The physics of small-amplitude oscillation of the vocal folds

TLDR

The study develops a vocal fold oscillation theory based on the body‑cover hypothesis. The model represents the cover as a distributed surface layer supporting a mucosal surface wave, linearizes its displacement and velocity under small‑amplitude assumptions, derives closed‑form oscillation conditions, and incorporates vocal‑tract acoustic loading. The theory predicts that lowering mucosal wave velocity, decreasing fold separation, and reducing glottal convergence angle lower the oscillation threshold pressure, while vocal‑tract inertance decreases and resistance increases it, and the model applies to falsetto, breathy voice, and phonation onset or release without fold collision.

Abstract

A theory of vocal fold oscillation is developed on the basis of the body-cover hypothesis. The cover is represented by a distributed surface layer that can propagate a mucosal surface wave. Linearization of the surface-wave displacement and velocity, and further small-amplitude approximations, yields closed-form expressions for conditions of oscillation. The theory predicts that the lung pressure required to sustain oscillation, i.e., the oscillation threshold pressure, is reduced by reducing the mucosal wave velocity, by bringing the vocal folds closer together and by reducing the convergence angle in the glottis. The effect of vocal tract acoustic loading is included. It is shown that vocal tract inertance reduces the oscillation threshold pressure, whereas vocal tract resistance increases it. The treatment, which is applicable to falsetto and breathy voice, as well as onset or release of phonation in the absence of vocal fold collision, is harmonized with former treatments based on two-mass models and collapsible tubes.