Noise sound absorbing surfaces

There is a practical limit to this approach. To a great extent, the effectiveness of additional treatment depends on the lack of sound-absorbing surfaces prior to treatment. The noise reduction is computed as... 

Uses. Sound-absorbing materials are frequendy used to reduce reverberation, or the persistence of sound in a space after generation of the sound ceases to reduce focused reflections from concave surfaces to prevent echoes, or delayed sound reflections from distant surfaces and to prevent the buildup of sound by multiple reflections within rooms and other enclosures. Sound-absorbing materials also are used to reduce the transmission of noise from one location to another by multiple reflections from sound-reflecting surfaces. 

Machinery enclosures Walls of acoustic enclosures should consist of heavy but flexible panels lined internally with sound-absorbing material. Adequate ventilation, demountability of the enclosure for repairs, and arrangements for operating and/or observing the machine to be provided. If hot gas fans are acoustically enclosed, the surface of the fan casing should additionally be heat-insulated. For information on design and performance of enclosures for noise control see VDI2711. 

Because of their cellular or open-matrix construction, most insulants have an inherent ability to absorb sound, act as panel dampers and reduce noise breakout from plant by their ability to be a flexible or discontinuous link between an acoustically active surface and the outer cladding. This secondary aspect of thermal insulation specification will gain more prominence when the UK adopts the EC Directive 86/1888, Protection of workers from the risks related to exposure to noise at work . 

Noise reduction by sound absorption Sound that originates at a source in an enclosed factory space will spread until it reaches the surfaces, where it will either be absorbed or reflected. If the room surfaces are hard (reflective), sound will reverberate, intermittent sounds will be mixed together, and steady sounds will add up. The result may be a relatively noisy space. If room surfaces are soft (absorptive), the space will be less noisy, because the... 

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