Page 153 - Master Handbook of Acoustics

FIGURE 7-3 The sound striking a solid traffic barrier will be partly diffracted and partly reflected.
(A) High-frequency traffic sounds are successfully attenuated on the other side of the barrier because
of limited diffraction. (B) Low-frequency traffic sounds are less attenuated because of more
prominent diffraction. Sound passing the top edge of the barrier acts as though the wavefronts are
lines of sources, radiating sound energy into the shadow zone.

The wavefronts passing the top edge of the wall can be considered as lines of point sources

radiating sound. This is the cause of the sound penetrating the shadow zone. The sound reflected from
the wall should also be noted. It is as though the sound is coming from a virtual image on the far side
of the wall.
Figure 7-4 illustrates the effectiveness of highway barriers, showing the attenuation of sound in the
shadow of a high, massive wall. The center of the highway is taken to be 30 ft from the wall on one