The animation above shows the resultant sound wave pattern from two sources, each of which can be turned on and off.
Why are there no dead spots in the sound distribution when either the left or the right source is transmitting but there are multiple dead spots when both sources are transmitting?
Wave superposition produces interference effects.
See Giancoli-PA: 12-7, Giancoli-SE: 16-7.
Physlet problem authored by Wolfgang Christian.