Brass Instrument Acoustics
The Mouthpiece Effect
The mouthpiece of a brass instument contributes to bringing the resonances into a harmonic sequence by bringing the high resonances down with respect to the resonances of a closed tube. The mouthpiece acts like a cavity resonator, and as the played frequency approaches this resonant frequency, the effective length of the tube becomes greater (approaching the tube length which would give that same resonant frequency. This increases the effective length for high frequencies lowering the high resonant frequencies.
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This trumpet mouthpiece is very solidly constructed. It forms a comfortable cup for the vibration of the players lips. Good discussions of mouthpiece construction and function may be found in Shilke and Wolfe. The following are some of the ideas covered. |  |
The mouthpiece can be divided into three parts:
- The rim of the mouthpiece affects flexibility and attack. The wider the rim, the more comfortable it feels to the player, but flexibility is reduced. With narrower rims, enhanced flexibility comes at the expense of tiring the player more quickly.
- The cup of the mouthpiece affects tone and attack. A deep cup gives a darker tone and low notes are easier to play. A shallow cup produces a brighter tone and the upper notes are easier to play. A flatter shape improves the precision of attack. A steep shape like the French horn provides gentler attacks, but changes the timbre of the instrument.
- The throat/backbore throat of the mouthpiece affects tone and air resistance. A larger diameter throat gives a mellower tone. Longer backbore (shorter throat) can make the higher register flat and shorter backbore (longer throat) can make it sharp.
Reference
Backus
pp. 263-4