Page 167 - Master Handbook of Acoustics

would not be refracted. It would speed up and slow down slightly as it penetrates the warmer and
cooler layers, but would still travel in a vertical direction. All sound rays, except the vertical, would
be refracted downward. The amount of this refraction varies materially: The rays closer to the
vertical are refracted much less than those more or less parallel to the surface of the earth.

FIGURE 8-4 Comprehensive illustration of refraction of sound from source. (A) Cool air near the
ground and warmer air above. (B) Warm air near the ground and cooler air above; note that
acoustical shadow areas result from the upward refraction.

Figure 8-4B is a distant view of the upward refraction scenario of Fig. 8-3C. Shadow zones are to
be expected in this case. Again, the vertical ray is the only one escaping refractive effects.