Evidence for a second laryngeal sound source

Abstract

Sondhi reflectionless tube and strobed video have been used to investigate single glottal pulse gestures in the vocal fry range. There appear to be two sources of sound in normal VF phonation, one monopole, the other quadrupole. It is quadrupole sound, in fact, that seems to define the shape of observed pressure trace in the single glottic pulse, or SGP. This sound pulse, which lasts 10 ms or less, resembles a single cycle of negative sine wave beginning just before the closing phase, and may be recognized even in sound emissions outside the tube, where continuous tone samples can be identified as SGP wave trains, each link beginning with a characteristic downturn. Monopole sound, emitted in shorter pulses during the abrupt zipping and sometimes during unzipping phases of the SGP, shows up along the main wave trace in the Sondhi tube as a small superposed peak, followed by a string of head echoes. The source of quadrupole sound can be traced to fluctuating Bernoulli pressures during closure which produce opposing forces on the vocal folds. The quadrupole or q-wave forms the acoustic signature of the SGP.