Whispering--a single-subject study of glottal configuration and aerodynamics

Whisper productions were produced by a single adult male subject over a wide range of subglottal pressures, glottal areas, and glottal flows. Dimensional measurements were made of these three variables, including glottal perimeter. Subglottal pressure was directly obtained by a pressure transducer in a tracheal catheter, and wide-band flow with a pneumotach mask. Four types of whispers were used-hyperfunctional, hypofunctional, neutral, and postphonation-in addition to three levels of loudness (soft, medium, loud). Sequences of the /pae/ syllable were used. Video recordings of the larynx were made. The glottis was outlined by hand with extrapolation for unseen parts, and area and perimeter were obtained through image analysis software. The whisper tokens resulted in the following wide ranges: subglottal pressure: 1.3-17 cm H2O; glottal flow: 0.9-1.71 L/s; glottal area: 0.065-1.76 m2; and glottal perimeter: 1.09-6.55 cm. Hyperfunctional whisper tended to have higher subglottal pressures and lower areas and flows than hypofunctional whisper, with neutral and postphonation whisper values in between. An important finding is that glottal flow changed more for small changes of area when the area was already small, and did not create much flow change when area was changed for already larger areas; that is, whisper is "more sensitive" to airflow changes for smaller glottal areas. A general equation for whisper aerodynamics was obtained, namely, P (subglottal pressure [cm H2O])=C X F (glottal flow [cm(3)/s]), where C = 0.052 x A(4) - 0.1913 x A(3) + 0.2577 x A(2) - 0.1523 x A+0.0388, where A is the glottal area (cm(2)). Another general equation for nondimensional terms (pressure coefficient vs Reynolds number) also is offered. Implications for whisper flow resistance and aerodynamic power are given. These results give insight into whisper aerodynamics and offer equations relevant to speech synthesis.