A sound trap is a special acoustical treatment of Heating Ventilating and Air-Conditioning (HVAC) ductwork designed to reduce transmission of noise through the ductwork, either from equipment into occupied spaces in a building, or between occupied spaces.
In its simplest form, a sound trap consists of an offset in the ductwork to reflect the sound back to its source. This configuration is often combined with the use of sound-absorbing material inside the trap. The physical dimensions of the sound trap may be selected to tune the trap to specific frequencies of sound.
