US2362859A - Acoustical building element - Google Patents

Description

NOV- 14 1944 M. c. RosENBLATT ACOUSTICAL BUILDING ELEMENT Filed Dec. 3l, 1940 INVENTOR MAURICE C. ROSENBLATT to outweigh the advantages.

Patented Nov.l 14, 1944 ACOUSTICAL BUILDING ELEMENT Maurice c. Rosenblatt, Philadelphia, Pa.

Application December 31, 1940, Serial No. 372,555

(Ci. 'l2- 18) 3 Claims.

This invention relates to acoustical building elements, pertaining particularly to tile-like structures to form a superficial surface of the interior structure of compartments such as rooms.

There have been many eil'orts in the past to vprovide the complete answer to all acoustic problems in a single structural component, but as so far developedk each has been possessed of certain undesirable attributes to balance and frequently While some materials have been used possessed of an apertured or porous surface, in the main the method of approach to the problem has been fairly similar in that an apertured supporting surface has been provided, the most popular of which, perhaps, has been a sheet metal pan, Ibehind which soundabsorbing material has `been disposed, or a material the practical embodiments of which have failed to attain the utmost in eiiiciency, either because of inability to comport with the architectural scheme, because of inefficiencies in the sound-absorbing properties of the construction, because of the unduly high cost entailed in such constructions or because of diiilculties in attaching same.

So far as I am aware the best construction having the most imiversal adaptability in the prior art was the form of building element disclosed in my Patent #2,002,510 of May 28, 1935. This disclosed a tile made of gypsum or the like as a molded unit having shallow flaring internal reinforcing ribs arising from an apertured face, upon the rear face of which, and upon and over- Lving the ribs, sound-absorbing material was more or less loosely deposited as a subsequent processing step. As pointed out in that patent the sheet metal pan with punched perfor-ations in its face, as extensively used in the art, also was more or less loosely filled with appreciable depths of absorbing material, was difficult of application, had a high resonance response, was subject to corrosion and rust, and, due to its electrical conductivity necessitated great care in use in ceilings adjacent to lights or conduits. Such sheet metal tile were primarily adapted for original insulation of hung ceilings only and were not well adapted for use upon side walls. The sheet metal pan also formed a poor base for subsequent painting operations as the paint film frequently became loose at the edge of the perforations, it is difficult to paint white or near white and if it became chipped or msted was diilicult to relinish. The sheet metal pans, being of thin unreinforced material will not remain planar and an outstanding objection to the sheet metal pan is the fact that its application is not conformable with the normal building trades practices. This finds expression in the difficulty in fitting sheet metal pans into spaces of less than pan area.

All of the tile of the prior art have required great depths or thicknesses of the sound-absorbing material for proper sound absorption and this has been ineiiicient both from the standpoint of thickness and from the standpoint of distribution with relation to the whole area, and the costs have therefore .been relatively very high.

