Sound transmission loss measurements using the sound intensity technique Part 1: The effects of reverberation time

Abstract

Two simplified geometric models have been considered to illustrate some characteristics of the sound intensity field in an enclosure and the results indicate that the sound intensity field is not affected by the reverberant component for distances from a source much greater than the reverberation radius (obtained from consideration of the sound pressure field) of the enclosure. The effects of reverberation time in the receiving room on sound transmission loss measurements using the sound intensity technique have been investigated. Six different reverberant conditions, ranging from 0·6 to 4·2 s at 500 Hz, have been used. Results indicate that the sound intensity measurements are virtually independent of the reverberant conditions (as illustrated by the simplified geometric models) provided that the pressure-intensity index of the measurements does not exceed the dynamic capability of the sound intensity measuring system. It has also been found that the pressure-intensity index of the measurements can be reduced by either increasing the distance of measurements from the test specimen or by reducing the reverberation time in the receiving room. A global indicator based on the pressure-intensity index has been formulated and is shown to be able to indicate the degree of agreement between sound transmission loss measurements determined using the conventional sound pressure and sound intensity methods.