A Fundamental Investigation on Geometrical Acoustic Prediction Method of Sound Fields with Scattering Coefficients for Room Boundary
Kunitaka Nakanoa, Hiroshi Furuyab and Soichiro Kurokic

This study deals with the problems of the scattering coefficients that should be assigned to a wall in geometrical acoustic simulations and a fundamental property of the prediction that may be used to model the diffuse reflections. Acoustic simulations in hybrid image/ray tracing model with variable scattering coefficients are performed for two kinds of sound fields: (1) sound field with a reflection from a single wall, which is a plane or a diffusive wall, (2) sound field in auditorium enclosures for three types of floor plan, namely, rectangular, fan-shape and reversed fan-shape. Firstly, the level distributions of reflections from a single wall are investigated in the receiving areas with and without a specular reflection, and the directivity characteristics are also calculated for three incident angles of sound. Secondly, room acoustics parameters are analyzed from impulse responses in auditorium models. In addition, physical scale model experiments are conducted in order to verify the practical approach applying scattering coefficients to geometrical acoustics prediction. As a result, the calculated values in proper assignment of scattering coefficients for the boundaries give close agreement with the measured ones. The difference between them and the behavior of the prediction affected by diffuse reflections are discussed.

Key words: Geometrical acoustics simulation, Surface diffusion, Scattering coefficient, Scale model measurement