US1912161A - Building construction - Google Patents

Description

May 30, 1933. IM. c. vRczvslanalJlvrT 1,912,161.

BUILDING CONSTRUCTION Filed May 28, 1930 INVENTOR. MAURICE CRQSENBLATT.

ATTORNEY.

Patented May 30, 1933 UNITED STATES PATENT OFFICE BUILDING CONSTRUCTION Application filed May 28,

This invention relates to building constructions, and constitutes a continuation in part of application :li-420,668, filed January 14, 1930.

It is 4among the objects of this invention; to obviate the disadvantages of` :previous constructions; to provide an acoustic treatment with an outer exposed stratum of material which is ornamental and pleasing;

l@ to providel as an element of an acoustic treatment a foraminous sheet as a support for an exposed finishing surface without adverse effect on its sound absorbing or acoustic value; to provide an acoustic treatl5 ment for building constructions which is simple and economical to install; to provide a building construction of high sound absorbing value that may be installed by standardized labor according to their practices;

to provide an acoustic treatment including a layer of porous material imposed upon a layer of foraminous material; to provide a foraminous. sheet with an external juxtaposed layer of material without preventing the transmission of sound through the fo-u raminous sheet; to apply a woven membrane as an external coating for a foraminous sheet metal or other foraminous .or perforated material layer of an acoustic treatment whereby the superficial aspect of the treatment is improved, reflect-ions from the under surface of the foraminous sheet are reduced, and the sound absorbing efiiciency of the treatment is improved; to provide a ire r proof acoustical treatment; to provide a complete ceiling construction. of acoustic value; to provide an aconstic treatment effecting an over-all treatment indistin- 40. guishable from a unitary surface;I to provide an acoustic treatment combining sound damping with sound absorbing Without appreciable cost; to provide an acoustic treatment combining high acoustic value with y v thermal insulation; .to vprovide an acoustic treatment susceptible to ornamental superfcial treatment without adverse effect on its sound absorbing eieicncy; `and many other objects and ladvantages will become more 5 clear as the .description Proceeds.

1930. Serial No. 456,364.

` In the accompanying drawing:

Fig. 1 represents al fragmentary vertical section through a ceiling construction involving this invention.

Fig. 2 represents a fragmentary perspec- 55 tive of a foraminous substantially rigid sheet according to this invention on enlarged scale, showing the application of a membrane of woven material thereto, and showing in dotted lines a hand roller which maybe used to apply paste to theunder surface of said sheet prior to the application of such membrane to prevent adhesive from entering the apertures, or which may be used 'when dry to secure the attachment of the membrane to the rigid sheet without permitting the membrance to enter into the apertures in the sheet, in the form of depressions in the face of the membrane,

Fig. 3 represents a fragmentary perspective view partially in section of a multiple membrane of the invention comprised of an apertured sheet with a layer of plaster, both 'the sheet and plaster having registering openings to provide a highly ornamental inishing element with an enhancement of the sound transmitting qualities of the multiple membrane,

. Fig. 3a represents a Vertical section on a iagniiied scale of the structure disclosed in `ig. 3b represents a vertical section on a magnified scale of a modification of the multiple membrane formed of the buriedsheet material and plaster layer, i

Fig. 4 represents a fragmentary vertical section of an application of this invention to curved surfaces,

Fig. 5 representsa. fragmentary perspective view partially broken away through an application of this invention to wooden buildings or the like.

Fig. 6 represents a fragmentaryv vertical section through another form of the application of this invention to wooden buildings, v.

Fig. 7 repxgesents an application of this invention to the roof elements of a wooden building and, i

Fig. 8 represents a fragmentary perspec- 10 tive view, partially broken away, through two abutting rigid apertured membranes with a plaster layer extending over the two sections to provide a continuous finish, and with apertures in the plaster both in registry with apertures in the rigid membrane and also over the abutting unapertured edges of the membranes, to conceal the eX- istence of a line of jointure between sections and enhance the over-all finish of the plaster layer.

The invention relates primarily to the provision of what might be designated as a composite or multiple membrane of general utility of itself in the building art, of utility of itself from an acoustic standpoint when supported in spaced relation to a surface to be treated, but particularly valuable when associated with sound absorbing material in a building construction. To take the acoustic treatment out of the realm of the specialized makeshift supericiality and into the realm of the building industry by providing the treatment as an integral inbuilt part of the building construction and in so doing to provide an exposed element for acoustic treatments which is aesthetically pleasing and ornamental, in sharp contrast to the peek-marked aspect of the ordinary alleged acoustic treatment, and which, far from involvingsacriice of acoustic value, enpthe contrary is characterized by an enhancement of that value, is a feature .of the invention.

