Finite element sound field analysis for investigation on measurement mechanism of reverberation time in non-diffuse sound field

As well known, the reverberation time is essential to evaluate room acoustics; however, it is not so easy to predict in a practical room where the assumption of diffuse sound field is not satisfied. On the other hand, the numerical analyses based on the wave equation have been intensively used to explore many kinds of acoustic problems. In this study, 15 kinds of rooms with different absorption surfaces are analyzed by time domain finite element method. This study shows effectiveness of the analysis for investigation on measurement mechanism of the reverberation time of sound field in rooms where the assumption of diffuse sound field is not satisfied. 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. 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, and the ratios are calculated in the 15 kinds of rooms at each frequency. Finally, relationship among the ratios, mean absorption coefficients, reverberation times calculated from the results of TDFE analysis and those from Sabin’s formula is investigated.