It is among the objects of this invention to improve acoustic elements; to provide a selfcontained rigid strong molded tile; to provide a molded tile for acoustic purposes comprising a plurality of cells flaring from th e apertures in the surface of the cells as receptors for friction- -ally held absorbing material pads; to provide an acoustic tile comprising a plurality of individually resonating bells, cells, funnels, or chambers, to absorb the sound energy, with means to damp the vibrations of such bells, etc.; to provide an acoustic tile which can be cemented to a ceiling or wall; to provide an acoustic tile which is fire proof and is omamentally attractive; to provide an acoustic tile of molded plaster of great strength and resistance to fracture which can be shipped. great distances with safety; to provide a tile which can be either cemented with a proper adhesive or is susceptible to mechanical attachment to walls or ceilings or to suspended metal furring; to provide an acoustic tile with a webbed or gridironed concealed face to secure an improved keying with cement; to provide an acoustic tile having a plurality of rearwardly directed cells each filled with frictionally held absorbing material, capable of manipulation, shipping and attachment as a complete self-sustained unit; to provide improvements in the edged surfaces of tiles which conduce toward easy and secure attachment with juxtaposed tiles in close abutting relation; to provide a tile with fastening devices such that breathing between adjacent tiles of a series is precluded on all sides of, as well as through, the tile; to provide a tile `having an apertured face with sound-absorbing material automatically spaced from the face a distance sufficient to preclude absorption of paint into the material through the apertures; to provide a tile with mineral wool absorbing material in such relation to an apertured face of the tile as to whiten the shadow of the perforations to improve the appearance of the tile by reducing contrast between the light face of the tile and the ordinary darkness caused by the perforation and cavity behind it; to provide a tile with a plurality of cell walls of such relative adlacency as to secure a reflective action upon incident sound energy to reilect it into sound-absorbing material in such a way that the depth oi material used may be sharply diminished; to provide an acoustic tile of enhanced utility by securing high sound-absorbing efficiencies with an amount, depth and density of sound-absorbing material which is appreciably less than the prior art tiles required; to provide an acoustic tile which is immune to breathing; to provide a tile which is of such construction and material as to naturally comport with the normal building trades practices; to provide an acoustic tile which is of such construction and material as to render it subject to cutting, fitting, and joining to other building parts; to provide an acoustic tile with inherent high uniform light reflective and optical properties; to provide an acoustic tile the exposed surface of which remains completely planar; to provide an acoustic tile which is initially, and tends to remain, clean and which can be readily cleaned; to provide a tire proof tile which minimizes all hazards which adversely affect'insurance rates; to provide a tile of such construction that the basic element may be multiplied any number of times; to provide a construction of tile which provides interior surfaces of buildings of material and form such as these surfaces should be to comport with the building trades practices and the remaining building structures; to provide a tile which cannot warp, shrink, wind, dry out, disintegrate, discolor or corrode; to provide a tile and construction which has a life equal to the life of the building in which it is installed; to provide a tile and construction which is inexpensive and labor saving; and many other objects and advantages will becomemore apparent; as the description proceeds.

In the accompanying drawing, forming part of this description, Fig. 1 represents schematically the ideal development comprising the ultimate embodiment where a perforation through a diaphragm is employed. Fig. 2 represents a fragmentary transverse section through an illustrative embodiment of the ideal situation of Fig. 1. Fig. 3 represents a fragmentary bottom or reflected plan of a cluster of tiles incorporating the invention herein in operative assembled relation, with some of the cells of one tile containing sound-absorbing material which is removed in others in order to show the bottom construction of the parts. Figs. 4 and 6 represent respectively fragmentary transverse sections through a pair of juxtaposed tile embodying the invention, showing the manner of mounting same to a cross piece, Fig. 5 represents a fragmentary top plan of cluster of tile incorporating the invention showing the external or superficial apertures and indicating in dotted lines the reinforcing ribs. Fig. 7 represents a fragmentary section through a cemented tile.

It is an important feature of this invention to provide an acoustic element of predesigned and substantially predetermined sound-absorbing efficiencies by which, for the first time in the art, a sound-absorbing unit is created effecting a reconciliation between the conflicting points of view of the theory of sound energy propagation and absorption, with a `physical structure comporting with all practical requirements for manufacture and use and which also comports with the architectural features of appearance and ornamentation.

