A hybrid model of vocal fold vibration illustrating perturbations

Abstract

This study of vocal fold vibration examines the physics of vocal fold vibration and some possible causes of perturbed vibration. A multiple mass‐spring computer model is used to simulate the vibratory motion of the normal vocal fold and a fold with asymmetric parameters. Speech, displacement, acceleration plots, and a mathematical discussion reducing the model to a function of lateral tissue motion are presented. Acceleration‐displacement (energy exchange) diagrams from the simulation model are compared to the behavior of the mathematical equations, showing that the system driving forces can be associated with physical phenomena such as vocal tract loading, vertical phasing, Bernoulli forces, and negative damping. Simulations have produced perturbed vibrations, suggesting that 1/2 and 1/3 subharmonics are present. The 1/2 subharmonic results from vocal tract resistive and inertive loading, while the 1/3 subharmonic arises due to inertive loading and nonlinear tissue stiffness. It is necessary to derive a fourth‐order system using vertical phasing of the upper and lower tissue margins, in order to drive the system into modes other than the fundamental. Irregular random perturbations also appear when parameter changes are localized.