A BEM study on the effect of source-receiver path route and length on attenuation of direct sound and floor reflection within a chamber orchestra

In past work stage acoustic parameters have been used with limited success to assess musicians‟ subjective impressions of acoustic conditions. These parameters are commonly measured either on unoccupied stages, or on stages with furniture only (no musicians) but with a radius of 2 m cleared around both the source and receiver. This study investigates the validity of undertaking such measures on unoccupied stages, by considering the difference in on stage sound fields with and without a chamber orchestra present. This paper uses a previously validated BEM (boundary element method) model of a chamber orchestra for this investigation, and examines six source-receiver paths within the orchestra, two distinct paths each of three different lengths. Consideration is also given to the impact of randomly perturbing the orchestra for each of the six paths, and to the most appropriate distance to clear around the source and receiver to avoid significantly impacting results while maintaining a realistic stage set-up. Using the results of the BEM orchestra model, it was found that, in contrast to the 2.0 m normally recommended, a clear radius of 0.5 m was a good compromise between giving consistent results and clearing too much from the stage for meaningful results. It was also found that the attenuation was strongly affected by path length, but weakly affected by the path route or by perturbations of the orchestra set-up, and corrections are proposed to empty stage measurements (of direct sound and floor reflection only) to account for the presence of an orchestra on stage, for several source-receiver distances.