,As applicant pointed out in an article entitled "A problem in acoustics published in "The American Architect in the September 20, 1926. issue, itis possible to utilize a free curve method in the creation of predetermined acoustical propertie's in a given material or assembly of materials. This is based upon the incontrovertible fact that sound absorption is zero at the upper and lower thresholds of audibility. The free curve must undulate from one minima to the other in passing through all of the octaves between the respective thresholds. The maximum absorption, whatever it may be less than unity, must lie in the middle register and must fall away from this maximum on either side of the middle register toward zero at the respective thresholds. This valid principle denies the validity of the formalized and established laboratory findings of alleged sound absorption of materials upon which commercial exploitation of various supposed acoustic materials depend, because of the inordinately high'percentages of absorption ascribed to such materials not only in the middle register but in octaves on each side close to the audibility threshholds. It is known that the effective free expansion of sound energy radiating from a source defines a logarithmic curve, which if incorporated in a physical structure would provide a horn-like device with relation to which sound energy either arising from a source or passing through an aperture exposed to the wave would expand without fn'ctional losses. It is of course impractical to provide a single aperture in a wall for the purpose of absorbing sound energy and it is necessary to provide a great many apertures in practical sound absorbing installations. It will be clear that with the hornshape'd curve of expansion of the sound energy passing through each aperture the apertures would have to be widely spaced apart to enable each to communicate with its own individual horn-shaped chamber without overlap. It is necessary, therefore, in the practical embodiment that the apertures be brought suiiiciently close together as to cause a substantial overlap of their expansive paths, which if represented by actual physical walls would represent dead losses of energy and distort the isocoustic and the stereocoustic free expansion of the wave (euclidian expansion). The energy loss thus represented would probably be of the order of high frequency energy immediately behind or shadowed by the space between perforations, whereas the overlapping area defined by the overlapping skirt portions of the substantial cones would probably be of the order of low frequency loss. The problem now resolves itself to secure the mechanical essentials with optimum characteristics represented by inherent rigidity of structure and proof against breakage, the provision of cavities behind a restricted number of spaced apertures with such relation between confronting walls as to define pockets within which soundabsorbing material may be disposed and preferably frictionally held while insuring that the spacing of apertures through the front face of the unit is uniform throughout the unit regardless of the presence of reinforcing ribs comprising the confronting walls in the structure. The reconciliation between the theory' of sound energy propagation and the physical limitations of the structure are secured by modifying the angle of the face of the ribs or walls to something which may be characterized as conventionalized hom-like with a consequent reduction of transaseasse 3 verse thickness oi' the rib such as to cause it to lie between, but free of, adjacent apertures communicating respectively with diiferent but adjacent cells. The relation of walls of a given cell is such thatalthough the paths of expanding sound waves may begin to intersect, no appreciable interferences nor distortions are present. Because of the fact that with expansion there is attenuation of energy, the practical matter of dimensional reduction of the physical structure (as for instance in over all thickness) is safely accomplished by cutting off the hornlike cells yat a relatively shallow depth of cell with relation to the source of sound, so that the complete cell of this invention is shallower than has ever before been considered possible in the industry, and which further reconciles the physical structure of this invention with the universally acclaimed theory of acoustics. By the proportioning of the cells to the restricted predeterminedly spaced apertures communicating with the respective cells, the losses referred to by the overlap and blanketing or shadowing are substantially recovered or compensated for. However it will be clear that the normal expansion of sound energy entering through the aperture adjacent to the modified horn-likewall will be prevented from expansion by such wall only, which seems to have two effects, one being a slight absorption of energy and a frictional loss, and the other either a reflection or refraction depending upon the characteristics of the surface and the angle of incidence of the wave, apparently causing a reorientation of the axis of the planar wave impinging upon the rib. This recovers the loss incident to the difference between the actual curve of the partition or rib and the ideal curve of the wall of the horn-like cell.

Through experience with sound-absorbing materials, and knowledge of practical effects of installations thereof, it is possible for one skilled in the art to state in advance that a given thickness of a certain sound absorbing material will have a desirable and usable sound absorbing value in the middle register. This, regardless of the actual numerical value, must always be less than unity. Using the free curve method of prognostication, predetermination and anticipation, the probable relative values of the absorption at other octaves beside the middle can be accurately plotted within reasonable limits. This comports with engineering methods and analytical practices. Purely for purposes of illustration a sound absorber of rock or mineral wool of a depth of -11/2" to 2, depending upon the density, has been found to furnish a very desirable degree of absorption in the middle register, of the order of 90% according to the present best methods of testing. This of course must taper off to zero in each direction from said Amaximum without critical values anywhere in between, which is in accordance with the established theory of acoustics. This absorption is maintained substantially independently of the covering medium whether a perforated sheet metal pan, the perforated tile of the said Rosenblatt patent, or a porous or perforated woven membrane.

Referring to Fig. lvthere is disclosed a diaphram or facing designated T, the acoustic resistance of the cavity in the structure is indicated by the thickness R, the free space behind the acoustic resistance is indicated by F and the numeral S indicates the initial sound energy. S1 represents the sound energy in thel empty cavity of the ideal structure and P represents the diameter of the perforation in the -diaphram' or facing. The sound energy S approaching the face T in a wave indicated, passing through perforation P expands substantially in accordance with a logarithmic curve defining a bell or horn-shaped cavity H behind the perforation P, as has been previously explained.

The optimal condition is where S S-l-l and1t=0 gil AIS-login S1, S Put R=0 then AS=0 and S entire space behind the perforated facing were a void lacking any of the supporting or reinforcing quality of the ribbed structure. The ribbing to be described of the actual commercial structure, therefore does not detract from the acoustic value of the structure, but on the other hand, adds desirable features among which are the internal reflecting value of the structure to produce even a greater degree of absorption than is inherent in the sound absorbing lling alone thus conducing toward the economical use of smaller, denser, more compact volumes of soundabsorbing materials.

