Dual surface beamforming and acoustical holography for sound field visualization in reverberant environments

Abstract

Near-field acoustical holography is a technique that has been widely used to visualize noise sources from pressure measurements in spaces that can be assumed to be anechoic or semi-anechoic. Previously, a dual surface acoustical holography procedure based on making measurements on two surfaces between the source and a reflecting surface was introduced to remove the effects of reverberation. Little work has been performed in which beamforming has been used to visualize sources based on dual surface, near-field measurements in a reverberant environment: such a procedure is described here. Because many practical measurement environments are not completely anechoic, the source resolution accuracy of dual surface acoustical holography and beamforming procedures in reverberant environments is compared here by using numerical simulations. It has been found that dual surface acoustical holography provides the clearest representation of the source location when sound waves radiating from the source and the reflected waves are propagating in the opposite directions and when the measurement surfaces are conformal with the source geometry. However, it has also been found that dual surface beamforming provides more consistent source resolution performance regardless of the relative direction of wave propagation of the source and reflected waves.

A new beamforming microphones array with acoustic insulation baffle

“…Cross-spectral imaging function is the commonly used near field beamforming algorithm, which is achieved by assuming a model where the recorded field is generated by a distribution of monopole point sources, forming an error function between measured and modeled cross-spectra, and minimizing this error function. The resulting imaging function is [3,13,16,17]:…”

“…And traditional single-layer microphone array is not suitable in acoustic measurement when sources exist behind the array in practical engineering application such as automobile and aircraft cabin, engine compartment and other narrow space. Pascal et al [16] use the SOAP (Statistically Optimal Array Processing) beamforming method and Cho et al [17] apply acoustical holography method to distinguish acoustic sources which are located on both sides of microphone array in the reverberant environment, respectively. Both of them use a double-layer microphone array to separate the sound pressure and particle velocity in the measurement.…”