Reverberation mapping using instantaneous intensity estimates from a tetrahedron microphone array

Abstract

For hearing aids, the directivity index is a benchmark defined under two acoustical conditions that a hearing-aid user won’t encounter, namely, the ratio of sound power signal arriving from the on-axis target in an anechoic condition to the isotropic spherical noise. It would be useful to benchmark the speech signal to noise that is encountered in a typical environment. The purpose of this study is to map the instantaneous acoustic intensity in a room using a head and torso voice simulator as the source and a regular tetrahedron microphone array in the field. Four impulse responses from a small tetrahedron were measured in a reverberant conference room of gypsum walls, carpet, and absorptive ceiling tile. Welch’s method was used to compute one-third octave estimates of the auto- and cross-spectra from the impulse responses, and these spectra were used to estimate the steady-state, 3D instantaneous acoustic intensity vector via the time-averaged active intensity and the maximum amplitude of the reactive intensity. A histogram of the instantaneous intensity vector revealed an angular estimate for the arriving sound power that was, in general, cylindrically rather than spherically “diffuse.”