US3078948A - Acoustical panel - Google Patents

Description

J. H. GILDARD ETAL Feb. 26, 1963 ACQUSTICAL PANE 3 Sheets-Sh 1 Filed Dec. 17, 1959 IN V EN TORS,

0W y 5%. E W 15 6A 0 T Z .2, 4 i 2 Feb. 26, 1963 J. H. GILDARD ETAI. 3,078,948

' ACOUSTICAL PANEL.

Filed Dec. 17, 1959 3 Sheets-Sheet 3 gr III I IN VEN TORS. L/AMESH G'JLDARD RICHARD DLEMMERALAN Zizez'r A TTO EAIEY United States Patent Ofifice 3,673,948 Patented Feb. 26, 1963 3,078,948 ACOUSTICAL PANEL James H. Gildard, Baltimore, and Richard D. Lemmerman, Gibson Island, Md, assignors to Koppers @ornparty, line, a corporation of Delaware Filed Dec. 17, 1959, Ser. No. 860,256 7 Claims. (Cl. 181-33) This invention relates to panels and more particularly to acoustical panels employed as walls, partitions, and the like.

Panels of this type are required to have sufficient rigidity and strength to serve as walls and also to have the necessary properties to function as a sound barrier capable of substantially reducing the transmission of a wide range of sound frequencies through the panels. To produce a desirable sound barrier having the structural rigidity required, it is well known that the Wall may be formed of materials having a sutficiently large mass so that the mass of material in itself creates the sound barrier. Such a sound barrier reduces the sound propagated therethrough to an exponential degree provided that the material is impervious to air flow. However, it has been found that materials economically feasible for use in panels if used in the requisite amount to yield the desired mass would be unsuitable for partitions or walls, because of excess thickness or weight particularly when such walls are of the movable type. For this reason, it has become conventional to construct paneling of two or more spaced members rigidly attached to each other so as to form a stiif wall. It has been found that when exposed to the range of sound frequencies normally associated with speech, these prior panels do not achieve the sound level reduction or sound barrier characteristics normally to be expected by virtue of the mass employed. In other Words, the transmission loss characteristics of the mass of these prior panels over portions of the range of voice frequencies are often unexpectedly so low that sound is propagated through the panel.

It is known that such sound propagation through the panel is caused by the rigidity of the construction of these typical panels such that when sound strikes one of the stiff side members, the latter flexes and vibrates along its entire area, and the other stiif side member is also caused to vibrate in substantial synchronization therewith. As a result sound is caused to be emitted from the other side wall.

Briefly, the invention contemplates employing a structurally rigid panel comprising at least two spaced stiff outer members between which there is incorporated means for localizing the fiexure of the outer members when subjected to sound waves. This is accomplished by connecting the stiff outer members in spaced relation with structural elements arranged to allow movement relative to each other along a plurality of relatively closely spaced planes normal to the faces of the outer members, upon the application of a force thereupon suificient to flex oneof said outer members. Hence, when the sound waves strike one of the stiff outer members, the force exerted thereby flexes one of the structural elements and is substantially horizontally transferred to the opposite wall. This causes both outer members of the panel to flex in the same direction. However, since the connecting structural elements are arranged to shear in closely spaced planes transverse to the outer members, the flexure is restricted to spaced individual and localized areas such that the vibration reaction of the total area of the outer members is substantially prevented but instead more or less localized bulges or dimples are formed in the outer members. In this manner, the propagation of sound through the panel is substantially diminished and the panel re tains its transmission loss characteristics.

The transmission loss characteristics of the panel are achieved by the total mass of the materials employed in the construction of the panel. That is to say, the transmission loss characteristics of the panel are the sum of the characteristics of the outer members and the connecting structure. It is to be noted, that in conventional panels, the transmission loss characteristics are substantially dependent on the mass of the outer members only.

As a further feature, there may be incorporated into the panel of the present invention, sound absorbing structure which functions in the nature of a sound trap. Such structure is advantageous where it is desirable to reduce the sound reverberation characteristics in the room from which the sound is originating as, for example, in a broadcasting studio or the like.

The invention possesses other advantageous features some of which with the foregoing will be set forth at length in the following description with those forms of the invention which have been selected for illustration in the drawings accompanying and forming a part of the present specification. In the drawings, various forms of the invention are shown but it is to be understood that it is not limited to such forms since the invention as set forth in the claims may be embodied in a plurality of forms.

