Sound attenuators, Silencers or mufflers are widely used to control noise from building openings where airflow or gas medium shall circulate for other purposes. All these terms are used interchangeably.

Three types of HVAC duct silencers: Dissipative silencers (with acoustic media) that attenuate sound over a broad range of frequencies, Reactive silencers (no-media) that the broadband insertion loss is more difficult to achieve than with the dissipative silencers because of tuning, and active silencers that reduce noise at lower frequencies by producing inverse sound waves that cancel unwanted noise.