SOUND DEADENING PANELS

Abstract: A sound deadening panel (2) for attachment to a wall, floor or ceiling structure is of variable thickness over its area to provide acoustic insulation characteristics essentially by sound reflection rather than by absorption. The panel (2) is planar on its exposed surface so as to be available for decoration but on its rear surface is profiled due to the variation in thickness. The profiling may be continuous or in discrete steps.

Description: SOUND DEADENING PANELS The present invention relates to sound deadening panels for attachment to the face of a wall, floor or ceiling structure and to walls, floors and ceilings having such panels attached thereto. In order to improve the sound insulation provided by a wall, floor or ceiling structure it is known to attach a sound deadening panel or panels to a face of the structure. These panels typically comprise a flat sheet of plasterboard which is screwed, nailed or otherwise fixed onto a set of parallel spars secured to or forming part of the wall, floor or ceiling structure. In the regions between the spars, the panel abuts a confined volume of air formed by a small air gap, typically between 25mm and 300mm in dimension. Sound deadening panels dissipate vibrational energy and increase the sound insulation provided by the wall, floor or ceiling structure between adjoining rooms in a building. It is an object of the present invention to improve the sound insulating capability of sound deadening panels. According to a first aspect of the present invention there is provided a sound deadening panel for attachment to the face of a wall, floor or ceiling structure, the panel having a plurality of attachment sites at which the panel is secured to the structure, wherein the panel is relatively thin in the region of said attachment sites and is relatively thick in the regions remote from the attachment sites. Preferably, the panel is formed from one or more layers which may be formed of plasterboard although they may alternatively be provided for example by timber plank, chipboard, glass, styrofoam or other suitably dense material to enable the panel to achieve its sound deadening or insulating characteristics by sound reflection rather than absorbance. It has been recognised that sound transmission across a panel is mainly the result of two transmission mechanisms. Firstly, interaction between the panel and the confined volume of air formed by the air gap results in an effect known as the 'coincidence' effect. For panels of uniform thickness, this effect gives rise to a single 'critical' frequency at which sound insulation is considerably reduced. Secondly, the 'natural' resonance of the panel, and the associated harmonics, result in a set of frequencies where again sound insulation is reduced. As the critical frequency is found at a higher frequency, in the middle of the audible spectrum, than the natural frequency, the subjective effect of the critical frequency is usually more severe. By varying the thickness of the panel, the present invention provides panels having a set of critical frequencies, where sound insulation at each critical frequency is reduced to a lesser extent than the reduction which occurs at the single critical frequency which exists for conventional panels. From the point of view.of a human observer, the transmission of low levels of sound at a number of frequencies is less obtrusive than transmission of a relatively high level of sound at a single frequency. Furthermore, because the present invention provides a sound deadening or control panel which has increased stiffness at its unsecured regions the amplitude of vibration is reduced across a large area of the panel and as such the transmission of sound at the natural frequency is reduced. In contrast to conventional sound deadening panels which have a uniform thickness across their areas, panels according to the present invention tend to offer higher acoustic insulation across a wide range of acoustic frequencies . In an embodiment of the present invention, the variation in thickness of the panel is provided by constructing the panel from a plurality of panel layers forming a laminated-type construction where the layers are successively bonded to one another and have a successively decreasing area so that in cross-section the panel has a generally triangular structure (for example pyramid-like) . Where panel attachment sites are provided between edges of the panel, the panel may be constructed by securing groups of secondary panel layers to a main or front panel, the secondary panels being sized and arranged so that in cross-section the panel has the form of a series of pyramid-like structures arranged side-by-side and separated by a zone of the main panel containing panel attachment sites. In general, said panel attachment sites will be provided around the peripheral edges of the panel, for example to enable the panel to be secured to spars or other supports extending in parallel across the supporting structure and which define a fixed spacing for the confined air volume. A resilient pad, for example of flexible cellular foam, maybe provided at said panel attachment sites