Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine for
rough and ready measurements. They are not by any measure useful as accurate
devices.

Tone controls may be of some use, IF the problem being addressed can be
precisely matched by those tone controls AND the user has the requisite
equipment and expertise to adjust those controls. The chances of this are
approximately equivalent to that of a big lottery win.

Equalisers come in several flavours. For the sake of simplicity, I will lump
them into four, broad groups and assume that the listener owns and can
properly use the rather sophisticated testing equipment, which is VITAL to
ensure adequate results (Yes, I know it is an over-simplification):

Standard, analogue octave EQs. These are both better and worse than tone
controls, in their actions. Since frequencies and 'Q' cannot be adjusted,
they are of limited usefulness. These are marginally more likely of being
able to be adjusted correctly than a big lottery win.

Third octave analogue EQs. These are SIGNIFICANTLY more useful than octave
EQs. For obvious reasons. A good result is much more likely. About the same
as winning a mid range prize in a lottery.

Parametric analogue EQs. MUCH more useful than any of the above. A good deal
more experience is also required to get the best from these guys too.
However, I do acknowledge that these critters CAN solve problems.

Digital, zero phase shift EQs. Now we're talking. When used with the right
measurement equipment (nothing branded Radio Shack) these guys are capable
of doing the job that people THINK tone controls can do (but actually
cannot).


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine for
rough and ready measurements. They are not by any measure useful as
accurate devices.

Denial of reality noted. The fact is they are not what you claim and that
they are used by professionals along with corrections and have been measured
against precision devices and their differences noted. SVSubwoofers
recomends them and publsihes the corrections on their website.

Tone controls may be of some use,

That some small retraction.

IF the problem being addressed can be
precisely matched by those tone controls AND the user has the requisite
equipment and expertise to adjust those controls. The chances of this are
approximately equivalent to that of a big lottery win.

Not if you have a RS meter and test tones along with the corrections.

Equalisers come in several flavours. For the sake of simplicity, I will
lump them into four, broad groups and assume that the listener owns and
can properly use the rather sophisticated testing equipment, which is
VITAL to ensure adequate results (Yes, I know it is an
over-simplification):

Standard, analogue octave EQs. These are both better and worse than tone
controls, in their actions. Since frequencies and 'Q' cannot be adjusted,
they are of limited usefulness. These are marginally more likely of being
able to be adjusted correctly than a big lottery win.

Third octave analogue EQs. These are SIGNIFICANTLY more useful than octave
EQs. For obvious reasons. A good result is much more likely. About the
same as winning a mid range prize in a lottery.

It really depends on the user having test tones and an spl meter like the RS
with corrections and knowing where the problems are. A 1/3 octave EQ can do
more than lesser ones, but knowing where the problems lie is the key.

Parametric analogue EQs. MUCH more useful than any of the above. A good
deal more experience is also required to get the best from these guys too.
However, I do acknowledge that these critters CAN solve problems.

But they can't smooth out a room the way a graphic EQ can.

Digital, zero phase shift EQs.

They are all minimum phase devices.

Now we're talking. When used with the right
measurement equipment (nothing branded Radio Shack) these guys are capable
of doing the job that people THINK tone controls can do (but actually
cannot).


So the professionals who recomend the Radio Shack meters with the
correction, who have measured them to come up with the corrections and state
that they are very standardized form unit to unit are wrong and you are
right. Would you like another chair for your ego?

The Radio Shack meter is a wonderful unit. About a two and a
half
years ago, I did a calibration curve for the RS meter
using
lab
equipment, with Eric Busch from DLC Design adding the low
bass
down
to 10 Hz. This was published in PSACS Sound Bytes in two
issues.
These are the corrections that should be added to the
meter
readout
in order to achieve the correct SPL. These corrections are
only
valid for the meter set to C weighting, using 1/3 octave
pink
noise
(easily available from various CDs), with the mic pointed
at
the
speaker.
Both my analog meters and my digital meter measured the
same
in
October, 1996.These are corrections, they are to be added
to
the
meter readout for the correct response in dB SPL.

10Hz +20.5
12.5Hz +16.5
16Hz +11.5
20Hz +7.5
25Hz +5
31.5Hz +3
40Hz +2.5
50Hz +1.5
63Hz +1.5
80Hz +1.5
100Hz +2

125Hz +0.5
160Hz -0.5
200Hz -0.5
250Hz +0.5
315Hz -0.5
400Hz 0
500Hz -0.5
630Hz 0
800Hz 0
1KHz 0

1.25Khz 0
1.6KHz -0.5
2Khz -1.5
2.5Khz -1.5
3.15Khz -1.5
4KHz -2
5KHz -2
6.3KHz -2
8KHz -2
10Khz -1

12.5KHz +0.5
16KHz 0
20KHz +1

To measure the in-room response of your speakers with the
SLM,
find
a quiet and undistracted time, obtain a 1/3 octave pink
noise
CD,
mic stand, and worksheet. With the speakers in their
normal
positions and using a mic stand for the SLM (I've had good
results
just holding the meter too, pink noise is forgiving),
place
its
microphone where your ear would be at your favorite
position
or
"sweet spot". Set the meter to "C" and "slow". Play the 1
Khz,
1/3
octave pink band and set the level on the amp or preamp,
and
the
meter range, so the meter reads 80 dB at 0 dB on the
meter.
Higher
levels might cause driver compression in the frequency
extremes,
rolling off the response. Now go back to the first ISO
center
1/3
octave band on your CD (25 Hz on mine) and record the
response:
3.5, or -1.0 , or -5.0, or whatever it is. Now step
through
the
pink noise bands, recording the meter level each time.
This is
the
raw data.
Keeping the meter in the same measuring position, using an
accurate
CD, having a quiet room, repeating the measurements for
accuracy,
understanding what you are measuring, fresh batteries, not
talking
while measuring, having your meter calibrated for overall
level
(relative level comparison is unaffected), and doing only
one
speaker at a time if possible to avoid comb filtering
(variations
of plus or minus 2 dB are possible) are all important
factors.

Sometimes if I have to measure two speakers at a time, I
move
the
meter around in a figure eight pattern, slowly, and try to
obtain
an average reading, as the microphone moves in and out of
the
combing peaks and troughs. Best accuracy would be obtained
from
taking several measurements at different listening
positions,
if
one has the time and patience.
Now take the raw data and make the corrections on the work
sheet,
entering the new values in the appropriate column. Time to
either
moan or marvel, since this is the actual in-room 1/3
octave
pink
noise frequency response of your speaker/system at that
listening
position. Plotting the results on graph paper in different
colors
for left, right, center, etc. makes it look cool.

Yes, this way is tedious, but it is very inexpensive. And
very

accurate. For the third octave pink noise, I use Carver's
Amazing
Bytes CD, GRP Z-9907; other CD's with 1/3 octave pink
noise
ISO
centers a

My Disc, Sheffield 10045-2-T
Sheffield/Coustic Test and Demonstration Disc, Sheffield
10040-2
Autosound 2000 CD #103, $18, 800-795-1830
IASCA Setup and Test CD

HI-FI News and Record Review "CD-II", $30 Japan Audio
Society
Audio
Test CD-1, YDDS-2
--- these last two available from DB Systems,
603-899-6415.

For the others:
http://www.audioxpress.com/
http://www.mcmelectronics.com/main.html
http://www.parts-express.com/

There are other CD's that have warble tones on them, but I
am
not
comfortable using them. I also extensively use track 19,
disc
2,
from Delos "Surround Spectacular", DE 3179.
This has a slow sine sweep from 160Hz to 20Hz with the
voice
of
David Ranada announcing the frequencies as they
descend. A fantastic help when used with the Radio Shack
SLM,
you
can easily tell where the room peaks and dips are.

http://www.delosmus.com/

You have permission to copy and distribute this
information
freely,
as long as no commercial gain is involved.

