Observation of the brass player’s lips in motion

Abstract

Mouthpieces with flat windows are used to examine the lip reed’s motion during the steady parts of notes played on brass instruments. Magnified stroboscopic images show different parts of the upper lip moving out of phase with each other. Sighting directly along the channel between the lips, one can observe a Rayleigh wave propagating downstream in the flesh of the upper lip. Downward crests of this disturbance reach maximum amplitude at the downstream end of the channel, where they provide most of the valving action on the air flow. The lower lip moves more as a lumped element, and mostly in the longitudinal direction. A computer model for this behavior will be complicated and may not show much improvement over the two-dimensional model of Adachi and Sato [J. Acoust. Soc. Am. 99, 1200–1209 (1996)]. Of potentially greater value is a more accurate mental image for performers. Muscles controlling the embouchure just establish the boundary conditions for the motion of a thin, passive layer of flesh. This knowledge may help beginners to avoid such practices as jamming the mouthpiece against the lips and tensing muscles against each other unnecessarily.