Construction: The Harmonium has a set of reeds but, unlike the organ, has no pipes. It works on a system of bellows which make the reeds vibrate when the keys are pressed down. The left hand is used to operate the bellows while the right hand is used to play on the keys of the keyboard. The first key starts at a pitch of 1 kattai or C.

Tuning: It is basically a reed organ with a keyboard and a range of two and a half octaves. The keys are tuned to a tempered scale, like the piano, which limits its scope when it comes to ornamentations in Indian classical music.