The Investigation of Plenum Chamber Role in Noise Reduction of a Fan and Air Ducts



Forouharmajd F^{1, 2} ; Nassiri P² Show Affiliations
Source: 39th International Congress on Noise Control Engineering 2010, INTER-NOISE 2010 Published:2010

Abstract

HVAC equipment is one of the major sources of noise in a building, and its effect on the interior acoustical environment is important. Further, noise from outside equipment often propagates to the community. Noise propagates from the sources through the air distribution duct systems, structure, and combinations of paths, reaching the occupants. A plenum chamber is similar to a dissipative silencer, but it is also similar to a small room with a noise source in one wall. The dimensions of the plenum chamber are usually larger than the wavelength of the sound being attenuated. Above the cutoff frequency, as defined by the plenum's inlet duct dimensions, the wavelength of sound is small compared to the characteristic dimensions of the plenum. All values are in terms of sound pressure level in a situation of A for frequency weighting and slow for time weighting measured by B&K 2231sound level meter and 1625 analyzer. Input and output in this compartment as opposed to two-sided compartment was based on the ASHRAE instructions on the frequency of cutoff. This frequency indicates that the chamber dimensions that channel input and output frequencies higher than 436 Hz will be effective in reducing noise.