AU2008288674A1

AU2008288674A1 - An acoustic panel

Info

Publication number: AU2008288674A1
Application number: AU2008288674A
Authority: AU
Inventors: Mark Borroni
Original assignee: Bellmax Acoustic Pty Ltd
Current assignee: Bellmax Acoustic Pty Ltd
Priority date: 2007-08-17
Filing date: 2008-08-15
Publication date: 2009-02-26
Anticipated expiration: 2028-08-15
Also published as: AU2008288674B2; WO2009023900A1

Description

WO 2009/023900 PCT/AU2008/001185 1 AN ACOUSTIC PANEL FIELD OF THE INVENTION The present invention relates generally to acoustics. More particularly, the present invention relates to a panel which is acoustically transparent and/or 5 absorbent relative to conventional plasterboard panels. The panel according to the present invention is particularly suited for lining an interior wall of a building as a substitute to conventional plasterboard panels. It will therefore be convenient to describe the invention in relation to that example application. It should however be understood that the invention is equally suitable for lining other structures, for 10 example ceilings. BACKGROUND TO THE INVENTION The interior walls of buildings, for example houses, offices, restaurants, retail stores, hospitals and the like typically include a frame lined with plasterboard panels. The frame of the wall normally includes a series of upright 15 beams, commonly referred to as studs, to which the plasterboard panels are mounted. The panels are mounted to the studs such that the ends of adjoining panels abut one another. The ends are then covered with wet plaster and subsequently sanded when the plaster dries to provide a continuous wall surface. The wall surface created by the plasterboard panels is also usually painted to 20 provide an aesthetically pleasing appearance. In general, hard, solid materials, for example plasterboard panels, reflect sound better than softer materials. In this respect, sound waves incident upon an interior wall lined with plasterboard tend to be reflected well. The reflected sound waves can also undergo reflection by bouncing off other walls and surfaces, even 25 after the source ceases emitting sound. This phenomenon is known as reverberation and the time it takes for reverberant sound energy to dissipate by 60 dB is known as the reverberation time. The reverberation time in an enclosure, for example a room, can make a significant impact upon the intelligibility of speech. In this respect if the reverberation time is too long speech 30 can be difficult to interpret as the reverberant sound in the room acts as background noise. Ideally, the issue of reverberation is considered and addressed at the design stage of a building. However, in some instances, reverberation problems WO 2009/023900 PCT/AU2008/001185 2 may not become apparent until construction of a building is completed. In both cases there are various options available to address reverberation issues. These include the use of perforated acoustic tiles, carpet, curtains, fabric wall linings and other soft materials. Unfortunately, many of these options are not able to 5 adequately blend with the desired aesthetic appearance. Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material formed part of the prior art base or the common general knowledge in the relevant art in Australia or any other 10 country on or before the priority date of the claims herein. SUMMARY OF THE INVENTION In accordance with a first aspect of the present invention there is provided a panel including an outer portion and an inner portion. The outer portion includes a membrane layer, and the inner portion includes a sound absorbing 15 layer having apertures therein. The inner portion further includes a support layer having openings therein which, in conjunction with the apertures, define a plurality of passageways extending through the sound absorbing layer and the support layer, wherein sound waves incident on the membrane layer pass therethrough and into the passageways and/or sound absorbing layer. 20 Preferably, the support layer is located between the membrane layer and the sound absorbing layer. Preferably, the apertures in the sound absorbing layer include sidewalls through which sound waves within the passageways may pass. In this respect, sound waves which propagate through the sidewalls may have their mechanical 25 energy reduced by interacting with the sound absorbing layer. In this regard, a proportion of the mechanical energy of the sound waves can be converted to thermal energy due to friction. In a preferred embodiment, the sound absorbing layer is made of a porous, fibrous material. The apertures are preferably between approximately 4mm and 30 20mm in diameter and the sound absorbing layer preferably has a thickness of approximately 4 to 15mm. In a particularly preferred embodiment, the apertures in the sound absorbing layer are between approximately 10 to 15mm in diameter and the sound absorbing layer has a thickness of approximately 9mm.

