Acoustic characteristics of the human paranasal sinuses derived from transmission characteristic measurement and morphological observation.

This paper reports on the acoustic characteristics of the paranasal sinuses as determined from transmission characteristic measurements and morphological examinations. A new experimental approach was developed to explore the correspondence between antiresonance frequencies and the causal resonators [J. Dang and K. Honda, J. Acoust. Soc. Jpn. (E) 17, 93-99 (1996)], and it was adopted to determine the antiresonance frequency of each sinus cavity. In this study, the antiresonance frequencies and the locations of the sinus openings were estimated from transmission characteristics of the nasal tract for three subjects, and then MRI-based morphological data for the subjects were used to relate each antiresonance frequency to its causal sinus cavity. The results indicate that each of the three major sinuses, i.e., the sphenoidal, maxillary, and frontal sinuses, contributes its own antiresonances to the transmission characteristics of the nasal tract. The estimated antiresonance frequencies were compared with computed natural frequencies of Helmholtz resonators, and the differences were within 10% for the sinuses. On the basis of the frequency distribution of the sinus antiresonance, the acoustic characteristics of the paranasal sinuses were modeled by four Helmholtz resonators. The simulation with the four-zero model showed that the paranasal sinuses not only introduce antiresonances in the transfer function, but also change the spectral shape of the nasal formants.