Modelling of sound fields in enclosed spaces with absorbent room surfaces. Part I: performance spaces

Abstract

This paper introduces a three-part report describing research into the use of Millington absorption coefficients in the computer modelling of sound fields in enclosed spaces with absorbent room surfaces. The historical background to the prediction of reverberation time is presented together with three types of computer models used in the investigation. In part one, the computer models are described, the Millington reverberation time formula is validated, Millington absorption coefficients are derived and the sound field in a concert hall is predicted. This enables the accuracy of the three types of computer models to be compared and the effect of applying different absorption coefficients to be studied. Part two of the report consists of an extensive investigation into the prediction of reverberation time in multiple configurations of an experimental room with absorbent material partially covering the room surfaces. This determined the accuracy of reverberation time formulae and the computer models using both standard and Millington absorption coefficients under controlled conditions. The final part contributes a verification of the accuracy of the predictions using Millington absorption coefficients in a factory space with a barrier installed, and a refined diffraction model based on a ray-tracing model.