ON THE DIRECT PROPAGATION OF SOUND INTENSITY USING CROSS-SPECTRAL NAH

For the localisation of sound sources, usually the acoustic pressure is propagated by means of acoustic holography techniques. In this paper the merits of the propagation of sound intensity instead of acoustic pressure are addressed. A newly developed theory based upon Planar Nearfield Acoustic Holography (PNAH) is described which propagates cross-spectra directly. Using this theory, called cross-spectral NAH, it is possible to propagate, in approximation, sound intensity spectra directly without the need to propagate the acoustic pressure and acoustic particle velocity spectra individually. In this paper, the cross-spectral PNAH theory is applied to an acoustical set-up with four baffled pistons, which can be solved analytically. The sound intensity is propagated towards the source by means of cross-spectral NAH and is compared with both the more commonly used indirectly propagated sound intensity and with the analytical sound intensity. It is shown that an accurate reconstruction of the sound intensity can be obtained by means of cross-spectral NAH, which is less sensitive to measurement noise in comparison with the indirect propagation of sound intensity.