In the drawings:

FIG. 1 is an isometric view of the first embodiment for carrying out the present invention with some of the parts being broken away and shown in section to show details.

FIGS. la and lb are views showing modifications of the panel structure of FIG. 1.

FIG. 2 is a cross-sectional view of a second embodiment of a panel constructed in accordance with the present invention.

FIG. 2a is an isometric view of the block employed in the panel shown in FIG. 2.

FIG. 2b is a view showing blocks made from a different material from that shown in FIG. 2.

FIG. 3 is a cross-sectional view of a third embodiment of the invention.

FIG. 3a is a partial isometric view of the panel rigidifying members employed in FIG. 3.

FIG. 4 is a fourth embodiment of the invention.

FIG. 5 is a schematic view showing on a greatly exaggerated scale the reaction of the panel structure of FIG. 4 when it is subject to sound waves.

in FIGS. 1 and 2, a panel denoted 10 comprises generally two spaced sheet or plate members 11 and 13 and an internal spacing structure generally designated as 15.

The face sheets 11 and 13 are spaced apart about one to six inches and are preferably formed of substantially rigid material impervious to the flow of air and imparting strength to the panel such that it may be employed for acoustical and structural purposes. Materials suitable for these purposes are sheet metal, metal plate, plywood, composition board and the like. Such material may be covered by plaster or fabric covering so as to more closely simulate the conventional wall.

The thickness of the material employed to form the side members varies in accordance with the overall mass desired for acoustical purposes. For example, if a high loss transmission to provide an etficient sound barrier is essential such as, for example, in panels employed in school rooms or the like, it is preferable that the paneling have sufficient mass to minimize sound transmission over a relatively wide range of frequencies. Generally adequate sound transmission loss for this purpose may be secured by the use of opposed 16 gauge steel metal plates for the face sheets 11 and 13. The effectiveness in terms of sound transmission loss per square foot of panel for these 16 gauge faces would be the equivalent of the transmission loss per square foot of a single steel face of A2 inch thickness. If plywood should be employed as the facing of the panel, the total requisite thickness of the plywood would range between about to one inch.

To prevent the vibration of the face sheets 11 and 13 such that sound propagation therethrough is minimized when face sheets 11 and 13 are subjected to sound waves, the internal spacing and connecting structure 15 is constructed such that there are numerous closely spaced shear planes lying transversely to the faces of the side members. The connecting structure is preferably made of a high density material imparting rigidifying and transmission loss characteristics to the panel additive to the transmission loss characteristics of the two side members thereby forming a substantial barrier to sound. When the transmission loss characteristics of the side members if employed alone are inadequate because of insufficient mass, the remaining desired transmission loss characteristics may be achieved by the proper selection of material forming the connecting structure 15.

In FIGS. 1 and 2, the internal spacing structure 15 is constructed so as to provide transverse shear planes and at the same time to impart the requisite acoustical and structural properties to the panel. As shown, structure 15 includes a waffie 17 having a bottom wall which is adhered by suitable adhesive 19 such as an epoxy resin to the inner surface of the solid face sheet 11.

The waffle 17 is preferably formed of a plastic which is compressible and provides outer surfaces having a relatively low coeificient of friction. Materials found to be suitable for this purpose are those classified as polymeric and copolymeric foams and include polystyrene foam, polyethylene foam, polyvinyl chloride or polyisocyanite foams. The wafile 17 so constructed using any of the above mentioned materials is then loaded with rigid blocks 21 made of high density, non-porous material sized to fit snugly within the wafile openings or cavities 23. Suitable block materials may be plastic, plaster or wood as illustrated in FIGS. 1, 1a and 112, respectively.

The blocks 21 are bonded by a suitable adhesive at their! tops to the face sheet 13 and to the other face sheet 11 by way of an integral projection 22 which fits within a perforation 18 provided in the wafile 17. In this manner, face sheets 11 and 13 are held structurally rigid in spaced face-to-face relation.

When plastic is employed to form the blocks 21, it has been found advantageous to use linear polyethylene, a polymer of ethylene containing a minimum of branched chains. The greater incidence of linearly arranged chains produces a stiffer, higher density product. Such an arrangement imparts greater structural rigidity to the panel.

