Consideration of wall reflection and diffraction in the room acoustic prediction using the phased beam tracing method

Abstract

The geometrical acoustics methods have been used to simulate the acoustics of rooms at high frequencies whereas the wave based methods have been devoted to calculate the low frequency response. The modified method, so called phased geometrical acoustics technique, was suggested for the extension of the applicability of the geometrical methods to mid frequency. Several studies on this method have demonstrated a good possibility to analyze the sound field in an enclosure at mid frequency. In this study, further considerations on wall reflection and diffraction have been investigated. The main suggestions are the use of approximated reflection coefficient and the integration with the theory of diffraction. This study aimed to improve the precision of the present method in mid frequency range and extend the applicability to the low frequency below Schroeder cutoff frequency. Because this method is originated from the geometrical acoustics, the wave-particle duality can be discussed by comparing with result from modal method. The calculation parameters were thoroughly investigated. The number of beams and the frequency resolution were proved to be the most important parameters in the analysis and consequently the guidelines were suggested for these parameters. The approximate angle-dependent/independent reflection coefficients were tested. The angle dependent reflection coefficient can take the angle dependence of the incident wave into account as well as the size effect of the surface. Also, the merit of representing the negative real part was discussed. The PBTM result shows a good agreement with the measurement especially in the early part of impulse response and at mid frequency. The new method of binaural simulation for the PBTM was suggested. The peculiar feature of frequency domain calculation of the PBTM gives advantages in the binaural simulation. Particularity in the early part of the impulse response at mid frequency, the binaural simulation result show...