US 3111188 A
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Description (OCR text may contain errors)
Nov. 19, 1963 w. REES ETAL ACOUSTICAL TILE Filed Feb. 26, 1960 s 0 1 $5M M30 Em //v MEG m E n 5 w. N IM w 0 B Y /N 1 W 5 f 0 E w v r w w 5 "WV/U1 u m do F 7 M m m m N 2 United States Patent 1 3,111,188 ACOUSTICAL TILE Willis M. Rees and Donald N. Huggins, Newark, Ohio,
assignors to Owens-Corning Fiberglas Corporation, a
corporation of Delaware Filed Feb. 26, 1960, Ser. No. 11,222 2 Claims. (Cl.18133) This invention relates generally to sound absorbing panels or acoustical tiles for mounting upon walls or installed upon or to form ceiling structure. The invention pertains particularly to tiles adapted (for mechanical suspension as sound absorbing and transmission reducing media above adjacent rooms and spaced below a main ceiling structure.
Such acoustical tiles are customarily compressed panels of wood fibers, shredded wood, wood pulp, cane fibers, cork granules, gypsum, rock wool or glass fibers. A popular size is twelve by twelve inches in broad dimensions and one-half inch thick. The tiles are also available in thicknesses up to two inches and with planar dimensions in multiples of twelve inches.
Those of lighter weight when no larger than twelve inches square are most commonly attached directly to wall and ceiling surfaces by spots of adhesive. These light tiles as well as the larger panels are frequently secured to wood furring strips by nailing or stapling.
In ceiling treatment of offices and other commercial establishments, the acoustical tiles are frequently installed upon a grid suspension system hung below the original ceiling structure. This arrangement may improve the dimensional proportions of a room as well as add to the attractiveness of the ceiling. The air space or plenum above the sub-ceiling of tiles also contributes to the sound deadening properties of the installation.
In business offices, such a suspended acoustical Ceiling extends over, in contact with partitions between rooms which generally reach up to the level of the tiles and may in some instances interrupt the suspended ceiling and extend above it. For purposes of preserving the privacy of the individual ofiice areas, the intervening partitions should be of a nature to reduce sound transmission there through preferably as much as thirty-five decibels. This rating indicates a loss in transmission sutiicient to reduce the loudness level from one side to the other side of the wall the specified number of decibels. Decibel units are conventionally used to roughly indicate the response by the ear to noise and are equal in number to ten times the logarithm of the ratio of the intensity of the sound in watts per square centimeter to the standard reference intensity of watts per square centimeter at the low limit of human perception.
Of the various commercial acoustical products available, those of mineral fibers, particularly glass fibers, are most highly regarded. Their sound absorption is very effective because of the porosity derived from the high number of communicating air cells in the maze of fibers. In contrast to tiles of organic components, they are non combustible and unaffected by moisture. They also have the advantage of lightness in weight as well as superior sound absorbing capacity when compared to panels of cellulose or to boards of inorganic materials.
When acoustical tiles are applied to walls and directly upon a ceiling surface, the transmission of sound energy through the tiles is ordinarily not of serious consequence as the further travel of the sound is quite eifectively curtailed by the mass of the structures upon which they are mounted.
However, where the tiles are suspended below the regular ceiling, there is normally no member to prevent the continued upward movement of sound waves traveling through the tiles. This piercing action may not be too serious with the more solid type of panels such as the more compact organic products and those of gypsum as these panels are not so easily penetrated by the sound waves. This factor of greater density is, of course, mainly responsible for their lower eifectiveness in sound absorption, the principal function of such products.
Acoustical tiles of bonded fibrous glass have noise absorbing coefficients as high as .90. This coefficient is the fraction of complete absorption of incident air-borne sound. Being highly porous these panels of glass fibers allow a certain proportion of sound energy to pass therethrough. This permeable property is objectionable in false ceiling installations above adjoining rooms which are otherwise quite satisfactorily acoustically separated by partitions and by close fitting doors.
In such a situation, the sound waves emerging upwardly from the tiles covering one room, upon impinging against the surface of the permanent ceiling are reflected down and enter the adjacent room through the tiles thereover. If of sufficient intensity, this transmitted sound may not only be annoying, but may also carry conversation of a confidential nature.
This problem may be minimized by backing the tiles of glass fibers with gypsum or other heavy plaster boards. The sound movement is thus considerably reduced. However, the added cost of both the extra material and installation labor is commercially objectionable.
It is accordingly a prime object of this invention to provide a low cost acoustical tile of mineral fibers, and one preferably of glass fibers, adapted for mechanical suspension and which adequately curtails the transmission of sound waves while retaining excellent properties of sound absorption.
A further object of the invention is to provide a panel of mineral fibers which not only possesses top capability to absorb sound and reduce sound transmission, but is also light in weight.
