Geometric dependence of phonation threshold pressure and phonation onset frequency.
Zhaoyan Zhang · The Journal of the Acoustical Society of America · 2009
Dependence of phonation threshold pressure and phonation onset frequency on vocal fold geometry was numerically investigated in a continuum model of the vocal folds. The geometric parameters of interest include the medial surface thickness, vocal fold depths of the body, and cover layers. Changes in these parameters may occur either due to laryngeal muscle activation, vocal pathology, or aging. Simulations show that both threshold pressure and onset frequency increased with decreasing vocal fold depth. However, depending on glottal geometry, increasing medial surface thickness may either increase or decrease phonation threshold pressure and frequency. Variation of the medial surface thickness also led to phonation onset occurrence at a different eigenmode, leading to sudden changes in onset frequency and vocal fold vibration pattern. These numerical predictions were further supported by experiments using a self-oscillating physical model. The result of this study confirms previous findings that phonation onset occurs as a matching between the flow stiffness, which is proportional to subglottal pressure, and vocal fold stiffness, which scales with natural frequency squared and depends on geometry and boundary conditions of the vocal fold structure as well as material properties of the vocal folds. [Work supported by NIH.]