Abstract: The disclosure is directed broadly to a thin metal sheet containing a multitude of small openings therethrough. Typically, the sheet will contain at least 400 openings per square inch with the openings having an average cross-sectional area of from about 0.0005 to about 0.005 square inch. The sheets are used to overlay a series of perpendicularly aligned walls which define air chamber(s) behind the sheet. Sound waves pass through the porous sheet and are absorbed in the air chamber(s).

Abstract: An improved acoustical material, which is simple in construction and uses conventional, inexpensive materials, for use as a lining material in association with noise generating machinery is disclosed. It comprises two woven fiberglass layers and an intermediate non-woven fibrous layer to form a composite which will not deteriorate, swell or retain oil, solvents, or water such as are found in machinery, and which has acoustical flow resistance of between 20 rayls and 80 rayls. The flexible composite may be used over a highly porous layer which is or acts as a dead air space relative to the composite.

Abstract: An improved acoustical material, which is simple in construction and uses conventional, inexpensive materials, for use as a lining material in association with noise generating machinery, comprising, in combination, a composite layer of plural layers of porous material which will not deteriorate, swell or retain oil, solvents, or water such as are found in machinery, and which has acoustical flow resistance of between 20 rayls and 80 rayls, and a highly porous layer which is or acts as a dead air space relative to the composite.