WO 2009/023900 PCT/AU2008/001185 3 In a particularly preferred embodiment, the apertures in the sound absorbing layer cover between 10% and 50% of the surface area of the sound absorbing layer. Further, the sound absorbing layer is preferably bonded to the support layer and the support layer is preferably made of a rigid material. In this 5 regard, the rigid material may be cardboard. In addition, the openings in the support layer can overlie the apertures in the sound absorbing layer. In an embodiment of the present invention, the membrane layer is made of paper, for example kraft paper. In an alternative embodiment the membrane layer is made of a polymer film or a paper having a foil backing. The membrane 10 layer is preferably bonded to the support layer and regions of the membrane layer which overlie the openings in the support layer and apertures in the sound absorbing layer can form a series of diaphragms. In accordance with a second aspect of the present invention there is provided a panel including an outer portion and an inner portion. The outer 15 portion includes a membrane layer, and the inner portion includes a sound absorbing layer having apertures therein. The inner portion further includes a first and second support layer having openings therein which, in conjunction with the apertures, define a plurality of passageways extending through the sound absorbing layer and the support layers, wherein sound waves incident on the 20 membrane layer are able to pass therethrough and into the passageways and/or sound absorbing layer. In accordance with a third aspect of the present invention there is provided a panel including an outer portion and an inner portion. The outer portion includes a membrane layer and the inner portion includes a sound absorbing 25 layer having apertures therein which define a plurality of passageways extending through the sound absorbing layer, wherein sound waves incident on the membrane layer pass therethrough and into the passageways and/or sound absorbing layer. In accordance with a fourth aspect of the present invention there is 30 provided a panel including an outer portion and an inner portion. The outer portion includes a membrane layer and a sound absorbing layer having apertures therein. The inner portion includes a support layer having openings therein. The openings, in conjunction with the apertures, define a plurality of passageways WO 2009/023900 PCT/AU2008/001185 4 extending through the sound absorbing layer and the support layer. Sound waves incident on the membrane layer are able to pass therethrough and into the passageways and/or sound absorbing layer. The inner portion of the panel according to the fourth aspect of the 5 invention may further include a protective layer and the support layer may be located between the protective layer and the sound absorbing layer. The protective layer is preferably air permeable and made of a fibrous material. Further, the support layer of the panel according to the fourth aspect of the invention is preferably made of a rigid material and may include a plurality of 10 indentations. At least one of the indentations in the support layer preferably has side walls which extend around and converge towards one of the openings. In a particularly preferred embodiment, a multiple number of the indentations each include side walls which extend around and converge towards a respective opening. The rigid material from which the support layer is constructed may be 15 metal, for example aluminium. The sound absorbing layer may be adhesively bonded to the support layer and assists to dampen any vibrational sound wave energy within the support layer. In a particularly preferred embodiment, the panel is a wall panel of a wall structure. The wall structure includes a frame upon which panels may be 20 fastened. In a particularly preferred embodiment, a plurality of panels are incorporated into the wall structure with the panels being mounted to the frame to provide a continuous wall surface. The frame preferably includes a plurality of wall studs having sound absorbing material located there between. The panels are mounted to the wall studs such that the inner portion faces towards the frame 25 and the outer portion faces away from the frame with the membrane layer of each panel preferably lying flush with the membrane layer of adjoining panels. Further, each panel preferably has an overall thickness of approximately 10 mm, which matches the overall thickness of a conventional plasterboard panel. Accordingly, panels in accordance with the present invention are able to lie flush with adjoining 30 conventional plasterboard panels when mounted to the frame. The present invention advantageously provides a panel which is able to be incorporated into a wall structure to thereby provide the wall structure with optimal sound absorption properties compared with a wall structure consisting of only WO 2009/023900 PCT/AU2008/001185 5 conventional plasterboard panels. In this respect, the acoustic transparency of the panels, relative to conventional plasterboard panels, enables sound waves incident upon the membrane layer to pass there through and subsequently interact with the passageways and sound absorbing layer. Sound waves may 5 also pass through the panel and subsequently be absorbed by sound absorbing material located between wall studs within the wall structure. The reverberation time of an enclosure having interior walls consisting of panels according to the present invention will advantageously be lower than enclosures having interior walls consisting of conventional plasterboard panels. 