THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

18.10 Wind Instruments 551cylindrical. It covers the frequency range from G 3 to B 5 . The French horn, arguablythe most beautiful appearing brass instrument, consists of a mouthpiececoupled to a slightly tapered coiled tube of 365 cm length, which terminates in alarge bell-shaped mouth. The modern version of the horn is equipped with threesets of rotary valves controlled by three keys. This valve system provides eightdifferent lengths for the resonating tube, and hence a series of different resonantfrequencies corresponding to the notes of the musical scale. The large size of themouth of the French horn renders it possible for the player to inert his hand andraise or lower the pitch or to produce a sound (e.g., muted) effect. The Frenchhorn can sound over three octaves, from B 1 to F 5 . Its overall length is nearly58 cm.The trombone and the bass trombone differ from the other brass instruments inthat they each feature a telescoping section of the tube that can be moved by theperformer to vary the length of the tube and hence the resonant frequency. Thetrombones are the only instruments besides the violin family that can provide acontinuous glide through the musical scale. The pitch is determined by the positionof the slide as well as the performer’s lips and the applied lung pressure. As with thecase of performers of the violin family, the player must possess an accurate sense ofpitch and the ability to produce the correct note. The trombone’s U-shaped tube isnearly 3 m long, with a slight conical taper that culminates in a bell-shaped mouth.It is capable of covering nearly 2 1 / 2 octaves, from E 2 to B 4 . The bass trombone islarger, covering three octaves from A 1 to G 4 .The tuba’s mouthpiece is attached to a coiled tube nearly 6minlength thatgradually increases in its cross-sectional area until nearly the end when it terminatesin a large bell-shaped flare. Three piston valves are provided, each addinga different length to the tubing. Thus, eight different lengths are provided, in thesame basic manner as the trumpet or cornet. Some versions of the tuba include afourth valve, with a corresponding increase in the number of different resonant frequencies.Largest of the brass instruments, a typical tuba, measures approximately1 m. The tuba covers three octaves from F 1 to F 4 . Different versions of the tubaexist, with a variety of sizes and forms. The sousaphone (named after band conductor/composerJohn Sousa of the “March King” fame) is the largest of the tubafamily.In concluding this section on wind instruments, it might also be mentioned thatthe human voice also classifies wind instruments, i.e., it is a reed instrument inwhich the vocal cords serve as the reeds. The mechanism of the voice consistsof three sections: (1) the lungs and associated muscles to serve as the air supply;(2) the larynx bearing the vocal cords for converting the airflow into a periodicmodulation; and (3) the vocal cavities of the pharynx, mouth, and nose, all ofwhich help vary the tonal content of the output of the larynx. A sectional viewof the voice system in the human head is shown in Figure 18.36. The frequencyof the vibration is governed by the tension of the vocal cords, the inertance, andthe combined acoustical impedance of the vocal cords and the vocal cavities. Thevocal mechanism is a complex one, entailing a number of acoustical elements