The practical embodiment of the invention providing a plurality of generally or substantially horn shaped cavities or cells is found in a tile I0 made preferably of molded cementitious material such as gypsum or the like, and this preferably manufactured in some such manner as is disclosed of the tile in the earlier mentioned Rosenblat patent, with a significant addition that the instant tile during setting is subjected to very high frequency vibrations in order to strengthen and rigidify the whole. Obviously the tile may be a ceramic or plastic product. Each tile i0, purely illustratively, has the actual size and nurnber of cells variable in accordance with conditions, and, illustratively, may be roughly one foot square, having an outer exposed surface il, continuous Iover the entire surface, except for voids or apertures to be described, and having an inner surface i2 parallel to the surface ii but being discontinuous for reasons to be described.

The outer edge of the tile is formed by the four boundary walls or ribs I3, which externally may taper outwardly from the inner surface i2 toward the outer surface Il, as at I4, leading to a high point or ridge I5 comprising a line contact with an adjacent tile to form a breathing seal, disposed or spaced inwardly of the outer face Ii by a bevel or similar small sloping surface I6. Rearwardly of the breathing seal i5 and disposed in the sloping or recessed surface i4 on at least two parallel sides of the tile are the undercut longitudinally extending securing recesses I1. The recesses of juxtaposed tiles, as shown in Fig. 4, form the round or more or less oval apertures I3 closed toward the forward side of the tile by the contiguous contacting breather seal surface I5, and having a substantially slight opening toward the rear surface to permit a supporting clip to enter to support juxtaposed tiles at the joint between them.

A purely illustrative form of support is indicated in Fig. 4, in the form of a sheet metal bead 20, having a leg 2|, terminating in the reentrant flange 22, arranged to overhang spaced purlns or string pieces 23, to which they are preferably connected as by wires 24 or the like. It will be understood that the bead 20 may equally well be solid rod either supported at the ends in a suitable manner or connected by wire supports to the upper string pieces.

The important construction of this tile is a plurality of ribs extending the full depth of the tile as at 25, preferably tapering from a narrow inner edge 28 lying in the common plane I2 of the inner surface, to a widened base 21 integral with and merging into the facing portion or diaphram 28. The inner face of the diaphram 28 has a surface 30 parallel with the planes I2 and II but spaced from the later by an appreciable thickness of tile as shown. Purely illustratively the thickness of the facing sheet or diaphram 28 may comprise roughly 1/5 of the entire depth ofthe tile between plane surfaces I2 and II. In the preferred embodiment of the assembly the entire tile is, illustratively, less than an inch, so that the cavity, designated as 3|, defined by the walls 25, is of approximately not more than 3A of an inch in depth. The extremely compact nature of the tile will be obvious from these illustrative dimensions.

It is preferred to provide that the tapering ribs 25 extend in relatively parallel and intersecting relation respectively parallel to respective side walls so that purely illustratively they form approximately 49 horn-like chambers inl a l2" x 12" tile each flaring toward the rear surface from the diaphragm or face into which the walls merge. The tapered surfaces 32 of each rib being angularly divergent cause the enlarged base 21 thereof to be wider than the upper edge, so as to strengthen and rlgidify the whole and to conduce toward a flared horn-like resonating chamber. The flare also facilitates withdrawal of the unit from the mold, while strengthening the unit. It is an important feature that each thickened base 21 is correlated with the spacing between the apertures to be described so as to be disposed between adjacent rows without blinding off or interrupting the serial continuity or uniform spacing of the apertures thereof. The apertures 33 extend completely through the face 28, and, although they may be truly cylindrical or may even reversely taper, neither of such formations is preferred as in the preferred embodiment they are tapered from a relatively small aperture 34 in the exposed face Il to a wider mouth 35 in the surface 30 behind the diaphragm or face. It will be understood that a slight taper of the apertures also facilitates withdrawal of the molded unit from the mold. As indicated in Fig. the face apertures 34 are evenly spaced across the face of the tile in any geometric designs desired, illustratively in intersecting relatively normal rows which are continuous across the face without interruption by the presence of assassin the ribs 2l. AThe preferable arrangement is such that each cell or resonating chamber defined b1 4 walls eithenofribs or side edge walls or both,

contains a plurality of apertures 33 in its face or front wall, and illustratively 9 are provided disposed in 3 rows of 3 each in the illustrative 12" x 12" tile. Obviously the proportions, sizes and numbers and arrangement, both of the horn like cells and the apertures therein may be varied as' desired, within the scope of invention discussed.