From the sound absorbing standpoint alone it would be desirable to provide more or less thick layers of sound absorbing material, such as felt, (for instance, among other available materials) which is so supported vas to be exposed directly to the action of the waves of sound energy. With sufficient area and thickness of sound absorbing material, almost any desired degree of sound absorption could be attained. Unfortunately this cannot be the only desideratum. It is necessary to conceal the lsound absorbing element by a finishing element designed to comport substantially with the architectural scheme. Many attempts have been made to do this in such manner as will not seriously aectthe sound absorbing efficiency of the sound absorbing material, such as occurs by shielding or screening off the sound energy, but the results heretofore have been of two general classes. of such size as to be objectionable have had to be provided in the supposed concealing element else they would be closed by a film of paint when that was applied as a finishing coat, or else the'application of the coat of paint has provided a reflective film of such action as to seriously interfere with the transmission of sound energy to the absorbing material behind. In the one case a peck-marked effect accompanied by a Either holesmore or less perceptible reduction in sound absorption is achieved; in the other a shar reduction insound absorbing efficiency 1s noted.

Referring now to Fig. 1, there is disclosed a form of building construction involvin the provision of a concrete slab, designate as 1 0. There will be sound absorbing material associated with this slab as will be further described, but for the present we will consider the finishing or ceiling element of the building construction with which this invention deals. The finishing element may take several forms as will be described and may be for ceilings or other walls, but in general it may be characterized as a composite or multiple membrane regardless of its use. In one form there is provided in substantial parallelism with the slab, a punctured, apertured, reticulated or foraminous sheet of rigid material 11, such as of sheet metal, but obviously capable of formation from any sufficiently rigid workable 0r worked material including perforated asbestos sheets. It is contemplated for instance that a sheet of woven wire or screening of `rather heavy gauge may be formed, then passed through suitable rollers to form a flat sheet having its upper and lower surfaces in substantially parallel planes and obviously in this case having its greatest area of voids rather than of solid material. For usual purposes however fairly rigid self sustaining sheet metal will be preferred. The sheet 11 has a multiplicity of punctures, perforations or apertures 12, in which in one form of the invention at least, the material of the sheet has been punched out to form a smooth surfaced sheet, the opposite faces of which are substantially parallel. The sheets 1l which may be of any conven`i ent size may be attached in any desired manner to some part of the building structure, as for \instance by hangers 13, in Fig. 1, or to rafters or girders 14 as shown in Figs. 5, 6, and 7 as by nails or the like. Furring members may be provided, (not shown except by their counter parts in Figs. 5, 6 and 7), which may have channels or the like to receive the edges of the sheets. The furring members may have a cushion (not shown) to which the sheets lare fastened to give higher sound absorbing value. Such 'furring members may be provided in using this4 invention in connection with an ordinary superficial imposed acoustic treatment in place of the building construction in which it finds its largest usefulness, and are of the usual nature for suspended ceilings. The lperforated sheets may have furring spot welded or otherwise attached to the back before erection to stifi'en the sheet and facilitate positioning of `it. In ,any case the sheets are attached in a desired position, with the lower surfaces of all the sheets in a substantial plane and, preferably, with the edges of adjacent sheets in abutting relation to form a planar surface. The foraminous sheet metal, or the like, may be designated as a primary membrane. Obviously the sheet material may be used in single sheets in panels between supporting devices such as beams or the like (not shown), but it is preferred that the sheets be arranged in abutting relation to form a continuous surface made of a plurality of sheets.

