Absolute Method for Sound Intensity Measurement

Abstract

Since sound propagation is an adiabatic process, a temperature fluctuation accompanies the sound wave in media for which the specific heat ratio is greater than unity. If the equation of state and the sound field are known, this temperature fluctuation may be related to the intensity of the sound wave. A thermometer capable of measuring fast, small-amplitude temperature variations is described. Its output is calculated for the case of plane, sinusoidal sound waves in an ideal gas. Its use as a microphone and sound intensity meter is then considered.