Page 151 - Master Handbook of Acoustics

FIGURE 7-1 Diffraction varies according to the wavelength of sound and the size of an obstacle. (A)
An obstacle very much smaller than the wavelength of sound allows the wavefronts to pass
essentially undisturbed. (B) An obstacle larger than the wavelength casts an acoustical shadow.

Another way of looking at the relationship of wavelength and diffraction is to change our basis of
comparison, remembering that acoustic size depends on the wavelength of the sound. Consider Fig. 7-
2A where the obstacle is the same physical size as that in Fig. 7-2B. However, the frequency of the
sound in Fig. 7-2A is higher than that in Fig. 7-2B. We observe that the same obstacle casts a

considerable acoustical shadow for high frequencies (the obstacle is relatively large), but casts much
less of a shadow for low frequencies (the obstacle is relatively small).

FIGURE 7-2 The same-sized obstacle will exhibit different degrees of diffraction, depending on the
frequency (wavelength) of the sound. (A) When a high-frequency sound impinges on the obstacle,