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 either a calculator or computer. 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. The sound is captured using sound editor software. Run and click record before the sound is made. Click fingers. Click stop. The click part of the recording is separated out and examined closely.

This screen recording (NB large file of ca. 1 M) shows this being done with a trial limited edition version of the sound editor CoolEdit 2000 which was located here in an unregistered trial version. Alternatively, Audacity can be used.

This second screen recording (another large file of ca. 1 M) shows how the analysis can be started. This screen recording shows the same in Audacity (again a large file of ca. 3 M).

This sound pattern was obtained. This clearly shows not just one but several echoes: sound reflects from not just the closed but also the open end of the tube. This point is important in musical instruments.

In this example, the initial click of the fingers is so loud as to overload the mic.

To measure this yourself here is a larger picture of the trace ( filesize 120 k). The tube is from a vacuum cleaner and is 1.06 m long. Measure and calculate.

The distance and time data for all the echoes can be processed by entering the measurements into graphical calculator lists, running Physics and fitting the data to a straight line. These screengrabs illustrate the process.

Stat...Edit enter data in lists


App...Physics...Analyse...Curve fit...Linear L1,L2...Enter...Enter(for graph)


Or with calculator commands: Stat...Calc...LinReg(ax + b)...2nd_L1, 2nd_L2 ...Vars...Y-Vars...Function...Y1

giving LinReg L1, L2, Y1 on screen. Enter to get the fit, then Enter shows a graph.


This gives a speed of sound of 342.6 metres per second. The calculation could also be done in Logger Pro.