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Enhancing low-frequency absorption.

Polyurethane foams are often used to control noise by absorbing sound. A recent theoretical analysis shows that the material's effectiveness depends on how a protective facing or backing is attached to the foam. J.S. Bolton of Purdue University in West Lafayette, Ind., says that a small air gap, perhaps only 1 millimeter thick, between a thin foam layer and its facing or backing enhances the material's ability to absorb low-frequency sound. The facing film should not be bonded directly to the foam's surface. The new arrangement works just about as well as a sheet of bare foam, he says, with the added protection that a facing provides.
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Author:Peterson, Ivars
Publication:Science News
Date:Nov 23, 1985
Words:108
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