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Name: M. Y.
Status: Student
Age: 14
Location: N/A
Country: N/A
Date: June 2004


Question:
I will want to ask how does acoustic material work in sound insulation; what is the principle behind it? Is there any other ways to reduce the loudness of the sound?



Replies:
Sound waves are reflected when they hit a hard surface. Providing an absorbent surface can reduce some of the reflected sound. In a "hard" room, soft materials such as absorbent ceiling panels, carpeting on the floor, and drapes or special absorbent wall coverings, will reduce noise by reducing the reflected sound. Only reflected sound can be treated as described, while direct sound will not be affected.

Porous materials of varying density and composition are generally used as sound absorbers to convert sound energy into heat within the open pores of the material. In order to maintain the best absorption values of the chosen materials, the air channels should all be open to the surface so that sound waves can propagate into the material. If pores are sealed, as in closed cell foam material, the material is generally a poor sound absorber. Pores should not be sealed by paint, or coverings, and any protective shielding for the absorbing material should generally be perforated.

In evaluating materials for their ability to absorb sound energy, its ability to absorb sound is usually provided in the form of an absorption coefficient. The absorption coefficient is defined as the ratio of sound energy absorbed by a given surface, to the sound energy incident upon that surface. The absorption coefficient can vary from 0 to 1. If, for example the absorption coefficient is 0.9, then 90% if the sound energy will be absorbed by that material. Most porous absorbers are more efficient at high frequencies, while improving the materials thickness, or mass, can increase low frequency absorption..

The above has been taken from a web handout from SILEX Sound Corporation on the World Wide Web. I hope that this helps.

Sincerely,

Bob Trach



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