Brad H. Story Ingo R. Titze
Natl. Ctr. for Voice and Speech, Dept. of Speech Pathol. and Audiol., Univ. of Iowa, Iowa City, IA 52242
The classic two-mass model of the vocal folds [K. Ishizaka and J. L. Flanagan, Bell Syst. Tech. J. 51, 1233--1268 (1972)] has been extended to a three-mass model in order to represent more accurately the body-cover vocal fold structure [M. Hirano, Folia Phoniat. 26, 89--94 (1974)]. The model consists of two ``cover'' masses that are coupled to a ``body'' mass by nonlinear springs and viscous damping elements. The body mass, which represents muscle tissue, is also coupled to a rigid wall (assumed to represent the rigid laryngeal framework) by a nonlinear spring and damping element. The two cover springs are intended to represent the vocal ligament tension while the body spring simulates the tension produced by contraction of the thyroarytenoid muscle (TA). Additionally the two cover masses are coupled to each other through a linear spring that can be regarded as representing the surface tension of the cover and hence largely contributes to the mucosal wave velocity. Effects on the vocal fold movement due to changes in subglottal pressure, spring tensions, element masses, and vocal tract loading will be shown.