User Guide

Sound System Design Reference Manual
7-1
Chapter 7: System Architecture and Layout
Introduction
Just as the building architect interprets a set of
requirements into flexible and efficient living or
working spaces, the designer of a sound
reinforcement system similarly interprets a set of
requirements, laying out all aspects of the system in
an orderly fashion. A full sound system specification
will detail almost everything , including all equipment
choices and alternatives, rack space requirements,
wire gauges and markings, and nominal signal
operating levels. In addition, the electroacoustical
aspects of the system will have been worked out well
ahead of time so that there will be few surprises
when the system is turned on for the first time.
The consultant or design engineer lays out the
broad system parameters, but it is the sound
contractor who is responsible for all component
layout and orderly completion of the system, along
with documentation for usage as well as
maintenance. System architecture also addresses
signal flow and nominal operating levels, consistent
with the requirements of the system. The best
designs are usually the simplest and most
straightforward ones.
In this chapter we will cover several design
projects, beginning with basic design goals and
fundamental performance specifications. We will then
move on to system descriptions and layout,
suggesting ways that the specification can be met.
We will concentrate on the electroacoustical
problems that are fundamental to each case study.
By way of review, we will first discuss a few basic
audio engineering subjects, beginning with an
abbreviated signal flow diagram for a relatively
simple speech reinforcement system.
Typical Signal Flow Diagram
Assume that we have the following
requirements:
1. Up to ten microphones may be needed at
different locations.
2. The system is to be used primarily for
speech reinforcement.
3. The system shall be able to produce peak
levels up to 85 dB-SPL in all parts of the house under
all speech input conditions, including weak talkers.
The room noise level is about 25 dB(A).
The most basic interpretation of these
requirements tells us the following:
1. A small Soundcraft or Spirit console should
suffice for all input configurations and routing control.
2. A single central array is the preferred system
type, based on the desire for most natural speech
reproduction. The array may be specified using
individual HF and LF components; alternatively, an
appropriate full-range system with integral rigging
capability may be specified, as we will show here.
3. Both biamplification and system response
equalization are recommended, and this suggests
that a digital loudspeaker controller be used for
frequency division, time alignment, and system
response equalization.
Note that there are many points in the system
where we can set or change gain. There is always
considerable gain overlap in the electronic devices
used in sound system work. The purpose of this is to
allow for a great variety of input conditions as well as
to allow the equipment to be configured in different
ways, as required. It is critical that the designer
specify a nominal setting of each gain control,
locking off, when possible, those controls that will not
— or should not — be altered during normal system
use. This important setting of gain relationships
should be based on the absolute requirement that
the input noise floor of the system should not be
degraded later in the chain, and that no early stage
of amplification should overload before the output
power amplifier overloads. In our exercise here, we