For an opening/object of a given size, diffraction is more pronounced for longer wavelengths.
Work Step by Step
This is discussed on page 548, and illustrated in Figure 29.11. The wavelengths of sound waves (roughly 2-1650 cm) are relatively long compared to those of visible light waves (roughly 0.00004-0.00007 cm). The diffraction of sound waves is more noticeable in our everyday environment.