Three–dimensional acoustic imaging using asynchronous microphone array measurements

Complex test models in aeroacoustic experiments often present an arrangement of noise sources within a three–dimensional space. Planar microphone array normally have difficulties in separating sound sources in the direction normal to the array plane due to their poorer spatial resolution in this direction. This paper evaluates the benefits of combining asynchronous microphone array measurements for three–dimensional acoustic source. An experimental setup consisting of three out–of–plane speakers was considered. A planar microphone array was employed for the acoustic measurements in a baseline position and then displaced around the speakers to provide different points of view. The acoustic source maps obtained from each array position were combined using the geometric mean of their source autopowers. The performance of this approach in combination with the following acoustic imaging methods was investigated: conventional frequency domain beamforming (as baseline), functional beamforming, orthogonal beamforming, robust adaptive beamforming, CLEAN–SC, Richardson–Lucy deconvolution, and global optimization methods. For each case, the performance is evaluated in terms of accuracy in source position localization and spectral quantification in sound pressure level. In general, it was determined that combining additional views considerably improved the accuracy in terms of position localization (especially in the depth direction).