Harmonium is a wind activated reed instrument. Air is blown using the hand bellow. A version with foot pump too exist but not very popular. A smaller version with no Key board called Sruthi box exist to provide drone. The key board is European and has many drone reeds peculiar to Indian music. Base drone is accomplished by keeping some of the reeds continuously activated by pulling the required knobs in the front side of the instrument.
There are a number of parts of the harmonium, the main ones are: Body, Bellows used for pumping air and also serves as a reservoir, Keys though similar to Western it does not follow the International standard for pitch (A = 440), Cover, Main Stops - a series of valves which control the way that air flows in the instrument, Drone Stops - the most distinguishing feature of Indian harmoniums (base stops control the flow of air over un-keyed reeds. They simply drone their particular pitch. There may be any number of drones set to any pitch; however they tend toward, A sharp, C sharp, D sharp, F sharp, and G sharp), Handles for transport, Reeds - a series of brass reeds set into a heavier brass base (Each base is roughly 1/4 inch by 2 inches. There must be a minimum of one reed per key while two or three are the most common. These small brass reeds vibrate whenever air passes over them), Coupler - a mechanical arrangement whereby another key is played along with the one being fingered (Normally this is a key located an octave below the selected key. This arrangement produces a richer sound than an uncoupled keyboard. This coupling may be enabled or defeated by the user), Scale Changer (not very popular), Reed Board (The reed board is a flat piece of wood with a series of long holes cut in them. There are a series of brass reeds covering these holes. These reeds are arranged in banks. If there are two banks of reeds, it is said to be a double-reed harmonium. If there are three banks of reeds, it is said to be a triple-reed harmonium. The triple-reed harmonium is generally considered to be superior to the double-reed variety. Sometimes this board is not flat, instead has the reeds set into perpendicular baffles. This style is said to produce a better sound).
The harmonium may be played sitting, standing or walking with the harmonium is slung by a strap around the neck.