In one form of thev invention a secondary membrane, of woven fabric, such as burlap or the like, is affixed to the lower surfaces of the primary membranes 11, as by an adhesive such as paste, glue, cement, or the like. The object of the provision of the secondary membrane is to conceal the sheet material 11 and the apertures l2 formed in the sheet material, without plugging up such apertures in any way. Where there are a plurality of abutting sheets 1l, the secondarymembrane functions to blind out the lines of jointure between such sheets and thus to provide an over-all finish. To

this end cement may be rolled over joints in sheets, or a tape may be pasted over joints to conceal an irregularities such as are lformed by the astening staples or the like. The secondar membrane `may be applied in several di erent ways, but a preferable method is to provide a roller as indicated at 9 in dotted lines in Fig. 2, upon which adhesive is spread, then the roller is moved back and forth across the lower surface of the sheet material 11 depositing a thinlayer of adhesive on the solid or-V tions of the plate or sheet, but which rol ing deposits no appreciable amount of paste in any part of the apertures 12. The secondary membrane 15, which lis preferably long enough to cover `several sheets 11 so as to -blind out their lines of jointure, is preferably placed under slight tension and pressed up into pasted engagement with the plate or sheet metal 11. This may be done by hand or by a suitable roller, such as 9, eX-

`erting uniform pressure on `the secondary membrane. It requires but little experience I to enable an ordinary Workman to apply the secondary membrane to the vprimary apertured membrane in such a manner as to maintain a. plane surface on the fabric secondary membrane, with such membrane unmarred by indentations of the membrane at points in registry with the apertures or holes 12. Obviously, the secondary membrane may be applied in any way that is deemed expedient although it is desirable to avoid the formation of a film of paste on the membrane in registry with the apertures, as this forms a reflective surface effectively interfering with the transmission of sound energy through the apertures in the primary membrane. If such film is formed it may-be removed according to my invention by subjecting the membrane to the action of a moving stream of air, either by a vacuum devi e or by projecting a compressed air orother moving stream upon itsv surface while the adhesive is still moist enough to be dislodged from,l the pores by such moving airstream. The secondary membrane may be painted and decorated in any way desired to secure a desired finish, but it is undesirable to permit the formation of a film of paint on the membrane in registry with such apertures and to this end While the paint is still wet enough to be dislodged from between the strands of the fabric the membrane is subjected to the action of a moving stream of air of sufficient force to blow the excess paint from the fabric membrane so as to maintain the porosity of such membrane where it is in registration with the apertures in the primary membrane.

The composite or multiple membrane may j be disposed as shown in the several figures, may be given a curvature, (preferabl prior to the application of the fabric mem rane), and provides an over-all finish which completely blinds out the linesl of'jointure that may exist between edges of the sheets of apertured` material. If desired, there may be two fabric membranes applied to the rigid backing sheet without appreciable reduction in sound absorbing efficiency, such for instance as a coarse membrane initially Iimposed upon the sheet metal, and then a secondary membrane of finer mesh mounted on the first one, as shown in Fig.'1, at 16. It will not usually be necessary to use two of the fabric membranes. Y y

Of course the reticulated or porous sheet vmaterial may be applied when desired during the building construction, but it is usually the last element to be applied after the introduction of the sound absorbing material. For the installation of sound absorbing elements it is usually preferred to provide -a series of transverse supports 17, (Fig. 1.), upon which a layer or layers of 'sound absorbing material as 18, may be draped or looped, preferably in substantially lsinusoidal form, and disposed `between the lower surface of the slab and the upper surface of the skin or membrane disclosed. On the other hand, it might suffice for certain purposes that the sheet material or primary membrane be applied in independent strips, suitabl supported, and upon the upper surface ofy which loose fibrous sound absorbing material may be deposited. This may be done by using a blower to propell the loose fibrous material to the positions needed. 'Theloose material is 'deposited as shown at 20, to any depth recglired. "If

desired both sorts of sound absor ing'mec ium may be utilized, as shown in Thus the upperlooped element may com-l prise felt, or other analagous stratified material such' as properly shaped liber boards, While the lower sound absorbing element may comprise felt, asbestos, mineral, rock, wool, or cellular refuse material or the like. If a great area of sound absorblng material is desired it may be desirable to provide a reticulated looped element, such as wire screen, or the like, hanging upon the transverse supports 17, and upon the upperA surface of which mineral, Wool or such cellularrefuse materials as may be expedient, may be dumped to a depth which is satisfactory. The amount may be regulated to give any degree of acoustic absorption. In auditoriums for instance Where there are high furred spaces above, after the auditorium is opened, more absorbing material may be provided or absorbing material taken out until exactly the proper degree of absorp- -tion is present for perfect hearing conditions. rlhis cannot be done with any other form of treatment.