More particularly, it is an object of this invention to provide a panel of mineral fibers which has on its rear face an integrated and impervious coating of paint.
Still more specifically, it is an object of this invention to provide ceiling treatment for partitioned rooms in which panels of mineral fibers, having a sealing coat on their rear faces, are suspended below a common air space above such adjoining rooms.
The objects of this invention are primarily attained through the placing of an impervious layer of paint on the back side of otherwise standard types of acoustical tiles or panels of bonded glass fibers.
Experience would indicate that quite a heavy rear sealing coat would be desirable. However, this invention utilizes the surprising discovery that an acoustical tile of fibrous glass with a very light coating reduces sound transmission through a suspended ceiling in which it is incorporated much more than would ordinarily be expected from the mass of the tile and the sealing coat.
The invention will be more [fully understood and further objects and advantages thereof will become apparent when reference is made to the more detailed description which follows and to the accompanying drawings in which:
FIGURE 1 is a perspective View of a tile, with a portion of the surface coating there-of broken away, embodying this invention;
FIGURE 2 is an isometric view of part of a room in which tiles such as the one pictured in FIGURE 1 are suspended in adjoining series; and
FIGURE 3 is a vertical section, on a reduced scale, showing the tiles suspended above two adjoining offices.
Referring to the drawings in more detail, .the panel or tile 10 of FIGURE 1 has a main body portion 12 composed of bonded glass fibers.
From the standpoint of lightness and acoustical efiec- 9 a tiveness of the body portion 12, glass fibers of a diameter in the range between twelve and twenty-two hundredthousandths of an inch serve most satisfactorily. Fibers of still smaller diameters would enhance some properties of the product, while fibers of larger diameters, up to more than seventy hun-dred-thousandths, give quite adequate results and may be more practical for some commercial purposes.
The size of the fibers is determined by the type and control of the forming equipment utilized. Such appara tus ordinarily employs air, steam or combustion gases for attenuating molten threads of glass issuing from small orifices. However created, the fibers are collected at the forming station in blanket form with an uncured binder component dispersed therethrough.
A resin combination of melamine and phenol formaldehydes, in a proportion of roughly one to two, successfully meets these requirements. The amount of binder may run between nine and twenty-six percent by weight of the finished panel, depending upon the balance desired between strength and fire protection in the product. Various other fibrous glass bonding agents are well known and would be quite equally effective. These include epoxy, urea, and polyester resins.
The density of the fibrous body portion of the tiles generally runs between nine and fourteen pounds per cubic foot as compared with densities from fifteen to twentyfour pounds per cubic foot for the panels of compressed cellulosic fibers.
Upon the upper or back surface of the tile shown in FIGURE 1 is a paint coating 1-4 broken away at 14a to show the underlying fibrous body '12. In order to limit the cost, this sealing paint may be a water emulsion, pigmented with a clay filler and with just sufiicient binder, such as polyvinyl acetate, to "hold the pigment particles together and to close the pores.
A more resinous composition providing the coating with appreciable elasticity may also be used. However, such a composition would lower fire safety and might not be economically feasible for general merchandising purposes. Whatever formulation is selected, the coating may be applied in a comparatively small quantity having a dry weight of no more than twenty-five or thirty grams per square foot. The weight of the coating is not critical, but it has been found that a light coating is quite equally effective as a much heavier layer of paint on the back of a fibrous glass panel. Cost may thus be held to a minimum without loss of function.
Most depositing means including spray equipment, brushes and rollers are feasible. Care should be taken, however, to insure uniform attachment of the coating as this is important.
The opposite or front face of the tile may be covered with a porous film 15 of paint with decorative and light reflecting properties. This paint has little resin, latex or other binding component as these ingredients would tend to make the coating impervious to air. Porosity is required to permit the entry of sound waves into the absorbing panel of glass fibers.
In FIGURE 2 tile such as that disclosed in FIG- URE 1, are: mounted in adjoining series on inverted T- beams 18 which are hung by wires 19' from joists or other elements 20 of the standard ceiling 22 of the enclosure. The tiles are supported along the side wall 24 by an angled bracket 25. As indicated, it may be necessary to trim the tiles to a reduced width to fit them into the final space along a wall area.
In FIGURE 3 is shown diagrammatically a fioor section 28 and a partition 29 separating two oflice rooms below the suspended ceiling system depicted on a larger scale in FIGURE 2. While the partition here extends above the tiles, ordinarily the tiles would lay across the top of the partition. As indicated the tiles 10 are arranged with the sides having the decorative porous facing directed downwardly and with the impervious coating 14 on the 4 upper sides of the tiles in opposing and spaced relation with the permanent ceiling structure 22.
