A compulsory sinusoid wave vibration ranging from 30 to 300Hz was induced to the vocal fold of fresh excised human larynxes by pressing a vibrator on the midline of the thyroid cartilage. The vocal fold vibration, thus created, was measured and recorded as a function of frequencies and Q-values of the resonance using Ultrasonic Pulse Methods.
The resonance pattern of the vocal fold was measured and recorded under the loading of mass and longitudinal tension.
From the resonance characteristics, damping ratio, effective mass, and effective stiffness of the vocal fold were estimated.
The results obtained were as follows:
1. The resonance characteristics were almost equal before or after vertical incision of the midline of the posterior wall of the larynxes. The mean value of the resonance frequency was approximately 100Hz, while the Q-values ranged from 2.0 to 3.0.
2. Under the loading of longitudinal tension posterioly, as the tension increased, so did the appearance rate of the secondary resonance wave. And the secondary resonance frequencies and Q-values also increased in proportion to the tension given to the vocal fold. On the other hand, the primary resonance frequency was always constant (about 100Hz), regardless of the given tension. The Q-values of the primary resonance wave were also constant, ranging from 2.0 to 3.0.
3. Under mass loading, as the mass increased, the resonance frequencies and the Q-values of resonance decreased. When the mass was over 60mg, the resonance frequency had a trend to be leveling off, probably because of the change in the stiffness of the vocal fold.
4. Damping ratio, effective mass, and effective stiffness were estimated as follows:
Damping ratio:0.21±0.04
Effective mass:0.13±0.02g
Effective stiffness:51±8k dyne/cm
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