10 In addition, the membrane layer of the panel is advantageously able to blend-in with an existing wall surface to thereby provide an aesthetically pleasing continuous wall surface which has the appearance of a wall surface made entirely of conventional plasterboard panels. BRIEF DESCRIPTION OF THE DRAWINGS 15 Further benefits and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. The description should not be considered as limiting any of the statements in the previous section. The preferred embodiments will be described with reference to the following Figures in which: 20 Figure 1 is a perspective view of an outer side of a panel, according to a first embodiment of the invention; Figure 2 is an end view of a portion of the panel illustrated in Figure 1; Figure 3 is a cross sectional view of a wall structure incorporating a plurality of panels illustrated in Figure 1; 25 Figure 4 is a cross sectional view of a portion of the wall structure illustrated in Figure 3, detailing the manner in which a panel as shown in Figure 1 is seamlessly joined to a conventional plasterboard panel; Figure 5 is a perspective view of a side of a support layer of the panel, in accordance with another embodiment of-the invention; 30 Figure 6 is an end view of a portion of a panel incorporating a support layer as illustrated in Figure 5, according to another embodiment of the invention; WO 2009/023900 PCT/AU2008/001185 6 Figure 7 is an end view of a portion of a panel incorporation a support layer similar to that shown in Figure 5, according to yet another embodiment of the invention; Figure 8 is an end view of panel, according to yet another embodiment of 5 the invention; Figure 9 is an end view of panel, according to yet a further embodiment of the invention; Figure 10 is an end view of panel, according to yet another embodiment of the invention; and 10 Figure 11 is a graph showing the absorption coefficient of various samples at a range of frequencies. DESCRIPTION OF PREFERRED EMBODIMENT With reference to the accompanying drawings there is shown a panel 1 which includes an outer portion and an inner portion. The elements of each panel 15 1 represented in the drawings are referred to by the same reference numerals. In the embodiments of the invention illustrated in Figures 1 to 4, 6 and 7, the outer portion of the panel 1 includes a membrane layer 3 and a sound absorbing layer 5 having apertures 7 therein, and the inner portion of the panel 1 includes a support layer 9 having openings 11 therein. The openings 11, in 20 conjunction with the apertures 7, define a plurality of passageways 13 which extend through the sound absorbing layer 5 and the support layer 9. In this respect the openings 11 and the apertures 7 preferably overlie one another. The inner portion of the panel 1 may further include a protective layer which is preferably in the form of a scrim layer 15 made of a fibrous material. In this 25 particular embodiment, the support layer 9 is preferably located between the scrim layer 15 and the sound absorbing layer 5. The scrim layer 15 is air permeable and functions to prevent debris from readily entering the passageways 13. In addition, the scrim layer 15 functions to protect the membrane layer 3 of adjacent panels 1 from being accidentally torn by edges of the support layer 9 30 when the panels 1 are stacked together during storage and transit. The sound absorbing layer 5 is preferably located between the membrane layer 3 and the support layer 9.

WO 2009/023900 PCT/AU2008/001185 7 In the embodiments of the panel 1 illustrated in the drawings, the membrane layer 3 is preferably impermeable to air flow and made of paper, for example a high wet strength kraft paper, or polymer film. The membrane layer 3 preferably has a thickness of no greater than 0.05 mm and a surface density of 5 less than 180 g/m 2 . In a particularly preferred embodiment the membrane layer 3 is made of a paper having a surface density between approximately 35 to 45 g/m 2 . The paper may also contain a clay component. In this respect the paper may be provided with a clay coating. The membrane layer 3 is effectively the outer skin of the panel 1 and can be painted if desired, preferably with flexible 10 acrylic or latex type paints. The sound absorbing layer 5 can be made of foam or a compressible fibrous material, for example a non woven polyester material. The sound absorbing layer 5 preferably has a thickness of approximately 4 to 15 mm and a surface density between approximately 1000 and 2000 g/m 2 . The apertures 7 in 15 the sound absorbing layer 5 can range between approximately 4 mm and 20 mm in diameter. Each aperture 7 includes side walls 17 which have a width corresponding to the thickness of the sound absorbing layer 5. The apertures 7 in the sound absorbing layer 5 cover approximately 10 to 50% of the surface area of the sound absorbing layer 5. In a particularly preferred embodiment, the 20 apertures 7 in the sound absorbing layer 5 cover approximately 25% of the surface area of the sound absorbing layer 5. Those regions of the membrane layer 3 which overlie the apertures 7 in the sound absorbing layer 5 form a series of diaphragms 6. The compressibility of the sound absorbing layer 5 cushions the membrane layer 3 thereby enhancing the membrane layers 3 ability to vibrate in 25 response to sound- waves incident on the membrane layer 3. In the embodiments of the panel 1 illustrated in Figures 1 to 4, 6, 7 and 10, the membrane layer 3 may be bonded to one side of the sound absorbing layer 5 by applying an adhesive. Alternatively, a bonding layer 39, which is preferably in the form of a thin layer of thermoplastic material, for example polyethylene, may 30 be provided on one side of the membrane layer 3. In this respect, by applying heat to the thermoplastic material the membrane layer 3 can be heat laminated to the underlying sound absorbing layer 5.

