Three-dimensional rectangular vocal-tract model with asymmetric wall impedances

A method to compute the acoustic characteristics of a simplified three-dimensional vocal-tract model with asymmetric wall impedances is presented. The acoustic field is represented in terms of both plane waves and higher-order modes in tubes. This model is constructed using a connected structure of rectangular acoustic tubes, and can parametrically represent acoustic characteristics in higher frequencies where the assumption of plane wave propagation does not hold. The propagation constants of the plane waves and the higher-order modes are calculated taking account of the asymmetric distribution of the wall impedances which can be specified as different values on four sides of each rectangular tube. The frequency characteristics of the propagation constants and the transfer characteristics of multiple section models are presented.