Acoustics – Sound-modifying means – Muffler – fluid conducting type
Patent
1975-04-14
1978-01-17
Tomsky, Stephen J.
Acoustics
Sound-modifying means
Muffler, fluid conducting type
181295, 181252, F01N 104, G10K 1104
Patent
active
040687368
ABSTRACT:
A device for reducing noise interiorly of air distribution ducts is comprised of at least one sound attenuating module which is adapted to be placed adjacent to a noise source or installed interiorly of conventional air distribution ducts. The module has a plurality of adjacently sandwiched glass fiber layers which are separated from each other by aluminum side walls. Each one of the layers is sealed by an aluminum membrane enclosure (with the outer membranes being substantially airtight to prevent any resultant friction between air passing through the duct and the glass fiber). Noise is reduced as the sound pressure (developed by the conditioned air flow in the duct) alternately contracts and expands the compliant glass fiber media interiorly of the module, thusly dissipating energy in the form of friction between the glass fibers that are in each layer. To reduce acoustic input impedance at the low frequencies, the layers are made approximately one quarter wavelength thick, thereby enabling the ordinarily high wall impedance to be transformed into a lower acoustic impedance at the outside surface thereof. However, in order to minimize necessary module thickness, the wavelength of the noise frequency of interest is decreased by reducing the speed of sound through the absorber.
A method for attenuating predetermined noise frequencies comprises the steps of using a compliant sound absorption media having a thickness of approximately one quarter of the wavelength of a sound frequency to be attenuated, sealing at least a portion of said media within a flexible air impervious membrane, and locating said sealed media in operative proximity to said noise.
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Dean Raymond H.
Roberts Michael M.
Tempmaster Corporation
Tomsky Stephen J.
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