Sunday, July 14, 2013
HARMONIUM, free-reed keyboard instrument that produces sound when wind sent by foot-operated bellows through a pressure-equalizing air reservoir causes metal reeds screwed over slots in metal frames to vibrate through the frames with close tolerance. There are no pipes; pitch is determined by the size of the reed. Separate sets of reeds provide different tone colours, the quality of the sound being determined by the characteristic size and shape of the tone chamber surrounding each reed of a given set; constricted chambers, for instance, induce powerful vibration and incisive tone. Volume is controlled by a knee-operated air valve or directly from the bellows pedals by an expression stop that allows the wind supply to bypass the reservoir. The instrument’s compass is normally four to five octaves.
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