Finite element sound field analysis for reverberation time in non-diffuse sound field with unevenly-distributed sound absorbing surfaces

摘要

This study shows effectiveness of the analysis for investigation on measurement mechanism of the reverberation time of sound field in non-diffuse sound field with unevenly-distributed sound absorbing surfaces. To evaluate a sound field in a room for the measurement, the ratio of incident sound energy to a part of boundary in those to all boundary of a sound field in a room is calculated from results of the time domain finite element analysis. In this study, 72 kinds of sound fields with different boundary condition are analyzed by time domain finite element method. At first, the calculation method of the ratio of incident sound energy to a part of boundary in those to all boundary of a sound field in a room is described. Next, the ratios are calculated in the 72 kinds of sound fields and are compared with ideal values of diffuse sound field in each room. In addition, the reverberation times are calculated from the results of TDFE analysis and from Sabin's formula and differences between both the reverberation times are calculated in the rooms. It is shown that the larger the difference of reverberation time, the larger the difference between the ratio and the ideal value regardless of room size, absorption coefficient of absorbing surface. Finally, it is tried to predict the ratio from room size and absorption coefficient of absorbing surface without the results of TDFE analysis.