TEAK WOOD SHRUTI BOX - C To C - 440Hz A shruti box is an instrument, originating from the Indian subcontinent, that traditionally works on a system of bellows. It is similar to a harmonium and is used to provide a drone in a practice session or concert of Indian classical music . The shruti box is also used in classical singing. In classical singing, the shruti box is used to help tune the voice. The use of the shruti box has widened with the cross-cultural influences of world music and new-age music to provide a drone for many other instruments as well as vocalists.