Sound-reducing, composite converting panel
United States Patent Larsson Apr. 15, 1975 1 1 SOUND-REDUCING, COMPOSITE 1,899,653 2/1933 Venzie 52/405 CONVERTING PANEL 2,350,363 6/1944 Massa 161/44 3,228,822 1/1966 Norman 52/615 [76] In ntor: Larsng B i! s 3,405,496 10/1968 Van Der Meer 52 615 Bjornbarsgatan 6, Lomma, Sweden 3,574,104 4/1971 Medler 161/60 [22] Filed: Aug. 25, 1970 C S l d Primary E.raminer-Henry uther an [211 App! 66801 Attorney, Agent, or FirmFred Philpitt [30] Foreign Application Priority Data [57] ABSTRACT Sept. 10, 1969 Sweden 12470/69 A composite covermg panel w1th sound-reducmg [52 us. 01. 428/101- 52/144 52/615 PmPerties, especially intema&#39; Walls and framed 428/188. A 428 I220 partitions, is composed of two boards of substantially 51 1111. C1 EOib 2/23; e046 2/34 Same Size filmed together face face with a 58 Field 61 Search 52/615 403 405 144- imerspace&#39; by means 01 misled Or braided 16l/39 4O 44 56 142 soaked in an elastically hardening, semi-fluid cement 7 181733 6 and stretched between the boards in widely spaced, parallel positions, at least the one of said boards, viz. [56] References Cited the one intended to face a room in the building when the panel is installed, having a low flexural strength 1 9] 709 rfigl 61/60 and being, preferably, a gypsum plasterboard. 1,334,796 3/1920 Robinson.,.......................:.... 161/60 8 Claims, 4 Drawing Figures K I t i K n. s l 1 1 L ;L.: w br.  
 SOUND-REDUCING, COMPOSITE CONVERTING AN &#39;fT i This invention relates to. sound qed&#39;u&#39;cing, composite covering panels for internal use inbuildi&#39;ngs and particularly usefulfor coveringifr amedpartitions. More specifically the invention relates toeti&#39;mposite&#39; covering panels of the kind comprising t woboards of substantially the same planar size jointed together in face to face relationship by means of spacer elements maintaining between the boards an openspace that is small as compared with the thickness of the respective boards, and in which at least one of said boards, viz. the one intended to :face a room in the building. has a relatively low flexural strength.  
  A board is, at least in this specification and in the appendedclaims, considered to have relatively low flexural strength, or in other words a relatively low stiffness combined :with a certain elasticity, if it is capable, under the influence -of sound transmitted thereto, to produce bending waves of a wave-length shorter than that ofthesouncl in air. A board having such a feature will, if properly permitted, to exhibit its capacity in that respect; considerablyreduce the sound radiated from its exposed face to the confronting air and, hence, highly assist in sound insulating building rooms. A typical exponent of the feature in question is an ordinary gypsum plasterboard, but there are many other types of boards of various materials and compositions meeting the same requirements as to a relatively high density, a relatively small thickness, and a low modulus of elasticity.  
  It is the main object of this invention to provide a covering panel of the kind just referred to, in which the properties of the board having a relatively low flexural strength can be utilized in the most favorable manner from an acoustical point of view, and the invention is based on the observation that there is a contrasting relationship between the desire for greatest possible freedom of flexure for the board and the demand for a high structural strength of the connection between the two boards of the panel. It is also an object of this invention to give directions how to properly join the two boards of a panel of the kind referred to hereinbefore in a manner to assure a reliable connection between them without unduly restricting the flexural freedom of the one or both boards and their possibilities to produce bending waves in response to sound waves transmitted to them from any source.  
  In accordance with this invention these objects are achieved by providing spacer elements between the boards comprising cords having at least approximately a round cross section and containing strands extending obliquely in relation to the longitudinal direction of the cords, said cords being secured between the boards in parallelly stretched, widely spaced relationship by means of an elastically hardening adhesive composition. I  
  The cords forming, in combination with the elastically hardening adhesive composition, the spacer elements have proved to garantee an extremely strong connection between the two boards, which is believed to primarily depend on the non-axial orientation of the strands of the cordsand nthe, fact that the adhesive composition will; as&#39;a&#39; result of capillary phenomena, form between each&#39;board and cord ori&#39;either side of the latter a recessed elastic fillet firmly adhering both to the board face and to the related portion of cord circumference. ln fact. the cords together with the elastically hardening adhesive composition will form a kind of hinges adhesively attached to both the opposed board faces by means of laterally extended wings, and this hinge-like action of the spacer elements is extremely advantageous for the freedom of flexure of at least the relatively weak board. At the same time the cords will, due to their elastical compressibility, act as linear cushions between the boards, and. consequently, to a certain degree reduce the sound transmission between the boards.  