to prevent conduction of sound into the support structure at the attachment sites. In an alternative embodiment of the invention, the panel may be provided by a single panel layer which is formed or machined to have a variable thickness across its area. This variation may be continuous (such that the coincidence effect is substantially eliminated) or may be provided by one or more step changes in thickness. Typically, the panels will be rectangular to enable a plurality of panels to be arranged to cover the entire surface of a wall or floor to be insulated. According to a second aspect of the present invention there is provided a wall or floor having attached to a side thereof one or more sound deadening panels according to the above first aspect of the present invention. For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which: Fig 1 shows a horizontal cross-section taken through a wall having a sound deadening panel embodying the present invention attached thereto; Fig 2 shows an enlarged detail of the wall and panel assembly of Fig 1; Figs 3 and 4 pictorially illustrate different forms of sound deadening panels embodying the present invention associated with wall structures, with parts cut away in the interests of clarity; Fig 5 illustrates a sound deadening panel in the form of a ceiling tile attached to a ceiling structure; and Fig 6 is a sectional view of a modified version of the tile shown in Fig 5. There is shown in Figure 1 a horizontal cross-section through a wall 1 carrying on one side thereof a sound deadening panel indicated generally by the reference numeral 2. As is shown more clearly in Figure 2, the panel 2 is composed of a single outer panel layer 3 which is secured at attachment sites by way of screws 4 to a set of parallel, vertically extending, U-shaped spars 5 (e.g. GYPROC metal studs; type 48S55; 48,70,146mm wide as required or, for ceilings, GYPROC M/F system) which are in turn secured to the wall 1. A plurality of first panel layers 6 are bonded at spaced apart intervals to the inner surface of the outer panel 3, with the first panel layers 6 running parallel to one another and extending from the top to the bottom of the wall 1. A further corresponding plurality of second panel layers 7 are bonded in turn to the inner surface of respective first panel layers 6 and again extend from the top to the bottom of the wall 1. In each instance bonding is provided over the entirety of the areas of the smaller panel, for example by a surface film of a suitable adhesive. As can be seen from Figure 1 this construction results in a set of pyramid-shaped laminated structures at spaced apart intervals across the width of the panel 2 whilst the outer surface of the outer panel 3 is planar and is available for surface decoration, eg by paint or wallpaper. Positioned in the gaps between adjacent second panel layers 6 are respective flexible cellular foam strips 8 (made for example of mineral or glass fibre or open cell flexible foam) which are compressed in the region between the spars 5 and the outer panel layer 3. The foam strips 8 serve to decouple structureborne sound passing between the wall 1 and the panel 2 via the spars 5. The strips 8 also serve to damp acoustic resonances within the cavity formed between the panel and the wall. Typically, the outer panel layer 3 and the first and second sets of panel layers 6, 7 are provided by plasterboard, for example GYPROC board. Gyproc board is generally available in thicknesses of 12.5, 15 or 19mm although it will be appreciated that any suitable thickness of board can be used. The foam strips 8 provided in the gaps between the first panel layers 6 are advantageously formed of a flexible open cell polymer foam (e.g. BARAFOAM) . Typically, known sound deadening panels comprise a single continuous plasterboard panel which is secured to a wall via spars of the type shown in Figures 1 and 2. However, because of the relatively large spacing between the spars, the panels are able to flex, with bending being greatest in the region centrally between two opposed spars. By increasing panel thickness in this region in accordance with the present invention, the sound deadening panel illustrated in Figures 1 and 2 is stiffer over a large area of the panel, i.e. the effect of the natural resonant frequency of the panel is reduced. Flexing of the panel is thereby reduced and consequently the sound deadening effect of the panel is increased. With conventional panels, at a critical frequency determined by the construction of the panel, transmission through the panel is greatly increased, with transmission levels decreasing on either side of the critical frequency. This critical frequency arises from the 'coincidence' effect which is a panel-air coupling mechanism. With embodiments of the present invention however, instead of a single critical frequency there are a number of critical frequencies determined by the number of discrete panel thicknesses, i.e. three in the case of the panel described with reference to Figs 1 and 2. As a result, acoustic transmission is reduced across a wide range of acoustic frequencies . It will be appreciated that various modifications may be