User Guide

Sound System Design Reference Manual
Critical Distance (D
C
)
The distance from the acoustic center to the
circle-black boundary is called the critical distance .
Critical distance is the distance from the acoustic
center of a sound source, along a specified axis, to a
point at which the densities of direct and reverberant
sound fields are equal.
Critical distance is affected by the directional
characteristics of the sound source. Figure 5-16
illustrates the same room as in Figure 5-15, but
with a more directional loudspeaker. In the instance
the circle-black boundary no longer describes a
semicircle. The black dots are concentrated along
the major axis of the loudspeaker and maintain their
dominance over the circle dots for a substantially
greater distance than in the preceding example.
However, at 45° or greater off the major axis, the
black dots die out more rapidly and the circle-black
boundary is much closer to the source.
5-14
Figure 5-18. Direct and reverberant fields, dead room
Figure 5-17. Direct and reverberant fields, live room