In thepreferred embodiment of the acoustic unit a plurality of individual clumps or clusters or miniature batts of sound-absorbing material, as 36, are inserted into each chamber or cell II, in resting contact against the inner surface III of the face and in substantially frictional enagement and cohesion with the tapered surfaces of the walls of the cells and having an upper surface disposed generally in the common plane I2 of the inner face. The preferred form of sound-absorbing material is mineral or rock wool which has a very desirable sound-absorbing factor. The spacing of the walls of the grid formed of the ribs is such that the small units of soundabsorbing material disposed in the walls in frictional contact with the side walls continues to be held frictionally therein. This is an important phase of the invention as it enables completion of the unit at the yfabricating plant, and its shipment and manipulation and attachment at the work without difficulties. It is a very interesting and significant feature of the invention that although the ribs 25 extending in both directions longitudinally of the tile are so disposed as to interfere in no way with the grouping and dis- -position of the apertures through which the sound energy enters, yet the aggregate volume of all of the ribs 25 is very appreciable indeed. The ribs are formed of material appreciably cheaper than the sound absorbing material and which also simultaneously secure better distribution of the more expensive sound-absorbing material, with an appreciable reduction in the volume thereof that otherwise would lie in the space required by the ribs. That is an important attribute of the invention.

The ribs extending the full depth of the unit enable highly satisfactory sound-absorption by the fact that lthe sound energy, the waves of which pass through the apertures 33 of a given cell, is absorbed by each passage through the vmaterial as the wave vibrates, and also the reflective material comprising the walls, which may partake of the nature of almost a glaze, seems to cause a reflection (re-orientation) of the sound energy and its retention and refraction in the sound-absorbing material, so that with far less material of the same density, sound-absorbing efficiencies are, as a fact obtained, comparing very favorably with that from sound-absorbing material of more than twice the thickness as compared with the gross area, and as great as three times as compared with the net area (excluding the ribs). To illustrate the point it should be observed that 3/4" of the rock wool disposed according to this invention would actually only represent approximately 1/2" when spread over an apertured surface according to prior practices without the ribs.

A further factor of important and unexpected outstanding importance in the enhanced sound absorbing efliciency of the unit of this invention is believed to lie in the fact that each cell of itself may be considered as a miniature acoustic tile separated from the adiacent miniature acoustic tile by ra space in the composite' tile disclosed. The space happens to be, in the instant invention, an integral rib having thickness. The ribs actually separate adjacent individual miniature tiles, whereas in the prior artthere are no such miniature individual tiles because there were no ribs, or because the sound absorbing material overlay the ribs. This separation factor actually seems to increase the absorption, in accordance with the test data and findings of the Bureau of Standards, which found that a closely grouped cluster of absorbing elements had less gross absorption than the same group possessed in more or less spaced relations. (See Research Paper R. P. 700, National Bureau of Standardsby V. L. Chrisler, of June 26, 1934.)

A modified form of supporting means for the tile, which is quick, positive and certain, and enables replacement of any given tile at any time is disclosed in an illustrative embodiment in Fig. 6. At suitable intervals across and below the ceiling supporting structure, such as the slat are suspended standard purlins 40 in level parallelism, say every 4 feet. Attached to these purlins rectilinearly thereof, are preferably, the channelshaped tile-joint overlying members 4|. In'the illustrative form the side Walls 42 have a grooved bead 43 close and parallel to the soiiit 44. The members extend the full length of the area to be treated and are on centers the same as the tile width, which, is illustratively, 1 foot.

To anchor the members to the purlins a preferably resilient wire clip 45 having a U shaped` foot 4B is disposed with the legs slidably engaged between the beads and sofilt. At the free ends the clip has legs 41 bent inwardly to clear the beads and upwardly substantially normal to the foot portion. The legs 41 are given a preliminary bend over the appropriate purlin as shown in full lines, while the supporting members are being aligned and positioned, after which preferably they are bent about the purlins as indicated in dotted lines. In order to facilitate positioning of the clips and members, the clips are arranged to be loosened in their guide channels by squeezing the legs together, as will be clear.

