The harmonium is a musical instrument with wind, free reeds, keyboard and wind tunnel. The musician who plays it is a harmoniumist.
The germs of the harmonium can be found in the free-reed instrument invented in France by Gabriel-Joseph Grenié at the beginning of the XIX century, organ pipes with free reeds on a regulated blower with variable pressure. In fact, unlike the fluttering reeds of the pipe organ, the free reeds, vibrating on either side of their frame, can withstand a variable vibratory amplitude and be expressive (from pianissimo to fortissimo) without seeing a significant modification of their agreement. Many instruments perfected this principle. We can mention the Haeckl physharmonica, the harmoniflute or the Cavaillé-Coll poikilorgue.
The harmonium, derived from the expressive organ of Grenié, was invented in Europe by the Frenchman Alexandre-François Debain (1809-1877) who patented it in 1842. Jakob Alexandre (1804-1876) and his son Edouard (1824- 1888) with Auguste Victor Mustel (1842-1919) and Alphonse Mustel (1873-1937) will lead the instrument, which they call organ-melodium, organ celesta, kunstharmonium, harmonium-celesta at its point of perfection. Victor Mustel adds a celesta to the second keyboard.
Similar to the organ with the principle of registers of different tones, in its most widespread form it includes a keyboard and the air supply is powered by a foot pump: the air is blown (in French models ), or sucked (in German, American and English instruments), and vibrates free reeds (same principle as harmonica and accordion). When the "expression" mode is activated, the tank is put out of service, the reeds are fed directly by the foot pumps; the musician can then produce very plastic shades by modulating his pumping of air, the main difficulty residing in the regular supply of the bed base. It is on the French harmonium that the greatest nuances are allowed, since the air blown into the reeds is sent towards the outside of the instrument, whereas in the case of the suction harmonium, the air and the sound is sucked into the bellows. But it is also one of the reasons for the bad reputation of the harmonium. Indeed, the use of the "expression" requires perfect control and coordination of the feet, otherwise the nuances sought are punctuated by hiccups.