US3037578A - Paper enclosed low density pad with septum - Google Patents

Description

June 5, 1962 w. A. JACK 3,037,578

PAPER ENCLOSED LOW DENSITY PAD WITH SEPTUM Filed Sept. 9, 1957 INVENTOR Wax/ 4 A Jhc/f United States Patent Ofice 3,037,578 PAPER ENCLOSED LOW DENSITY PAD WITH SEPTUM William A. Jack, Hampton, N.J., assignor to Johns-Manville Corporation, New York, N.Y., a corporation of New York Filed Sept. 9, 1957, Ser. No. 682,669 3 Claims. (Cl. 181-33) This invention relates to acoustical constructions and, more particularly, to improved sound-absorbing units for use in conventional sound-absorbing apparatus.

Sound-absorbing units of the type comprising pads of fibrous material, such as mineral wool, wood fiber, glass fiber and the like, usually enclosed in a sound-pervious wrapper, have been employed heretofore in acoustical treatments as a sound-absorbing medium. The pads are inserted in a plurality of perforated metal pans supported from a wall or ceiling, with each pan containing an individual sound-absorbing pad.

Heretofore, these pads have necessarily been formed of relatively high density mats, even though they are more expensive, because such mats have a higher efliciency of acoustical absorption over a wider range of sound fre quencies than the lower density mats, as the latter mats have a relatively low acoustical coefficient in the high frequency range of sound.

A main purpose of the present invention is to provide a new and improved sound-absorbing unit characterized by a novel, laminated pad construction employing fibrous material of much lower density than it has been possible to employ usefully heretofore in acoustical constructions.

A further purpose of the present invention is to provide a new and improved sound-absorbing unit of simple and light weight construction, which shows excellent acoustical efficiency over wide range of frequencies.

A sound-absorbing or acoustical unit constructed in accordance with the present invention consists of a pad comprising a plurality of layers of light weight, fibrous material, a septum interposed between such layers, and a paper Wrapper enclosing the laminated construction; the layers and wrapper cooperate to give the unit a high acoustical eificiency in the low frequency range of sound while the layers and septum cooperate to give the unit a high acoustical efiiciency over the high frequency range. The three elements consequently cooperate with each other to give the unit a high coefficient of sound absorption over a wide band of low and high frequencies These several features of the present invention are described in detail below in connection with the accompanying drawing, in which like numerals designate like parts, and in which:

FIG. 1 is a perspective view of a sound-absorbing unit embodying the present invention; and

FIG. 2 is a broken vertical section, on an enlarged scale, taken substantially along the line 2-2 in FIG. 1.

Referring now in detail to the drawing, the illustrated embodiment of the sound-absorbing unit of the present invention is indicated generally by the reference numeral 10, and comprises a pad 12 of porous, light-weight, soundabsorbing material composed of a mat or felt of fibrous or granular material, such as mineral Wool, wood fiber, glass and the like, having a suitable binder dispersed throughout the mat. As in the conventional practice, the sheet or layer of felted fibers in accordance with the instant invention is formed with an intermingled, and preferably heat setting, binder, such as a drying oil. The layer is compressed to the desired density and the binder is set by application of heat, whereby a relatively resilient mat is produced. The mat used is relatively light in weight, being of the order of 3 pounds per cubic foot and less than about 6 pounds per cubic foot, as contrasted with 3,037,578 Patented June 5, 1962 mats of 8-16 pounds per cubic foot presently in common use. The resultant mat is also relatively shape sustaining and, due to its relative rigidity, may be dimensioned with reasonably accurate limits.

