Approximate reconstruction of sound fields close to the surface of arbitrarily shaped sound sources using NAH

Investigations are presented on the reconstruction of the sound field close to the surface of arbitrarily shaped sound sources. The Nearfield Acoustical Holography (NAH) in spherical coordinates can be used for the reconstruction of sound field parameters. The applicability of the reconstruction method, however, is limited by the validity restrictions of the Rayleigh hypothesis, which are determined by a minimal sphere. Depending on the shape of the source the NAH-solution becomes non convergent if the validity conditions are violated. To overcome the limitations an algorithm is proposed for extracting local information from the non convergent NAH-solution. For the assessment of the results an appropriate virtual test rig is developed employing the Kirchhoff-Helmholtz-Integral-Theorem.