  In a preferred embodiment of the invention at least the one board having the relatively low flexural strength is a gypsum plasterboard. In some cases both the two boards can have a relatively low flexural strength, eg be gypsum plasterboards, so that there is no need for knowing which side of the panel should face the room, when the panel is installed.  
  The cords to be used when carrying out the invention can be built up by strands being twisted or braided together and the material of the cords may benatural as well as synthetic fibres. The adhesive composition used for securing the cords may suitably be an elastomeric cement based on rubber or plastics and having, when applied, a viscous or semi-fluid character.  
  In a further preferred form of the composite covering panel embodying the invention the outermost cords between the two boards are located inwardly of the lateral edges of the boards so as to leave an open groove inthe panel edges. Also, the thickness. of each cord is preferably in the order of one thirty-second to one-eighth inch.  
  It should be understood that the hinge-like connections formed between the two boards of a panel embodying this invention will form a kind of flexural nodes, when bending waves are produced in at least the one board in response to sound transmitted thereto. From this follows that the spacing of the cords, i.e. the mutual distance between the parallel hinges,&#34; should be adapted to the flexural properties of the board or boards. If, for example, the board producing bending waves is, as preferred, a gypsum plasterboard having a thickness in the order of one-half to three-fourths inch, the spacing of the cords should be in the order of 3 to 7 inches.  
  For further elucidation of theinvention a preferred form of a sound-reducing, composite covering panel for internal use in buildings embodying the same will now be described with reference to the accompanying drawing. in the drawing FIG. 1 shows an end view ofthe covering panel,  
  FIG. 2 is a fragmentary cross section of the same panel on an enlarged scale, and  
  FIG. 3 is a vertically shortened plan or front view of the panel which is partially broken through and shown on a reduced scale.  
  FIG. 4 is a fragmentary perspective view of one form of a cord spacer element in accordance with my invention.  
 Ordinarily, the composite covering panel embodying the invention is made in lengths approximately correever, the sizes and the manner of installation of the panels is not in itself critical for utilizing-the improved properties of the panels embodying the invention.  
  As will appear from the drawing, the panel comprises two boards 1 and 2, respectively, having substantially the same planar size. At least one of the boards, viz. that which is intended to face a room in the building, which is supposed to be board 1 in the drawing, has a low flexural strength, while the other board 2 can, in principle, be of any desired kind. Preferably, however, also the second board 2 has a low flexural strength. In the example shown, both the boards 1 and 2 are paper covered gypsum plasterboards of the same thickness.  
  As shown in FIGS. 1 and 2, the board I intended to face the room can have bevelled side edges and a slightly larger width than the other board 2, for example in order to more easily permit concealing of attachment or connection elements required for the installation of the panels in&#39;the respective joints between adjacent panels. This. has been most clearly illustrated in FIG. 2, where Ialso an attachment element is shown in dash-and-dot lines and designated by F.  
  The two&#39; boards land 2 are jointed together in face to facewrelationship bymeans of widely spaced twisted or braided cords 3 having at least approximately a round cross section. The cords 3 are secured in stretchedpparallel positions between the boards by meansxof an elastically hardening adhesive composition or&#39;cement4 (FlG. 2) to serve as spacer elements maintaining between .the boards an open space 5 that is passag&#39;es&#39;thus formed in the panel are suitably not closed &#39;atthe ends of the panel, although there is nothing to preventclosing of the passages at the panel ends, if so desired.  
  Before being inserted between the boards land 2 the twisted or braided cords 3 are suitably soaked with the elastically hardening adhesive composition by being passed through a bathe of the cement, which is preferably a semi-fluid elastomeric glue. Of course, there are also other ways to supply the cement to the cords and the boards, but soaking the cords has been found most appropriate. When the cement-soaked cords 3 in stretched positions have been interposed between the boards, the adhesive composition or cement will, because of capillary phenomena, not only adhere to the opposed board faces but also form between each board and the intermediate cord on either side of the latter a recessed fillet, approximately as shown in FIG. 2. As a result of this, there is obtained along each cord an extremely strong connection between the two boards and in cross section this connection will have the character of a hinge or fulcrum having a high degree of flexibility. The twisted or braided strands of the cords. 3 assure a high mechanical strength of each connection because of their non-axial orientation in relation to the cord itself. Nevertheless the cord remains somewhat elastically compressible and makes allowance for the flexi-- bility of the joint. The lateral extension of the fillets or wings formed by the elastically hardening cement 4 the cord circumference without, however, reducing the flexibility of the joint.  
