Harmonium

A Harmonium or Reed Organ is a free-standing musical keyboard instrument not dissimilar to a pipe organ. It consists of free reed pipes and sound is produced by air being pushed or sucked over reeds resulting in a sound similar to that of an accordion. The air is supplied by foot-operated bellows alternately depressed by the player.

Harmoniums consist of banks of brass reeds (metal tongues which vibrate when air flows over them), a pumping apparatus, stops for drones (some models feature a stop which causes a form of vibrato), and a keyboard. The harmonium's timbre, despite its similarity to the accordion's, is actually produced in a critically different way. Instead of the bellows causing a direct flow of air over the reeds, an external feeder bellows inflates an internal reservoir bellows inside the harmonium from which air escapes to vibrate the reeds. This design is similar to bagpipes as it allows the harmonium to create a continuously sustained sound. (Some better-class harmoniums of the 19th and early 20th centuries incorporated an “expression stop” which bypassed the reservoir, allowing a skilled player to regulate the strength of the air-flow directly from the pedal-operated bellows and so to achieve a certain amount of direct control over dynamics.) If a harmonium has two sets of reeds, it's possible that the second set of reeds (either tuned unison or an octave lower) can be activated by a stop, which means each key pressed will play two reeds. Professional harmoniums feature a third set of reeds, either tuned an octave higher or in unison to the middle reed. This overall makes the sound fuller. In addition, many harmoniums feature an octave coupler, a mechanical linkage that opens a valve for a note an octave above or below the note being played, and a scale changing mechanism, which allows one to play in various keys while fingering the keys of one scale.