SOUND-TRANSMISSION LOSS MEASUREMENTS USING THE SOUND INTENSITY TECHNIQUE .1. THE EFFECTS OF REVERBERATION TIME

Two simplified geometric models have been considered to illustrate som e characteristics of the sound intensity field in an enclosure and the results indicate that the sound intensity field is not affected by th e reverberant component for distances from a source much greater than the reverberation radius (obtained from consideration of the sound pre ssure field) of the enclosure. The effects of reverberation time in th e receiving room on sound transmission loss measurements using the sou nd intensity technique have been investigated Six different reverberan t conditions, ranging from 0.6 to 4.2 s at 500 Hz, have been used Resu lts indicate that the sound intensity measurements are virtually indep endent of the reverberant conditions (as illustrated by the simplified geometric models) provided that the pressure-intensity index of the m easurements does not exceed the dynamic capability of the sound intens ity measuring system. It has also been found that the pressure-intensi ty index of the measurements can be reduced by either increasing the d istance of measurements from the test specimen or by reducing the reve rberation time in the receiving room. A global indicator based on the pressure-intensity index has been formulated and is shown to be able t o indicate the degree of agreement between sound transmission loss mea surements determined using the conventional sound pressure and sound i ntensity methods.