Effect of vocal tract inertance on phonation threshold pressure: theory and measurements

In a previous analytical study [Titze, J. Acoust. Soc. Am. 83, 1536–1552 (1988)], it was shown that vocal fold oscillation is facilitated by the presence of a vocal tract, i.e., phonation threshold pressure is lowered by an inertive acoustic impedance of the vocal tract. Results of a recent simulation study [Titze and Story, J. Acoust. Soc. Am. 101, 2234–2243 (1997)] support the theory and show that a narrow ‘‘epilarynx tube’’ (area <1.0 cm2) in the lower vocal tract provides impedance-matching and gives the biggest facilitative effect. This small-amplitude oscillation theory was revised in the present study to simultaneously account for vocal fold mucosal wave propagation and vocal tract inertance, as energy transfer mechanisms for flow-induced oscillation. Analytical expressions of phonation threshold pressure were derived showing the relative contributions of the two mechanisms. Empirical data on the effect of vocal tract on phonation threshold pressure were also obtained in a physical model of the vocal fold mucosa [Titze et al., J. Acoust. Soc. Am. 97, 3080–3084 (1995)]. Both analytical and experimental results show that the facilitative effects of vocal tract on the ‘‘ease’’ of phonation are the most prominent under specific glottal geometry and biomechanical conditions. [Supported by NIH Grant No. P60-DC00976.]