There are two types of sounds:

	Airborne — These sounds are transmitted by way of the air and can be absorbed by insulation.
	Structure-Borne — These sounds are generated by vibrations in the ground and/or a structure and must be interrupted to reduce or eliminate the transmission of sound energy.

Many sounds are both airborne and structure-borne.

For example, speech is an airborne sound until it strikes a wall and becomes structure-borne. This causes a vibration that travels through the wall and once again becomes airborne sound, audible to listeners in an adjacent room.