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Figure 1. A modern trumpet with the parts labeled. Photograph courtesy of Yamaha Corporation of America.
is highly reflective and difficult to photograph.) Although there are several pieces to a modern trumpet, only three of these parts are necessary to identify it as a brasswind instrument. Be- ginning where the lips introduce the oscillations of the air, the three parts are the mouthpiece, tubing, and bell. The length of the modern trumpet is approxi- mately 1.4 m, most of which is
The Parts of a Modern Trumpet
A photograph of a trumpet with some of the parts labeled is shown in Figure 1. (The black lines on the trumpet are an artifact of the lighting and not part of the instrument, which
Figure 2. Calculated impedance as a function of frequency for a cy- lindrical pipe the length of a trumpet (a), a mouthpiece connected to the pipe (b), and a mouthpiece, pipe, and bell (c). The total length has been kept constant in all three cases. f0 (a) and f (c), Fundamen- tal frequency of the harmonic series.
cylindrical tubing. However, valves, which lie along the tub- ing, are used to change the length of the trumpet during play. The acoustics of the air column inside cylindrical tubing is well understood, so it is logical to begin the discussion there.
Because the lips impose a pressure antinode at one end of the tube and the other end is open to the atmosphere, the trumpet is an open-closed pipe. Therefore, considering just the cylindrical tubing of the instrument, the wavelength of the fundamental resonance is four times the length of the pipe. The overtones occur at odd multiples of the fundamen- tal resonance frequency as expected. The results of a simula- tion that calculates the input impedance of the air column of a cylindrical pipe the length of the modern trumpet are shown in Figure 2a. The resonances of the air column can be identified by the maxima in the input impedance. The de- creasing height of the maxima as the frequency increases is due to a loss of energy to the viscous boundary layer at the wall of the pipe and not to any incidental physical vibration of the pipe.
The input impedance is defined as the ratio of the pressure to the resulting volume flow of the air, so a large input imped- ance results in a standing pressure wave due to the reflec- tion from the end of the instrument. When the frequency of the vibration of the lips is near one of these resonances, the feedback tends to force the lips to vibrate at that frequency. The feedback of a modern trumpet is so strong that it is ex- tremely difficult to force the lips to oscillate at any frequency other than that of a resonance of the air column. One of the hallmarks of a good brass player is the ability to bend a note, that is, to force the lips to vibrate at a frequency that does not correspond to a resonance of the instrument. Although it is logical to ask why anyone would want to play an instrument off-resonance, the importance of this ability will become ob- vious later.
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