Mechanical properties of the human vocal fold in vivo--resonance characteristics by a single rectangular pulse excitation

Abstract

Investigation on the mechanical properties of the vocal fold and its change at various phonation is very important to elucidate the nature of the vibration system of the larynx.In the present study, resonance characteristics of the human vocal fold in vivo were measured. Oscillation waves of the vocal fold evoked by a single rectangular pulse (0.5msec.) were picked up by am ultrasonic uariant M-mode. These oscillation waves were analysed by a wave analyser with fast Fourier trasnform and the resonance frequencies were obtained. The following items have been examined:1) Resonance patterns of the vocal fold at various phonation neurtal gesture (without expiratory air flow).2) Sex related differences in the resonance pattern of the vocal fold during quiet respiration. The results were as follows:1) It was observed that there existed at least two resonances, which significantly shifted at each frequency of phonation. The lower one was very close but a little lower than the frequency of phonation and tended to closely correlate with the frequency. The higher one was observed in the range lower than the second harmonic of the lower one and directly proportional to the frequency of phonation. The rising rate of the lower resonance was gradually reduced when the phonation pitch became higher than 200Hz. Another weak resonance was constantly observed at around 100Hz when the phonation pitch became higher than 150Hz.2) In male adults, the means of the lower and higher resonance frequencies were 92.3Hz and 173.9Hz. In female adults, they were 100.7Hz and 194.3Hz, respectively. These results indicated that both resonance frequencies were significantly lower in males than in females.