This is from Rane's website:

RaneNote
EXPOSING EQUALIZER MYTHOLOGY
Exposing Equalizer
Mythology
.. Combining Filters
.. Phase Behavior
.. Marketing Buzzwords
.. Constant-Q
.. Passive and Active Equalizers
Dennis Bohn
Rane Corporation
RaneNote 115
© 1986 Rane Corporation
Introduction
John Roberts is one of my heroes. John wrote a regular
column for the now defunct magazine Recording Engineer/
Producer entitled "Exposing Audio Mythology". "Laying to
Rest. or at least exposing the false premises upon which
they are based. some of the Pro-Audio Industry's more
obvious 'Old Wives Tales' "- such was the opening for
John's first column. Great stuff, you could almost hear the
theme music and see the masked rider off in the distance.
He originally intended to do a few columns on the most
flagrant abuses, that was in early 1983. He continued until
mid-1986. Every issue, without fail, he waged war on the
myth-sayers. John is resting now. Myth exposing is too much
for one person. I'm arrogant enough, and angry enough, to
help out. So I thought I would expose some of the most
popular myths regarding equalizers.
Mythology-1

MYTH #1: There exists such a thing as a combining
filter.
Many contractors are very confused over just what a
combining filter is. So am I. Filter designers have many
names for different types of filters: Butterworth, Chebyshev,
Bessel, etc., but combining isn't one of them. The problem
here is with the use of the word filter. We must distinguish
between what is being thought and what is being said. Within
the context of using this phrase lies the real intent, i.e., how
much ripple exists in the output.
The outputs of filter banks combine (or actually, recombine)
to form a resultant curve characterized by an overall
shape and a ripple content with associated phase shift. How
this combining takes place and the bandwidth of the individual
filters dictates the amount of ripple. The type of filter
used has nothing to do with it. Combining is done by electronically
summing together all of the filter outputs. It is not a
filter at all: it is a means of summing individual filter's
outputs. All equalizers combine their filter outputs. It is
wrong to say an equalizer is non-combining. The only
examples of non-combining filters are real time analyzers and
crossovers. An example of the misuse of this term concerns
comparison between constant-Q and conventional graphic
equalizers. (Conventional, as used here, refers to any graphic
equalizer that is not constant-Q.) The popular, albeit false,
belief is that conventional equalizers use combining filters,
while constant-Q designs use non-combining filters. Both
designs sum their outputs together. The difference lies in the
smoothness of the combined curves. The fallacy lies in taking
the answer out of context.
Setting a conventional equalizer to have the same bandwidth
as a constant-Q design produces a combined result
exactly the same if the number of summers is the same.
However, the only condition where this occurs is either full
boost or full cut. Most users do not understand this is the only
position where the affected bandwidth is one-third octave
wide (for one-third designs). At all other boost/cut settings
the bandwidth degrades to over one octave wide. There is no
doubt that if two adjacent filters located one-third octave
apart degrade to where each is one octave wide, then the
summed result will be very smooth. There is also no doubt
that this is no longer a one-third octave equalizer. It now acts
as an octave equalizer. If that is what is required, then a
conventional equalizer is the correct choice; however, if onethird
octave control is required, then only a constant-Q design
will do.
MYTH #2: Minimum Phase behavior is an important
criteria when buying an equalizer.
Minimum phase is one of the few things you don't have to
worry about when buying an equalizer. It's not that it isn't
important, it is. It's just that no known examples of commercial
equalizers that are not minimum phase even exist. None.
Forget all the marketing hype to the contrary.
A precise definition of minimum phase is a detailed
mathematical concept involving positive real transfer functions,
i.e., transfer functions with all zeros restricted to the left
half s-plane. If the last sentence produced a zero in the middle
of your brain, don't worry. All you need to know is minimum
phase behavior is not a problem in any equalizer you may
consider purchasing.
Here again is an example of sloppy rhetoric. A failure to
communicate clearly what is being thought. Somewhere years
ago some marketing type needed a term, a buzz word if you
will, for distinguishing his company's equalizer from everybody
else's. Some engineer dropped the term minimum phase
and the marketing guy went nuts. That's it, thought he; never
mind that it doesn't fit what is trying to be said, it sounds
good. Nice and high-tech, so he used it to try to build a smoke
screen between comparable products.
What they wanted to say was their product could create
boost/cut curves with less phase shift than their competitors,
and that this was a good thing. Problem was, here comes the
engineer again to say this simply wasn't true. Any two
equalizers producing the same curve do so with exactly the
same phase shift. Same universe, same physics, same re-
sults-much to marketing's chagrin. So they compromised on
claiming their product had MINIMUM PHASE characteristics.
Never mind that all the competition also had minimum
phase behavior. The customer wouldn't know that. The
promotion implied that the other products didn't. Let the
buying public figure out otherwise.
Okay, now you know otherwise. Don't be hoodwinked by
this buzz word.
Mythology-2

MYTH #3: Only one brand of equalizer exhibits
complementary phase performance.
Speaking of buzz words, here's a beaut: complementary
phase shift. Somebody worked overtime on this campaign. I
guess what gets me so angry about this issue is the arrogance
of the manufacturer. The underlying premise is that the pro
audio public is so gullible they will believe anything, if
presented profoundly. Well, they are wrong. All of you are a
whole lot smarter than they give you credit for. Street smarts
go a long way in solving problems.
Complementary phase shift means nothing more than the
equalizer displays symmetrical boost/cut curves (and is
minimum phase). The boost curves are mirror images of the
cut curves. That means the phase shift of the boost is also a
mirror image of the cut. If two things are mirror images of
each other, they are complementary. Nothing too profound.
Now, it is not true all equalizers exhibit symmetrical boost/
cut curves. Therefore, not all equalizers have complementary
phase shift. At least two of the more popular brands do not.
So, if you perceive this to be an important parameter when
buying an equalizer, you are correct in asking whether the
unit has symmetrical boost/cut curves. I can give you a list of
a dozen manufacturers whose equalizers do. In truth, every
example of graphic equalizer I'm familiar with has symmetrical
boost/cut curves, as well as most of the parametrics on the
market. In fact, you have to look long and hard to find
examples of equalizers that are not complementary phase
performers. As I said, I know of two, there may be more.
The correct question at this point is why do you care if the
equalizer has complementary phase shift? Damned, if I know.
I can tell you why they say it is important, and I can tell you
why they are misleading you.
The popular demonstration involves setting up one channel
with an arbitrary curve and then adjusting the other channel for
the opposite response. Passing a signal through both channels in
series produces a flat frequency response. No phase shift. No
time delay. Now this result seems to have overwhelmed them.
They describe the results as bizarre, remarkable and baffling. I
can find no one else that is the least bit surprised. This is one of
the few places where your intuition is correct.
If you take two equalizers set for complementary curves
and put them in series you get a response of unity. You do not
get an all-pass response, as they claim. There is no amplitude
variation, no phase shift, and no time delay. Basic sophomore
electrical engineering tells us why. Something called a
transfer function represents each channel. This mathematical
equation completely describes the amplitude, phase and time
response of a signal passing through that channel. The
complementary channel's transfer function is the reciprocal
of the first. Putting them in series causes the two transfer
functions to multiply. Anything times the reciprocal of itself
produces the answer of unity, i.e., (1/X)(X)=1. Nothing too
difficult here. One is not the transfer function of an all-pass
filter. One is the transfer function of a piece of wire.
So what does all this have to do with what kind of equalizer
you may want to buy? Not much, really. The implication
is that you must have a complementary phase equalizer to
correct for a room's frequency anomalies - not true. Any
equalizer that produces the opposite room response works -
and works just as well.
MYTH #4: Constant-Q means non-symmetrical
boost/cut curves.
Until 1986, I wouldn't have considered this an official
myth. At that time, F. Alton Everest published a book,
entitled Successful Sound System Operation (TAB Books No.
2606). It is a well done introduction to the business of sound
reinforcement, and I recommend it to anyone just starting out.
His treatment of constant-Q equalizers (p. 252), however,
needs some revising.
Mr. Everest states erroneously and unequivocally that
constant-Q equalizers characterized themselves by having
asymmetrical boost/cut curves. (This occurred from a
misreading of a popular parametric equalizer's data sheet;
something easy to do.) This myth involves a mixing of two
separate issues.
Reciprocity of boost/cut curves and constant-Q have
nothing to do with each other. You can find constant-Q
symmetrical and non-symmetrical equalizers and you can find
non-constant-Q symmetrical and non-symmetrical equalizers.
The terms characterize two different aspects of an equalizer.
Constant-Q refers to the bandwidth behavior for different
amounts of boost or cut. If the bandwidth stays constant as a
function of boost/cut amounts, then it is constant-Q. If it does
not, then it is not a constant-Q design.
If the cut curves are mirror images of the boost curves,
then the equalizer has symmetrical (or reciprocal) response.
If the curves are not mirror images of each other, then the
equalizer is of the non-symmetrical school.
Two separate issues, both available in any combination
from several manufacturers. Your choice.
Mythology-3

