Frequency dependence of vocal-tract length

The purpose of this study was to estimate the vocal-tract length based on the distribution of sound pressure in the three-dimensional (3-D) vocal tract during the pronunciation of Japanese vowels. The 3-D shapes of a vocal tract and a dental crown were measured using Magnetic Resonance Imaging (MRI). A male subject was asked to produce Japanese vowels while wearing a dental crown plate that contained a contrast medium for MRI processing. The distribution of sound pressure was estimated in the 3-D vocal tract using the Finite Element Method (FEM). The distribution of sound pressure shows that a sound wave propagates in the vocal tract as a non-plane wave in the high frequency region. The vocal-tract length was estimated based on the distribution of sound pressure in the 3D vocal tract. The results suggest that the vocal-tract length is long in the high frequency region.