Just what is the difference between Structure-borne and Air-borne noise?

	The noise given off by a particular source can usually be categorised into one of the following forms: Structure-borne noiseThis is the sound generated from a vibrating source or impact event. The acoustic energy created by these vibrations is transmitted into the structure of a building (e.g. floors, walls, pipe-work etc,) or into mechanical elements (e.g. metal frames, panel work, supports etc.) This energy travels through solid structures and is released as air-borne noise at different locations within the building or mechanical system. Air-borne noise This is the sound that travels through the air and into the surrounding environment. In closed environments such as rooms and enclosures, air-borne sound may reverberate and increase the levels of noise both in and outside the contained space. Most forms of noise will contain contributions from both air-borne and structure-borne sound. Although measures can be taken to limit structure-borne components, such as by isolation and damping, air-borne sound can be treated with the use of absorbing materials. ArmaSound RD has an extremely high absorption performance per unit thickness, offering a solution for the most demanding applications.
	By way of example, someone who is hammering a nail into a wall (See diagram) will create structural noise, causing vibration of the surrounding structure. However, they will create a significant amount of air-borne noise, which will be clearly heard in the room where the action is taking place. As the noise travels, it may also change forms. I.e. Structure-borne noise may eventually cause sympathetic vibrations in other structures and release airborne sound. In this example, the structure borne components of the noise may travel towards the light fitting that’s in the same room causing it to shake and release audible clatter. Airborne noise may also change into structure-borne and back to air-borne. This process is often called ‘transmission’ of sound energy. Once again, in the example above, the air-borne components of the noise may travel into the far wall, and then out through the other side and into an adjoining room.