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An acoustical panel construction useful as a suspended ceiling tile having a rectangular shape bounded by edges and establishing a face area comprising at least one corrugated layer or layers of a total thickness, the layer or layers having a multitude of parallel flutes extending across an expanse

An acoustical panel construction useful as a suspended ceiling tile having a rectangular shape bounded by edges and establishing a face area comprising at least one corrugated layer or layers of a total thickness, the layer or layers having a multitude of parallel flutes extending across an expanse of the rectangular shape substantially from one edge of the panel to an opposite edge, the flutes being formed by walls of the layer or layers and being of known volume, a series of apertures each of known area through the wall or walls of the flutes communicating with the atmosphere at the face, the aperture area, flute cavity volume associated with an aperture, and the total thickness of the corrugated layers associated with an aperture being arranged to produce a maximum absorption frequency between 200 and 2,000 Hz.

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1. An acoustical panel useful as a suspended ceiling tile having a rectangular shape bounded by edges and establishing a face area comprising at least one corrugated layer or layers of a total thickness, the layer or layers having a multitude of parallel flutes extending across an expanse of the rec

1. An acoustical panel useful as a suspended ceiling tile having a rectangular shape bounded by edges and establishing a face area comprising at least one corrugated layer or layers of a total thickness, the layer or layers having a multitude of parallel flutes extending across an expanse of the rectangular shape substantially from one edge of the panel to an opposite edge, the flutes being formed by walls of the layer or layers and being of known volume, a series of apertures each of known area through the wall or walls of the flutes communicating with the atmosphere at the face, the aperture area, flute cavity volume associated with an aperture, and the total thickness of the corrugated layers associated with an aperture being arranged to produce a maximum absorption frequency between 200 and 2,000 Hz. 2. An acoustical panel as set forth in claim 1, wherein the corrugated layers are of a type that have a curvilinear cross-section characteristic of cardboard. 3. An acoustical panel as set forth in claim 1, wherein the corrugations are rectangular in cross-section. 4. An acoustical panel as set forth in claim 1, wherein the apertures are round, coaxial holes in the face and interior walls parallel or near parallel to said face. 5. An acoustical panel as set forth in claim 1, wherein the apertures are cross-sectional openings in the layer or layers formed by slotting the same perpendicularly to said flutes. 6. An acoustical panel as set forth in claim 1, wherein the apertures are disposed along the flutes and the volume of a flute cavity is the product of the cross-sectional area of a flute and the length of the flute devoted to the respective aperture. 7. A method of making an acoustical panel by providing a rigid rectangular sheet having at least one layer of corrugations, the corrugated layer or layers having a plurality of flutes with interior hollow cavities and extending parallel to one another between a pair of edges of the sheet, the sheet having a front face on one side and a rear face on a side opposite the front face, the front face being formed with apertures communicating with the flute cavities, a total thickness of the corrugated layer or layers, the area of an aperture, and the effective volume of a flute cavity associated with an aperture being selected to permit the cavities to operate as pseudo Helmholtz cavities with a maximum sound absorbing frequency of between 200 and 2,000 Hz. 8. A method as set forth in claim 7, wherein a plurality of samples are made on a preliminary basis using a pseudo Helmholtz formula, empirically testing the samples, and making further refinement by extrapolating the empirical results, to more finely adjust the aperture area, thickness of the panel, and flute cavity volume relationship to more closely obtain a desired maximum absorption frequency.