The invention contemplates a modified skin or multiple membrane, as indicated in Figs. 3, 3a, and 3b, and at the right hand side of Figs. 1, 4, 5, 6, and 7. In this modification the sheet metal 21 if metal is the material used, and others are available of course, has a multiplicity of apertures 22 punched or pierced and drawn or otherwise formed in the sheet, with the material drawn out forming flanges surrounding the apertures, such as in the form of burrs, as at 23. Obviously the shape of the burrs Will vary in accordance With the nature of the punching operation and may vary from those which are of inverted conical of frustoconical outline, to those which are frustoconical with the base at the outwardly flared end of the burr. For purposes of illustration, the burrs are shown in Figs. 3 and 3a as forminfr substantial continuations of the inner surf-ace of the apertures so that they are of substantially the same diameter throughout, from the upper end in the plate to the lower end formed by the burr edges.

The form of burred sheet shown in Fig. 3b is preferred for certain purposes. In this form the burrs are constricted or tapered so as to be each of increasingly smaller diameter than the diameter of the aperture in the sheet as it approaches its end or termination. The effect of this form of burris to provide a suitable bond' with the plaster but to arrange that the mouth of the burr, which determines the size of the aperture 'in the plaster, shall be smaller than the hole or aperture in the sheet material. This, for utmost efficiency requires that the apertures in the sheet be closely grouped so that there are a multiplicity of the appreciably smaller openings in the surface of the plaster. The smaller plaster openings may be of such visual insignificance as-to be substantially unnoticeable, although forming in the aggregate a great pore or void area. This construction, when the plaster surface 1s properly applied and-tooled, cannot readily be told from an ordinary plaster surface and yet has such an appreciable pore or aperture area as to be highly efficient in permittin sound energy to pass through the multipe membrane. These burred holes will'in either case preferably be relatively small and. on closel grouped or spaced centers. The sheets, p ates or strips of punched or pierced metal will be applied in the same relation to the under side of the slab or to the rafters or yjoists shown in the other fi res either before or after the insertion o the Vdamping or sound absorbing material7 which, having been once described need not .be repeated, as the same reference characters apply to the materials associated with either plate or composite membrane form.

The plates, sheets or strips having been I properly placed are then coated with a coat of plaster 24, substantially to the level of the burrs surrounding the apertures, and possibly covering same. The plaster 24 may initially cover the entire surface so that no apertures are visible, and the finish may be of any desired sort, and, temporarily at least, there may be a small film ofy plaster lodged in the burrs and openings in registry therewith. The plaster may then be treated while Wet or it may Wait until it has at least partially set before further treatment is in order.

With the plasterpkeyed or bonded to the plate by the burrs, it Will be clear that the film of plaster covering the apertures in the plate may be. removed and form Well defined closely grouped inconspicuous apertures in the plaster surface. The removal of such lm may be done in several Ways. The plaster may while still moist be subjected to the action of a moving stream of air, Whether by vacuum treatment or by a stream or jet of air projected upon the surface. Or it maybe brushed, stippled, or otherwise treated with a brush, or it maybe rolled with a roller having more or less yielding points so as to break out the loose plaster, it may be treated as called for in my Patent :#1,751,249 in order to provide a multiplicity of visually insignificant pores, each pore that registers with the opening in' a burr being slightly enlarged, or the plaster in the burrs may be picked out from behind in any desired manner, assby rolling the upper surface with a device built in accordance with the provision of burred apertures in the sheet, so that each hole is entered to break out the film of plaster in the burr. On the other hand,' interesting effects may be attained by treating the surface to break out the plaster in the burrs in accordance with a design, as by applying a stencil or the like to the surface. The effect of the plaster to the eye of the observer is excellent, and may be enhanced in ornamental value by suitable hand tooling operations, or by imparting a rough sand cast finish. With such construction the visual effect is, as stated, very desirable, the apertures are relatively insignificant and merge into the texture of the plaster to such a degree as to require keen eye-sight to be discernible. f

If desired, the plastered apertured sheet may in turn support a secondary imposed fabric membrane as shown at in Fig. 1.

