The color of early sound arrivals in an auditorium

Abstract

In computational room acoustics, most present-day methods calculate specular reflections complemented by various models for surface scattering. A recent method of edge diffraction calculation [U. P. Svensson et al., J. Acoust. Soc. Am. 106, 2331–2344 (1999)], builds on the BTM technique which has been proven to be accurate in such diverse situations as noise control by barriers and sound scatter from the rough ocean surface. Here, it is applied to a large concert hall. The hall chosen is one of those in an International Round Robin study. It is shown that calculations of edge diffraction give quantitative details of what has until now been approximated and loosely called ‘‘scattering.’’ Here, the early part of the impulse response is considered in order to study aspects such as the frequency content of individual early diffractions and reflections and the low-frequency energy distibution in the room. Only rigid surfaces, and up to second-order edge diffraction and/or specular reflections are taken into account, but the possible extension towards realistic wall impedances and higher-order reflections are discussed. Since the BTM technique is exact and deterministic rather than approximate and statistical, it provides a secure basis for predictions in room acoustical modeling.