Dept. of Electron., Faculty of Eng., Shizuoka Univ., 3-5-1 Jouhoku, Hamamatsu, 432 Japan
ATR Human Inf. Process. Res. Labs., 2-2 Hikaridai, Seikacho, Soraku-gun, Kyoto, 619-02 Japan
Morphological measurement of the nasal and paranasal cavities were performed by means of the magnetic resonance imaging (MRI) technique. Three-dimensional acoustic tube models were constructed using the MRI data. Using the finite element method (FEM), the Helmholtz equation was solved for sinusoidal pressure wave input at the velopharyngeal port to obtain sound pressure, particle velocity, and sound intensity in the nasal cavity. In the FEM modeling, the nasal tract containing the paranasal sinuses is divided into 3470 meshes and 4625 nodes. The cross-sectional shape of the tract was approximated by an elliptical shape whose area and circumference were matched to the observed data. The frequency transfer function as a ratio of sound pressure at the velopharyngeal port to that at the nostrils, and input impedance at the velopharyngeal port were calculated and compared with those of the classical electric circuit model of the nasal tract. A FEM model incorporating shape asymmetry between the left and right passages as defined by the MRI observation was compared with that of the hypothetical models having symmetrical shapes. The results showed that the complicated spectral shape of nasal sounds can be successfully accounted for using the 3-D FEM approach.