MYTH #5: Given identical equalizers, one passive
and one active, the passive unit will sound different.
The key to whether this is a myth involves the crucial
word, identical. If two equalizers do not produce the exact
transfer function, then they will definitely sound different.
That is not the issue here. At issue, is whether there exists
some sound quality attributable to active or passive circuits
per se. There does not.
A transfer function exists characterizing every equalizer's
output behavior to a given input change. Any two equalizers
with the same transfer function, when operating within the
constraints necessary to behave according to that function,
will give the same results no matter what physical form
makes up the equalizer. In general, any equalizer response
can be implemented by many different types of circuits, both
active and passive. The perceived differences between
equalizers designed for the same response function must be
explained by factors other than whether the equalizer is active
or passive. Some characteristics that can contribute to the
misbehavior of the circuit are nonlinearities that occur
because the components are being used improperly or
stressed beyond their linear operating region. Sometimes the
perceived differences are nothing more than one circuit is
quieter than another.
Any two equalizers with the same frequency domain
transfer function will behave the same in the time domain.
The transfer function determines responses such as overshoot,
ringing, and phase shift regardless of implementation.
Nothing mysterious exists within the realm of active and
passive equalizers. Simple electronic theory explains all
differences between these two, if differences exist. If not,
they will perform and sound the same to the objective
observer. Never assume that because an equalizer is active or
passive it is automatically better or worse for your application.
Study your needs and consult with knowledgeable
people to make the correct equalizer selection.
MYTH #6: An ideal equalizer would add no phase
shift when boosting or cutting.
Phase shift is not a bad word. It is the glue at the heart of
what we do, holding everything together. That it has become
a maligned term is most unfortunate. This belief stands in the
way of people really understanding the requirements for room
equalization.
The frequency response of most performing rooms looks
like a heart attack victim's EKG results. Associated with each
change in amplitude is a corresponding change in phase
response. Describing them as unbelievably jagged is being
conservative. Every time the amplitude changes so does the
phase shift. In fact, it can be argued that phase shift is the
stuff that causes amplitude changes. Amplitude, phase and
time are all inextricably mixed by the physics of sound. One
does not exist without the others.
An equalizer is a tool. A tool that allows you to correct for
a room's anomalies. It must be capable of reproducing the
exact opposite response of the one being connected. This
requires precise correction at many neighboring points with
the associated phase shift to correct for the room's opposing
phase shift. It takes phase shift to fix phase shift. Simple as
that.
One way people get into trouble when equalizing rooms is
using the wrong type of equalizer. If an equalizer is not
capable of adding the correct amount of phase shift, it will
make equalizing much more difficult than it has to be. The
popularity of the many constant-Q designs has come about
because of this phenomenon. Equalizers that produce broad
smooth curves for modest amounts of boost/cut make poor
room equalizers, and good tone modifiers. They lack the
ability to make amplitude and phase corrections close
together. Lacking the ability to make many independent
corrections with minimal interference to neighboring bands
restricts their usage primarily to giving a shape to an overall
response rather than correcting it. Serious correcting requires
sharp constant-Q performance, among many other things.
Only by adding many precise, narrow phase shift and
amplitude corrections do you truly start equalizing a system's
blurred phase response. You do not do it with gentle smooth
curves that lack the muscle to tame the peakedness of most
rooms. Broad smooth curves do not allow you to correct for
the existing phase shift. Its just that simple, you must preshape
the signal in both amplitude and phase. And that
requires narrow filters that preserve their bandwidths at all
filter positions.
©Rane Corporation 10802 47th Ave. W., Mukilteo WA 98275-5098 USA TEL
(425)355-6000 FAX (425)347-7757 WEB http://www.rane.com
Mythology-4 02224 3-98

as is this next bit, rather long but worthwhile:

Home THX Equalization Manual Rev. 1.5
Home THXÒ Audio System
Room Equalization Manual
Rev. 1.5
This document is Copyright 1995 by Lucasfilm Ltd
THX and Home THX are Registered Trademarks of Lucasfilm Ltd
Dolby Stereo, Dolby Pro Logic, and Dolby AC-3 are trademarks of Dolby
Laboratories Licensing Corporation
1

Home THX Equalization Manual Rev. 1.5
Table of Contents
Introduction and Background: Why Room Equalization?
...................................... 3
Test Equipment Requirements
.................................................. ..........................
4-5
The Home THX Equalizer
.................................................. ......................................
5
Equalization Procedures
.................................................. ..................................
5-22
Section 1: EQ Procedure Using the THX R-2 Audio
Analyzer............................ 6-13
1.1 - 1.3Test Equipment Set-Up
.................................................. .................. 6-9
1.4 - 1.7 LCR Equalization
.................................................. ........................
10-11
1.8 - 1.10 Subwoofer Equalization
.................................................. .............. 11-13
1.11 Listening Tests
.................................................. ................................
13
Section 2: EQ Procedure Using a Conventional
RTA...................................... 14-21
2.1 - 2.3Test Equipment Set-Up
.................................................. ............... 14-17
2.4 - 2.6LCR Equalization
.................................................. ........................
17-18
2.7-2.9Subwoofer Equalization
.................................................. .............. 19-21
2.10 Listening Tests
.................................................. ................................
21
Equalization Checklist
.................................................. .........................................
22
Appendix: "WOW!" A User's Guide to the Laser
Disc..................................... 23-24
2

Introduction and Background:
The goal of the Home THX Audio Program is
to reproduce in the home the film sound experience
exactly as the director heard it on the film
dubbing stage. Even with all the elements of a
Home THX Audio System correctly installed, one
challenge remains to our ability to perfectly "close
the loop" connecting the dubbing stage to the
home environment. That challenge is the almost
infinite variability of room acoustics. To achieve a
consistency of performance under varying acoustical
conditions, some form of room equalization is
necessary.
Why Room Equalization?
In the room volumes (under 6000 cu ft) for
which the Home THX Audio System was designed,
several problems exhibit themselves no
matter how "flat" or "accurate" a speaker is designed.
The first problem is the existence of room
modes or standing waves. These modes are a
function of each room's shape and dimensions,
and cause uneven frequency response with
peaks and dips in the low frequency range. Since
these standing waves occur at fixed locations for
fixed frequencies within a room, there is no way to
completely avoid these artifacts. However, since
the audience for a home theater remains generally
in one specific area of a room, prudent equalization
can usually level these peaks and troughs
and produce smoother response in the listening
area. The proper positioning of the Subwoofer
elements of a Home THX Audio System can do
much to minimize these standing wave artifacts
(see the Home THX Newsletter #2), but even with
careful placement, bass equalization is usually
necessary to restore a flat and accurate bass
response.
The second problem which room equalization
is designed to correct is that of speaker/room
boundary interactions. These boundary interactions
are the same ones that make a loudspeaker
appear to have more bass when placed in a
corner versus the center of a room. As you can
see, the placement (for example) of the screen
LCR loudspeaker asymmetrically in a room can
Home THX Equalization Manual Rev. 1.5
have serious repercussions. The speakers placed
nearer to the room's boundaries will have a
different tonal balance to those placed more
centrally. The result of unequal tonal balance is
that sounds can vary dramatically as they are
panned across the three front channels, and
dialogue from boundary-close loudspeakers may
have poor intelligibility.
In both circumstances, with room modes or
with room boundary problems, a properly set up
room equalizer can restore the accurate spectral
and inter-channel tonal balance of a home theatre
system. Remember that these effects will vary
from room to room and installation to installation.
As valuable as room equalization is in restoring
correct spectral balance, the measurements
required to obtain consistent and repeatable
response are very tricky. During the 60's and
70's, graphic equalizers were introduced by the
home audio industry. Unfortunately, these products
were used for everything from tone controls
to a means of forcibly obtaining flat frequency
response from grossly inaccurate loudspeakers.
One test method of the period was to use records
with tracks separated into 1/3 octave pink noise
bands and to plot a speaker's output band by
band with an uncalibrated SPL meter! In most
cases, the results were highly unsatisfactory. The
concept of equalization to correct for room modes
and boundary effects was, without accurate test
procedures, almost forgotten in the consumer
audio field.
However, within professional audio circles,
and in particular the motion picture industry, the
use of equalization to improve the accuracy of
sound reproduction has been continuously refined
and perfected. Over the past decade the Professional
THX Theatre program has equalized over
600 motion picture auditoriums world-wide on a
yearly basis. Since the inception of the THX
Sound System program, records have been
maintained of the thousands of auditorium analyses
and equalizations that we have performed. It
was from this experience that the standards for a
Home THX Room Equalizer and the enclosed EQ
procedure were developed.
3

Home THX Equalization Manual Rev. 1.5
Test Equipment Requirements
1.) Real Time Analyzer
This procedure requires the use of a realtime
(spectrum) analyzer and a pink noise source.
The analyzer approved for use is theR-2 THX
Audio Analyzer. The R-2 analyzer contains the
following:
.. a 4 input real-time analyzer with measurement
bands at ISO one-third octave and ISO octave
intervals
.. four calibrated omnidirectional microphones
.. spatial averaging through microphone multiplexing
.. averaging over time (10 seconds up to 2
hours)
.. a calibrated internal pink noise source
Along with real-time analysis, theR-2 Analyzer
can measure room reverberation (RT-60) and
background noise (NC levels).
If the R-2 Audio Analyzer is unavailable, the
following equipment may be used with ca
.. A real-time analyzer with measurement
bands at ISO one-third octave intervals and a
display range of ± 5 dB (minimum)
.. A calibrated omni-directional microphone, or
microphones.
.. The analyzer must be capable of defeating
any weighting which may be applied to the
real-time display
.. The real-time analyzer must be also capable
of correctly storing and averaging a minimum
of four measurements and have a slow response
mode.
The use of a single RTA, a large number of
multiple measurements, and the averaging of
these measurements is a time consuming
process and can be subject to a high degree
of operator error. It is therefore highly recommended
that R-2 be employed whenever
possible.
2.) Pink Noise Sources
Pink Noise can be obtained from one of the
following sources:
.. the R-2 analyzer
.. the "Wow!" laser disc Chapters 8-10
.. the Delos/Stereo Review Surround Sound
Test CD
.. any calibrated true pink noise source (this can
be verified by measuring the noise source into
the line input of the analyzer for flat response)
Why Pink Noise
What is Pink Noise and why choose it over
White Noise? Simply put, white noise is a random
signal with equalamplitude per frequency,
and pink noise is a random signal with equal
energy per octave. Let's look at two octave
bands; say from 500 Hz to 1 kHz and 1 kHz to 2
kHz. If each of these bands had equal amplitude
per frequency, it's apparent that the 1-2 kHz band
would contain more energy than the 500 Hz to 1
kHZ band because it contains twice the number of
frequencies. Consequently white noise sounds
very bright. Pink noise, however, containing equal
energy per octave, closely reflects our psychoacoustic
expectations of flat response. Because
of this perception of flat tonal balance, pink noise
is a very useful tool when using a spectrum
analyzer with 1/3 octave or octave measurement
intervals, and when comparing loudspeakers for
spectral similarity by ear .
One element of caution is necessary,
though. Because pink noise has a random element
to it, when you measure pink noise using a
4

