Nijman E., Machetta I.

The inverse sound source reconstruction addressed in this paper seeks, given a transmission matrix, to reconstruct the monopole distribution on the source surface using measured sound pressure data. Here the focus is on the transmission matrix. Conventional inverse methods use transmission matrices with point to point transfer functions, that is, transfer functions from volume velocity in discrete source positions to local acoustic field variables. The resulting transmission matrix is ill-conditioned and needs regularisation, with consequent loss of accuracy. Unlike the conventional methods, the new method proposed in this paper uses transfer functions from source positions to global field variables. These global variables, the components of the spherical wave spectrum, are obtained through expansion of the pressure field in terms of spherical harmonics. The inversion problem proves very robust and the size of the matrix to be inverted turns out considerably reduced. The theory has been validated through laboratory experiments.