On the use of microphone arrays to visualize spatial sound field information

Microphone arrays represent today a state of the art solution to many acoustic problems. In architectural acoustics, for example, one of the most interesting applications is the possibility to analyse the directional information associated to a given reflection. Ambisonics microphones could provide similar information based on zeroth and first order spherical harmonic decomposition, but larger microphone arrays allow the determination of higher order components providing even better accuracy. In this case, directional information may be obtained through beamforming techniques that, although potentially more accurate and capable of resolving simultaneous reflections, are computationally heavier and provide a "discrete" sampling of the sound field. The paper compares the localization accuracy of a 32 channel microphone array by processing its output using a simple Ambisonics decomposition and a spatial sampling carried out using 32 "virtual" third-order hyper cardioid microphones. In addition, a comparison with conventional Ambisonics microphones is provided in order to point out possible differences. Results show that, when single reflections are involved and the sound field is highly polarized, the Ambsionics decomposition given by the microphone array gives good accuracy over the whole spectrum, while conventional Ambisonic microphones shows less stable results and greater variations as a function of frequency. Spatial sampling is intrinsically less accurate but allows a clearer resolution of simultaneous reflections