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In-depth:
How to set optimized gain structure
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Over the years I’ve seen many haphazard approaches in establishing
gain structure through a sound reinforcement system. Often rough
adjustments can be made to make the problem less apparent, because
gain is easily and cheaply available in today’s industry.
Years ago, when a 100-watt power amplifier was used to power the
main loudspeaker system, gain structure was a critical issue. Today,
with the advent of amplifiers that can output levels of 1,000 watts
or more per channel, proper gain structure can be easily overlooked
as a critical element in the performance of a system.
Powerful amplifiers, however, are not an excuse for an individual
to lack a firm understanding of proper gain structure. Many of today’s
signal processors and amplifiers have jumpers, switches, or knobs
that, if adjusted properly, will maximize the systems signal to
noise ratio while also ensuring the system will safely operate at
the levels that are required.
First we’ll determine how much gain is required throughout
the system, from the console to the listener. Then, once overall
gain requirements are known, we can then discuss the approach to
setting the system’s gain structure.
How much gain is enough?
A good designer will always have an established sound pressure level
(SPL) criteria for each system in which he/she is working on. Without
this predetermined resultant SPL, you may often find yourself over
or under specifying the total gain required in a system.
So, let’s establish a criteria for the purpose of discussion.
We will assume that we are designing a sound system for a church
that has a contemporary music program. During the music portion
of the program, it is anticipated that peak levels in the room need
to reach nominal levels of 95dB SPL, with peaks of 101dB. It is
also the intent to provide 10dB of headroom. Our design criteria
is now determined, and we can begin our discussion of gain structure.
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