HARMONIUM. - It is a keyboard instrument whose sound is produced by free reeds without resonators, placed horizontally beneath the keyboard. The air is supplied by a bellows set in motion by two pedals. It derives from the ancient "regal," a small portable organ with reed stops without resonators or with very small resonators. After the various experiments made by C. Perrault, S. Erald, C. Buffet, Cavaille Coll, Debain (1809-77) built the first models of the present-day harmonium. Improvements were made by subsequent manufacturers: Vittorio Mustel (1815-90) may be called the father of the modern instrument.
It can be built according to two different systems: by pressure or by suction, depending on the different way in which the air acts on the reeds. The complete set of reeds producing a sound of a given timbre across the entire range of the keyboard is called a stop [jeu]. The flute, clarinet, bourdon, oboe, English horn, bassoon, dulciana, eolina, vox celeste, etc., are among the principal stops, which, with respect to their pitch, may be of 16, 8, 4, 2 feet. The mechanical means by which the performer makes use of the stop and of other devices is called the "register." The principal mechanical registers are: the expression, a register of great aesthetic importance and one that gives the harmonium a particular character; the percussion, most useful for the clear execution of agile passages and of pianissimos; the fixed forte, which opens or closes a kind of shutter; the expressive forte (Mustel), by which the shutter is opened more or less by a small bellows depending on the varying pressure exerted on the pedals; the prolongation, by which one or more sounds of the low register can be indefinitely sustained without hindering the free play of the two hands; the super and sub octave; the tremolo; the mute. Two knee levers serve to operate a grille divided into two parts, one for the low register, the other for the high register of the keyboard, which opens or closes the sound. The two parts of the grille can be operated independently (double expression). Another device makes it possible to open all the stops simultaneously.
The most common type of harmonium has a single keyboard, but there are also ones with two keyboards and a pedalboard. It serves most commonly to support choirs in church and in school; but the art harmonium tends to become a concert instrument, having been enriched by an important literature with the works, above all, of C. Franck, L. Boëllmann, A. Guilmant, C. M. Widor, Max Reger, S. Karg-Elert.
Alessandro Santini