WO 2009/023900 PCT/AU2008/001185 8 In the panel 1 illustrated in Figures 1 to 4, 6 and 7, the support layer 9 is the main structural layer of the panel 1. The support layer 9 is preferably a sheet material that is rigid and made of metal, for example aluminium or steel. The metal preferably has a thickness of between approximately 0.5 mm and 2 mm. 5 The support layer 9 provides the panel 1 with structural rigidity and preferably has one side adhesively bonded to the sound absorbing layer 5. The openings 11 in the support layer 9 are preferably circular and have a diameter of between approximately 3 mm and 15 mm. As mentioned previously, the openings 11 in the support layer 9, in conjunction with the apertures 7 in the sound absorbing 10 layer 5, define a plurality of passageways 13 extending through the sound absorbing layer 5 and the support layer 9. Sound waves incident on the membrane layer 3 are able to be readily transmitted therethrough, particularly in those regions of the membrane layer 3 where the diaphragms 6 are formed. In the passageways 13 behind the diaphragms 6, sound pressure can be dissipated 15 in the sound absorbing layer 5 by passing through the sidewalls 21. In the embodiment of the panel 1 illustrated in Figure 8, the outer portion of the panel 1 includes the membrane layer 3, and the inner portion of the panel 1 includes a sound absorbing layer 5. The inner portion further includes first and second support layers 9, 10 between which the sound absorbing layer 5 is 20 located. The first and second support layers 9, 10 provide the panel 1 with rigidity and are preferably made of a bonded, fibrous polyester, thick paper or cardboard, a polymer sheet or a metal foil. The sound absorbing layer 5 is effectively encased by the first and second support layers 9, 10 which is particularly advantageous when the sound absorbing layer 5 is made of an open cell foam 25 material. In this respect, the rigidity of the first and second support layers 9, 10 advantageously compensates for the relative pliancy of the foam material. Accordingly, the panel 1 is able to maintain a sufficient degree of overall stiffness. In addition to providing a degree of rigidity, the support layer 10 is advantageously able to provide a smooth surface upon which the membrane 30 layer 3 is placed. The support layers 9, 10 can be bonded to opposite sides of the sound absorbing layer 5 by applying an adhesive. Alternatively, a thin layer of thermoplastic material, for example polyethylene, may be provided on the support layers 9, 10. In this respect, by applying heat to the thermoplastic material the WO 2009/023900 PCT/AU2008/001185 9 support layers 9, 10 can be heat laminated to the sides of the sound absorbing layer 5. The membrane layer 3 in this embodiment is preferably made of a high wet strength paper and may be bonded to one side of the support layer 10 by applying an adhesive. Alternatively, a bonding layer 39, which is preferably in the 5 form of a thin layer of thermoplastic material, for example polyethylene, may be provided on one side of the membrane layer 3 and/or the support layer 10. By applying heat to the thermoplastic material the membrane layer 3 can be heat laminated to the support layer 10. The embodiment of the panel 1 shown in Figure 9 is the same as that 10 shown in Figure 8 except that the inner portion only includes a support layer 10 on one side of the sound absorbing layer 5. In this regard, the support layer 10 is located between the sound absorbing layer 5 and the membrane layer 3. In this particular embodiment, the panel 1 has an overall thickness of approximately 10mm. The membrane layer 3 is preferably made of paper having a thickness 15 which is no greater than approximately 0.05mm, the support layer 10 is preferably made of cardboard having a thickness of approximately 0.5mm, and the sound absorbing layer 5 is preferably made of a compressed fibrous polyester having a thickness of approximately 9.5mm. The fibrous polyester preferably has a surface density between approximately 1000 and 2000 g/m 2 . The sound 20 absorbing layer 5 provides the panel 1 with structural rigidity. The rigidity of the sound absorbing layer 5 also ensures that the process of forming the apertures 7 can be performed relatively easily by punching. Further, the apertures 7 in the sound absorbing layer 5 may be formed after the support layer 10 has been adhered to the sound absorbing layer 5 such that the openings 11 and apertures 25 7 can be formed simultaneously in a single punching action. This assists to ensure that the openings 11 and the apertures 7 overlie one another. In the embodiment of the panel 1 shown in Figure 10, the outer portion of the panel 1 consists of the membrane layer 3, and the inner portion of the panel 1 consists of the sound absorbing layer 5. In this particular embodiment, the sound 30 absorbing layer 5 is preferably made of a fibrous material which is compressed to provide rigidity. Alternatively the sound absorbing layer 5 may consist of one or more layers of corrugated cardboard.

