US3058411A

US3058411A - Ventilated ceiling constructions

Info

Publication number: US3058411A
Application number: US863005A
Authority: US
Inventors: Frederick L Hanson; William A Jack
Original assignee: Johns Manville
Current assignee: Johns Manville Corp; Johns Manville
Priority date: 1959-12-30
Filing date: 1959-12-30
Publication date: 1962-10-16
Anticipated expiration: 1979-10-16

Description

1952 F. HANSON ET AL 3,058,411

VENTILATED CEILING CONSTRUCTIONS Filed Dec. 50. 1959 INVENTORS Fasocmcn L. HAusou BY WILLIAM AJAcK Unite States atent fiice 3,058,411 Patented Oct. 16, 1962 This invention relates to ventilated acoustical ceiling constructions; more particularly, it relates to an acoustical construction comprising false ceilings for room compartments and a common plenum chamber thereabove, and which construction utilizes the common plenum chamber as a ventilating duct, with provision being made in the false ceilings for the absorption of sound and the passage of ventilating .air into or out of the common plenum chamber.

In many ventilating and acoustical constructions, wherein false ceilings are used to enhance the esthetic eifect of room interiors and to provide for sound absorption, it has become quite common to utilize the plenum chamber formed between the false ceilings and a base construction, such as, for example, the true ceiling or the basic framework of a building, as a return or a supply conduit for ventilating air. Since the basic framework of a particular building, including the main bearing portions, is ordinarily constructed long before the individual room compartments are formed, the walls of the individual room compartments need not extend fully to the basic framework ceiling, but only to the false ceiling or slightly thereabove. As a result, the plenum formed between the false ceilings and the overhead basic structure is common to a plurality of room compartments. Where such a plenum chamber is used as a return or supply duct or conduit for ventilating air and flow passages are provided in the false ceiling for the ingress or egress of ventilating air, sound waves are capable of escaping from a room interior through the flow passages in a suspended ceiling, thereby to pass through the plenum chamber and the grillwork in an adjacent room compartment, and to enter such adjacent compartment. Thus, in a sense, where a common plenum chamber exists between a plurality of room compartments, such compartments are not necessarily acoustically sealed one from the other if the chamber is used as a fluid conduit.

In brief, the present invention comprises a perforated false ceiling suspended from a base construction to form a plenum chamber therebetween, which chamber is common to a plurality of adjacent room compartments and is used as a fluid duct of a conditioning system. Sound absorbing pads are superposed over a major portion of each false ceiling, .and sound traps are provided over selected areas of each false ceiling, not covered by a sound absorbing pad; the remaining areas comprise conventional structure, as, for example, lighting troughs, irnperforate pans, and the like. Each sound trap has provided therein an effective passage therethrough for ventilating air, so that effective pneumatic communication is obtained between each room interior and the common plenum chamber. In addition, each sound trap isso constructed that the sound waves tending to escape through the fluid ducts within the trap are effectively absorbedythereby blocking off the passage of such sound waves from one compartment to an adjacent compartment via the common plenum chamber and the air distributing means of the adjacent compartment.

An object of the present invention therefore is to provide a novel ventilating and acoustical ceiling having a plenum chamber thereover.

An additional object of this invention is to provide a ventilating and acoustical ceiling having thereover a plenum chamber utilized as an air conduit, with sound traps provided in the ceiling which allow the proper flow of air therethrough and which also absorb the sound tending to escape or pass through the air passage means within the ceiling to an adjacent room compartment via the common plenum chamber.

Still an additional object of this invention is to provide a suspended ventilating and acoustical ceiling having a plenum chamber thereover utilized as a fluid conduit and having simple but effective sound traps therein which provide for the passage of ventilating air therethrough and at the same time effectively .absorb the sound waves received by such sound traps.

Still an additional object of this invention is to provide a ventilating and acoustical ceiling having sound traps therein which allow the passage of ventilating air therethrough and also provide for eifective sound absorption, wherein the ceiling need not be specially adapted to accommodate the traps, thereby permitting to be maintained a consistent design pattern or esthetic appearance produced by the members comprising the false ceiling.

