Where has all the power gone? Energy production and loss in vocalization

Abstract

Human voice production for speech is an inefficient process in terms of energy expended to produce acoustic output. A traditional measure of vocal efficiency relates acoustic power radiated from the mouth to aerodynamic power produced in the trachea. This efficiency ranges between 0.001% and 1.0% in speech-like vocalization. Simplified Navier–Stokes equations for non-steady compressible airflow from trachea to lips were used to calculate steady aerodynamic power, acoustic power, and combined total power at seven strategic locations along the airway. A portion of the airway was allowed to collapse to produce self-sustained oscillation for sound production. A conversion efficiency, defined as acoustic power generated in the glottis to aerodynamic power dissipated, was found to be on the order of 10%, but wall vibration, air viscosity, and kinetic pressure losses consumed almost all of that converted power. Thus, the acoustic power, reflected back and forth in the airway was dissipated at a level on the order of 99.9%, with a small fraction being radiated to the listener.