GB721860A - Improvements in sound-absorbers for use in fluid media - Google Patents

Abstract

721,860. Silencing gaseous &c. currents. BOLT BERANCK & NEWMAN, Inc. Nov. 11, 1952, No. 28416/52. Class 7 (2). A sound-absorbing device for a fluid medium, flowing, for example, in a silencer or the conduits of air-conditioning systems, comprises a housing which is substantially completely filled with sound-absorbing material such as fibre-glass, packed felt or rock wool, and one of the walls 7 of the housing is acoustically transparent, e.g. constituted of perforated metal sheet or wire mesh, and connected to the other walls 1, 3, 19, 21, which may be of sheet metal. As shown in Fig. 1, the wall 7 has opposite and substantially the same curvatures at the lines of connection 2, 4 with the walls 1, 3, and preferably the curved surfaces are of substantially sine-wave shape. The sound-absorbing packing may comprise a section 12 of predetermined density, a section 13 of increased density, a section 15 of still further increased density, and a section 17 of a density corresponding to that of section 13 ; alternatively, the density of the sound-absorbing packing may (a) be uniform, (b) successively increase or decrease from the wall 7 to the junction 5 between the walls 1, 3, and (c) comprise three sections the density of the intermediate section being less than that of the adjoining sections ; or the density of the intermediate section is.greater than that of the adjoining sections. There may be intermediate separator walls 22. Two or four devices may be assembled together as shown in Figs. 4 and 5, and such assemblies may be stacked one on another to form columns for use, for example, in an aerodynamic test chamber, Fig. 2, wherein the largest transverse dimensions of each row of the devices are situated opposite the smallest transverse dimensions of the adjacent row or rows of the devices to provide successively converging and diverging adjacent zig-zag paths. Specification 721,859 is referred to.