Sound source directivity estimation via a spherical wave decomposition of the radiated field : application to human voice directivity measurements

The experimental evaluation of the directivity of a nonrepeatable sound source necessitates the simultaneous acquisition of signals from microphones distributed on a sphere centered on the source with a high spatial resolution.Placing a high number of microphones at precise, pre-determined positions is a laborious task that is subject to inaccuracies.The Helmholtz Equation Least Squares (HELS) method is an imaging technique originally used in near-field acoustic holography.This method involves decomposing the sound field measured around a source into a basis of functions that solve the Helmholtz equation.Once this decomposition has been identified, any acoustic quantity can be reconstructed around the source.Recent simulated and experimental studies have demonstrated that the HELS method consistently estimates the far-field directivity of a sound source from measurements performed on an arbitrary surface around the source.The present study utilizes a sphere-like array of 3 m-diameter and around 600 MEMS microphones installed in an anechoical room to measure the directivity of a reference sound source.The truncation order of the basis function