The actual tile engaging elements comprise preferably a sheet metal clip 48 of a single piecel of metal having a central lower bead 50 Von the lower edge of a median tile aligning web 5I. The web merges into a yoke 52 having preferably resilient spaced parallel lateral walls 53, each of which is longitudinally beaded at 54 so to engage in the respective grooves of the beads 43 in which they are longitudinally slidable vwith the clip. The clip is quickly attachable by a snap action with pressure of the clip against the members 4|. and is anchored against retractions.

The sheet metal clips are provided in the order of 1 clip for each tile, althoughfas will be clear with the tiles in assembled juxtaposition the clip is actually in engagement with and in turn helps to support 4 tiles. The ability to slide the metal clips conducing both toward quick tile mounting, as well as quick tile dismounting. l'I'his latter necessitating the insertion of a thin element between the meeting edges of the tile, one of which is to be removed, to retract the bulbous beads 50 of the several metal clips holding itin place. After replacement of a new tile by similar but reversed procedure, any abrasions are covered or obliterated by applying a plug of plaster of Paris or the like.

It is to be understood that the cells described m tors may be added as by introducing a piece ofl provide structure permitting sound-absorbing material to be pressed into the cavities or cells to such a degree that it is of proper density for maximum sound absorption. This is in contradistinction tothe previous greater quantities of llse. batt, or blanket wool employed in the prior a It will' also be obvious that this specific form described is subject to wide variation, as the ribs need not be tapered as'shown, but may be very close to or even be untapered, which 'of course will lighten the structure if desired.

The structure shown contributes to easy and quick attachment in the fact that in addition to mechanical fasteners as indicated the kdiscontinuous rear face I2 has sufllcient area of surface extending directly across thel entire title as to enablequick and facile attachment to a surface on which cement has first been spread. All that is required is pressure suillcient to force the ribs into contact with thev cement and to force .the excess cement 62 into the cavities to key with the ribs. The 'ribs thus may be provided with a BI is applied. :The title of the invention is pushed v thereagainst, and because of the reduced area of 'each rib 25, it penetrates slightly into the cement to force the latter to rise on each side thereof as at 62 to bond the ribs and cement on three surfaces of the ribs. Owing to the aggregate area of the ribs, and the excellentbond thus secured,

applicant for the first time in the art is able Y safely, satisfactorily and quickly to cement up or on` his titles l with assurance of permanent adhesion. I The use ofspecial materials with the plaster of Paris or 'gypsum or the like to make the tile stronger is contemplated.

. It will befurther understood that various faccheese cloth into the respective cavities which is colored to impart the desired effect upon the eye of the observer looking through the apertures, and obviously the apertures may be more closely u grouped and may have blind apertures" registering with the enlargement 21 of the ribs 25 if the en'ect is enhanced thereby.

It is an important feature of this invention that a monolithic tile is constructed which requires no w internal reinforcement and .which can be manipulated and applied as a unit, and which has the sound-absorbing material spaced as far from the exposed surface of the title as to allow the latter to be painted without danger of contacting with the sound-absorbing material, to the impairment of its functioning as is common in the thin sheet metal devices oi.' the art.

`It is believed that the series of pyramidal cavitiesl in the tile comprise sonorous. responding structures of bell-like nature, but which have random and non-determinable pitch or tone so th'at with a large number of such bells in a single unit there is a new and useful eiect created in the absorption of the various random vibration of sound incident thereon. It is believed that these coupled bells co-vibrate at random and thereby both absorb or deslrably modify the impinging sound. Sound-absorbing material such as rock wool pressed into the cavities is believed to have an added damping function to damp the natural response and frequency of the bell, and thereby additionally damp or quench the sound energy, to be absorbed. This characteristic extends th'e range of the sound-absorbing property of the material beyond the capacity the thickness and density of the material would lead one to expect from the prior art and thus secures a new and unexpected result, therefrom.

In introducing the sound-absorbing material such as rock wool this is done preferably by ernploying a nodulated or pellet Wool which may be either disposed in place in a dry condition or may be lightly sprayed with an adhesive to facilitate the attachment of the wool in the cavities.