Home THX Equalization Manual Rev. 1.5
peak level meter or some RTAs you will notice
peaks far above the average. This is more
noticeable through a Subwoofer than through an
LCR speaker. This is because a random bass
peak can last for a longer time (lower frequency =
longer period) than most RTAs or SPL meters
average for. Higher frequency peaks last for a
shorter period. This is why most measurements
using pink noise are averaged for a long time or
are made by averaging multiple measurements.
That way these instantaneous peaks won't throw
your readings off.
3.) The Home THX Room Equalizer
The Home THX Room Equalizer meets the
exacting specifications of the Lucasfilm Home
THX Audio program. It is specifically designed to
have the wide dynamic range, low noise, and low
distortion required by the demands of motion
picture soundtracks. Careful attention was also
paid to musical transparency.
The frequency centers of each channel's
controls are carefully chosen to provide the
precise control necessary for accurate room
equalization, and the "constant Q" nature of each
control assures the operator that corrections to
one band don't "spill over" into adjacent bands.
Parametric controls (where provided) allow for the
pin-point correction of mid-frequency problems,
and every equalizer is provided with a security
cover to help keep a tuned system tuned.
Equalization Procedure
NOTE: THE FOLLOWING TEST PROCEDURES
ASSUME THAT A HOME THX AUDIO SYSTEM
HAS BEEN PROPERLY INSTALLED, AIMED AT
THE LISTENING AREA, AND LEVEL CALI-
BRATED. FAILURE TO CORRECTLY INSTALL
A HOME THX AUDIO SYSTEM MAY RESULT IN
INCORRECT ANALYZER READINGS, IM-
PROPER EQUALIZATION, AND AN ACTUAL
REDUCTION IN THE OVERALL PERFOR-
MANCE OF THE SYSTEM.
Please refer to theHome THX Audio System
Installation and Operation Manual (available from
any Home THX Licensee) for details on system
design, setup, and calibration.
For your convenience, an Equalization Procedure
Checklist is located on page 22 of this
Manual. We recommend that you use it as a
handy reference only after thoroughly studying
this Manual.
Graphic Conventions: When referring to the THX
R-2 Analyzer, specific, numbered function keys
on the control computer are identified by the
following graphics:
F-7
5

Home THX Equalization Manual Rev. 1.5
SECTION 1: Room Analysis Using the R-2 Analyzer
1.1) Define The Listening Area:
The first step in correctly equalizing a Home THX Audio System is to
identify the listening area.
The equalized response of the system will be averaged over this area to
provide a balanced sound
field for all listeners. Equalizing for a single position can result in poor
performance at other points in
the listening area. However, calibration of SPL (Sound Pressure Level) may
be done from a single
reference position using the internal test signals of the Home THX
Controller. These bandwidth limited
signals minimize room mode effects.
You should pay particular attention if the listening area is particularly
deep (several rows) or wide.
With some measurement positions very close to Left or Right screen speakers,
care will be needed in
averaging the RTA measurements to prevent unintentional weighting.
1.2) Choose Measurement Positions:
1
2
3
4
Mic Positions
Suggested Microphone Positions for 1 Row Seating
Fig 1
6

Home THX Equalization Manual Rev. 1.5
.. Choose four positions that represent prime listening positions spaced
equally throughout the
listening area (Fig. 1).
.. Position your analyzer's microphones at seated ear height (38" to 48" off
finished floor). Place the
microphone(s) on a stand.
.. Do not attach any microphone directly to the analyzer or hold it in your
hand. Your body is an
acoustical object large enough to influence what is supposed to be a room
measurement.
.. Label in your notes each position and note any related information (e.g.,
Microphone 3 located
under loft overhang) which can affect your interpretation of the
measurements.
.. Do not point any microphone directly at a loudspeaker. Point it straight
up. You are looking for a
room measurement, not just the direct field of the loudspeaker.
.. If you are placing a microphone on any piece of furniture (i.e., a chair
or couch), make sure that
the mic is away from any cushion or seat back by at least 1 foot. This will
improve the accuracy of
measurements at that position above 800 Hz.
For multiple rows of seats, see Fig. 2 below.
1
2
3
4
Mic Positions
Multiple Row Seating and Microphone Positions
Fig 2
7

Home THX Equalization Manual Rev. 1.5
1.3) Home Theatre and Test Equipment Set-Up
Home Theatre Equipment:
.. Switch your Home THX Controller to the "Dolby Pro Logic Surround" mode.
The Home THX
Cinema mode must be switched off for this procedure. Note: For Controllers
featuring Dolby
AC-3 Decoders, there is no easy method to insert broad band pink noise into
this signal path.
Equalization should be done through the Dolby Pro Logic mode on these
controllers as well.
.. Calibrate the individual channel levels as usual using the internal test
signals and a reliable SPL
meter.
.. Disconnect or disable the Subwoofer and the channels you are not
measuring. You want to analyze
each channel individually and disconnecting unused channels helps prevent
assignment
errors. One installer spent a frustrating hour trying to EQ a Center Channel
speaker only to find
that he had been playing pink noise through the Right Channel speaker.
.. Set the System Volume at Reference.
Pink Noise Sources:
Pink Noise may be obtained from one of the following sources:
.. The internal pink noise source of theR-2 Audio Analyzer
F-7
.. The "Wow!" laser disc, Chapters 8-10.
.. The Delos/Stereo Review Surround Sound Test CD
.. External calibrated pink noise source (200 mV RMS) placed into each
channel's EQ input.
R-2 Setup:
Defeat any weighting on the RTA portion of R-2 (e.g., "C" weighting).
Measurements are to be taken
with flat response.
,
,
F-3 F-4 F-4
Set the analyzer to Slow Response.
,
F-2 F-2
Set your analyzer's scale to the appropriate SPL range, and the dB per
division scale to 2 dB.
F-3 , F-2
8

Home THX Equalization Manual Rev. 1.5
Set the measurement time to a minimum of 20 seconds.
,
F-4
F-2
Begin the multiplexing operation. F-1
,
F-5
1.4) Real-Time Analysis:
.. Begin with the Center Channel
.. Start your pink noise source.
If using "Wow!" Chapters 9, put the appropriate track on A-B
repeat so that it conveniently cycles automatically.
F-7(Note: "Wow!" pink noise chapters will allow for
a maximum measurement interval of 20 seconds, so when using "Wow!" as a
noise source the
minimum and maximum measurement intervals are the same.)
.. Begin your measurement interval.
F-8
IF USING "WOW!" AS THE SOURCE, BE SURE
THAT YOU BEGIN THE INTERVAL IMMEDIATELY AFTER THE CHAPTER HAS REPEATED!
Any blank spot during the measurement interval will corrupt the data.
.. Analyze your spatially and temporally averaged data.
NOTE: DISPERSION AND AIR ABSORPTION AT HIGHER FREQUENCIES WILL CAUSE A
GENTLE ROLL OFF IN RESPONSE BEGINNING AROUND 6 kHz. THIS IS NORMAL AND DOES
NOT REQUIRE EQUALIZATION. (Fig. 3)
Typical Unequalized LCR Room Response
dB
SPL
60
65
70
75
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 3
9

Home THX Equalization Manual Rev. 1.5
1.5) Equalize:
The resulting spatial average will approximate the inverse of the correct EQ
curve. As a starting
point, assume that a dip of -3 dB on the analyzer calls for an increase at
the appropriate EQ frequency
of +3 dB. Remember the scale on the analyzer is 2 dB per division.
Since we will re-measure a number of times, any over correction or under
correction will be
caught. When analyzing the averaged RTA curve, try to look for the mean SPL
for all frequencies and
adjust the peaks and dips to that mean.
Remember that we are trying to achieve a response in the LCR channels of ±1
to 2 dB from 100
Hz to 1 kHZ without drastic EQ shifts. A boost of 6 dB places many demands
on both amplifiers and
loudspeakers.
1.6) Re-analyze:
After applying the corrections to the appropriate channel frequency centers,
re-run the procedure
described in 1.4 to verify the corrections. You will find that you will have
to measure and correct
several times to achieve a balanced and repeatable response.
NOTE: ABOVE 1 kHz, IN TYPICAL ROOM ENVIRONMENTS, THE SOUND FROM HOME THX LCR
SPEAKERS IS DIRECT FIELD DOMINATED AND THE FREQUENCY RESPONSE MAY BE POSI-
TION DEPENDENT. AVOID DRAMATIC EQ CHANGES ABOVE 1 kHz. SINCE WE ARE MORE
SENSITIVE TO FREQUENCY PEAKS THAN DIPS, USE THE CONTROLS AVAILABLE SPARINGLY
TO REDUCE HIGH FREQUENCY PEAKS, RATHER THAN TRYING FOR RULER FLAT RESPONSE
..
Avoid radical EQ beyond this point.
Typical Unequalized Room Response
dB
SPL
60
65
70
75
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 4
10

