A sound attenuator, also known as a duct silencer, sound trap, or muffler, is a noise control acoustical treatment of HVAC ductwork meant to limit noise transmission via the ductwork, either from equipment into occupied rooms in a building or between occupied spaces.

A sound attenuator is essentially just a baffle inside the ducting. Sound-absorbing materials are frequently used in these baffles. The physical parameters and baffle arrangement of sound attenuators are chosen to attenuate a certain frequency range. Sound attenuators may offer broader band attenuation in very short lengths, in contrast to typical internally-lined ductwork, which is primarily effective in reducing mid- and high-frequency noise. A Helmholtz resonator is essentially what some forms of sound attenuators are when utilized as a passive noise-control mechanism.