Propagation of sound in long enclosures

Abstract

The propagation of sound in long enclosures is addressed theoretically and experimentally. In many previous studies, the image source method is frequently used. However, these early theoretical models are somewhat inadequate because the effect of multiple reflections in long enclosures is often modeled by the incoherent summation of contributions from all image sources. Ignoring the phase effect, these numerical models are unlikely to be satisfactory for use in predicting intricate patterns of interference due to contributions from each image source. In the present paper, the effect of interference is incorporated by coherently summing the contributions from the image sources. To develop a simple numerical model, the walls of long rectangular enclosures are represented by either geometrically reflecting or impedance boundaries. Measurements in a one-tenth-scale model are conducted to validate the numerical model. In some of the scale-model experiments, the enclosure walls are lined with a carpet to simulate the impedance boundary condition. It has been shown that the proposed numerical model agrees reasonably well with experimental data.