A note on using panel diffusers to improve sound field diffusivity in reverberation rooms below 100 Hz

Abstract

In many standard acoustic tests, the sound field in a reverberation room is required to be sufficiently diffuse. The standard deviation of sound pressure levels is commonly used to evaluate the spatial uniformity of a sound field; however, this paper shows that the standard deviation of squared sound pressures is a better indicator of sound field diffusivity at frequencies below 100 Hz where the sound field is very uneven. Fixed diffusers are recommended in ISO 354 to improve sound field diffusivity in reverberation rooms, and performing sound absorption measurements with an increasing number of diffusers is employed as a check on the diffusivity of the sound field above 500 Hz. This paper demonstrates that typical panel diffusers (as suggested in ISO 354) cannot increase the sound field diffusivity at low frequencies. While low frequency diffusivity can be improved with large panels at some frequencies, the diffusivity at other frequencies generally deteriorates. Experimental results in a reverberation room are presented to support the numerical simulation results and analyses.