Scattering as a key to improved room acoustic computer modelling

It has been known for a long time that surface scattering plays a very important role in room acoustics. With room acoustic computer models like ODEON it is possible to study the influence of scattering coefficients, which can be assigned to the surfaces of the room. In the latest version of the program an additional effect has been modelled, namely the attenuation of sound due to diffraction, which is particularly pronounced for small surfaces, low frequencies and long reflecting paths. The present paper describes a parameter study of how to optimize the choice of the number of rays and the transition order. In order to evaluate the quality of a room acoustic calculation, the results were compared with measured values in real halls. The relative deviation in terms of subjective limen was calculated for each parameter at each position, and this was averaged over ten positions and six or seven room acoustic parameters. Results from two different halls have shown that a relative low number of rays are sufficient for reliable and stable calculation results. The optimum value of the transition order is two or three. The inclusion of diffraction effect leads to clearly improved results.