Home THX Equalization Manual Rev. 1.5
You will have achieved a correct EQ curve when successive measurements show
the same flat response.
Repeat this procedure for each remaining screen channel and the subwoofer.
Use the appropriate
track on "Wow!" or your pink noise source, and remember to connect only the
speaker that you are
testing. Your front channels are now equalized.
1.7) Compare EQ Settings
NOTE: IN INSTALLATIONS THAT ALLOW FOR SYMMETRICAL L/R SPEAKER ROOM PLACE-
MENT, CONFIRM THAT THE EQ SETTINGS FOR L & R CHANNELS ARE SIMILAR. Small
variations
of 1 dB in individual 1/3 octave bands are tolerable. In asymmetrical L/R
speaker placement,
larger variations in EQ curves are acceptable; particularly at the lower
frequencies where boundary
effects are most common.
Using R-2, the comparison function compares the curve in memory to a curve
on the disk drive.
This means that the stored curve on the disk drive is always assumed to be
the reference. The resulting
difference curve shows the deviation of the curve in memory from the
reference curve. To compare
a curve on display to a stored curve, select F-2 , then select the reference
curve from the
items listed. You can save the resulting comparison by hitting F-9 .
1.8) Equalizing the Subwoofer
Measuring the Subwoofer is very similar to measuring the LCR channels with
one exception.
Because the pink noise source will exhibit larger instantaneous fluctuations
in amplitude at lower
frequencies (see the section on pink noise in the introduction), longer
averaging times may be necessary
to improve measurement consistency. If you are using "Wow!" as the pink
noise source, use the
Center Channel Pink Noise (Chapter 9). Otherwise connect your pink noise
source into the both Left
and Right channel inputs of your decoder.
Unequalized Subwoofer Room Response
75
70
dB
SPL
65
60
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 5
11

Home THX Equalization Manual Rev. 1.5
When equalizing the Subwoofer Channel, you should concentrate on reducing
the serious peaks.
You may find that because of the depth of the room modes a ruler flat
response is not within the range
of the equalizer. This not a major concern since a response within ± 3 or 4
dB is very acceptable.
One tip; a reduction of energy in the 20-30 Hz range will enable the
subwoofer to play louder without
before encountering excursion problems.
1.9) Confirm the Subwoofer Splice: Center Channel
The next step is to activate the internal test signals present in your Home
THX Controller and readjust
all SPL's to their correct 75 dB C weighted levels. This will even out any
level variations introduced
by equalization.
After level check, return to your "Wow!" Center Channel pink noise; Chapter
9. Observe on your
RTA the relative levels of the Subwoofer and the Center Channel. The overlap
area is referred to as
the splice point. Follow the same averaging procedure you used in Section
1.4. In particular, look at
the crossover area between 80 Hz and 200 Hz. This area will usually appear
uneven (Fig. 6).
Uneven Subwoofer Splice
dB
SPL
60
64
68
72
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 6
The most common cause of an uneven Subwoofer splice is the relative
difference in positions
between the LCR speakers and the Subwoofer(s). These position differences
can cause frequencies
common to all the speakers to arrive at different times at the listening
position, and partially cancel or
reinforce themselves. At this point use the Center Channel EQ to adjust the
response at the
splice. DO NOT use the Subwoofer EQ .
1.10) Confirm Subwoofer Splice: Left and Right Channel
Next, in the Stereo or Bypass mode play both the Left and RightPink Noise
from "Wow!"; Chapters
8 & 10. Measure and analyze as described in Section 1.4. Adjust both the
Left and Right Chan12

Home THX Equalization Manual Rev. 1.5
nel splices to the Subwoofer channel by using your Left and Right Channel
EQs.
Remember, if the relative levels are off, use your Home THX Controller to
adjust the levels.Use
only the Left, Center, or Right EQ controls to adjust for uneven frequency
response at the
Subwoofer splice point.
WARNING! If a dip remains at the Subwoofer splice point even after drastic
EQ, check for
correct loudspeaker polarity. Subwoofers or LCR speakers connected out of
phase can cause
a "suck-out" at the crossover point. Subwoofers offset from the LCR plane by
a large distance
or multiple Subwoofers can do the same. If you are using a single Subwoofer
and have a large
offset, reverse the polarity of the Subwoofer signal. If multiple and offset
Subwoofers are used, you
should attempt to smooth the response by reversing the polarity of the
Subwoofer furthest from the
LCR speakers, or by repositioning the offset Subwoofer.
1.11) LISTEN!
When you have completed your room equalization, play the circulating pink
noise from "Wow!"
(Chapter 7). Each front channel, Left, Center, and Right, should tonally
sound very similar within the
listening area. If the circulating noise sounds very different, go back and
re-measure any offending
screen channel. The reference channel for any timbre comparison is the
CENTER CHANNEL.
Correct EQ with Subwoofer Splice
80
76
72
dB
SPL
68
64
60
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 7
Please Note: The above curve represents a typical room EQ. Since rooms vary
greatlyyou should
not expect every equalized room RTA to look like the above illustration. A
smooth curve, without
radical peaks or dips, is what is desired. With difficult rooms, acceptable
tolerances can be up to ±3 dB.
Your system is now correctly equalized.
13

Home THX Equalization Manual Rev. 1.5
SECTION 2: Room Analysis with a Conventional RTA
This method of room analysis was written tomimic the spatial and temporal
averaging of the R-2
THX Audio Analyzer. The procedures for choosing microphone positions and the
techniques for
equalization are identical with both types of instruments.
2.1) Define The Listening Area:
The first step in correctly equalizing a Home THX Audio System is to
identify the listening area.
The equalized response of the system will be averaged over this area to
provide a balanced sound
field for all listeners. Equalizing for a single position can result in poor
performance at other points in
the listening area. However, calibration of SPL (Sound Pressure Level) may
be done from a single
reference position using the internal test signals of the Home THX
Controller. These bandwidth limited
signals minimize room mode effects.
You should pay particular attention if the listening area is particularly
deep (several rows) or wide.
With some measurement positions very close to Left or Right screen speakers,
care will be needed in
averaging the RTA measurements to prevent unintentional weighting.
2.2) Choose Measurement Positions:
1
2
3
4
Mic Positions
Suggested Microphone Positions for 1 Row Seating
Fig 8
14

Home THX Equalization Manual Rev. 1.5
.. Choose four positions that represent prime listening positions spaced
equally throughout the
listening area (Fig. 8).
.. Position your analyzer's microphone(s) at seated ear height (38" to 48"
off finished floor). Place
the microphone(s) on a stand.
.. Do not attach any microphone directly to the analyzer or hold it in your
hand. Your body is an
acoustical object large enough to influence what is supposed to be a room
measurement.
.. Label in your notes each position and note any related information (e.g.,
Microphone 3 located
under loft overhang) which can affect your interpretation of the
measurements.
.. Do not point any microphone directly at a loudspeaker. Point it straight
up. You are looking for a
room measurement; not measuring the direct field of the loudspeaker.
.. If you are placing a microphone on any piece of furniture (i.e., a chair
or couch), make sure that
the mic is away from any cushion or seat back by at least 1 foot. This will
improve the accuracy of
measurements at that position above 800 Hz.
For multiple rows of seats, see Fig. 9 below.
1
2
3
4
Mic Positions
Multiple Row Seating and Microphone Positions
Fig 9
15

Home THX Equalization Manual Rev. 1.5
2.3) Home Theatre and Test Equipment Set-Up
Home Theatre Equipment:
.. Switch your Home THX Controller to the "Dolby Pro Logic Surround" mode.
The Home THX
Cinema mode must be switched off for this procedure.
.. Disconnect or disable the Subwoofer and the channels you are not
measuring. You want to analyze
each channel individually and disconnecting unused channels helps prevent
assignment
errors. One installer spent a frustrating hour trying to EQ a Center Channel
speaker only to find
that he had been playing pink noise through the Right Channel speaker.
.. Calibrate the individual channel levels as usual using the internal test
signals and a reliable SPL
meter.
.. Set the System Volume at Reference.
RTA Equipment:
.. Defeat any weighting on the RTA portion of the analyzer (e.g., "C"
weighting). Measurements are
to be taken with flat response.
.. Set the analyzer to Slow Response.
.. Set your analyzer's scale to the appropriate SPL range, and the dB per
division scale to 2 dB.
Pink Noise Sources:
Pink Noise can be obtained from one of the following sources:
.. The "Wow!" laser disc, Chapters 8-10.
.. An external calibrated pink noise source (200 mV RMS) placed into each
channel's EQ input.
2.4) Real-Time Analysis:
Start your pink noise source. If using "Wow!" Chapters 8-10, put the
appropriate track on A-B
repeat so that it conveniently cycles automatically. Placing your microphone
at a reference position
(Microphone 1). Take three or four measurement samples and store each
reading into a memory
position of the analyzer. Average these readings and store the average in a
memory location. Repeat
the procedure at each of the other three locations chosen.
16

