Analysis of acoustic characteristics in the vocal tract with inhomogeneous wall impedance using a three‐dimensional fem model

Abstract

AbstractThe vocal tract can hardly be considered as having a uniform wall impedance. The palate, for example, is hard and the tongue is soft. The wall impedance is obviously nonuniform. However, so far, there is no detailed knowledge about the acoustic characteristics in the vocal tract when the impedance distribution is nonuniform along the vocal tract with a three‐dimensional structure. It may be possible that this nonuniform distribution is one of the factors for naturalness or individuality in the speech production process. From such a viewpoint, it is necessary to investigate this point.This paper considers the sound tube with a circular or elliptic cross section as a simplified model for the vocal tract. The acoustic characteristics within the tube, when the distribution of the wall impedance is varied, are analyzed in three dimensions using FEM; and the result is reported. The following properties are shown as a result.When the wall becomes softer or when the cross section is deformed from circular to elliptic, the formant bandwidth increases. At the same time, the sound pressure distribution as well as the particle velocity distribution decrease their amplitude. Another aspect is that the sound wave deviates from the planar wave due to the wall impedance and the shape of the wavefront is affected by the impedance distribution.