It is to be understood as a further advantage of the invention that when the tiles are attached with contiguous edges in contact, breathing of the tile at the joints is precluded, as is breathing through the tile itself from the construction described.

Having thus described my invention, I claim:

1. An acoustic tile comprising an integral monolithic structure h'aving a rigid facing portion defined by an outer and an intermediate surface and having a plurality of substantially evenly spaced apertures extending in relatively perpendicular rows from one surface to the other in such number and even distribution throughout the portion as to transmit substantially all sound energy incident upon the portion to the interior of the structure, a plurality of rigid ribs arranged in a grid and each merging integrally into the intermediate surface of the facing portion and having its outer free end lying in an inner surface plane parallel to the outer surface and common to all ribs, each rib having a base thinner than and being disposed in the spacing between adjacent rows of apertures and out of registry with all of said apertures while maintaining the eveness of the pattern of distribution of said apertures, each rib tapering inwardly to an edge appreciably thinner than the base thereof and of a length from said intermediate surface more than three times the thickness of said rib base, adjacent ribs being spaced apart a distance far greater than the spacing between rows of apertures so that mutually intersecting ribs in the grid, form with enclosed areas of facing portion containing a plurality of apertures, a plurality of resonating inwardly flared chambers, a plurality of batts of sound-absorbing material disposed in the respective chambers and the whole so constructed and arranged that sound energy entering the plurality of apertures is reflected and refracted therein and by and between said material and said ribs to such degree that a high absorption of energy is attained by said chamber Without undue depth of sound absorbing material.

2. An acoustic tile comprising an integral rigid monolithic tile having a facing portion defined by an outer and an intermediate surface and a marginal flange. running peripherally about' the.

tile from the intermediate surface, the entire area of facing portion within the boundary flange being provided with a plurality of through apertures evenly spaced in relatively perpendicular rows throughout the area and of auch diameter and of such even spacing as to transmit substantially all of the sound energy incident upon said tile through the facing portion thereof, a plurality of elongated ribs extending perpendicularly from the intermediate surface integral with the facing portion of the tile, each rib being of such width as to be disposed between adjacent rows of apertures Without blocking of! any of the apertures in the facing portion and therefore without disturbing the evenness of the distribution of apertures, said ribs being mutually intersecting to define with respective enclosed areas of facing portion each containing a plurality of apertures, a plurality of resonating chambers, the ribs being at least three times as long as the thickness of the facing portion as well as the average thickness of the ribs and having their free edges lying in a common plane containing the edge of the flange, and sound absorbing material disposed in the respective resonating chambers, the respective chambers and sound absorbing material being so disposed and arranged that sound energy entering said apertures can expand in the chambers through said material and be reflected and refracted to cause a high degree of absorption of such energy.

3. An acoustic tile comprising an integral rigid monolithic tile having a facing portion defined by an outer and an intermediate surface and a marginal flange running peripherally about the tile from the intermediate surface, the entire area of facing portion within the boundary flange being provided with a plurality of through apertures evenly spaced in relatively perpendicular rows throughout the area and of such diameter and of such even spacing as to transmit substantially all of the sound energy incident upon said tile through the facing portion thereof, a plurality of elongated ribs extending perpendicularly from the intermediate surface integral with the facing portion of the tile, each rib being of such width as to be disposed between adjacent rows of apertures without blocking ofi any of the aperltures in the facing portion and therefore without disturbing the evenness of the distribution of apertures, said ribs being mutually intersecting to define with respective enclosed areas of facing portion each containing a plurality of apertures, a plurality of resonating chambers, the ribs being at least three times as long as the thickness of the facing portion as well as the average thickness of the ribs and having their free edges lying in a common plane containing the edge of the flange. and sound absorbing material disposed in the respective resonating chambers, the respective chambers and sound absorbing material being so disposed and arranged that sound energy entering said apertures can expand in the chambers f through said material and be vreflected and refracted to cause a high degree of absorption of such energy, the upper ends of the ribs and of the flanges being so thin and the weight of the entire tile being so relatively low that the yinner surface thereof can be pushed against a layer of cementitious material to secure penetration and displacement of same by the ribs and flange sufficiently far as to bond and permanently anchor the tile to a supporting surface without mechanical fastenings.

MAURICE C. ROSENBLA'I'I.

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