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A sound attenuator, or duct silencer, sound trap, or muffler, is a noise control 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.
The attenuator is a specialty duct accessory that typically consists of an inner perforated baffle with sound-absorptive insulation. Sound attenuators may take the place of ductwork; conversely, inline attenuators are located close to the blower and have a bellmouth profile to minimize system effects.
Round duct is made using a continuous spiral forming machine which can make round duct in nearly any diameter when using the right forming die and to any length to suit, but the most common stock sizes range evenly from 4" to 24" (10-60 cm) with 6"-12" (15-30 cm) being most commonly used. Stock pipe is usually sold in 10' (300 cm) joints.
A unit ventilator is a fan coil unit that is used mainly in classrooms, hotels, apartments and condominium applications. A unit ventilator can be a wall mounted or ceiling hung cabinet, and is designed to use a fan to blow outside air across a coil, thus conditioning and ventilating the space which it is serving.
A fixed skylight consists of a structural perimeter frame supporting glazing infill (the light-transmitting portion, which is made primarily of glass or plastic). A fixed skylight is non-operable, meaning there is no ventilation. Operable skylight. An operable (venting) unit skylight uses a hinged sash attached to and supported by the frame.
For this reason, glass fiber (which has a low attenuation) is used for long-distance fiber optic cables; plastic fiber has a higher attenuation and, hence, shorter range. There also exist optical attenuators that decrease the signal in a fiber optic cable intentionally. Attenuation of light is also important in physical oceanography.
Many experimental and field measurements show that the acoustic attenuation coefficient of a wide range of viscoelastic materials, such as soft tissue, polymers, soil, and porous rock, can be expressed as the following power law with respect to frequency: [7] [8] [9]
Air volume regulator. Variable air volume (VAV) is a type of heating, ventilating, and/or air-conditioning system.Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow at a constant or varying temperature.