User Guide

Sound System Design Reference Manual
Effects of Temperature Gradients on
Sound Propagation
If sound is propagated over large distances
out of doors, its behavior may seem erratic.
Differences (gradients) in temperature above ground
level will affect propagation as shown in Figure 1-8.
Refraction of sound refers to its changing direction
as its velocity increases slightly with elevated
temperatures. At Figure 1-8A, we observe a situation
which often occurs at nightfall, when the ground is
still warm. The case shown at B may occur in the
morning, and its “skipping” characteristic may give
rise to hot spots and dead spots in the listening area.
Effects of Wind Velocity and Gradients
on Sound Propagation
Figure 1-9 shows the effect wind velocity
gradients on sound propagation. The actual velocity
of sound in this case is the velocity of sound in still
air plus the velocity of the wind itself. Figure 1-10
shows the effect of a cross breeze on the apparent
direction of a sound source.
The effects shown in these two figures may be
evident at large rock concerts, where the distances
covered may be in the 200 - 300 m (600 - 900 ft)
range.
1-6
Figure 1-8. Effects of temperature gradients on sound propagation
Figure 1-9. Effect of wind velocity gradients on sound propagation