Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Changing the pitch of a wind instrument

Question: A saxophone player normally selects which note to play by choosing a certain fingering, which gives the saxophone a certain resonant frequency. The musician can also, however, change the pitch significantly by altering the tightness of her lips. This corresponds to driving the horn slightly off of resonance. If the pitch can be altered by about 5% up or down (about one musical half-step) without too much effort, roughly what is the Q of a saxophone?

Solution: Five percent is the width on one side of the resonance, so the full width is about 10%, FWHM / f res=0.1. This implies a Q of about 10, i.e. once the musician stops blowing, the horn will continue sounding for about 10 cycles before its energy falls off by a factor of 535. (Blues and jazz saxophone players will typically choose a mouthpiece that has a low Q, so that they can produce the bluesy pitch-slides typical of their style. "Legit," i.e. classically oriented players, use a higher-Q setup because their style only calls for enough pitch variation to produce a vibrato.)

Last Update: 2009-06-21