User Guide

Sound System Design Reference Manual

6-19

System Design Overview

There is a rational approach to indoor sound

reinforcement system design, and it can be broken

down into the following steps:

1. Lay out the coverage requirements, generally

starting with a central array. Determine the drive

requirements for each element in the array.

2. Calculate both direct field and reverberant

field levels at various parts of the audience area, and

then determine if their ratios, in combination with the

reverberation time of the room, will result in adequate

intelligibility. These calculations are most important in

the 1 kHz range, but they should also be made in the

125 Hz and 4 kHz ranges as well. Determine the

requirements for adequate gain, noting the value of

that will be required in normal operation.

3. If the intelligibility criteria are met, then the

system can be completed. If the intelligibility criteria

indicate an inadequate direct-to-reverberant ratio,

consider the possibility of increasing R through the

addition of acoustical absorption in the room. In

existing rooms, this may not be possible; however,

for rooms still in the design phase, it may be possible

to increase the amount of absorption.

4. If a recalculation of the room parameters

indicates that a central array will work, then the

design can be completed. If not, the next step is to

determine the nature of a distributed system that will

satisfy the requirements of intelligibility. A central

array can often be designed to cover just the front

part of a room, with delayed loudspeakers covering

the rear of the room. In marginal cases, this is likely

to be more satisfactory than an all-out distributed

system.

The entire process described above has been

reduced to the flow chart shown in Figure 6-20.

Figure 6-20. Flow diagram for system design