A method for evaluating the spatial uniformity of sound pressure in a small room by using power spectra at fewer measurement points

Abstract

Sound pressure levels in low frequencies vary greatly depending on a measurement point, especially in a small room. The standard deviation of the spatial distribution of sound pressure level (σSPL) is used as one of the parameters to evaluate the spatial uniformity of sound pressure. However, many measurement points are required for an accurate evaluation using σSPL. In this study, we investigate a method for evaluating the spatial uniformity with fewer points. We had proposed the frequency-domain coefficient of variation (FCV) to evaluate the diffuseness of a sound field focusing on the frequency domain. The FCV is defined as the coefficient of variation of a power spectrum. The lower density of room modes in low frequencies would give large σSPL. Thus, larger FCV should be obtained when larger σSPL due to room modes occur. Generally, the power spectrum is obtained from a room impulse response (RIR). However, the bandwidth of each mode is changed depending on the decay of the RIR, namely, a reverberation time. To obtain the FCV avoiding the change of the bandwidth, the decay of RIR is canceled. The results of numerical simulation showed that the FCV at fewer points can evaluate the spatial uniformity than the σSPL.