The INTERFERENCE pattern that results from two or more SOUND WAVEs travelling in the same space usually includes positions or times when the sum of the individual pressure variations approaches or reaches zero. This process is known as destructive interference or cancellation.
In the simplest case, two signals that are 180° out of PHASE will cancel. In environmental propagation, the points of cancellation are sometimes fixed and thus are experienced as dead spots, although this may also be caused by poor DIFFUSION. A specialized case of cancellation occurs with two sounds of similar frequency and is experienced as BEATS.
See also: INTERFERENCE, LAW OF SUPERPOSITION, PHASE-SHIFT, PHASING, SOUND PROPAGATION, STANDING WAVES. Compare: DIFFRACTION, SOUND SHADOW.
Interference pattern between the wave fronts of two sound sources. Constructive interference is indicated by lines C, and destructive interference (cancellation) by lines D.