Spherical acoustical holography of low-frequency noise sources

Abstract The performance of near-field reconstruction at low frequency using spherical holographic techniques is investigated. The spherical Hankel function with small argument (near-field and low frequency) has divergent behaviour in the near-field. This divergent phenomenon influences the precision of holographic reconstruction. Two computer simulations based on the derived equations are used to demonstrate the capability of holography to construct the source surface pressure and particle velocity for noise source identification. The results of multipole source simulation show that the precision of backward holography to the near-field depends on using the optimum order of holographic wave. Analysis of another simulation shows that more precise reconstruction of source surface pressure and particle velocity can be obtained from original pressure data at a smaller radius.