These and other objects will be readily apparent from the preceding brief description and the following more detailed description and appended drawings wherein:

FIG. 1 is a cross-sectional, perspective view of a plurality of room compartments showing primarily the ceiling of the present invention;

FIG. 2 is an enlarged perspective View, in cross-section, of an exemplary embodiment of the sound trap used in j the ventilating and acoustical ceiling illustrated in FIG.

1; and

FIG. 3 is a perspective view, partially broken away for purposes of clarity,'of an additional exemplary embodiment of a sound trap capable of being used in the ceiling illustrated in FIG. 1.

Referring to FIG. 1, the basic framework 1 of a building, in its simplest form, comprises a plurality of walls 1b supporting a ceiling 1a. For the purposes of this invention, the ceiling 1a may be considered to be the true ceiling of a room interior, even though the ceiling may be open, as, for example, when it is comprised of only the basic girder or joist construction. The area enclosed by the basic framework 1 can be divided into a plurality of individual room compartments by the erection of a plurality of partitions 2, where necessary, and the provision of false ceilings 3 for the wall enclosed areas. The ceilings may be suspended from the true ceiling 1a in any conventional manner, such as, for example, by the suspension system disclosed in United States Patent, Serial No. 2,401,906, issued to C. B. Burnett et al., on June 11, 1946.

Each ceiling 3 may comprise a plurality of sheet-like members 5 juxtapositioned in a manner so as to form a planar type ceiling. The members may be in true sheet form, or the members may comprise a plurality of panlike members supported from the basic framework 1. in the exemplary false ceiling construction disclosed herein, the members 5 are of the pan-like type, as, for example, disclosed in United States Patent, Serial No. 2,334,484, issued to J. Y. Dunbar on November 16, 1943. It is to be understood, however, that numerous other types of individual ceiling members may be used without departing from the scope and intent of this invention.

The members 5 are perforated at least over the visible portions thereof and have superimposed thereover, except for selected areas swbjacent the sound traps, a layer 6 of sound absorbing material. The latter absorbs the sound waves emanating from the room interior and passing through the perforations 5a in the ceiling members 5. The layer 6 comprises a plurality of individual sound absorbing pads 7 situated within each of the pans of the ceiling 3. The pads are of the type, for example, shown in United States Patent No. 2,401,906 or in United States Patent No. 2,357,115 issued to W. A. lack, Bid, on August 29, 1944.

If desired, selected pans may be removed from within the false ceiling and replaced by lighting troughs 5b, usually of the type which are adapted to be received precisely within an area covered by one or more pans.

The plenum chamber 4 formed between the false ceilings and the true ceiling is common to the exemplary room compartments 2b, illustrated. Such chamber is therefore adaptable to be used as a fluid conduit, in the event an air conditioning system is used as the heating and cooling system. to condition the room interiors. For example, the ventilating heating or cooling air may enter the room compartments through a supply grill 14 from a pressure source, such as a circulating fan, and exhaust into the common plenum chamber 4 through selected areas of the false ceiling via the perforations 5a therein, which areas have removed therefrom the superposed sound absorbing pads. From the chamber, the air can be directed to a conduit 15 by an exhaust fan (not shown) and returned back to the conditioning apparatus and the blower system for resupply to the

room compartments

2b, 20.

However, with such a plenum chamber duct system, the air is not only eflfectively passed through the ceiling, but a portion of the sound Waves emanating from room 21), for example, is also undesirably permitted to escape through the fluid exhaust areas within the ceiling. These waves also travel through the common chamber 4 and enter chamber 20, for example, through a fluid exhaust system within its ceiling 3. In order to provide a proper fluid flow system within the ceiling and to suppress or absorb such escaping sound waves, a sound trap 8 is utilized over selected areas of the false ceiling 3, while the remainder of the ceiling is superposed by the sound absorbing pads.

