Finite element sound field analysis for correction of absorption coefficient in reverberation room

In this study, sound fields for the measurement of sound absorption coefficient by reverberation room method are analyzed by time domain finite element method. This study shows effectiveness of the analysis for investigation on causes of variation in the measurement results and improvement methods of the measurement. To evaluate an actual sound field for the measurement, the ratio of incident sound energy to the test material in those to all boundary of the measurement sound field is calculated from results of the finite element sound fields analysis. First, square sound pressure amplitudes of plane sound wave incident on absorption material are calculated in one-dimensional sound field. Next, the calculation method of the ratio of the measurement sound field is described. Finally, relationship among the ratio, shape of the measurement room, and characteristics of the test material is investigated, and it is shown that the bigger normal incident sound absorption coefficient of test material, the larger the change of the ratio for decay sound field regardless of room shape and surface area of test material.