Ex-vivo and replica measurements of nasal tract resonances

The nose is a resonator, the acoustic properties of which are determined by its shape. Due to its complex anatomy and hence intricate acoustical response the identification of universal acoustic characteristics of nasalized vowels and consonants is challenging. The purpose of this investigation was to 1) elucidate acoustic properties of the nasal resonator, 2) document how the paranasal sinuses affect it, and 3) examine if 3D-replicas of anatomical specimens provide reliable data for acoustic analysis.

In this experimental study the resonance properties of the nasal tract were analyzed in ex-vivo specimens as well as in their 3-D replicas. Their sound transfer characteristics were recorded by sending a sinewave, gliding from low to high frequency from an earphone airtightly sealed into the velopharyngeal port. The response was picked up at a nostril. The acoustical influence of the sinuses was reversibly eliminated by occlusion of the sinus ostia.

Response curves of the nasal tract were found to possess two main resonances, one in the vicinity of 600-750 Hz and one in the 2500 â€" 3500 Hz range. Comparison of the acoustical responses obtained while including and excluding the influence of the paranasal cavities showed a great inter-individual variation in the response curve morphology. The cavities were found to introduce V-shaped sound level minima in the response curves.

When the influence of the paranasal cavities is eliminated, the nasal cavity presents two main resonances, which are determined mainly by its anatomical length. The resonances of the paranasal cavities introduce minima and maxima in the frequency response of the nasal tract at frequencies with substantial inter-individual variation. Replicas of anatomical specimens provide reliable data for acoustic analysis.