In the form of multiple membrane shown in Fig. 2 the membrane 15 extending over several strips of sheet material 11, effectively blinds out the joints between adjacent or contiguous sheets. In the form of multiple membrane shown in Figs. 3 and 3a, the edges of the apertured sheet material usually forming a marginof unperforated material, may bring two contiguous sheets or strips into vabutting engagement in such manner that .it u

might appear as an appreciable area of unperforated sheet metal between Aperforated areas. These marginal portions may be punched or otherwise treated to form a bond with vthe plaster if such is desirable, and the area is plastered to the same level as the apertured or bnrred portions, then this intermediate area of plaster is rolled with rollers having indentations or raised portions, while still moist,`in order to provide a surface that simulates any other area ofv the element. Thus there will be a substantially unbroken area of similar` superficial and visual contour or appearance over the entire surface so treated. This will be clear from a consideration of Fig. 7 in which this is illustrated. The two ends of the adjacent .sheet strips abut at line 26, with the marginal portions 27 forming an area of no apertures. This area is covered with a llayer of plaster to the same thickness as that on the burred areas superficial appearance. Y v

Obviously the composite membrane of this invention lmay be pre-formed and attached in units if desired. It is not necessary to first attach'the apertured sheet metal before applying the secondary membrane, although the general purposes such procedure is preferred. n

The invention involves certain improvements of importance in other types of buildings such as homes or similar structures in which the supporting elements` are of woodV or the like..` Thus, in Fig. 5 the treatment is shown applied to ja ceiling having wooden or similarjoists, as`28. These as usual are arranged in parallel spaced relation, and ma ave cross supports or rods 30, upon which sound absorbing material of any desired sort is sup orted, preferably arranged in a longitudina 1y extending series of loops,

of such width as to substantially fill the distance between joists, as designated at 31. To the lower faces of the joists the skin devices or multiple membranes of this invention may be directly attached, either type being available in the connection, as shown.

A feature of importance is the use of the invention as a combined vibration damper and sound absorber. For this purpose with the floor of a structure to be dealt with, and with the usual wooden joist construction comprised of spaced joists 32, the roll of felt or the like is arranged transversely of the joists, arranged to pass over each j oist, and to be suspended in loops therefrom, as shown at 33. Then a' sub-floor 34 is nailed to the joists compressing the felt wherel it goes over the joists, which therefore acts as an isolating support for the sub-Hoor, while the felt between joists is used as a sound absorbing element to absorb sounds arising from below. The lower edge, or ceiling of the room below, has the rigid apertured sheet material and composite membrane of this invention applied to the lower faces of the joists as shown.

In the construction of certain buildings at points such as the roof, (although obviously available for other points), it is desirable to combine the sound absorbing efficiency. of the treatment ldescribed herein, with thermal insulation. To this end, as shown in Fig. 7, the rafters of` the roof, as 35, form the support for strips of sound absorbing mate rial such as 36, arranged in loops between the joists or rafters, and having a planar layer of thermal insulating material 37 laid upon the upper loops of the material 36, and through which the nails attaching the sheathing 38 to the rafters 35 pass. The undersurface of the roof may be finished with the multiple membrane of this invention,

.either such a sheet assembly as is shown by 11 and 15, or by the sheet and plaster assembly shown' at 22 and 24:,A or by combinations of the sheet, plaster and membrane as hown at the lower right hand corner of am aware that attempts have been made in the past to utilize a perforated vsheet met# al strip in such relation hitherto, but in all such previous attempts the sheet metal plate has, except for a coat of paint, been the ultimate exposed surface, and has been used to conceal the sound absorbing material disposed behind such sheet and the surface of the slab or the like, to bedescribed. This has been opento certain lobjections which, as they are obviated by the invention herein, might well be pointed out. v Such previous efforts have necessarily been provided in the form of tiles or panels andthe line of jointure between tiles has been obvious,y

and thus the provision of an over-all surface hasbeen precluded; in order to prevent the formation of a paint film over the apertures in the plate or sheet material, they have had to be made of large area, else the normal film forming characteristics of the .5 paint would close them up and render the exposed surface more highly reiiective, ac-

cording toknowledge in the art prior to my invention herein; the superficial'aspect of the device was displeasing, having a pock- 10 marked effect.

For these and other reasons the stamped metallic sheets of the past have not been of very great commercial interest. In the instant invention, however, owing to the fact that the foraminous or reticulated sheet is to be covered as will be described, it is possible to use small or large apertures, and as closely spaced or grouped as is desired in order to secure the maximum of void area 2o in order in turn' to secure the utmost sound energy transmitting qualities in the sheet.

