A synthesized boundary condition for wave-based room acoustics simulations using ensemble averaged impedance measured in-situ

Abstract

The importance of wave-based room acoustics simulation has been increasing in various fields of researches and design-stages. The problem remained, however, is how to model the rooms’ absorptive boundary conditions. It is known that traditional absorption indices like sound absorption coefficient and normal impedance are not always suit for such a fine method like finite element method. Then, the concept and measurement technique of ensemble averaged impedance were presented. In our previous studies, a series of in-situ measurement of ensemble averaged impedances were successfully performed to result excellent reproducibility and repeatability. Herein, the outline of the concept of ensemble averaged impedance including the measurement technique is summarized, first. Second, several example results of practical measurements are given to exhibit that their uncertainties stay within the range for wave-based simulations to keep their resulting uncertainties less than just noticeable difference. Then, a mathematical-physical model of synthesized boundary condition is given using the ensemble averaged impedance in the sound field analysis by finite element method. Finally, the results of sound field simulations of realistic rooms are shown to examine the plausibility of the model.