Effects of subglottal acoustics on phonation onset
Juergen Neubauer, Zhaoyan Zhang, David Berry · The Journal of the Acoustical Society of America · 2005
The effect of subglottal acoustic loading on the vocal fold vibration was investigated using a self-oscillating mechanical model of the folds. Although the influence of the supraglottal tract on vocal fold vibration has received more attention than the subglottal system, the influence of the subglottal system on vocal fold vibration is also potentially significant, and merits investigation. In this study, the subglottal system consisted of a uniform tube connected to an expansion chamber on the flow supply end (e.g., a pseudo-lung). The length of the subglottal tube was varied systematically over a relatively large range in order to investigate the influence of subglottal acoustics on vocal fold vibration. Phonation onset and offset pressures were measured in the subglottal tube as a function of tube length. Over the range of investigation, the fundamental frequency of phonation was found to be negatively correlated with the subglottal tube length. However, both phonation onset and offset pressure were positively correlated with subglottal tube length, with the onset pressure increasing faster than the offset pressure. This hysteresis effect vanished and the two pressures merged at a small value of the subglottal tube length, indicating a change in the onset behavior from a subcritical Hopf bifurcation to a supercritical Hopf bifurcation (a codimension-2 bifurcation point). In addition, phonation did not exist below a critical subglottal tube length.