In accordance with the present invention, the felted pad 12 is composed of two sheets or layers 16 and 18 of the interfelted fibers laminated together. The mat of the pad 12 may be sliced at the center to form the two layers 16 and 18 if it is sufficiently thick or, if it is relatively thin, two separate, preformed sections may be employed as the separate layers. A septum 20 of a layer or sheet of thin, flexible, air-impervious material, which is also sound-pervious and desirably flameproofed, such as flameproofed krfat paper and the like, is interposed between the layers 16 and 18 and may be adhered thereto in any convenient manner, as by cementing. As is well known, sound absorption is obtained through sound decadence in the numerous interstices and openings provided in the fibrous structure. With the use of light weight material, it has been discovered that the absorption of the high range of frequencies is sharply reduced. The septum 20 cooperating with the layers 16, 18 compensates for this loss by giving a desirable increase in sound-absorption of such high frequencies.

The pad assembly 12, having any suitable thickness, say about 1 to 4 inches, is enclosed by a paper wrapper 14, in any suitable manner. The wrapper 14, of relatively thin, flexible and sound-pervious but air-impervious material similar to that used in septum 20, may be formed into a bag of accurate dimensions, as by being cemented along the top overlapping marginal portions, as indicated at 22, and at one end thereof. The bag is held with the other end open and distended, and the pad 12 is slightly compressed between its outer surfaces and inserted into the open end of the bag 14. The bag may then be sealed by cementing a suitable closure flap 24 over the open end. Alternatively, the wrapper 14 may be simply folded over the pad 12 and sealed at the overlapping portions thereof. The wrapper 14, in addition to maintaining the two layers 16 and 18 and the septum 20 in proper relationship, serves also to prevent air breathing through portions of the pad 12, thereby preventing soiling of the acoustical facing and also prevents falling out of fibers or granules from the pad 12. At the same time, the wrapper acts as an additional low frequency sound absorber, increasing thereby the sound-absorption of the pad over a wider range.

It will thus be appreciated that in the laminate or sandwich construction of the sound-absorbing unit 10 of the present invention, a low-density, inexpensive fibrous material is employed in lieu of the higher density, more expensive materials. To compensate for the loss of soundabsorption in the high-frequency range, a paper septum is utilized between layers of the inexpensive fiber. To increase the sound absorption in the low frequency range and to provide a proper retainer for the materials, the laminate structure is enwrapped in a paper covering or bag.

With such an enwrapped laminated structure, acoustical efiiciencies obtained are comparable to the efficiencies of pads utilizing a higher density mat. However, the relative cost of the units has been reduced sharply, principally in the reduction of the amount of material used in the mat, as the relative cost of the septum and wrapper is minor compared to the cost of the pad.

Having thus described my invention in rather full detail, it will be understood that these details need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.

What I claim is:

1. An acoustical unit comprising a sound-absorbing, porous, self-sustaining pad, said pad comprising layers of relatively light weight, fibrous material having a density Within the approximate range of 3 to 6 pounds per cubic foot, a thin, paper-like, imperforate, sound-pervious septum interposed between said layers, and a sound pervious wrapper enclosing said pad and septum.

2. An acoustical unit comprising a sound-absorbing, porous pad, said pad composed of a pair of layers of light-weight, fibrous material having a maximum density of approximately 6 pounds per cubic foot, a paper-thin relatively flexible layer of sound-pervious material interposed between s'aid layers of fibrous material, said layer of sound pervious material being imperforate and a relatively flexible air impervious, sound pervious wrapper enclosing said pad.

3. A sound-absorbing unit comprising a preformed, porous pad assembly, said pad assembly including a pair of layer of sound-absorbing fibrous material, said material having a density of less than about 6 pounds per cubic foot, a relatively thin, sound-pervious septum interposed between said layers, a sound-pervi0us, air-impervious paper wrapper enclosing said pad assembly, said material providing good sound absorbing efficiency in the lower frequency range of sound waves and the septum cooperating with the fibrous material to provide good sound absorbing efiiciency in the higher frequency range of the sound waves.

References Cited in the file of this patent UNITED STATES PATENTS 1,915,611 Miller June 27, 1933 1,955,443 Spafford Apr. 17, 1934 2,064,327 Upson Dec. 15, 1936 2,357,115 Jack et al Aug. 29, 1944 2,802,764 Slayter et al Aug. 13, 1957 FOREIGN PATENTS 183,937 Switzerland July 16, 1936

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