WO 2009/023900 PCT/AU2008/001185 10 The overall shape of the one or more support layers 9, 10 can be varied to suit specific applications. In the embodiments of the panel 1 shown in Figures 1 to 4 of the drawings, the openings 11 in the support layer 9 are separated from each other by a surrounding region which is generally planar. As a result, the 5 entire surface of one side of the support layer 9 generally abuts with the sound absorbing layer 5, as shown in Figures 1 to 4. To further improve the support layers 9 rigidity and increase the depth of the passageways 13, alternative embodiments of the support layer 9, as shown in Figures 5 to 7, can be utilised. As mentioned previously, like reference numerals are used in all of the 10 embodiments to identify the same features. The support layers 9 shown in the panel 1 illustrated in Figures 5 to 7 all include a plurality of indentations 19 which each include sidewalls 21 which extend around and converge towards their respective opening 11. The openings 11 in the support layer 9 shown in Figure 5 are circular, however the openings 11 may be of any other desired shape, for 15 example square, triangular, etc. The support layers 9 illustrated in Figures 5 to 7 are similar to the sheet materials disclosed in Australian Provisional Patent Application No. 2007902701, the contents of which are hereby incorporated by reference. The overall thickness of the support layer 9 shown in Figure 5, and the 20 support layers 9 shown in the panel 1 in Figures 6 and 7, ranges between approximately 3 and 6 mm, depending upon the depth of the indentations 19 and the thickness of the metal. In Figures 3 and 4 of the accompanying drawings, there is shown a wall structure 23. The wall structure 23 includes a frame consisting of a plurality of 25 wall studs 25. The panels 1 are fastenable to the wall studs 25 in a conventional manner by using nails, screws, adhesives of the like. The panels 1 depicted in the wall structure 23 shown in figures 3 and 4 are of the type shown in figures 1 and 2. Panels 1 in accordance with the other embodiments can be fastened to the wall studs 25 in the same manner. 30 As shown in Figure 3, cavities are provided between adjoining wall studs 25. Each cavity effectively becomes an enclosed air volume when the panels 1 are mounted to the walls studs 25. Sound absorbing material 29 can be located in the cavities to absorb sound waves which, instead of being absorbed by the WO 2009/023900 PCT/AU2008/001185 11 sound absorbing layer 5, pass through the panel 1. In Figure 4 an edge portion 31 of a panel 1 is shown in abutment with an edge of a conventional plasterboard panel 27. The overall thickness of the panel 1 is the same as the conventional plasterboard panel 27. However, the thickness of the panel 1 in the vicinity of the 5 edge portion 31 is reduced 1 by the compression the sound absorbing layer 5 near the edge portion 31. As a result the thickness of the panel 1 tapers towards the edge portion 31, as shown in Figure 4. The panel 1 is thereby provided with an edge portion 31 which resembles the edge of the conventional plasterboard panel 27. By using conventional wet plaster jointing techniques an infill of plaster 10 33 can be provided over the edge portion 31 such that the panel 1 is seamlessly incorporated into the wall structure 23 with the membrane layer 3 providing a continuous wall surface with the infill of plaster 33 and an outer face 37 of the plasterboard panel 27. Once painted, the continuous wall surface 35 has the same appearance of a wall structure 23 made solely of plasterboard panels 27. 15 The sound absorbing material 29 can be slightly spaced from the panels 1 such each panel 1 is able to oscillate in response to sound waves incident on the panel 1. In this regard, the panels 1 in combination with the enclosed air volumes behind the panels 1 act like a series of panel absorbers. A panel absorber is a form of resonant oscillating mass-spring system. A panel absorber typically 20 includes a non rigid, non porous planar material which is positioned over an enclosed air space. The planar material is able to resonate in response to sound waves incident on the material with dampening being provided by the enclosed air space. A panel absorber is generally able to absorb a narrow range of frequencies with the range being dependent upon the mass of the planar material 25 and the dimensions of the air space. The general equation for determining the frequency absorbed is: F = 60/4M.D where F = frequency 30 M = mass per square meter of the planar material D = the depth of the air space behind the planar material WO 2009/023900 PCT/AU2008/001185 12 When