Abstract
In this paper, the transfer functions and the active sound intensities of a vocal tract model
with and without a nasal cavity were computed by a three-dimensional FEM. The models were based on vowel
MRI data of the vocal tract with a nasal cavity during phonation of the Japanese /a/. An oral cavity were also coupled with the nasal cavity in a three-dimensional volume of radiation. The effects of wall impedance
were also examined. The coupling of the nasal cavity to the oral cavity indicated the following aspects: The additional peaks appeared below 3 kHz for the lossless condition. However, they disappeared in the simulation for the soft wall condition. The sound energy circulation did not occur in the simulation for the soft wall condition. As for the effects of the wall boundary condition on the spectral envelope, the upward shift of lower formant frequencies were confirmed based on the three-dimensional simulations. However the disagreements of the formant frequencies between the simulation and real speech should be further investigated by adjusting the wall boundary condition to a more realistic one.
