PURPOSE: To measure the speed of sound by determining the travel time of a pulse between two microphones.
DESCRIPTION: A loudspeaker sends pulses past the two microphones, and the oscilloscope displays the pulses on its time axis. The oscillator is set for 2 Hertz square waves to produce well-separated pulses. The speed of sound is the distance between the two microphones divided by the time delay read from the oscilloscope. In the photo above the microphones are 34.5 cm apart and the scope is set at 200 microseconds/div (The math is simple if you move the second microphone so that the two pulses are 1 ms apart.).
REFERENCES: (PIRA unavailable.)
EQUIPMENT: Oscillator, small speaker, two microphones with holders on optical rail, mixer amplifier, and oscilloscope.
SETUP TIME: 10 min.
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