Hi All,
 
I just read some information about system PA balancing, in some
information from Apogee, that I never thought about before, which made
me realize I probably have been adjusting things wrong all these years
if I'm to believe what I just read.
 
The article dealt with fixed gain on various amplifiers in a system. It
said all amplifiers have a fixed design gain, and that mixing different
amplifiers in a system with different gains would cause mismatched
sound. For example: one amplifier might have a gain of 40, which means
for a 1 volt input it will produce 40 volts output (assuming it has
that much output), while another amplifier can have a gain of 35,
producing 35 volts output. This suggests to me that the system balance
would change as the overall system gain was increased at the mixer. The
article stated that the input volume controls on each amplifier needs
to be balanced - without speakers attached - so that all amplifiers
produce the same voltage output for the same voltage input.
 
This started me to thinking because I have always used the input volume
controls on the amplifiers to match the various speaker volume's in a
system (before EQ), since different speakers have different
efficiencies. For example: a bass speaker might have a 96 db rating at
1 watt, while a midrange speaker might have a 98 db rating at 1 watt. I
would adjust this 2 db difference at the power amplifier, so that my EQ
setting would stay closer to a straight line across the bands. With the
matching of gain concept, the EQ curve would reflect the speaker
efficiency differences, as well as the room itself, in other words, in
a perfect room, a flat EQ curve would not indicate a flat sound unless
the speaker efficiencies were matched and the amplifier gains were also
matched.
 
My question is, is the gain matching I described really as important as
Apogee makes it sound, and are my conclusions correct? In my home
theater system, I have an Adcom 545 running a (mono) pair of JBL
subwoofer's, an Adcom 535 running the (stereo) JBL main speakers, an
Adcom 535 running the (mono) center and (mono) rear channels. With 4
distinct speaker sytems, each with different efficencies, and 2 models
of power amplifiers, with unknown gain and no volume control to adjust
on thte amplifier anyway, I can't test out this theory, but on the
other hand I have never noticed the system balance changing as I adjust
the preamp volume. Anybody have any comments on this theory?
 
dschmoll@nyx.net (David Schmoll)
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