Speed Of Sound - Phase Change


To determine the speed of sound.


Wave generator, small loudspeaker, microphone, oscilloscope, and optical rail with mounts, assembled as photographed on request.

Setup Time

10 min.


A sine wave is sounded by a loudspeaker and picked up by a microphone. The original sine wave triggers the oscilloscope, which displays the signal from the microphone. Motion of the microphone away from the microphone,measured by a ruler or the optical rail scale, is accompanied by a phase or time delay, measured by motion of the oscilloscope trace. The speed of sound is the distance the microphone is moved divided by the additional time lag. This works best at frequencies of at least 3000 Hz.


PIRA 3B30.10)