A coherent image source method for flat waveguides with locally reacting boundaries

Abstract

An image source method is presented for coherently evaluating the sound field from a point source in flat waveguides

with two infinite and parallel locally reacting boundaries, where one is sound absorbing and the other is reflective.

The method starts from formulating sound reflections into integrals by plane wave expansion, and the inherent intractability

in solving these integrals in such spaces is avoided by introducing a physically plausible assumption that

wave fronts remain the same before and after the reflection on a near-rigid boundary. By comparisons to the classical

wave theory and the existing coherent ray-based methods, it is shown that the proposed method is considerably accurate

to predict the sound propagation in flat waveguides with a sound absorbing ceiling and a reflective floor over a

broad frequency range and for various source/receiver geometries, even if at large distances from the source compared

to the waveguide height while the existing methods are shown to be erroneous.