Approximate model of sound source in consideration of evanescent waves in far-field acoustical holography

Far-field acoustical holography methods reconstruct the sound fields mainly based on the simple point source model because of the loss of abundant information compared with near-field acoustical holography (NAH). It brings problems that the reconstructed sound sources are different from the actual measured sound sources especially because of the evanescent waves which attenuate rapidly in the near field. In the recent study, we establish the approximation formulation of evanescent wave propagation which suggests that evanescent wave can be considered as the interference of dipole model and quadrupole model with different weighting factors distributed on the incident wave-front. Without the evanescent wave component, the constructed sound sources are actually the components that are effective in the far-field and we proposed the concept of “far-field effective sound source” to show its physical meanings. With simulations and actual experiments with known speakers, the approximation method of sound source model is validated and the far-field acoustical holography has been improved to achieve more accurate quantitative reconstruction results. The study explored the evanescent wave which is hard to capture and for engineering practice, this research can give more accurate reconstruction as well as the approximation.