Beats

BEATS are a further, distinctly audible consequence of the principle of superposition. When two sound waves of the SAME amplitude but SLIGHTLY DIFFERENT frequencies travel through a medium in the same direction and superpose, the resulting intensity of sound at a fixed listening point does not stay constant -- instead, it periodically rises to a maximum and falls to a near-minimum, over and over, at a regular rate. Moments of maximum loudness are called WAXING, and the intervening moments of minimum loudness are called WANING; one waxing followed by the next waning toge …