ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

5aMU1. Interaction of lips and mouthpiece in a brass instrument.

Gabriel Weinreich

Fang-Chu Chen

Randall Lab. of Phys., Univ. of Michigan, Ann Arbor, MI 48109-1120

The difference between the frequency of a played note on a brass instrument and the frequency of the resonator (defined as the location of the maximum of its input impedance at the mouthpiece) has been experimentally investigated. To avoid the complexity of the lips interacting simultaneously with many modes, a Helmholtz resonator with an attached ``mouthpiece'' whose diameter is that of a trumpet was used. By having a loudspeaker as one of the walls of the resonator, and driving it with a signal derived from an attached microphone, it was possible to adjust both the resonant frequency and the Q. The input impedance is measured (without the player's lips leaving the mouthpiece) by comparing the passive response of the resonator with and without a known increase in volume. In the considerable majority of cases, the playing frequency is higher than the resonator frequency, indicating that the lips ``beat outwards.'' Possible error sources will be discussed. [Work supported by NSF.]