In an exemplary embodiment thereof, referring to FIGS. 1 and 2, the sound trap comprises a block of sound absorbing material of a size suitable to fit Within a pan 5. For example, since the pans are ordinarily 12" x 24-, the block 8 is slightly less than 12" x 24 in order to be received within the upturned edges of the pan. The trap 8 was laminated from a plurality of relatively thin layers of sound absorbing material; in the exemplary embodiment shown, four layers, 9, 10, 11, and 12, were used, each of which was approximately 1" to 1% in thickness. A plurality of openings or ports 13 were formed completely through the laminated block, each of which was /2 in diameter, with 180 holes being formed therein. In an ordinary room compartment, for example, approximately 14 x 14, or thereabouts, one or two sound traps acting as connecting ducts are all that are ordinarily necessary to accommodate the flow of air therethrough. The particular size of the holes and the number of holes are not critical and are governed by the amount of air necessary to be passed through the sound trap. However, the size and number of the holes should be such that an appreciable fluid pressure drop is not created; at the same time, the holes should not be so large as to freely permit the passage of soundwaves therethrough without appreciable absorption thereof.

Where the common chamber 4 is used as an exhaust duct, a pressure differential must be maintained between the chamber and the room interior to provide for the proper air circulation. However, such a differential not only continually passes air through the sound trap but also leaks air through the openings between panels 5 subjacent the sound absorbing pads 7. Although the rate of air leakage is relatively minute, over an extended period of time such leakage will cause contamination of the finished false ceiling adjacent the openings. To eliminate such contamination and also to provide for fiow primarily through the sound trap and the pans subjacent the trap only, whereby the openings of the sound trap may be precisely designed for a particular flow of air, an air impervious septum 30 is superposed over the sound absorbing pads. Such septum prevents the flow of air through and around the pads and through the perfor-ations in the subjacent pans 5. The septum 30 may be a kraft paper, for example, applied as a continuous sheet over the sound absorbing pads or as individual sheets over the individual pans. Numerous other types of septums may be utilized, if so desired, as, for example, sheets of metal, aluminum foil, and sheets of plastic material. With sheets of metal or foil, an additional advantage is obtained in that such sheets may be used as sound attenuation members, assisting to prevent sound waves from entering the plenum chamber or, if they are within the plenum chamber, from passing therefrom into subjacent room compartments. Where the common cham ber 4 is used as an air supply duct, the septum 30 can also be used, as it assists to confine the flow through the sound trap.

In an additional exemplary embodiment of the sound trap of the invention and where, as in the previous embodiment described, pans 5 are utilized to form the false ceiling, a layer 20 of sound absorbing material is seated within each pan receiving a sound trap (FIG. 3). The layer may be of the same over-all size and of the same type as the size and type of sound absorbing pads 7 of FIG. 1. A plurality of relatively large openings 21 were made in the layer, which openings act as fluid conduits for the air passing into or out of the room interior. In the instant embodiment, three square cut-outs were formed, each of which was 3 on a side. A plurality of small blocks 22 were centrally located along the edges of the sound absorbing layer 20, and a second layer 25 of sound absorbing material was rested upon the blocks to be spaced from the first layer 20 a distance equal to the thickness of the blocks 22. The layer 25 was comprised of a pair of laminated sound absorbing pads 26, 24, each of which can be made from the same material and be of the same overall size as the sound absorbing pads 7 in the remaining pans of the ceiling.

When the common plenum chamber 4 is used as an exhaust duct, the air exhausting from the room interior passes through the perforations 5a of the pans containing the sound trap, flows through the ducts 21, is deflected transversely to the edges of the superposed layer 25 and enters the common plenum chamber 4. The sound waves received by the sound trap through the perforations 5a are for the most part initially absorbed by the first layer 20. The sound waves entering duct 21 are absorbed partially by the side walls of the duct and partially by the superposed layer 2'5. Since the layer 20 is approximately the same thickness as the thickness of the adjacent pads 7, the outlet passages adjacent the edges of the sound trap are sufliciently above the adjacent pads 7 and the overlying septum 30, so that a relatively free flow of air occurs over the pads and septum and no appreciable pressure drop or restrictions to flow are created.

