From Academic Kids
The harmonium is a type of reed organ that uses a pressure bellows.
There are two main types of harmonium: a foot-pumped version that resembles a small organ, and a hand-pumped portable version that is sometimes made in a collapsable version that folds up for easy transport. The foot-pumped version was common in the late 19th century, replacing the melodeon. It was used as a practice instrument by organists, most notably Franck, who composed several collections of works specifically for it, taking advantage of the expressive capacity of varying the bellows pressure using the feet. It was also common in the rural U.S., where it was a popular source of home entertainment. It was cheaper than a piano, the tuning was more stable, it was lighter, and it withstood the bumpy shipment by rail better. They were also used in many pioneer churches in the U.S., where the harmonium was used for accompaniment of congregational singing instead of an organ.
In western culture both types of harmonium have largely fallen out of use, having been replaced by the piano, the pipe organ, and electronic organs. Many harmoniums were shipped overseas to support missionary efforts, though they remain common (though disused) in both private and ecclesiastical ownership.
The Harmonium in India
During the mid-19th century missionaries brought hand-pumped harmonium to India, where it quickly became popular due to its portability and its low price. Its popularity has stayed intact to the present day, and the harmonium remains an important instrument in many genres of Indian music, as well as being commonly found in Indian homes.
A popular usage is by followers of the sikh faith, who use it it the devotional singing of prayers, called kirtan. In any gurdwara (sikh temple) around the world there will be at least one harmonium. The harmonium is also commonly accomponied by the tabla. To sikhs the harmonium is known as the vaja/baja.
In Indian music, the harmonium is considered to be one of the most versatile instruments. The harmonium is used in classical, semi-classical, and devotional music. It is usually used as an accompanying instrument for vocalists in classical music. However, some musicians have began playing the harmonium as a solo instrument. One of the largest pioneers of this style is Pandit Tulsidas Borkar of Mumbai. More and more music students are learning in this fashion.
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 the keyboard. The harmonium's timbre, or sound, is similar to an accordion, but works 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 is similar to bagpipes and allows the harmonium to create an continuously sustained sound. The quality of the sound is generally believed to improve over time as the instrument ages. If a harmonium has multiple reeds, its possible that the second set of reeds is tuned an octave lower and can be activated by a stop, which means each key pressed plays two notes an octave apart. This overall makes the sound fuller. In addition, many harmioniums feature an octave coupler, a mechanical linkage that opens a valve for a note an octave below the note being played. Harmoniums are made with 1, 2, 3 and occassionally 4 sets of reeds. Classical instrumentalists usually use 1-reed harmonium, while a musician who plays for a qawaali (Islamic devotional singing) usually uses a 3-reed harmonium.