Relation between the phonation threshold pressure and the prephonatory glottal width in a rectangular glottis

Recent experimental measurements have shown a nonlinear relation between the phonation threshold pressure and the prephonatory glottal width, with a minimum for the threshold pressure which would indicate the existence of an optimal glottal width for ease of phonation [I. R. Titze et al., J. Acoust. Sec. Am. 97, 3080-3084 (1995)]. This relation is studied analytically using a simplified vocal fold model which includes an explicit term for the air pressure losses due to glottal viscous resistance. It is shown that the observed nonlinearity may be a consequence of the viscous pressure losses, which cause an increase of the threshold pressure at small values of the prephonatory glottal width. (C) 1996 Acoustical Society of America.