Measurement of 3-D directional characteristics of reverberant sound fields using a spherical microphone array

Abstract

A new measurement system has been used to analyze directional characteristics of reverberant sound fields in several small- and medium-sized rooms. The system employs a pair of 32-element spherical microphone arrays to obtain the room impulse response in each of 60 steering directions. The two different-sized arrays are used to cover the frequency range from 300–3300 Hz with an angular (directional) resolution of about 28 degrees. An analysis of these directional room impulse responses enables the variation of arriving sound energy with (3-D) direction and time to be studied. Specifically, the isotropy of the sound field at the receiving position can be assessed at any time instant, or over any time range desired. Directions from which significant or insignificant proportions of sound energy arrive are identifiable. Furthermore, the time and direction of incidence of the direct sound and discrete early reflections can be identified. This can be of use in localizing sources, finding reflections, and in decomposing the sound field into arriving components.