ABSTRACT
Air conditioning systems employ fans, which are characteristically noisy, and if a room is to be successfully ventilated without exposing its occupants to unacceptably high noise levels then some sort of sound attenuator will be required between the fan and the conditioned area. When applied to combustion engines and compressors, the filters are usually called ‘silencers’ (or ‘mufflers’ in the USA). For ventilation systems the term ‘attenuator’ is more common; although for widely differing applications, the requirements of the acoustic devices in the above examples are similar in principle.
