A Time-of-Flight Method To Measure the Speed of Sound Using a Stereo Sound Card

Abstract

Most homes in developed countries have a sophisticated data acquisition board, namely the PC sound board. Designed to be able to reproduce CD-quality stereo sound, it must have a sampling rate of at least 44 kHz and have very accurate timing between the two stereo channels. With a very simple adaptation of a pair of regular PC microphones, a computer with a stereo sound board, and sound analysis software, we were able to implement a method of accurate measurement of the speed of sound with several attractive features: a) The most expensive equipment, the PC, the sound board, and sound analysis software, are available in many homes and almost all schools; the two microphones and the additional electronics (see below) can be acquired for less than $50. b) The concept of the experiment is sufficiently simple to be grasped by very young students, 13–14 years old. c) The experiment itself is so straightforward that in a recent Open Day at our department, every group of students passing through the experiment was able to complete, in a couple of minutes, several measurements of cs, the speed of sound in air. d) It is possible to use the same apparatus to measure the speed of sound in solids.