Acoustic Analysis of Detailed Three-Dimensional Shape of the Human Nasal Cavity and Paranasal Sinuses

The nasal and paranasal cavities have a labyrinthine shape and their acoustic properties affect speech sounds. In this study, we explored the transfer function of the nasal and paranasal cavities, as well as the contribution of each paranasal cavity, using acoustical and numerical methods. A physical model of the nasal and paranasal cavities was formed using data from a high-resolution 3D X-ray CT and a 3D printer. The data was acquired from a female subject during silent nasal breathing. The transfer function of the physical model was then measured by introducing a white noise signal at the glottis and measuring its acoustic response at a point 20 mm away from the nostrils. We also calculated the transfer function of the 3D model using a finite-difference time-domain or FDTD method. The results showed that the gross shape and the frequency of peaks and dips of the measured and calculated transfer functions were similar, suggesting that both methods used in this study were reliable. The results of FDTD simulations evaluating the paranasal sinuses individually suggested that they contribute not only to spectral dips but also to peaks, which is contrary to the traditional theories regarding the production of speech sounds.