  As shown in the drawing the outermost cords 3 between&#39; the two boards 1 and 2 of the panel are located slightly inwardly of the side&#39;edges of the boards so as to leave an open groove in the panel edges. This is particularly useful for accomodatin&#39;g the attachment or connection elements F as illustrated in FIG. 2. The cords interposed&#39;between the two outermost ones are suitably evenly spaced as shown, and the spacings between the cords should be selected to take advantage of the flexural properties&#39;of the boards in the most favorable manner. Thus, for example, in a panel comprising two gypsum plasterboards having a thickness of one-half inch it has been found most appropriate to use a spacing of the cords in the order of approximately 4 inches. The same spacing may be used also if only the front board 1 has flexural properties while the other or backing board 2 is a stiffer one, which may beadvantageous in some installations. If the thickness of the front board is increased, it is usually advisable to also increase the spacing between the cords.  
 I claim:  
 1. A sound reducing, composite covering panel for internal use in buildings comprising:  
 a. a first planar sheet of gypsum plasterboard, b. a second planar sheet of gypsum plasterboard, c. said first and second sheets having substantially the same size and being between about one-half and three-fourths inch thick, d. said first and second sheets being positioned in a face-to-face spaced apart relationship, e. a plurality of cord spacer elements interposed between said spaced apart first and second sheets, f. said cord spacer elements 1. being spaced apart along substantially parallel lines that are between about 3 and 7 inches apart,  
 2. each having a diameter that is in the order of between about one thirty-second and one-eighth inch,  
 3. each having a substantially round cross section sition which forms between each cord spacer ele-.  
  ment and the plasterboard on each side of the spacer element a recessed elastic fillet firmly adhering both to the plasterboard face and to the ad jacent portion of the spacer element, whereby each spacer element will form a highly flexible hingelike connection between the two facing sheets of plasterboard. 2. A sound-reducing, composite covering panel for internal use in buildings comprising:  
 a. a first board, b. a second board, c. said boards being planar sheets same size, i d. at least oneof said boards having a relatively low flexual strength and being a gypsum plasterboard having a thickness between about one-half and I three-fourths inch,  
 of substantially the e. said boards being positioned in face-to-face spaced relationship,  
 f. a plurality of cord spacer elements interposed between said spaced apart first and second boards.  
 g. said cord spacer elements 1. being spaced apart between about 3 and 7 inches, stretched and essentially parallel,  
 2. each having a substantially round cross section with a diameter that is small as compared with the thickness of said first and second boards,  
 3. containing fibrous strands extending obliquely in relation to the longitudinal direction of the cord and substantially filling out the entire cross section thereof,  
 4. being spaced apart at a distance which is consid erably greater than the cord diameter so as to leave between said two boards an open passageway of slit-like cross section,  
 h. each of said cord spacer elements being secured to each of said two boards by means of an elastically hardening adhesive composition which forms between each cord spacer element a recessed elastic fillet firmly adhering both to the board face and to the adjacent portion of the cord spacer element, whereby each cord spacer element will form a highly flexible hinge-like connection between the two facing surfaces of said boards.  
  3. A sound-reducing, composite covering panel according to claim 2 wherein both of said boards have a relatively low flexural strength.  
  4. A sound-reducing, composite covering panel according to claim 2 wherein both of said boards are gypsum plasterboards.  
  5. A sound-reducing, composite covering panel according to claim 2 wherein the strands of each cord are twisted together.  
  6. A sound-reducing, composite covering panel according to claim 2 wherein the strands of each cord are braided together.  
  7. A sound-reducing, composite covering panel according to claim 2 wherein the outermost cords between the boards are located inwardly of the edges of the boards so as to leave an open groove in the panel edges.  
  8. A sound-reducing, composite covering panel according to claim 2 wherein the thickness of each cord is between about one thirty-second and one-eighth inch.