attenuation. Sound attenuators are typically located near ducted mechanical equipment, to attenuate noise which propagates down the duct. This creates a trade-off: the sound attenuator should be located near the fan and yet the air is typically more turbulent closer to fans and dampers. Ideally, sound attenuators should straddle the wall of the mechanical equipment room provided there are no fire dampers. If a sound attenuator is located over occupied space, the noise control engineer should confirm that duct breakout noise is not an issue prior to the attenuator. If there is significant distance between the attenuator and the mechanical room penetration, additional duct cladding (such as external fiberglass blanket or gypsum lagging) may be required to prevent noise from breaking into the duct and bypassing the attenuator. Sound attenuators can also be used outdoors to quiet cooling towers, air intake of emergency generators, and exhaust fans. Larger equipment will require an array of sound attenuators, otherwise known as an attenuator bank. See also Ductwork HVAC References External links Acoustical Society of America American Society of Heating, Refrigerating and Air-Conditioning Engineers ASTM International Price Industries IAC Acoustics Vibro-Acoustics Heating, ventilation, and air conditioning Noise control