. If you no longer used your head unit to power speakers, you
would be in the 1-150 class.

Competition is usually most vicious in the 151-300 and 301-600
categories at typical contests.


6.6 Where can I find out when these Sound-Offs are? [IDB]
================================================== ===============

The best way to get the most current list is to call either of the
sanctioning bodies (IASCA or USAC). They can be reached at
602/437-4678 or 601/939-7828, respectively. You can also visit the
Official IASCA and USAC pages on the web at the following URLs:

IASCA - `http://www.iasca.com'

USAC - `http://www.soundoff.org'


6.7 How do I get sponsored by a manufacturer? [CM]
================================================== =======

Ah, the green grass on the other side of the competitor's fence;
sponsorship. Sponsorship is not the easiest thing to obtain. And it
might cause more problems than you anticipated. Obtaining sponsorship
really depends on how much dedication you show for competing and finding
the right manufacturer sponsorship deal at the right time.

Keep in mind that car audio manufacturers consider sponsorship a form of
advertising. Each manufacturer has a different policy concerning
sponsorship. They are looking for a competitor that has shown they are
committed to competing for a long time. They want someone that has
shown that they know how to win, but also, how to handle defeat
gracefully. They want someone that is well known in competition
circles, someone that new competitors can come to and ask questions
about the system and the manufacturer's products. They are basically
looking for people that will put their product out there for people to
see and help sell the equipment.

As a competitor, you must show that you are committed by to going to as
many shows as possible. You must open up your their vehicle and show
off the system. Manufacturers want a show system, which often means
turning your vehicle into a "trailer queen." That may require you to
buy a trailer and tow the vehicle to the shows you compete in (this also
means that you may need a new daily driver). And of course, if your
bought equipment below retail or were given the equipment, then you will
be forced to compete in the Pro or Expert class.

There are different levels of sponsorship. It usually starts with
manufacturer technical support. The manufacturer will give direct
technical assistance to the competitor. At larger shows, they may
reserve a space for you in their "tweek and tune" area.

Next, the manufacturers may let you buy equipment from one of their
dealers or the factory and a discounted price. This will definitely put
you into the Pro or Expert class. Some manufacturers will let you mix
and match equipment from different manufactures. Others want you to use
their equipment only.

Then the manufacturer might start giving you equipment and providing
some or all of the installation costs.

The holy grail of sponsorship is when the manufacturer provides the
equipment, installation, and pays some or all of your competition
expenses. It takes a lot of money to travel to shows. By the time
someone reaches this level, they are frequently hired as an employee of
the manufacturer. This is a good way of making the car audio business
your career.


7 Literature
*******************

This section describes various literature which you can read to brush
up on your car audio skills, or to keep current, or to see other
people's installations, or whatever else you'd like.


7.1 What magazines are good for car audio enthusiasts? [JSC,
MI, NML, JR]
================================================== =================

Car Audio and Electronics $19.95/year
P.O. Box 50267 (12 issues)
Boulder, CO 80323-0267 800/243-6400


Car Stereo Review $17.94/year
P.O. Box 57316 (6 issues)
Boulder, CO 80323-7316 303/447-9330

Auto Sound and Security $28.95/year
P.O. Box 70015 (12 issues)
Anaheim, CA 92825-0015 714/572-2255

Car Sound Buyer's Guide $17.95/year
939 Port Washington Blvd. (Quarterly)
Port Washington, NY 11050 516/944-5940


Car Hi-Fi #23.60/year
Freepost (8 issues)
TK660 081 943 5943
Leicester KE87 4AW

Bilstereo Forlags AB Skr ??
Box 230 84 (? Issues)
104 35 Stockholm 08-34 29 70
Sverige (Sweden)



7.2 Are there any newsletters I can read? [IDB]
================================================== ====

Unfortunately, AutoSound 2000 Tech Briefs is no longer in publication,
and as a result, there are no more newsletters currently in publication.


7.3 What books can I read? [JSC, JW, TT]
===============================================

_Loudspeaker Design Cookbook_
by Vance Dickason
Published by Audio Amateur Press
ISBN 0-9624191-7-6
$25-$30

_Designing, Building and Testing Your Own Speaker System_
by David Weems
Published by McGraw Hill
ISBN 0-8306-3374-X
$16.95

_Killer Car Stereo on a Budget_
by Daniel L. Ferguson
Published by Audio Amateur Press
ISBN 0-9624191-0-9
$19.95

_The Car Stereo Cookbook_
by Mark Rumreich
Published by McGraw-Hill
ISBN 0-07-058083-9
$24.95


7.4 Can I contact any manufacturers on-line? [IDB]
================================================== =======

Yes, there are a number of manufacturers who have started to use the
Internet and can offer advice for component selection, installation and
advice. A list of these manufacturers is available on the WWW, at the
URL:

`http://www.mobileaudio.com/intdir/'


8 Credits
****************

Here is a list of many of the people that have helped to build this
document. Many others (not mentioned here) have also made small
contributions, pointed out errors, or have provided moral support.

[JSC] Jeffrey S. Curtis
[JLD] Jason Lee Davis
[MI] Matt Ion
[JW] Jerry Williamson
[CD] Cal Demaine
[MO] Mark Obsniuk
[HK] Harry Kimura
[RDP] Dick Pierce
[BG] Brian Gentry
[JM] Jeff Meyers
[MH] Marvin Herbold
[TT] Trevor Tompkins
[MM] Matthew E. Meiser
[NML] N. M. Lines
[IDB] Ian D. Bjorhovde
[JG] John Graley
[DK] Dan Kreft
[JR] Jason A. Reiser
[PW] P. Wilson scratchy.mi.net!ccbbs!pwilson
[JGr] Jerry Grooms
[PK] P. Kaufmann
[MS] Manville Smith
[LC] Ligeng Cao
[AO] Andrew C. Ohnstad
[MB] Michael Brennan
[RK] Russell Kinder
[MHa] Mike Harmon
[ST] Steven Tolleneer
[JD] John Durbin
[PO] Paul Ozello
[PS] Phil E. Salisbury
[CM] Chuck Music
[BW] Brian Waplington
[AK] Andrew Krause
[MZ] Mark Zarella

Note: Many of these email addresses may be out of date.


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