When plaster is employed to form the blocks 21a as shown in FIG. 1a, the blocks may be molded directly in the wafile 17. it is to be understood, however, that the plaster blocks may be formed individually and inserted into the waffie openings as described above in connection with the plastic blocks 21.. The plaster blocks 21 are also formed with a projection 22a which extends through the perforation 18. The projection 22a and top of the block 21a are bonded to the face sheets 11 and 13.

When wood is employed to form the connecting structure 15 as shown in FIG. 112, the blocks 21b are preferably cut such that the grain extends normal to the face plates 11 and 13.

Thus, panel is constructed such that it has the desired characteristics of structural rigidity and acoustical limpness to form a sound barrier substantially diminishing the transmission of sound therethrough. When sound originates on one side of the panel as, for example, by speech originating adjacent the side 11, the sound waves strike the face 11. This causes the face 11 to be flexed by the force of the sound wave at points spaced on the surface thereof. This fiexure causes the rigid blocks 21 to move toward the opposite face sheet. However, because the blocks are connected to the faces 11 and 13 at opposite ends and are separated by the wafile 17 the surfaces of which have a low coefiicient of friction, the blocks are free to move relative to each other in a direction normal to the face sheets. This relative movement of the blocks dampens the fiexure of the face sheets such that the face sheets do not vibrate over their entire area but merely bulge or dimple in spaced localized areas somewhat analogous to the action of a rubber sheet when the latter is exposed to sound waves. In other words, the interconnecting structure renders the panel structurally rigid and acoustically limp.

The second embodiment, FIGS. 2, 2a and 2b, there is incorporated into the panel construction a sound absorbing chamber. As shown, the panel includes a pair of spaced stiff side members 11 and 113 made from material similar to that employed in the first embodiment of the invention. To achieve sound absorbing characteristics, the exterior plate 113 which is exposed to the origin of sound, such as for example the sound originating in a radio or television studio, is provided with perforations 115. Adhered by a suitable adhesive to the imperforate plate 11 is a waffie 17 similar in structure to that shown in FlG. l. The openings 23 of the waffle 17 are filled with blocks 121 which are formed With cavities 127 therein rather than being solid as shown in FIG. 1. The cavities 127 provide a series of sound absorbing chambers.

The blocks 121 may be formed of plastic, plaster (blocks 121b in FIG. 2b) or of similar stiff, dense loading material such as wood and may either be preformed and inserted snugly into the openings 23 of the waille 17 or in the case of plaster may be moulded directly in the Waffle itself. A typical block 121 is shown in FIGURE 2a in isometric view. Covering the exterior of the perforate plate 113 to provide acoustic resistance by way of a sound absorptive face is a woven material 129 which, in the preferred form as shown, is fabric or canvas. However, other woven material such as screening or the like may also be employed.

When the sound strikes the composite plate comprising the perforate plate 113 and the fabric covering 129, some of the sound is absorbed by the fabric face and some is entrapped within the cavities 127 of the blocks 121. in this manner, the level of sound reverberations on the perforate side of the panel is reduced. It is to be further observed that the cavity blocks are movable (such as 121 or 1121b) relative to each other along the transverse shear walls of the wattle 17 and function in the same manner as previously described in connection with the first embodiment of the invention under the impact of sound energy such that the mass characteristics of the outer walls and the cavity blocks are retained.

Referring now to FIGS. 3 and 3a illustrating the third embodiment of the invention, the panel is advantageously employed where lightness is a factor in the design. As shown, the panel comprises a solid imperforate plate 11 to which is adhered the compressible polymeric foam waffle 17 heretofore described in connection with the other embodiments of the invention. The opposite plate 113 is preferably perforate, as shown, and covered with a suitable acoustically absorbent fabric covering 12% previously described. The plate 113 may be imperforate in which case, the fabric covering 129 may be eliminated. Mating with the wafile 17 is a rigid honeycomb-like structure 433 having a plurality of spaced hollow rectilinear elements or projections 435 (otherwise described as hollow prisms each having an open end) disposed snugly within the openings of the waffle 17. A bottom wall 437 is adbored to the face 11 by a suitable bonding agent which communicates therewith through the aperture 18. A top wall 439 connects each of the rectilinear elements 435 to form a unitary structure. The connecting Walls 439 overlie the top ridges of the waffle. The honeycomb structure is formed of a rigid plastic such as, for example, a high density polyethylene. It is to be understood, however, that other rigid plastics may also be employed. The connecting walls 439 are adhered by a suitable adhesive to the plate 113. As explained hereto fore, the transverse walls of the wafile provide transverse shear surfaces and are also compressible. Hence, when either face sheet 11 or 113 is flexed by sound Waves, the contacting surfaces of the transverse walls of the watlle 1'7 and the side walls 441 of the rectilinear elements 435 are free to move relative to each other. Because the waffle transverse walls are compressible, the honeycomb walls move substantially transverse to the face sheets 11 and 113 as explained in connection with the embodiment illustrated in FIGS. 1, 1a, and 1!) so that overall vibration of the opposite face sheet is prevented.

