mike;661966 Wrote:
My questions are these:
1) In a well-installed car stereo, what are the typical resistances in
the
wiring, connections, batteries etc.?
2) What is a typical speaker impedance for a high power system?
3) If I add a big cap, What improvement would I HEAR under what
conditions?
4) If I hooked up an oscilloscope to the power supply at the amp and
to
it's audio output,
what improvement would I SEE under what conditions if I added a cap?
5) Why would lights dim? IF the lights connect to the battery.
And the stereo connects to the battery.
And the sense point for the alternator/regulator connects to the
battery.
And the alternator is big enough.
??
6) What percentage of people actually care about the technical merits
of
their
car stero...as long as their ride is "fly" and gets 'em laid? ;-)
mike
Mike,
You didn't post any time-domain approximation.
CMRR doesn't affect the power supply in any way. CMRR is the rejection
of a signal that is common to 2 signals, for instance, noise picked up
in the ground and hot of an RCA is rejected by the CMRR of a
differential amplifier. The term you mean is PSRR, or power supply
rejection ratio.
The 'voltage upconversion' you're talking about is the power supply.
All car amps I've seen use a push-pull SMPS. Push-pull supplies can be
regulated or unregulated. If they're regulated, the output voltage is
largely unaffected by fluctuations of the input voltage - unregulated
supplies have a fixed boost and the output moves just as the input
moves or the load changes. Most car audio amplifier supplies I've seen
were unregulated for reasons that hopefully will be more clear later in
my response. Regulated supplies also have a specific loop gain which
affects the power supplies' ability to react to changes in input or
output. With regulated supplies this is also a factor.
1. I think 'this chart'
(
http://www.interfacebus.com/Copper_Wire_AWG_SIze.html) will help you
out. Keep in mind these values are for a specific temperature and type
of cable jacket. This can vary with different winding techniques of the
strands in the cable as well.
2. As above, 1-4ohm is typical for a car subwoofer.
3. You won't hear any difference. Adding more capacitance will help
continuous power a bit, because CV will be greater, but the voltage
rails won't change so peak power will remain the same. Audio has high
crest factors, and thus peak power is actually relevant and meaningful
for audio. RMS power tells you more about how robust the amp is, but
peak power won't change if you add more capacitance. And that is what
will tell you more about audible difference between amplifiers.
4. Same as above. You'll see high peaks before clipping if the input
signal is a sine wave or something with a low crest factor. With audio
or pink noise, you wouldn't see any tangible difference. The capacitor
will create a LPF which may decrease any HF noise on the power rails,
but this ultrasonic noise is of little consequence for audio.
5. Lights dim when voltage falls. This is because the alternator cannot
output enough current to the system. Because audio amplifiers have SMPS,
they are constant power; this means if input voltage decreases, input
current increases. The voltage in the entire system decreases when the
amp pulls a lot of current. Adding a capacitor won't help much because
capacitors can't do much about transients, like audio, and help mostly
with continuous signals. Think of each circuit [lights, stereo, ECU,
etc.] being in parallel. Since each load looks like a resistor [with
likely some reactance], the voltages are equal. So if the stereo drags
the voltage down, the voltage in the entire system goes down.
6. I care about the technical merits of audio, but then again I get
paid to
--
eezip