Sound Velocity Measurement by Real-Time Correlation Methods

Abstract

Experiments for determining sound velocity, using a class of pseudorandom sequences, known as m-sequences, are described. The m-sequence signal generated by a shift register are applied to a sonic system formed by a speaker and a condencer microphone. On the surface of the microphone the phase of the sonic signal is controlled constant by varying the shift pulse frequency which gives the sound velocity. Detection of the phase was carried out on real-time by 1) ordinary input-output crosscorrelation and 2) stroboscopic correlation method. The first method affords a simplified measuring system, while the second method enables stable and accurate measurement compared with the first one, though it requires two m-sequence generators. Continuous record of pendulum motion, room temperature and wind velocity obtained by the second method are also presented. The accuracy of the room temperature determination was estimated to 0.005m/s in terms of sound velocity change.