User Guide

Sound System Design Reference Manual
Calculations for a Medium-Size Room
Consider a more typical (and more
complicated) situation in which the sound system is
used in a larger room and in which a directional
microphone is employed. Figures 6-4 and 6-5 show a
room having a volume of 918 m
3
, a total surface area
of 630 m
2
and α = 0.15.
The first step is to calculate the room constant,
and we would do well to examine the actual
distribution of absorptive material in the room.
Chapter 5 explains why the effective room constant
R’ in a particular situation may vary substantially from
the figure given by the equation R = Sα/(1 -α).
Rather than complicate the example, however,
assume that the equation really does work and that
the room constant is about 110 m
2
.
The next step is to calculate critical distances
for the talker and the loudspeaker. Since the
loudspeaker does not have a uniform radiation
pattern, we must calculate its critical distance at the
particular angle in which we are interested. Figure
6-5 shows the distances involved and the
geometrical relationships between talker,
microphone, loudspeaker and listener.
Figure 6-4. A sound system in a medium-size room
Figure 6-5. Sound system in a medium-size room, gain calculations
6-5