Figure 1-18. Sound wave 180 "out of phase"
c. Beat Frequencies. A beat frequency results from the partial union of like or unlike
frequencies. At any instant of time the waves may be in phase with each other, out of phase, or in some
degree of phase relationship between each other. This continual shifting back and forth of phase
relationship results in a beating or pulsating sound and is referred to as beat frequency (fig 1-19).
Figure 1-19. Examples of beat frequencies