David A. Berry
Ingo R. Titze
Natl. Ctr. for Voice and Speech, Dept. of Speech Pathol. and Audiol., Univ. of Iowa, Iowa City, IA 52242
Much of the theoretical groundwork for treating vocal fold vibrations as
viscoelastic waves in a continuum can be found in earlier publications [Titze
and Strong, J. Acoust. Soc. Am. 57, 736--744 (1975) and Titze, J. Acoust. Soc.
Am. 60, 1366--1380 (1976)]. Both of these papers are based on small-amplitude
vibrations where linearization is assumed to be valid, allowing normal modes
and natural frequencies to be calculated. Although vocal fold tissues are known
to be nearly incompressible, the first analytic expression for the normal modes
of vocal fold tissues were based on the assumption of complete compressibility.
The present study shows how the analytic normal modes deform and how the
natural frequencies of oscillation shift as the vocal fold tissues are
gradually changed from being strictly compressible to absolutely
incompressible, leaving all other factors constant. [This research was
supported by Grant No. P60 DC00976 from