Conceptual Physics

The principle of conservation of energy applies to sound waves. When two waves destructively interfere at some position, the energy does not disappear. Rather, there must be another area where the waves are constructively interfering, as well. For any area of silence, there must be a louder area. Positioning loudspeakers or designing concert halls to minimize the severity of these “dead spots” and “hot spots” is a topic of interest to audiophiles and sound engineers alike.

Path lengths differ by one-half

wavelength

Destructive interference

Constructive interference:

ǻp = nȜ

Destructive interference:

ǻp = difference in path lengths

n = 0, ±1, ±2, ...

Ȝ = wavelength

17.8 - Beats

Beats: The pattern of loud/soft sounds caused by two sound sources with

similar but not identical frequencies.

So far in this chapter, we have studied combinations of traveling waves with the same amplitude, frequency and wavelength. You may wonder

Beats

Periodic variations in amplitude produced by two waves of different frequencies