Home THX Equalization Manual Rev. 1.5
NOTE: CHECK THE OVERALL SPLs AT EACH MICROPHONE LOCATION. IF THESE VARY BY
MORE THAN ± 1 dB, ADJUST THE MASTER VOLUME ON THE CONTROLLER TO COMPENSATE
THE SPL AT EACH LOCATION TO APPROXIMATE THE SPL AT THE REFERENCE POSITION
(Microphone 1). FAILURE TO DO SO MAY RESULT IN SKEWED SPATIAL AVERAGES.
With the four positions stored in memory, now average to obtain the spatial
response for the
entire listening area. Notice that we have used the method of obtaining
several samples for each
microphone position to smooth out the stochastic effects of the pink noise.
NOTE: DISPERSION AND AIR ABSORPTION AT HIGHER FREQUENCIES WILL CAUSE A
GENTLE ROLL OFF IN RESPONSE BEGINNING AROUND 6 kHz. THIS IS NORMAL AND DOES
NOT REQUIRE EQUALIZATION. (Fig. 10)
Typical Unequalized LCR Room Response
dB
SPL
60
65
70
75
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 10
2.5) Equalize:
The resulting spatial average will approximate the inverse of the correct EQ
curve. As a starting
point, assume that a dip of -3 dB on the analyzer calls for an increase at
the appropriate EQ frequency
of +3 dB. Since we will re measure a number of times, any over correction or
under correction will be
caught. When analyzing the averaged RTA curve try to look for the mean SPL
for all frequencies and
adjust the peaks and dips to that mean.
Remember that we are trying to achieve a response in the LCR channels of ± 1
to 2 dB, from 100
Hz to 1 kHZ, without drastic EQ shifts. A boost of 6 dB places many demands
on both amplifiers and
loudspeakers.
17

Home THX Equalization Manual Rev. 1.5
2.6) Re-analyze:
After applying the corrections to the appropriate channel frequency centers,
re-run the above
procedure to verify the corrections. You will find that you will have to
measure and correct several
times to achieve a balanced and repeatable response.
NOTE: ABOVE 1 kHz, IN TYPICAL ROOM ENVIRONMENTS, THE SOUND FROM HOME THX LCR
SPEAKERS IS DIRECT FIELD DOMINATED AND THE FREQUENCY RESPONSE MAY BE POSI-
TION DEPENDENT. AVOID DRAMATIC EQ CHANGES ABOVE 1 kHz. SINCE WE ARE MORE
SENSITIVE TO FREQUENCY PEAKS THAN DIPS, USE THE CONTROLS AVAILABLE SPARINGLY
TO REDUCE HIGH FREQUENCY PEAKS, RATHER THAN TRYING FOR RULER FLAT RESPONSE
..
Avoid radical EQ beyond this point.
Typical Unequalized Room Response
dB
SPL
60
65
70
75
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 11
Repeat the above procedure for each front channel. Use the appropriate track
on "Wow!" or your
pink noise source, and remember to connect only the speaker that you are
testing.
Your LCR channels are now equalized.
NOTE: IN INSTALLATIONS THAT ALLOW FOR SYMMETRICAL L/R SPEAKER ROOM PLACE-
MENT, CONFIRM THAT THE EQ SETTINGS FOR L & R CHANNELS ARE APPROXIMATELY THE
SAME. Small variations of 1 dB in individual 1/3 octave bands are tolerable.
In asymmetrical L/R
speaker placement, larger variations in EQ curves are acceptable;
particularly at the lower frequencies
where boundary effects are most common.
18

Home THX Equalization Manual Rev. 1.5
2.7) Subwoofer Equalization:
All Subwoofer measurements should be done using the Center Channel Pink
Noise band on
"Wow!" (Chap. 9) or with your pink noise source into the Left and Right
inputs of the decoder. Disable
or disconnect the LCR speakers.
Unequalized Subwoofer Room Response
75
70
dB
SPL
65
60
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 12
Measuring the Subwoofer is very similar to measuring the LCR channels with
one exception.
Because the pink noise source will exhibit larger instantaneous fluctuations
in amplitude at lower
frequencies (see the section on pink noise in the introduction), more
averages will be necessary to
improve measurement consistency. It is therefore recommended that, rather
than attempting to
spatially average the microphone positions with a non-multiplexing RTA, you
take the maximum number
of readings at Position 1 that you can store and average them. Then adjust
your EQ setting for flat
response for that average.
If you are using "Wow!" as the pink noise source, use the Center Channel
Pink Noise (Chapter 9).
Otherwise connect your pink noise source into the both Left and Right
channel inputs of your decoder.
When equalizing the Subwoofer Channel, you should concentrate on reducing
the serious peaks.
You may find that because of the depth of the room modes a ruler flat
response is not within the range
of the equalizer. This not a major concern since a response within ± 3 or 4
dB is very acceptable.
One tip - a reduction of energy in the 20-30 Hz range will enable the
subwoofer to play louder without
before encountering excursion problems.
Reconnect your front speakers.
19

Home THX Equalization Manual Rev. 1.5
2.8) Confirm the Subwoofer Splice: Center Channel
The next step is to activate the internal test signals present in your Home
THX Controller and readjust
all SPL's to their correct 75 dB C weighted levels. This will even out any
level variations introduced
by equalization.
After level check, return to your "Wow!" Center Channel pink noise; Chapter
9. Observe on your
RTA the relative levels of the Subwoofer and the Center Channel. The overlap
area is referred to as
the splice point. Follow the same averaging procedure you used for Subwoofer
EQ. In particular, look
at the crossover area between 80 Hz and 200 Hz. This area will usually
appear uneven (Fig. 13).
Uneven Subwoofer Splice
dB
SPL
60
64
68
72
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 13
The most common cause of an uneven Subwoofer splice is the relative
difference in positions between
the LCR speakers and the Subwoofer(s). These position differences can cause
frequencies common
to all the speakers to arrive at different times at the listening position,
and partially cancel or reinforce
themselves. At this point use the Center Channel EQ to adjust the response
at the splice. DO
NOT use the Subwoofer EQ .
2.9) Confirm Subwoofer Splice: Left and Right Channel
Next, in the Stereo or Bypass mode play both the Left and RightPink Noise
from "Wow!"; Chapters
8 & 10. Adjust both the Left and Right Channel splices to the Subwoofer
channel by using your
Left and Right Channel EQs.
Remember, if the relative levels are off, use your Home THX Controller to
adjust the levels.Use
the Left, Center, or Right EQ controls only to adjust for uneven frequency
response at the
splice point.
20

Home THX Equalization Manual Rev. 1.5
WARNING! If a dip remains at the Subwoofer splice point even after drastic
EQ, check for
correct loudspeaker polarity. Subwoofers or LCR speakers connected out of
phase may cause
a "suck-out" at the crossover point. Subwoofers offset from the LCR plane by
a large distance
or multiple Subwoofers can do the same. If you are using a single Subwoofer
and have a large
offset, reverse the polarity of the Subwoofer signal. If multiple and offset
Subwoofers are used, you
should attempt to smooth the response by reversing the polarity of the
Subwoofer furthest from the
LCR speakers, or by repositioning the offset Subwoofer.
2.10) LISTEN!
When you have completed your room equalization, play the circulating pink
noise from "Wow!"
(Chapter 7). Each front channel, Left, Center, and Right, should tonally
sound very similar within the
listening area.
Correct EQ with Subwoofer Splice
80
76
72
dB
SPL
68
64
60
16000100006300400025001600100063040025016010063402 5
Frequency Hz
Fig 14
Please Note: The above curve represents a typical room EQ. Since rooms vary
greatlyyou should
not expect every equalized room RTA to look like the above illustration. A
smooth curve, without
radical peaks or dips, is what is desired. With difficult rooms, acceptable
tolerances can be up to ± 3 dB.
21

