Two separated, identical speakers on a turntable are connected to a sine generator. A listener will hear sound from the two speakers interfere destructively as the turntable is rotated. One may also poll the class at a single position of the turntable to identify locations where the destructive interference condition is met.
A tone of 200-600 Hz works well. When you go to about 1 kHz, your ears may hear different intensities. Trippy.
L3, A0
PIRA DCS 3B55.10