Chest wall vibrations in singers.
The chest wall vibrations generated by phonation were examined with respect to origin, amplitude, and spectrum in seven singers. The vibrations were picked up in male and female singer subjects by means of small accelerometers, which were fastened to the skin on the center of the sternum, and, for the purpose of comparison, on the thyroid cartilage and on the trachea a few cm below the larynx. Among the factors which influence the chest wall vibrations, the subglottal pressure oscillations seem to represent the most important excitation, while the mechanical shocks from the vocal fold vibrations seem secondary. Supra- and subglottal resonances seem moderately influential. The results of the investigation suggest that it is the voice source, particularly the amplitude of its fundamental, which is reflected in the chest wall vibrations. The amplitude of these vibrations seem to lie above the threshold of the Pacinian receptors for vibratory sensation as long as the fundamental frequency is below approximately 300 Hz. The amplitude of the voice source fundamental and hence the sensation of chest vibrations vary considerably as phonation is changed along the phonatory dimension which ranges from "pressed/tense/strained" through "flow" to "breathy" phonation. For this reason it seems likely that the sensation of chest vibrations can serve as a useful nonauditory and hence room-independent signal for the voluntary control of phonation.