In the embodiment disclosed in FIG. 4, the wafiie 17 has been omitted. In this embodiment, only the rigid plastic structure 433 is employed. The connecting walls 439 as shown may be somewhat narrower than the bottoms 437 such that there is a narrow air space between the adjacent walls 441 of rectilinear elements 435'. The rigid plastic honeycomb is adhered to the plate 11 at the bottoms 437 and to the opposite plate 113 at the narrow connecting walls 439. As shown in FIG. 5, adjacent walls 441 are in shear movement during flexure of the plates ill and 113 inasmuch as upon fleXure, the walls 437 and 439 are free to deform as shown in FIG. 5 such that the separated transverse Walls 441 move within the narrow air space 443 and remain in planes transverse to the faces 11 and 113. The perforate face 113 is covered with an acoustic resistant fabric 129 which permits the sound to communicate with the cavity 445. In this manner, the cavities 445 serve as sound absorbing chambers.

What is claimed is:

1. An acoustical panel comprising a pair of spaced rigid side plates, a plastic foam member disposed between said sides and having bottom and top walls with said bottom well only adhered to the inner surface of one of said side plates, a plurality of cavities formed in said plastic foam member defined by side Walls extending transverse to said side plates, and rigid block-s formed of a dense material snugly seated in each of said cavities and bonded to said side plates, said blocks being slidable 6 relative to each other in a direction transversely of said side Walls upon fiexure of said side plates.

2. The invention as defined in claim 1 in which one of the side plates is perforate and each of the blocks is formed with a cavity communicating with the perforations in said perforate plate.

3. The invention as defined in claim 2 in which the outer surface of the perforate plate is covered with a woven acoustic resistance means.

4. The invention as defined in claim 1 in which the blocks are formed from plaster.

5. The invention as defined in claim 1 in which the blocks are formed from linear polyethylene.

6. The invention as defined in claim 1 in which the blocks are formed of wood.

7. An acoustical panel comprising a pair of side plates, means connecting said plates in spaced and face-to-face relation including a foam plastic member secured to the inner face of one of said plates, said foam plastic member having a plurality of substantially rectilinear cavities therein extending in a direction transverse to the faces of said plates, and a substantially rigid honeycomb-like means, said honeycomb-like means having rectilinear projections snugly received in said openings in said foam plastice member, said honeycomb-like means being adhered at its top and bottom to the inner faces of said side plates.

References Cited in the file of this patent UNITED STATES PATENTS 2,069,413 Leadbetter Feb. 2, 1937 2,159,488 Parkinson May 23, 1939 2,184,482 Austin et al Dec. 26, 1939 2,270,902 Rubissow Ian. 27, 1942 2,542,428 Peik Feb. 20, 1951 2,891,036 Stacy et al. June 16, 1959 FOREIGN PATENTS 642,722 Great Britain Sept. 13, 1950 206,535 Australia Apr. 18, 1956

Claims (1)

1. AN ACOUSTICAL PANEL COMPRISING A PAIR OF SPACED RIGID SIDE PLATES, A PLASTIC FOAM MEMBER DISPOSED BETWEEN SAID SIDES AND HAVING BOTTOM AND TOP WALLS WITH SAID BOTTOM WALL ONLY ADHERED TO THE INNER SURFACE OF ONE OF SAID SIDE PLATES, A PLURALITY OF CAVITIES FORMED IN SAID PLASTIC FOAM MEMBER DEFINED BY SIDE WALLS EXTENDING TRANSVERSE TO SAID SIDE PLATES, AND RIGID BLOCKS FORMED OF A DENSE MATERIAL SNUGLY SEATED IN EACH OF SAID CAVITIES AND BONDED TO SAID SIDE PLATES, SAID BLOCKS BEING SLIDABLE

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