In each of the exemplary embodiments disclosed, the sound trap is approximately four times the thickness of the adjacent pads. Since a simplified construction is used, the sound trap will usually be quite thicker than the adjacent pads, ranging usually between approximately 2 to 4 times thicker than the adjacent pads. In the exemplary embodiment illustrated in FIG. 2, the thickness of the trap was four times the thickness of the adjacent pads 7, since four layers, each layer of which is basically similar to an adjacent pad 7, are used. In the exemplary embodiment illustrated in FIG. 3, each layer was basically the same as an adjacent pad. The thickness of the layers taken with the spacing maintained for the proper air flow, resulted in a thickness of the trap also approximately four times the thickness of any adjacent pad.

The theory of sound absorption between the two traps is the same even though the constructions differ slightly from each other. In the trap of FIG. 2, sound absorption is obtained by the length of travel of the sound waves through the openings 13. During the passage of a wave through an opening, the wave is gradually absorbed along the length thereof. In thetrap of FIG. 3, very little absorption is obtained during passage of a sound wave therethrough, since the openings 21 are quite large. Most of the sound absorption is obtained when a wave encounters the direct obstacle in its path of travel, which is the superimposed sound absorbing layer 25.

Any escaping sound waves must, of course, pass through a pair of sound traps before entering an adjacent room compartment. Thus, a sound wave emanating from compartment 2b, for example, must pass through a sound trap in the ceiling of this compartment before it can enter the common chamber 4. The at least partially absorbed wave, if it is to enter the compartment 20, must also pass through a sound trap 8 in the false ceiling of that compartment. In the event an air impervious septum 30 is not used, additional sound absorption of the wave is also obtained during the waves travel through the common chamber.

With either basic acoustical approach noted, one of the marked advantages of the present invention is the fact that the sound trap may be fabricated from materials similar to the sound absorbing pads or from other materials of a similar nature also commonly used in sound absorbing installations, the pads of which materials are usually readily available in standard sizes. For example, in the embodiment illustrated by FIGS. 1 and 2, the sound absorbing pads 7 were fabricated from mineral wool having a density of approximately 34 pounds per cu. ft.; however, other pads having densities below pounds per cut. ft. are commercially available in many standard sizes and may be used. The relatively homogeneous sound trap 8 was fabricated from a glass fiber type of acoustical pad of a density of approximately 3 pounds per cu. ft. Pads of this type were used for the sound trap, as they could be worked somewhat easier than the mineral wool pads. The glass fiber type pads are similarly available in a range of densities below 10 pounds per cu. ft. and in many different standard sizes.

An additional advantage of the present invention is the fact that the proper sound absorption and air flow is provided for with either type of sound trap described without disturbing the continuity and esthetic effect of the false ceiling. Thus, the areas of the ceiling used as fluid conduits need not be modified in any way to accommodate the air flow into or out of the plenum chamber 4. This is particularly important in relatively large installations, wherein the ceiling continuity is often maintained according to a basic design of ceiling in one room compartment.

Moreover, it is quite common in oifice installations to alter the size and/or number of room compartments from time to time by changing the position of the nonload bearing partition walls. With such changes, it is necessary only to relocate the sound traps, where required, without corresponding relocation of the subjacent perforated member 5.

While the invention has been described in rather full detail, it will be understood that these details need not be strictly adhered to and 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. For example, the efliciency of the system may be increased slightly by the use of an air impervious septum 30 having sound reflective characteristics. Sound waves attempting to leak into the plenum chamber from a room interior through the gaps between adjacent pans or sound waves passing through the pads not completely absorbed thereby find this additional sound barrier in their path. In addition, sound waves passing through the plenum chamber cannot leak into a room through the openings between the pans, but are reflected back by the sound reflective septum.