It being understood that the effort in every acoustic treatment of this type is to provide a superficial skin, or the like, which of itself may or may not have sound absorbtive value, so long as it has the necessary porosity to permit the sound waves to pass through the outer skin to have their energy absorbed behind the skin in such sound absorbing material as may be provided. The sheet l1 then, has preferably a multiplicity of the apertures 12, on closely grouped or spaced centers so as to provide, preferably, that at least 50% and preferably the maximum area of the sheet is void. That is, with more hole area than solid area.

It will be observed that the invention provides a substantially rigid, self sustaining assembly, capable of in itself supporting the sound absorbing material, but which provides an attractive finish not heretofore obtainable from any form of foraminous assembly. It will be noted that the invention is of the utmost simplicity, that the application of the foraminous sheets falls within the scope of activities of metal lathers, while the plastering falls within the scope of 'activities of plasterers, so that ordinary labor skilled in those fields is adequate to make the complete installation. In every case the installation is ire resistant, and can easily be made completely reproof if thisiis desired.

I claim as my invention:

l. In a building construction, a surfacing element comprised of a thin self-sustaining rigid layer of non-absorbing material having inner and outer surfaces and a multiplicity of apertures extending from one surface of the layer to the other. of such size as to admit sound energy,^the outer surface between the apertures being a smooth continuous reflective surface, a thin exible porous decoratable membrane adherent to the 65 outer surface between apertures with the portions of the membrane in registry with the apertures in stretched condition, the whole so arranged as to conceal the apertures and present a planar membrane surface substantially free of surface indentations while admitting sound energy to the apertures.

2. In a building construction, a surfacing element comprised of a .plurality of thin .self-sustaining rigid layers of non-absorbing material having inner and outer surfaces and a multiplicity of apertures extending from one surface of the layers to the other of such size as to admit sound energy, the outer surface between the apertures being a' smooth continuous reflective surface, the la ers being disposed with their outer sur aces in parallelism with adjacent layers in laterally abutting relation, a thin fiexible porous decoratable membrane stretched in parallelism with the outer surfaces and overlying a plurality of layers, said membrane adherent to the surfaces between apertures and concealing the apertures and the joint between adjacent layers, the tension on themembrane being such as to provide a planar membrane surface substantially free of indentations while admitting sound energy to the apertures.

3. A finishing element for building constructions comprising a substantially rigid layer of material having apertures, portions of said sheet struck up from the external surface thereof surrounding the apertures in the form of burrs, a layer of plaster imposed on the external face of said sheet to substantially the average level of said burrs, said layer of plaster having apertures in registration with some of the apertures on said sheet.

4. In a building construction, a pair of joists, sound absorbing material mounted between the joist-s, and a multiple membrane mounted on the joists in spaced relation to the sound absorbing material and comprising an apertured sheet of substantially rigid material,` and a coat of ,plaster on the apertured sheet having apertures registering with some of the apertures in the ri `d sheet.

5. A finishing element for buil ing constructions comprising a substantially rigid layer of material having apertures, a layer of plaster mounted on said rigid sheet and also provided with apertures registering with some of the apertures in said sheet, and a sheet of textile membrane mounted upon said layer of plaster having oresreg: istering with the apertures in said sheet.

6. A finishing element of a building con.- struction comprising a. sheet of fairly rigid material having1 a plurality of apertures, portions of the s eet struck up to form burrs substantially surrounding each-aperture on one side of the sheet, the mouth of the burr being of smaller averagediameter than the diameter of the aperture, and a coating of a thickness substantially the same as the average length of the burrs on the burred side of said sheet having apertures registering with the mouths of some of the burrs.

7. In a building construction, a multiple membrane comprised of two sections of rigid sheet material havin each a plurality of apertures, and dispose with their edges so disposed as to form a perceptible joint, a

plaster finishing element imposed upon both sections and covering the line of the edges thereof, said finishing comprising a secondary membrane, and having apertures in registry with some of the apertures in said sheets, said membrane having some apertures out of registry with apertures in said sheets to effectively conceal the existence of such joints formed by the edges of said sections and effect an over-all finish.

8. A finishing element for building constructions comprising a substantially rigid plate having a surface comprised of plaster' having apertures passing through the plate,

a sheet of textile membrane mounted on the plate and having pores registering with the apertures in said plate.

Signed at Philadelphia, county of Philadelphia and State of Pennsylvania, this 22 day of May, 1930. A a

MAURICE C.v ROSENBLATT.

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