*2.2.1 Transmission of noise*

Any type of noise is transmitted to the room through walls, floors, ceilings or conduits. The origin of transmitted noise may be air-borne or may be due to impact.

Air-borne noise can be transmitted to the receiving room in two ways: (i) by air path between two rooms such as doors, windows, ventilators, key holes, ducts, pipes, and cracks and (ii) by forced vibrations set up by the transmitting room to the walls, floors and ceiling of the receiving room. It is found that air-borne noise sets up forced vibrations in the walls, floors and ceiling of the transmitting room and they in turn set up corresponding vibrations in the walls, floors and ceiling of the receiving room. These surfaces of the receiving room create sound waves and noise is thus transmitted to the receiving room.

Impact noise or structure-borne noise is developed in solid structures and it is then transmitted as air-borne noise. Closing of doors, vibrations of machines, etc., set up vibrations in solid materials of the structure which result in transmission of noise to the receiving room.

Air-borne noise possesses less power, continues for a long duration and is confined to places near its origin. Impact or structure-borne noise possesses more power, continues for a short duration and is often propagated over long distances.
