Numerical modelling of the spatial acoustic response of the human pinna

This paper is concerned with the spatial acoustic response of the human pinna modelled with the boundary element method (BEM). Accurate geometric models of five pinnae are captured by using state-of-the-art 3-D laser scanners and digitisers. These computer models are converted to valid BEM models and analysed acoustically up to 20 kHz. Using baffled pinnae models, we first repeat and validate numerically the normal concha modes as measured in the classical experiments made by E.A.G. Shaw in the 1970s. We then study the spatial mode shapes of a baffled cylinder (as a simplified model of the concha) and accurate pinnae by applying the singular value decomposition (SVD) technique. The method is used to analyse at discrete frequencies a matrix of Green functions relating the acoustic pressure at "field" points and "source" points in space. We demonstrate how the singular vectors which appear as spatial mode shapes couple to the singular vectors of the sound field. The relationship between these basis functions found with the SVD and the normal concha mode shapes is demonstrated. The method is also used in producing "reduced order" transfer functions by taking into account only the most dominant features of the singular vectors for the cases of a baffled cylinder and accurate baffled pinnae.