And so it came to pass, on 06-27-97 08:23,
   that DAVID SCHMOLL spake unto TERRY SMITH:
 DS> Actually what I described was from a booklet from Apogee called
 DS> sound reinforcement for worship, written by the Director of
 DS> education and senior systems engineer of Apogee, Patrick Price.
[snip]
 DS> The exact text is as follows:

 DS> Amplifier Gain - Amplifier spec sheets usually list a "gain" or
 DS> "voltage gain" specification. Gain is usually expressed in decibles
 DS> (such as +32db) or as a multiplier (such as 40 times). Given an
 DS> amplifier with a gain of 32db or 40X, this means that the amplifier
 DS> signal is amplified by 32db or multiplied by a factor of 40.

I find myself questioning Patrick Price's qualifications to write such a 
piece.  For one thing, it SOUNDS like he's saying 32dB = a power of 40... 
which it doesn't.  The "decibel" scale is logarithmic and does not denote any 
specific units, but rather a ratio or relationship.  A 3dB change is 
equivalent to a factor of two (-3dB = x1/2, +3dB = x2); a 10dB change denotes 
a factor of ten.  Decibels are additive -- in fact, increasing a signal 30dB 
is the equivalent of increasing the signal by a factor of 1000.  A 33dB boost 
would be a gain of 2000.

 DS> It is important for you to know the gain of all your power
 DS> amplifiers in order to properly "balance" your sytem at the offset.

Umm... "balance".  Uh-huh.

 DS> The point you should be concerned with is that if you use an
 DS> assortment of power amps in your system, and your high frequencies
 DS> are amplified by a factor of 40X, your mids are amplified by a
 DS> factor of 45X, and your lows are amplified by a factor of 35X, The
 DS> high/mid/low balance through the speakers will be severely messed
 DS> up.

[snip]
 DS> I attempted to say the same thing in less words in my original
 DS> post, so the question remains is the above valid or hype? 
It's taken somewhat out of context (I don't know if other factors are covered 
elsewhere) but offhand it just sounds like BS.
 DS> I can't see how not including the speaker efficiencies in the
 DS> overall balance makes sense.
Bingo!  Driver efficiency VERY MUCH comes into play.  If the amp driving a 
speaker with 93dB efficiency ("efficiency" being typically defined as dB SPL 
with "x" power input  measure at "y" distance -- 1W @ 1m is commonly used) 
provides 30dB gain, then another amp driving a speaker rated 96dB/1W@1m 
should only produce 27dB gain to "balance" the output levels.
Frequency and frequency division also comes into play, which makes Mr. 
Price's assertions apepar even more erroneous.  Also taken into account 
should be the effect of horns and their directionality on compression drivers 
(a compression tweeter may be rated 93dB/1W@1m, for example, while different 
horn designs on that tweeter may produce on-axis output of anywhere from, 
say, 103dB to 112dB SPL).
-------------------------------------------
Love, luck, and lollipops...
Matt


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