Finite Element Sound Field Analysis of Diffuseness in Reverberation Rooms

Standard deviations of sound pressure levels and spatial correlation functions of sound fields in reverberation rooms are calculated from sound pressures obtained by sound field analyses based on the authors' finite element method. Distinct differences are found among the standard deviations under four sound source conditions in a regularly shaped reverberation room, while there is not much difference among them for an irregularly shaped reverberation room. Difference between standard deviations of sound fields under the best and worst conditions was found to be 1.0 dB within 1/3 octave band in the regularly shaped reverberation room. Next, spatial correlation function values obtained by the finite element sound field analysis are compared with values in the perfectly diffuse sound field. Differences between actual values in reverberation rooms and theoretical values in the perfectly diffuse sound field (i.e. sin kr / kr) are also compared with standard deviations of sound pressure levels. As a result, both correlation functions and standard deviations are greatly affected by differences in room shape and sound source positions; in contrast, standard deviations are not affected by absorbing material on their boundaries.