Page 283 - The Master Handbook Of Acoustics

258 CHAPTER TWELVE

Refraction of Sound

Refraction changes the direction of travel of the sound by differences in
the velocity of propagation. Diffraction is changing the direction of travel
of sound by encountering sharp edges and physical obstructions (chapter
11). Most people find it easy to distinguish between absorption and
reflection of sound, but there is often confusion between diffraction and
refraction (and possibly diffusion, the subject of the next chapter). The
similarity of the sound of the words might be one cause for this confusion,
but the major reason is the perceived greater difficulty of understanding
diffraction, refraction, and diffusion compared to absorption and reflec-
tion. Hopefully Chaps. 9, 10, 11, 13, and this chapter will help to equalize
and advance understanding of these five important effects.
Figure 12-1 recalls a very common observation of the apparent
bending of a stick as one end touches the water surface or is actually
immersed. This is an illustration of refraction of light. As the present
subject is refraction of sound, which is another wave phenomenon, the
relative refractive indices of air and water will be passed over.

Refraction of Sound in Solids

Figure 12-2 illustrates sound passing from a dense solid medium to a
less dense medium. The sound speed in the denser medium is greater

FIGURE 12-1

Touching a stick to the water surface illustrates refraction of light. Sound is another
wave phenomenon that is also refracted by changes in media sound speed.