made to the above described embodiment without departing from the scope of the present invention. For example, in place of plasterboard it is possible to use chip board, wood or cement particle fibreboard, timber planks, glass, perspex or any combination of these. In order to cover a relatively large wall surface, a plurality of panels of the type shown in Figures 1 and 2 may be arranged side by side. These panels may comprise one or more spaced apart layered structures. The spars (studs or channels) may extend horizontally rather than vertically as described above. Alternatively, both horizontally and vertically extending spars may be provided. Fig 3 illustrates an arrangement in which the spars 5 are not connected to the wall 1 but instead are connected to transverse spars 5A connected at floor and ceiling level, only the floor-level spar 5A being shown. This arrangement eliminates structureborne transmission of acoustic noise through the spars 5 and into the wall 1. The panel 2 is formed of a planar base panel 3 which is a sheet of plasterboard 12.5mm in thickness and on its rear surface between the vertically disposed spars 5 it is provided with a profiled panel 6 which has a vertically extending peak or apex 10 and tapers latterly from that apex towards the spars 5. In the interests of ease of manufacture the panel 6 terminates in shoulders 11 adjacent the spars 5 so that the main panel 3 can be directly secured to the spars 5. The profiled panel 6 is conveniently formed of dense polystyrene which is a rigid cellular foam and the panel 6 is bonded throughout its entire surface area to the rear surface of the panel 3. A corresponding panel 6 is located between every pair of spars 5 and a fibreglass quilt may be provided within the air space between the panel 6 and the wall 1. In the Fig 3 embodiment the depth of the peak or apex 10 is preferably of the order of 40mm from the rear surface of the plasterboard panel 3 since this figure provides a convenient compromise between the control of acoustic transmission and loss of space within the room. To accommodate the 40mm figure the spars 5 conveniently have a depth of about 75mm. In Fig 4 a panel 2 of similar structure to the panel of Fig 3 is secured to spars 5 carried by the wall 1. In this case the spars 5 extend horizontally and consequently the peak or apex 10 and the shoulders 11 also extend horizontally. In this case in order to achieve a very low profile in the sense of loss of dimension within the room the apex 10 is only of the order of 15mm in depth and typically the spars 5 are therefore only of the order of 20mm in thickness (including the metal attachments which effectively form part of the spars 5) . Fig 5 illustrates a panel 2 which is generally similar to that illustrated in Fig 4 but which is adapted for use as a ceiling tile. In this case the spars 5 are connected by hangars to the joists 1 which form the ceiling structure and the panel 2 is connected by screws (for example) to the spars 5. A fibreglass quilt 12 is schematically illustrated which typically is about 100mm in thickness. In the Fig 5 case the apex 10 is preferably 40mm and the shoulders 11 are 10mm in dimension. Fig 6 illustrates a modified form of ceiling tile or panel 2 which is generally similar to that illustrated in Fig 5 but the non-exposed surface of the panel 2 is provided with a laminated coating of an open cell foam absorbent such as polystyrene which in addition to absorbing sound renders the panel 2 rectilinear which is convenient for transport and handling. The panels 2 illustrated with reference to Figs 3-6 may additionally include the open-cell foam resilient strip

Claims: CLAIMS 1 A sound deadening panel for attachment to the face of a wall, floor or ceiling structure the panel (2) having a plurality of attachment sites (4) at which the panel is secured to the structure, wherein the panel (2) is relatively thin in the region of said attachment sites (4) and is relatively thick in the regions remote from the attachment sites (4) . 2 A sound deadening panel as claimed in Claim 1, wherein the or each relatively thick region of the panel (2) is provided by one or more laminated layers (6,7) adherent to a base layer (3) . 3 A sound deadening panel as claimed in Claim 2, wherein the laminated layers (6,7) provide a stepped profile on only one side of the base layer (3) . 4 A sound deadening panel as claimed in Claim 2, wherein the laminated layers (6,7) provide a substantially continuous stepless profile of thickness variation on only one side of the base layer (3) . 5 A sound deadening panel as claimed in any preceding claim, wherein the panel (2) is made from one or more of the materials; plasterboard, timber plank, chipboard, glass, dense closed cell polymer (eg styrofoam) . 6 A sound deadening panel as claimed in any preceding claim, wherein a resilient pad (8) is provided at the or each attachment site (4) .

Inventors: MACKENZIE ROBIN KENNETH, MACKENZIE, ROBIN, KENNETH
Applicants: EDINBURGH ACOUSTICAL CO LTD, MACKENZIE ROBIN KENNETH, EDINBURGH ACOUSTICAL COMPANY LIMITED, MACKENZIE, ROBIN, KENNETH
Application year: 1997
Main classification: E04B1
IPC codes: E04B1, E04B9