Abstract:
Recent experimental studies [I. R. Titze et al., J. Acoust. Soc. Am. 97, 3080--3083 (1995); R. W. Chan et al., J. Acoust. Soc. Am. 99, 2471(A) (1996)] have shown the existence of optimal values of the glottal width and convergence angle for ease of phonation, at which the phonation threshold pressure is minimum, not predicted by the previous theory [I. R. Titze, J. Acoust. Soc. Am. 83, 1536--1552 (1988); J. C. Lucero, J. Acoust. Soc. Am. 98, 779--784 (1995)]. This phenomena is analytically investigated using low-dimensional dynamical models of the vocal folds. The threshold pressure is determined through numerical techniques, linearizing first the equations of motion about the equilibrium position and calculating next the value of lung pressure for instability. The results agree with the experimental evidence, showing that the threshold pressure is minimum when the vocal folds are slightly separated and the glottis is rectangular. The minimum occurs as a consequence of large viscous losses at small glottal widths and airflow separation from a divergent glottis, which were not considered in the previous theory. [Work supported by the CNPq, Brazil.]