Text: From: j.nolte@worldnet.att.net.geentroep (John Nolte) To: Date: Tue, 11 Apr 2000 10:40:56 -0500 Subject: Beating Reeds & Reed Pipe Resonators Robert Linnstaedt wrote: "I hope Professor Liljencrants in his next discussion can include a word about cylindrical vs. conical resonators. I have wondered at the 'why' behind their special characteristics and how one causes the nodes to aggregate at one end only." I'm not the good professor, but I'll take a crack at it. The resonator of a beating reed behaves like a stopped flue pipe, only the reed is the stopper and the top of the resonator is the mouth. The air column in a stopped cylindrical pipe will resonate at half the frequency of the same pipe if it is open. To achieve the same pitch, a stopped pipe is approximately half the length of an open pipe. Furthermore, stopped and open pipes exhibit different harmonic structure. An open pipe will produce overtones at 2, 3, 4, 5... times it's fundamental frequency, until the diameter of the pipe is too large for higher overtones to be produced. A stopped cylindrical pipe will only produce half of the overtones, at 3, 5, 7... times the fundamental frequency, again, until the diameter suppresses higher overtones. When a stopped pipe is tapered, something amazing happens. The even numbered harmonics are also produced. A tapered, stopped pipe will produce overtones 2, 3, 4, 5... times the fundamental frequency. A tapered and stopped pipe is about 1-1/2 times the length of a cylindrical stopped pipe, or 3/4 as long as an open pipe. Thus a cylindrical reed resonator like a clarinet supports only the odd numbered partial series, while a tapered resonator, like a trumpet, supports the entire series. The reed tongue itself does not vibrate audibly. It is simply a switch that opens and closes sequentially to modulate a stream of air. This causes the compressions and rarefactions that the resonator supports as standing waves. John Nolte To put all his very well explained technical words into your more basic everyday organ guy talk: the reed boot is longer because the reed doesn't care what resonator it resonates to. It can resonate to the boot or the resonator. Making the boot extra long on a Vox forces the reed to vibrate to the resonant frequency of the actual resonator and not the boot. You will notice that without extension, the boot would be nearly the same length, and therefore, near the same resonant frequency, as the resonator. Extending the boot puts it way out of the ball park for the reed to use it as resonator.

See Also:

Source: