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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.
A 1973 report cites a university study of fifty cases of people complaining about a "low throbbing background noise" that others were unable to hear. The sound, always peaking between 30 and 40 Hz (hertz), was found to only be heard during cool weather with a light breeze, and often early in the morning. These noises were often confined to a 10 ...
The hissing of high voltage transmission lines is due to corona discharge, not magnetism. The phenomenon is also called audible magnetic noise, [1] electromagnetic acoustic noise, lamination vibration [2] or electromagnetically induced acoustic noise, [3] or more rarely, electrical noise, [4] or "coil noise
A whistle is a device that makes sound from air blown from one end forced through a small opening at the opposite end. They are shaped in a way that allows air to oscillate inside of a chamber in an unstable way. The physical theory of the sound-making process is an example of the application of fluid dynamics or hydrodynamics and aerodynamics ...
A long-range acoustic device (LRAD), acoustic hailing device (AHD) or sound cannon is a specialized loudspeaker that produces sound at high power for communicating at a distance. It has been used as a method of crowd control , which has caused permanent hearing damage , having an extremely high decibel capacity (up to 160 dB measured at one ...
Blowing pressure – Sound level increases as blowing pressure is raised, [59] [60] although there may be an optimum pressure at which sound level peaks. [48] Aspect ratio – Sound level increases as whistle length is reduced, increasing frequency. For example, depressing the piston of a variable-pitch steam whistle changed the frequency from ...
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Although many vent hoods exhaust air to the outside, some recirculate the air to the kitchen. In a recirculating system, filters may be used to remove odors in addition to the grease. The device is known as an extractor hood in the United Kingdom , as a range hood in the United States , and as a rangehood in Australia .
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