Peter L. Hoekje
David Kjar
Dept. of Phys., Univ. of Northern Iowa, Cedar Falls, IA 50614-0150
The vibrations of the metal shell of a brass instrument can be discerned by the player through the player's lips and hands. This is in addition to the vibrotactile feedback to the player's lips from the acoustic vibrations in the air column of the instrument. Many players claim an improvement in playability when the mass of the mouthpiece is increased. Measurements of the body vibrations of a trumpet under playing conditions were obtained with an accelerometer at six locations: at three points on the mouthpiece, and also on the receiver, valve casing, and bell. The greatest amplitudes were observed at the bell. When mass was added to the mouthpiece, while keeping the sound level output of the instrument constant, the vibration amplitudes at the mouthpiece decreased as expected. However, the same degree of decrease was not observed at the other locations. This and other evidence suggests that increasing the mouthpiece mass does not significantly alter the coupling between the air vibrations and the shell vibrations. Thus, it is postulated that the playability benefits derive from a reduction in the conflict between the two channels of feedback to the lips.