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The relationship between the voice intensity (sound pressure level), the subglottic pressure, the air flow rate, and the glottal resistance was investigated. Simultaneous recordings were made of the sound pressure level of voice, the subglottic pressure, the flow rate, and the volume of air utilized during phonation. The glottal resistance, the subglottic power, and the efficiency of voice were calculated from the data. It was found that on very low frequency phonation the flow rate remained almost unchanged or even slightly decreased with the increase in voice intensity while the glottal resistance showed a tendency to augment with increased voice intensity. In contrast to this, the flow rate on high frequency phonation was found to increase greatly, while the glottal resistance remained almost unchanged as the voice intensity increased. On the basis of the data it was concluded that at very low pitches, the glottal resistance is dominant in controlling intensity (laryngeal control), becoming less so as the pitch is raised, until at extremely high pitch the intensity is controlled almost entirely by the flow rate (expiratory muscle control).
Nobuhiko Isshiki (Sun,) studied this question.