Home THX Equalization Manual Rev. 1.5
Equalization Checklist:
Set-UP
.. Set Up Home THX Audio System
.. Aim L, C, R loudspeakers using pink noise on "Wow!" disc
.. Calibrate individual channel levels with controller's internal test
signals
.. Set Up Microphone positions
.. Set RTA weighting for Flat
.. Set Up Scale Range and Divisions
With R-2 Audio Analyzer only
.. Set Measurement interval for 20 sec. minimum
.. Begin Microphone Multiplexing
Analyze & Equalize
.. A) Disconnect Subwoofer, Left, and Right Channels
.. B) Play Pink Noise through Center Channel
.. C) Measure multiple locations, average readings, and equalize Center
Channel
.. D) Repeat C until measurements are consistent
.. Repeat operations A,B,C, &D for Left, Right, and Subwoofer channels
Confirm EQ
.. Reconnect System
.. Confirm splice of Subwoofer with Center Channel by playing Center pink
noise in Dolby Pro Logic
mode
.. Confirm splice of Subwoofer with Left and Right Channels by playing Left &
Right Channel Pink
Noise in Stereo or Bypass mode
Check System Set-up
.. Re-calibrate individual channels with controller's internal test signals
.. Listen to circulating Pink Noise on "Wow!" disc to compare timbre of LCR
speakers
.. Return to Home THX Cinema Mode and playWow! demo listening for accurate
Foley*, clear
dialogue, precise localization, smooth pans, and overall detail
*Foley is a term used to describe the all of the "natural" sound effects
which contribute to our sense of
reality in motion pictures. These effects are created in a special sound
stage in sync with the action of
the film. The process was named after Jack Foley who invented the system of
adding the sound of
footsteps to early talking motion pictures in order to enhance their
believability.
22

Home THX Equalization Manual Rev. 1.5
Appendix:
"WOW!"- A User's Guide
The "WOW!" laser disc was created by
Lucasfilm for use with Home THX Audio systems.
"WOW!" consists of exciting demonstration,
educational, and testing material to help you best
appreciate the Home THX Audio System. "Wow!"
is available to consumers with the purchase of a
Home THX Audio System controller.
"WOW!" should only be played through a
Home THX Audio System, and should never
be sold, rented, copied, broadcast, or used for
any commercial purposes. Any unauthorized
use of this copyrighted material is strictly
prohibited, and violators will be prosecuted.
The following table of contents outlines the various
chapters on the WOW! laser disc, and provides
some suggestions on their use.
Side 1:
Chapter 1: WOW!;
This is a remarkable thematic montage of
various George Lucas films, with fast, tight editing
to emphasize interest and excitement. All of the
soundtracks are essentially unchanged with one
exception: a new musical score was commissioned
to tie the entire piece together. WOW!
provides a short and complete movie going
experience, and shows off all of the potential of
the Home THX Audio System. WOW! contains a
wide variety of sounds, from very quiet passages,
to loud, explosive ones; there are sounds panning
between Left and Right, and from front to
back; there is soft dialog buried in the midst of
competing, loud sound effects; there are powerful,
deep bass sounds that make you feel fully
involved in the action. The Home THX Audio
System will deliver all of these sounds with startling
realism, and unequaled clarity!
Chapter 2: The Home THX Audio System;
Tomlinson Holman discusses the elements
of the Home THX Audio System and what sets it
apart from more conventional home theatre
systems.
Chapter 3: Mode Selections;
Five short selections illustrate the most
appropriate use of the various modes of your THX
controller. These selections show the best use of
the Home THX Cinema, Dolby Pro Logic, and
Stereo modes.
Side 2:
Chapter 4: Soundtrack;
This chapter outlines the process whereby
the soundtrack of a movie is created. It gives you
an appreciation of what you are missing when you
watch a movie on a non-THX system. There is far
more to making a film soundtrack than most
people imagine.
Alignment Test Signals:
Chapter 5: Input Level Calibration Tone;
This 1 kHz tone is recorded at 0 dB (Dolby
reference level), and can be used to calibrate the
input level of your THX controller. Adjust the level
so that the meter on the controller reads
0 dB(reference level) when this signal is
playing.
Chapter 6: Pink Noise, Left & Right, In-Phase,
-10 dB;
This signal is comprised of broad band noise
and can be used to adjust the Center output level,
or check the phase of the Left, Right, and Center
speakers, as well as the Subwoofers. When
played back through a correctly adjusted system,
this signal should yield 75 dB SPL (Sound Pressure
Level) on a sound level meter, C-weighted,
slow mode.
23

Home THX Equalization Manual Rev. 1.5
Chapter 7: Pink Noise, Circulating L-C-R-S,
-10 dB;
This signal is comprised of broad band noise
and can be used to calibrate all the individual
output level controls after the input level controls
have been calibrated. Set the level to read 75 dB
SPL on a sound level meter, C-weighted, Slow
mode in each channel in turn, measured from the
primary listening position.
Chapters 8-11: Pink Noise, Left, Center, Right,
Surround Channels, 0 dB;
This signal is comprised of broad band noise
and can be used to assist in aiming the Left,
Center, or Right speakers directly at the primary
listening area (especially in the vertical plane).
Simply listen for the best high frequency response
at your seated position. The Surround Channel
Test Signal (Chapter 11) may be used to test the
Surround Speaker positions for the best evenness
and envelopment of the Surround Field. When
played back through a correctly adjusted system,
these signals should yield 85 dB SPL on a sound
level meter, C-weighted, slow mode. These
signals can also used for spectrum analysis if
room equalization is performed.
Chapters 12-15: Frequency Sweep, 20 Hz to 20
kHz, Left, Center, Right, & Surround Channels,
0 dB;
This sine wave sweep covers the entire
audible range and can be used to measure the
frequency response of the Left, Center, Right, or
Surround channel electronics. Use in conjunction
with a chart recorder set for a 3 mm/sec. pen
speed. It is not recommended to use this test for
loudspeaker adjustments since room standing
waves make the results unreliable.Warning: this
signal can be damaging at high volumes. Care is
required in setting the volume for this test.
Chapter 16: Rattle Test, Frequency Sweep, 20
Hz to 500 Hz, 0 dB;
This is an extremely slow low frequency
sweep, intended to help pinpoint rattles, structural
resonances and other potential problems in the
bass. Warning: this signal can be damaging at
high volumes. Care is required in setting the
volume for this test.
Chapters 17-18: Slap Echo Test, Center and
Surround Channels;
This recording of a hand clap is repeated
several times to facilitate the identification of "slap
echoes" which might be stimulated by the system.
Slowly walk around the room, listening for a
fluttering, percussive echo following each initial
clap. Treat room surfaces accordingly. For best
results it is recommended to shut off the L, R, and
S speakers on the Center Channel Test, and the
L, C, and R speakers on the Surround Test.
Chapter 19-20: Video Test Patterns;
These patterns will enable a video technician
to correctly set you TV set, monitor, or video
projector to the correct levels of color, hue, contrast,
and brightness.
Copyright 1992 LucasArts Entertainment
Company
©Rane Corporation 10802 47th Ave.W., Mukilteo WA, 98275-5098 TEL
(206)355-6000 FAX (206)347-7757

Then there's this from SVSubowwofers:
Maybe you already know how powerful a tool a simple Radio Shack Sound
Pressure Meter is. If you use some of the popular test disks out there to
check your room response there are some things you need to know about the
meter. Some of these disks, like the popular "Autosound 2000 Bass CD #101",
have sweeps or even chapter stops that show how even (or not) the response
of your system is down low, below 20Hz even.

The problem? The Radio Shack sound meter is not totally "linear" in its
accuracy down there. All such meters are off by the same amount depending on
the frequency however, which is good news! So that while its sensitivity
below 20Hz is not what it is at 50Hz, there is a simple way to compensate
for this deficiency. It's called a compensation chart. Using one is very
simple, and a pencil and paper is all you need.

Simply look to the below frequencies and add the required decibels (dBs) at
the frequency in question. So if your system seems to be measuring 70dBs
with a 20Hz tone, then really it's putting out 77.5dBs. This is a VERY
substantial difference, roughly TWICE the acoustical energy, requiring many
times the amplifier to achieve. You can see then how critical the below
chart is if you are using an equalizer to even out room response of your
bass. Maybe you are not bothered by any such variances, but if you are
desirous of getting the most from your system it's something well worth
investigating. Adding a simple equalizer like the ART 351 or the more
complex and powerful Rane PE17 allow you the flexibility to affect your
system response in the low bass regions easily.
NOTE: Using sine waves at high SPLs can easily damage any subwoofer given
their extreme stress on woofer voice coils. Use only a few seconds for any
given tone during measurements, allow a minute or so in between frequencies,
and keep actual SPL's low, in the 75-85dB range. Contact SVS if you have
questions about room response measurements or proper use of sine waves in
this process.

So find out what your subwoofer(s) are REALLY doing, and add the following
numbers as appropriate to your SPL meter readings:

At 10Hz add 20dBs to the meter's readings and at ...

12Hz add 16.5dB
16Hz add 11.5dB
20Hz add 7.5dB
25Hz add 5dB
31.5Hz add 3dB
40Hz add 2.5dB
50Hz add 1.5dB
63Hz add 1.5dB
80Hz add 1.5dB
100Hz add 2dB
125Hz add .5dB

You could simply type in Radio Shack meter into a browser and come back with
many hits all giving good reports on the meter and publishing correction
numbers.

But of course they are all wrong and Trevor is right.

"Trevor Wilson" wrote in message
...

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine for
rough and ready measurements. They are not by any measure useful as
accurate
devices.

Among the other flaws, this meter does not have an internally regulated
power supply. Consequently, the level readings vary by how long the meter is
turned on. The 9V battery is not stable under the load required by the
meter.

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine
for
rough and ready measurements. They are not by any measure useful as
accurate
devices.

