Analysis of acoustic properties of the nasal tract using 3-D FEM

In order to examine acoustic effects of complicated morphological construction of the nasal tract, we have analyzed acoustic models constructed according to a measurement by a magnetic resonance imaging (MRI). A prototype model was made to be as similar as possible with the actual nasal tract, which is asymmetrical in the left passage and the right, and has complicated cross sectional shapes. Sound pressure and particle velocity and sound intensity in the model were calculated by finite dement method (FEM). Several modifications were applied on the shape of the prototype model in order to learn what acoustical effects are produced by such modifications: (1) models having elliptic shape, (2) models with and without a pair of maxillary sinuses, (3) a left-right symmetry model in which the one passage is modified to be identical with the other passage, (4) models having narrowed or stuffed passages. Result shows that the poles and zeros are produced and shifted by a mutual branching effect caused by left-right asymmetry of the nasal passages and the additional side branch effect of the sinus cavities. Those effects are also produced by complicated cross section shapes of the nasal tract at 3 kHz region The reduced cross section in the narrowed passage models causes the shift of pole and tao frequency and weakens the mutual side branch effect of the left and right when either of two passages are excessively narrowed.