An experimental and theoretical investigation of the high frequency broadband soundfield

Abstract

A relatively simple theoretical model of a rectangular enclosure with sound sources on one wall, an absorptive end-wall, and two absorptive side-walls is developed. Using a power balance at cross sections, a differential equation for mean-square pressure in the acoustic enclosure is derived. A simple formula for the mean-square pressure as a function of distance from source-wall to absorbing end-wall is obtained. The other variables in the formula include the random incidence absorption coefficients, the cross-sectional area and perimeter, and the source power. This formula is compared to results from numerical simulations, to a revised Sabine prediction for mean-square level, and to experimental results. For the most absorptive cases, however, a more refined theoretical model is needed in order to have reasonable agreement with the experimental data. In the refined model, it is assumed sources are distributed on an end-wall and the resulting sound waves are considered on an angle-by-angle basis. The mean-square pressure is calculated by integrating over all possible angles. Although still a fairly simple result, the effects of angle of incidence on the absorption and the reflection field in the enclosure are retained.