Abstract:
Speakers with vocal-fold nodules commonly use higher than normal subglottal
pressures to produce a particular sound pressure level (SPL). The SPL may be low
because of a decreased maximum flow declination rate (MFDR) of the glottal flow
waveform, increased first formant bandwidth, or increased spectral tilt. A
modified two-mass model of vocal-fold vibration is proposed, which suggests that
the MFDR can be decreased because of increased coupling stiffness between the
masses, altered equilibrium positions for the masses, and the presence of
nodules that interfere with the normal closure activity of the vocal folds. A
parallel acoustic and aerodynamic study of selected patients with vocal nodules
was conducted. Preliminary findings show higher than normal calibrated
amplitudes of the first harmonic (H1) normalized by the SPL, as well as larger
amplitude differences between the first harmonic and first formant (H1--A1).
These results agree with the previous finding of a larger ac component of the
glottal flow waveform [Hillman et al., J. Speech Hear. Res. 32, 373--392
(1989)]. The presence of a glottal chink may also widen the first formant
bandwidth. Relationships between modeling results and experimental data will be
discussed. [Work supported by NIH Grants DC00075 and DC00266.] [sup