Harmonium
Overview
A harmonium is a free-standing keyboard instrument
Keyboard instrument
A keyboard instrument is a musical instrument which is played using a musical keyboard. The most common of these is the piano. Other widely used keyboard instruments include organs of various types as well as other mechanical, electromechanical and electronic instruments...

 similar to a reed organ
Reed organ
A reed organ, also called a parlor organ, pump organ, cabinet organ, cottage organ, is an organ that generates its sounds using free metal reeds...

. Sound is produced by air being blown through sets of free reeds
Free reed aerophone
A free reed aerophone is a musical instrument where sound is produced as air flows past a vibrating reed in a frame. Air pressure is typically generated by breath or with a bellows.- Operation :...

, resulting in a sound similar to that of an accordion
Accordion
The accordion is a box-shaped musical instrument of the bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist....

. The air is usually supplied by bellows
Bellows
A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location.Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet...

 operated by the foot, hand, or knees.

In North America, the most common pedal-pumped free-reed keyboard instrument is known as the "American reed organ", (or "parlor organ", "pump organ", "cabinet organ", "cottage organ", etc.) and along with the earlier melodeon
Melodeon (organ)
A melodeon is a type of 19th century reed organ with a foot-operated vacuum bellows, and a piano keyboard. It differs from the related harmonium, which uses a pressure bellows. Melodeons were manufactured in the United States sometime after 1812 until the Civil War era...

, is operated by a suction bellows where air is sucked through the reeds to produce the sound.
 
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