In the context of the total building environment, comfort cannot be achieved with excessive sound or noise levels. By definition, sound is a change in pressure for a medium, such as air. This change in pressure involves a radiation of energy. Energy is used in the generation of sound and this energy is radiated from a source. All sound has a source and travels down a path to a receiver.
Air terminals are one source of sound in a mechanical system.
The path for sound emanating from the air terminal is through the plenum or down the duct into the conditioned space where it reaches the occupant or receiver. Mechanical system designers should not be concerned so much with sound, but rather with noise. Noise can be thought of as unwanted or excessive sound. Good design practice dictates that a designer establish the acceptable noise for the occupied space and then determine the selection criteria for the mechanical system components. In any application, both radiated and discharge sound should be considered.