Instead, organs produce sound by means of flowing air. Organs date back to medieval times, when they originated as portable instruments used for accompaniment in choral music. As the instruments became larger, they were installed permanently in a fashion similar to the church organs of today.
The sound-producing elements in organs are generally reeds and flutelike pipes. The flutelike pipes, which work using vibrating columns of air, are to be found in organs of all sizes. Reeds --thin strips of metal fastened at one end with the rest allowed to vibrate freely-- are only used commonly on instruments from a certain size.
Other instruments which are played from a reservoir of gas and have separate tone-producing mechanisms for each pitch include:
- the accordion and concertina, in which the bellows is operated by the squeezing action of the instrumentalist;
- the melodeon, a reed instrument with an air reservior and a foot operated bellows, popular in the USA in the mid 19th century;
- the parlor organ, a reed instrument usually with many stops and two foot-operated bellows which the the instrumentalist operates alternately;
- the steam calliope, being essentially a pipe organ operated on steam rather than air;
- the band organ, essentially a pipe organ, but instead of a keyboard, mechanical means are used to play a prepared song.
- various sorts of novelty instruments operating on the same principles.
- the harmonica, where the musician effectively blows directly onto the reeds;
- the pan-pipes
The pipe organ is a common kind of organ, with churches often housing such an instrument - when the word "organ" is used on its own in a classical music context, the pipe organ is most often meant. It is this instrument that is sometimes called the "king of instruments" in that, when played by a capable perfomer, richer and more complex music can be produced than with any other single instrument.
The organ's typical, stable and broad sound is often associated with eternity and divinity, reason why the most beautiful instruments are to be found in churches, although many major concert halls around the world boast organs too. Saint-Saens' popular Organ Symphony is a good example of how the sound of a large organ can be effectively combined with that of a symphony orchestra.
The versatility of the organ is attributable to the builders' ability to attach any number of instruments, or 'voices', to the keyboards which can be selected individually or in multiples by the operator. A good organist can produce a complex symphony of sounds simply by selecting which voices are used by which keyboard.
Voices are selected by 'stops'. The colloquial phrase "to pull out all the stops" originates from the simultaneous use of the multiple voices of an organ to produce a rich and complex sound. Much air is used to power an organ when all the stops are pulled out, and in days when there were no electric motors, the profligate use of air required much labor, and was used only for special occasions.
The word organ, which has nothing to do with anatomical organs, originates from the latin word "organum", the earliest predecessor of the instrument used in ancient Roman circus games and similar to what we now know as "portative".
There are also various electrically operated and electronic organs, such as the Hammond Organ. While the Hammond was of imitative intent, it has developed something of a cult following and is at its best when used to produce a sound of its own rather than an attempt at a pipe-organ-like sound. The Hammond B3 model is an important instrument in jazz, and in particular was the central instrument in soul jazz. Electric organs also figure prominently in rock and gospel.