It will be presumed that the partition 29 is in itself a satisfactory sound barrier between the rooms which it separates. For instance, it may be constructed of masonry plastered on each side. If the joints around it are tight, this wall should then have an average transmission loss in the region of thirty-five to forty decibels.
This curtailment of sound travel is sufficient to reduce the noise level of loud conversation to that of quiet whispering. It would also be the equivalent to the difference between the level of an average otfice with typewriters and that of a quiet living room.
Since this partition does not extend up to and join the standard ceiling structure, sound would travel between the rooms above the partition unless this transmission path is otherwise blocked. As previously stated conventional acoustical tiles of mineral fibers are not effective as a barrier for this purpose.
However, with the tiles 10 constructed according to this invention installed in the suspended ceiling, a sound transmission loss may be attained approaching that provided by the heaviest acoustical panels now commercially available.
It should be considered, however, that there are two separate ceilings of the suspended back-sealed tiles through which sound must pass in either direction and that their suppression action is additive with each contributing an important part.
Either with or without the back sealing layers upon the panels, the transmission loss would vary depending upon the size of the upper air space and the nature of materials of the standard ceiling, but without the back sealing layers the loss could be no more than fourteen decibels, under ordinary conditions.
It may be concluded therefore that the addition of the seal-ing coat may be employed to increase the sound transmission loss through this overhead path as much as three or four hundred percent. This transmission loss is superior to that accompanying the use of the heavier, less absorbent panels of organic fibers. At the same time the sealed panels of mineral fibers retain their original light weight, and their superior sound absorbing performance is affected, at most, to only a slight degree.
It is natural that better noise isolation is secured with acoustical tiles back-sealed according to this invention with panels of increasing thickness. This is due to the greater absorption provided by the extra depth. Also, extra heavy sealing layers may slightly improve the sound shielding action of the tiles because of the added mass.
Experience has shown that reduction of sound transmission is obtained by increasing the mass per unit area of a partition, by constructing the partition of material having large viscosity for bending, or by the use of double partitions, vibrationally isolated.
The addition of mass to the sealing layers of the tiles of this invention has, as mentioned, limited possibilities. Reliance on effective performance has been placed principally on constructing the sealing layers with low vibratile properties. Also it is concluded that the two separate ceilings of the back coated tiles contribute to transmission reduction by acting as double partitions, vibrationally isolated.
While the invention has been described in connection with tiles having a porous, decorative paint deposit on the outer facing, it is also quite equally suitable for tiles having a tight, washable outer coating of paint with spaced holes, through which sound waves are admitted. Likewise, the rear sealing layer may be applied to tiles faced with an unattached film which transmits sound by vibration to the tile interior as well as to tiles with the outer facing left unfinished.
Having described the invention in detail and with reference to particular materials, it will be understood that such specifications are given for the sake of explanation,
and various modifications and substitutions other than those cited may be made without departing from the scope of the invention as defined in the following claims.
1. A building structure including two adjacent rooms, a common permanent ceiling above the two rooms, and a partition having low sound transmission properties between the roorns and terminating upwardly substantially below the permanent ceiling, said structure characterized by a sub-ceiling above each room and fitting against the partition, each sub-ceiling being composed of series of abutting acoustical tiles of mineral fibers, said tiles having sound admitting facings, porous bodies of high sound absorbing capacity and rear sealing coats of sound blocking properties, whereby sound originating in one of the rooms is heavily damped upon entering the tiles and is restrained by the rear sealing coats from passing through the tiles and traveling over the partition into the other room.
2. A building structure including two adjacent rooms, a common permanent ceiling above the two rooms, and a partition having low sound transmission properties between the rooms and terminating upwardly substantially below the permanent ceiling, said structure characterized by a sub-ceiling extending over both rooms in sealing connection with the top of the partition, the sub-ceiling being composed of series of abutting acoustical tiles of mineral fibers, said tiles having sound admitting facings, porous bodies of high sound absorbing capacity and rear, thin sealing coats of paint of sound blocking properties, whereby sound originating in one of the rooms is heavily damped upon entering the tiles and is restrained by the rear sealing coats from passing through the tiles and traveling over the partition into the other room.
References Cited in the file of this patent UNITED STATES PATENTS Re, 24,658 Hollister June 16, 1959 1,697,521 Collins Jan. 1, 1929 1,950,420 Stitt Mar. 13, 1934 2,022,161 Spafford Nov. 26, 1935 2,028,180 Arnold Jan. 21, 1936 2,046,296 Roos et a1. June 30, 1936 2,086,433 Prudden July 6, 1937 2,177,393 Parkinson Oct. 24, 1939 2,221,001 Lucius Nov. 12, 1940 2,694,233 Page Nov. 16, 1954 2,920,357 Ericson Jan. 12, 1960 2,931,468 Keller Apr. 5, 1960 3,058,411 Hanson et a1. Oct. 16, 1962