What we claim is:

1. A ceiling construction for a room conditioned by ventilating air comprising a base ceiling, a plurality of perforated sheet-like members supported from said base structure to form a suspended false ceiling, sound trap means superposed over selected areas of said sheet-like members, sound absorbing pads having a predetermined thickness superposed over the remaining areas of the sheetlike members to absorb the sound passing through the perforations in the subjacent members, said pads being substantially air impervious thereby impeding the flow of air between the areas above and below the false ceiling through the subjacent pans, each of said trap means comprising a body of sound absorbing material having an over-all thickness of approximately 2-4 times the thickness of the pads, and said trap means having continuous perforations through the body of sound absorbing material permitting the passage of ventilating air through the body of material while absorbing the sound passing therethrough.

2. The ceiling construction of claim 1 wherein the sound absorbing pads are superimposed by an air impervious septum to prevent the passage of air through the perforations in the members subjacent the pads.

3. The ceiling construction of claim 1 wherein the perforated sheet-like members comprise a plurality of perforated metallic bands.

4. A ceiling construction for each of a plurality of adjacent room compartments conditioned by ventilating air comprising a base structure, a plurality of sheet-like members having perforations therein suspended from said base structure to form a false ceiling in each compartment, said ceilings being spaced from the base structure thereby forming a common plenum chamber over the room compartments, with said chamber being used as a fiu-id duct for the conditioning air, sound trap means superposed over selected areas of the sheet-like members of each compartment false ceiling, sound absorbing pads superposed over the remaining areas of the sheet-like members said pads being air impervious thereby impeding the flow of air between the plenum chamber and the room compartment through the subjacent pans, said sound trap means having openings therethrough acting as a connecting fluid duct between the room interiors and the common plenum chamber, said sound trap means being comprised of sound absorbing material having a density below about 10 pounds per cu. ft. and being at least several times greater in overall height than the height of the sound absorbing pads, said sound trap means effectively preventing the transmission of sound between room compartments while allowing conditioning air to pass therethrough.

5. A ceiling construction for a room conditioned by ventilating air comprising a base ceiling, a plurality of sheet-like members supported from said base ceiling to form, a suspended false ceiling, sound trap means superposed over selected areas of said sheet-like members, sound absorbing pads superposed over the remaining areas of the sheet-like members to absorb the sound passing through the perforations in the subjacent members said pads being substantially air impervious, each of said trap means comprising a homogeneous mass of sound absorbing material formed from .a plurality of juxtapositioned layers of sound absorbing material, and said homogeneous mass having a plurality of relatively large size openings formed continuously therethrough allowing the ventilating air to pass therethrough and through the subjacent perforations in a sheet-like member, and said relatively large size openings being lined by sound absorbing material so as to assist in effectively absorbing the sound Waves encountered by said body of material while permitting the ventilating air to pass therethrough.

6. A ceiling construction for each of a plurality of adjacent room compartments conditioned by ventilating air comprising a base structure. a plurality of perforated sheet-like members suspended in each compartment from said base structure .to form a false ceiling in each compartment, said ceilings being spaced from the base structure thereby forming a common plenum chamber over the room compartments, said chamber being used as a fluid duct for the ventilating air, sound trap means superposed over selected areas of the sheet-like members of each compartments false ceiling, sound absorbing pads superposed over the remaining areas of the sheet-like members, said sound trap means comprising a body of sound absorbing material having an over-all thickness of approximately two to four times the thickness of the pads and having continuous passages therethrough permitting the passage of ventilating air through the body of material while absorbing the sound passing therethrough, and means superposed over the sound absorbing pads assisting to prevent the leakage of air through adjacentpads and also assisting to attenuate the sound attempting to pass from one compartment to another via the common plenum chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,705,778 Munroe Mar. 19, 1929 2,172,771 Norris Sept. 12, 1939 2,180,945 Morey Nov. 21, 1939 2,587,884 Palmer Mar. 4, 1952 2,692,547 Ericson Oct. 26, 1954 2,718,383 Frenger Sept. 20, 1955 2,973,703 Jack Mar. 7, 1961