simple ideas on measuring the speed of sound

using a mic and calculator based measurement

using a mic and computer






One method to measure the speed of sound in air uses a microphone attached to a calculator and interface. The microphone is held at the lip of a tube but not touching it. The tube rests vertically on a flat smooth surface like the floor or a CD case.

Fingers are clicked just at the entrance to the tube but without touching it or the mic. For a picture see the "using a mic and computer" page. The calculator runs Physics:

App...Physics...Setup probes...One...Microphone...Cbl... Waveform/trigr

This sets up a preset where the interface will collect 100 samples at 10000 samples per second but only when the sound level rises above a triggering value: when the fingers are clicked.

For some users the preset is not sensitive enough. It can be reset as: App...Physics...Setup probes...One...More..Voltage...Triggering...

Try various settings: channel 1, increasing, 0.001, prestore 5 (%), etc, to make the interface more sensitive.


Note that by measuring the time for the first peak and then for the second that the time for an up and down motion of the sound along the tube can be calculated. From the length of the tube, the speed of sound in air can be calculated. This routinely gives the measurement to within 1%.

When a wave reflects the phase changes: a crest becomes a trough and vice versa. This should be taken into account.

This experiment demonstrates that sound is reflected. An echo is reflected sound. Sometimes more than one echo is detected. This is a demonstration that sound reflects from both open and closed ends of tubes. This is very important in music. Computer data shows this more clearly.