Sound attenuators or duct silencers
When HVAC systems are in operation, they can be quite noisy. Various
electrical and mechanical devices in the HVAC system, such as fan, transmit
noise when in operation. In addition, vibration of the system and pressure drops
occuring at various points, such as when air passes through filters or dampers,
also cause noise. Both circular and rectangular sound attenuators, also known as
duct silencers, introduce sound absorbing media in the air stream, thus removing
acoustic energy from the air as it passes. The result is a reduced overall HVAC
noise.