An experimental comparison of various methods of nearfield acoustic holography.

An experimental comparison of four different methods of nearfield acoustic holography (NAH) for planar acoustic sources is presented in this study. The four NAH methods considered in this study are based on: (1) spatial Fourier transform, (2) equivalent sources model, (3) boundary element methods and (4) statistically optimized NAH. Two dimensional measurements were obtained at distances ranging from one-half to sixteen microphone spacings away from a sound source and the NAH methods were used to reconstruct the sound field at the source surface. Reconstructed particle velocity and acoustic pressure fields presented in this study showed that the equivalent sources model based algorithm along with Tikhonov regularization provided the best localization of the sources. Reconstruction errors were found to be smaller for the equivalent sources model based algorithm and the statistically optimized NAH algorithm. The effects of hologram distance on the performance of various algorithms are discussed in detail. The study also compares the computational time required by each algorithm to calculate the reconstruction. Four different regularization parameter choice methods were compared. The L-curve method provided more accurate reconstructions than the generalized cross validation and the Morozov discrepancy principle at larger measurement distances. The performance of fixed parameter regularization was comparable to that of the L-curve method. [ABSTRACT FROM AUTHOR]