Among the other flaws, this meter does not have an internally regulated
power supply. Consequently, the level readings vary by how long the meter
is
turned on. The 9V battery is not stable under the load required by the
meter.

Some people are bright enoug to figure out how to hook it up with an AC
converter.

wrote in message
ink.net...

"Trevor Wilson" wrote in message
...

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine
for rough and ready measurements. They are not by any measure useful as
accurate devices.

Denial of reality noted.

**WTF?

The fact is they are not what you claim

**Rat Shack SPL meters are EXACTLY as I claim. They're fine for rough and
ready measurements. That is it.

and that
they are used by professionals

**Sure they are. Even professionals need a rough and ready measurement
occasionally. I use mine that way. When I want PROPER, ACCURATE
measurements, I use a system which has a calibration standard, with
tracability.

along with corrections and have been measured
against precision devices and their differences noted.

**You still don't get it, do you? EVERY SINGLE Rat Shack SPL meter is
different from every other one. Correction curves are an AVERAGE only.
They're not accurate.

SVSubwoofers
recomends them and publsihes the corrections on their website.

**I don't care what SVSubwoofers (whoever the Hell they are) suggest. Rat
Shack SPL meters are OK for rough measurements. They are not precision
instruments.


Tone controls may be of some use,

That some small retraction.

**Read the words in context.


IF the problem being addressed can be
precisely matched by those tone controls AND the user has the requisite
equipment and expertise to adjust those controls. The chances of this are
approximately equivalent to that of a big lottery win.

Not if you have a RS meter and test tones along with the corrections.

**You still don't get it, do you? All EQs (which includes tone controls),
except parametics and digital EQs have rigidly set curves. If the desired EQ
does not match the curve in the EQ (or tone control), you're screwed. THAT
is what makes tone controls and EQs useless.


Equalisers come in several flavours. For the sake of simplicity, I will
lump them into four, broad groups and assume that the listener owns and
can properly use the rather sophisticated testing equipment, which is
VITAL to ensure adequate results (Yes, I know it is an
over-simplification):

Standard, analogue octave EQs. These are both better and worse than tone
controls, in their actions. Since frequencies and 'Q' cannot be adjusted,
they are of limited usefulness. These are marginally more likely of being
able to be adjusted correctly than a big lottery win.

Third octave analogue EQs. These are SIGNIFICANTLY more useful than
octave EQs. For obvious reasons. A good result is much more likely. About
the same as winning a mid range prize in a lottery.

It really depends on the user having test tones and an spl meter like the
RS with corrections and knowing where the problems are. A 1/3 octave EQ
can do more than lesser ones, but knowing where the problems lie is the
key.

**Exactly. Considerable expertise is required. After all, not even you know
where to place microphones. What chance does an amatuer have? Even so, 1/3rd
octave EQs still have preset curves, which may be of no use in a particular
situation.


Parametric analogue EQs. MUCH more useful than any of the above. A good
deal more experience is also required to get the best from these guys
too. However, I do acknowledge that these critters CAN solve problems.

But they can't smooth out a room the way a graphic EQ can.

**HUH? They can and do a MUCH better job. The last parametic I used (a
digital one, BTW) was configured to represent a 31 band parametric EQ. Can't
beat that for flexibility.


Digital, zero phase shift EQs.

They are all minimum phase devices.

**I said: ZERO phase shift.


Now we're talking. When used with the right
measurement equipment (nothing branded Radio Shack) these guys are
capable of doing the job that people THINK tone controls can do (but
actually cannot).


So the professionals who recomend the Radio Shack meters with the
correction, who have measured them to come up with the corrections and
state that they are very standardized form unit to unit are wrong and you
are right.

**Correct.

What does Dick Pierce say?


--
Trevor Wilson
www.rageaudio.com.au

wrote in message
.net...

"Robert Morein" wrote in message
...

"Trevor Wilson" wrote in message
...

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine
for
rough and ready measurements. They are not by any measure useful as
accurate
devices.

Among the other flaws, this meter does not have an internally regulated
power supply. Consequently, the level readings vary by how long the meter
is
turned on. The 9V battery is not stable under the load required by the
meter.

Some people are bright enoug to figure out how to hook it up with an AC
converter.

Mikey, you love junk!
In order to work, the supply would have to be very tightly reguated. And
thermal drift inside the appliance cannot be ruled out. The low cost option
is the Behringer measurement mike, at about $50. I have two of them. Better
mics start around $150.

"Trevor Wilson" wrote in message
...

wrote in message
ink.net...

"Trevor Wilson" wrote in message
...

wrote in message
nk.net...
Isn't it time for you to offer up an I stand corrected regarding tone
controls, EQ and Radio Shack SPL meters?

**No. Rat Shack SPL meters are EXACTLY as I say they a They're fine
for rough and ready measurements. They are not by any measure useful as
accurate devices.

Denial of reality noted.

**WTF?

The fact is they are not what you claim

**Rat Shack SPL meters are EXACTLY as I claim. They're fine for rough and
ready measurements. That is it.

and that
they are used by professionals

**Sure they are. Even professionals need a rough and ready measurement
occasionally. I use mine that way. When I want PROPER, ACCURATE
measurements, I use a system which has a calibration standard, with
tracability.

along with corrections and have been measured
against precision devices and their differences noted.

**You still don't get it, do you? EVERY SINGLE Rat Shack SPL meter is
different from every other one.

Testing of those meters shows that you are wrong.

Correction curves are an AVERAGE only.
They're not accurate.

Another denial of reality.


SVSubwoofers
recomends them and publsihes the corrections on their website.

**I don't care what SVSubwoofers (whoever the Hell they are) suggest. Rat
Shack SPL meters are OK for rough measurements. They are not precision
instruments.

They are when the corrections are used.

Tone controls may be of some use,

That some small retraction.

**Read the words in context.


IF the problem being addressed can be
precisely matched by those tone controls AND the user has the requisite
equipment and expertise to adjust those controls. The chances of this
are approximately equivalent to that of a big lottery win.

Not if you have a RS meter and test tones along with the corrections.

**You still don't get it, do you? All EQs (which includes tone controls),
except parametics and digital EQs have rigidly set curves. If the desired
EQ does not match the curve in the EQ (or tone control), you're screwed.
THAT is what makes tone controls and EQs useless.

In your opinion.

Equalisers come in several flavours. For the sake of simplicity, I will
lump them into four, broad groups and assume that the listener owns and
can properly use the rather sophisticated testing equipment, which is
VITAL to ensure adequate results (Yes, I know it is an
over-simplification):

Standard, analogue octave EQs. These are both better and worse than tone
controls, in their actions. Since frequencies and 'Q' cannot be
adjusted, they are of limited usefulness. These are marginally more
likely of being able to be adjusted correctly than a big lottery win.

Third octave analogue EQs. These are SIGNIFICANTLY more useful than
octave EQs. For obvious reasons. A good result is much more likely.
About the same as winning a mid range prize in a lottery.

It really depends on the user having test tones and an spl meter like the
RS with corrections and knowing where the problems are. A 1/3 octave EQ
can do more than lesser ones, but knowing where the problems lie is the
key.

**Exactly. Considerable expertise is required. After all, not even you
know where to place microphones. What chance does an amatuer have? Even
so, 1/3rd octave EQs still have preset curves, which may be of no use in a
particular situation.


Parametric analogue EQs. MUCH more useful than any of the above. A good
deal more experience is also required to get the best from these guys
too. However, I do acknowledge that these critters CAN solve problems.

But they can't smooth out a room the way a graphic EQ can.

**HUH? They can and do a MUCH better job. The last parametic I used (a
digital one, BTW) was configured to represent a 31 band parametric EQ.
Can't beat that for flexibility.


Digital, zero phase shift EQs.

They are all minimum phase devices.

**I said: ZERO phase shift.


There is no such EQ.


Now we're talking. When used with the right
measurement equipment (nothing branded Radio Shack) these guys are
capable of doing the job that people THINK tone controls can do (but
actually cannot).


So the professionals who recomend the Radio Shack meters with the
correction, who have measured them to come up with the corrections and
state that they are very standardized form unit to unit are wrong and you
are right.

**Correct.

What does Dick Pierce say?


Why don't you ask him.

Morein the moron wrote:


Mikey, you love junk!
In order to work, the supply would have to be very tightly reguated. And
thermal drift inside the appliance cannot be ruled out. The low cost option
is the Behringer measurement mike, at about $50. I have two of them. Better
mics start around $150.


I don't need another high quality mic.

I have one that is flat from 20-20K, it was more than $150.00 by a good
bit.
It also confirms the basic accuracy of the RS meter when the
corrections I posted
are factored in.

I sure would like to read Trevor's mic placement ideas for doing a room
EQ.
It must be a secret, since nobody else seems to know of another method
other than placing the mic at ear level at the listener position.

What does Dick Pierce say?


--
Trevor Wilson
www.rageaudio.com.au


IIRC he thought other methods should be exhausted first and wasn't much
in favor
of them.

Why not ask him yourself?
Did he spank yo the last time you asked him something?