Although technically a keyboard instrument, pipe organs are based on tubes. Instead of changing the length of a single pipe (with holes or other mechanisms) to get different frequencies there is a large collection of pipes of different lengths and a mechanism to blow air through them. The sound generating part may be either a fipple or a reed and some organs have different pipes with each type. The tubes may be made of wood or metal, may be open or closed on the end and have various shapes, as shown below. A variety of methods are used to tune an individual pipe by slightly changing its length or modifying the end of the pipe. As in the case of reed instruments different pipe shapes lead to different overtones that change the timbre of the note being played. Because a large number of pipes can be employed (the Wanamaker Pipe Organ has 28,604 pipes), pipe organs can produce a wide variety of sounds. The longest pipes may be as long as 19.5 m which makes an 8 Hz pitch.
A final class of instruments that use reeds but not tubes are called free reed aerophones. These include harmonicas, accordions, bandoleóns and similar instruments. In these instruments a reed vibrates as air is forced over it, so they are blown open reeds, unlike clarinet or saxophone reeds. There is a reed with different tension to produce each note. The mouth and cupped hands form the resonating bodies for harmonicas. In accordions and similar instruments a set of bellows are used to force air over the reed and the air box forms the resonating cavity.
Performance of the Wanamaker Organ.
Slow motion of harmonica reeds.
The didgeridoo is an instrument used by the aboriginal peoples of Australia and consists of a long tube of wood. The lips are buzzed to make a sound but the voice is also used. Because of the large diameter and length there are many interesting resonances that can be excited while playing the instrument.
- Wikipedia on: free reed aerophone, pipe organs.
- A web site about harmonicas and other mouth blown, free reed instruments with sound samples.