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Figure 10.4 Vibration and sound emission at a vibrating reed standing alone. a: Air blowing past the edge of a reed generates turbulent eddies that set the reed into vibration. b: The chaotic variation of sound pressure resulting from secondary components of the reed's vibration. c: The power spectrum of an undamped vibrating reed.

quency, but the "buzziness" shows up as a "smearing" of the energy at frequencies on either side of the resonant frequency. The sound energy coming out of the reed is distributed among all these frequencies. Consequently, the loudness of the sound at the resonant frequency will be limited by the sound energy expended in all those ancillary frequencies.

If the relatively massive body of air in a horn is set into resonant motion, the air will now drive the vibration of the reed (Fig. 10.5). The energy in those messy secondary vibrations of the reed is now entrained to the resonant vibration of the air in the horn, with two benefits. First, it makes the sound emerging from the reed purer—that is, dominated more strongly by the resonant frequency. Second, the sound emerging at

Figure 10.4 Vibration and sound emission at a vibrating reed standing alone. a: Air blowing past the edge of a reed generates turbulent eddies that set the reed into vibration. b: The chaotic variation of sound pressure resulting from secondary components of the reed's vibration. c: The power spectrum of an undamped vibrating reed.

the resonant frequency is absolutely louder. Energy in those secondary frequencies has not disappeared—it has simply been diverted to the resonant frequency.

The Klipsch Horn

Musical instrument makers know another trick for turning the acoustical shortcomings of a finite horn to advantage. Horn and wind instruments do not consist of just the sound emitter and the horn—the mouth cavity of the musician is also part of the instrument. Acoustically, the entire system is a series arrange-

wind wind

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