applying this equation to the present invention, the panels 1 can be regarded as the planar material which is able to oscillate and the enclosed air volumes between the wall studs 25 can be regarded as the air space. As conventional plasterboards have a relatively high mass per square meter the 5 frequency absorbed according to the above equation will be relatively low due to the mass of conventional plasterboards. In this regard, the frequencies absorbed tend to be in the range below 500 Hz. In contrast, the relatively low mass per square meter of the panels 1 of the present invention enables the frequencies absorbed to be of a much higher. In addition, the ability of sound waves to be 10 readily transmitted through the membrane layer 3, particularly in those regions where diaphragms 9 are formed, provides improved sound absorption over a broad range of frequencies. Accordingly, the relatively low mass of the panels in combination with the panel's ability to enable incident sound waves to interact with the sound absorbing layer 5 and/or pass through the panel, provides 15 improved absorption over a broad range of frequencies and absorption at higher frequencies than conventional plasterboards. The graph in Figure 11 shows the absorption coefficient of various acoustic shield samples at a range of frequencies. The samples where all mounted to a frame structure having wall type timber studs and sound absorbing material 20 located therebetween. The sample panels identified in the graph as BellMax WP1, BellMax WP2 and BellMax WP3 ("the BelIMax samples") all consist of an outer portion including a membrane layer made of a clay coated paper, and a sound absorbing layer made of fibrous polyester. The inner portion of these three samples all include a support layer made of an aluminium mesh. In the samples 25 identified as BellMax WP1 and BellMax WP3 the apertures in the sound absorbing layer are 15mm in diameter. In the BellMax WP2 sample the apertures in the sound absorbing layer are 10mm in diameter. In the BellMax WP1 and WP2 samples the apertures cover approximately 25% of the surface area of the panel. In contrast, the apertures cover approximately 50% of the surface area of 30 the panel in the BellMax WP3 sample. The other samples in the graph in Figure 11 are a commercial ceiling tile, a commercial wall tile and a plasterboard panel having a thickness of 10mm. The graph in Figure 11 demonstrates that the BellMax sample panels all have an absorption coefficient between approximately WO 2009/023900 PCT/AU2008/001185 13 0.8 and 1.0 at frequencies of approximately 250Hz to 1000Hz. In comparison, all of the other samples in the graph have a much lower absorption coefficient over this frequency range. Whilst the commercial ceiling and wall tiles provide reasonably good absorption at frequencies above 1300Hz their absorption ability 5 declines steadily below 1300Hz with their absorption coefficient declining to approximately 0.1 below 300Hz. The performance of the plasterboard panel is even worse with the absorption coefficient being below approximately 0.1 over all frequencies above 200Hz. Although the frequency range of speech can vary widely the fundamental frequency range for speech is approximately 135 to 10 400Hz. The graph demonstrates that the BellMax samples provide excellent absorption over the fundamental frequency range for speech. This is particularly advantageous as most background noise in offices, restaurants and the like falls into this range of frequencies. Accordingly, by incorporating the panels of the present invention into the walls of such localities the background noise can be 15 readily absorbed into the walls. The present invention advantageously provides a panel which can be used as a substitute for conventional plasterboard panels. The panels according to the present invention are lightweight and acoustically transparent, relative to conventional plasterboard panels, in that sound waves incident on the panels are 20 able to readily penetrate the panels rather than be reflected. Accordingly, by incorporating the panels into interior walls lower reverberation times can be achieved, thereby reducing reverberated noise and subsequently improving the intelligibility of speech. Further, the membrane layer 3 of the panel 1 advantageously provides the panel 1 with an outer surface which is smooth and 25 flat and has the same appearance as a conventional plasterboard panel when painted. Accordingly, the panel 1 of the present invention is advantageously able to be used in a wall structure to create a wall having the same aesthetic appearance as a wall lined with conventional plasterboard panels. The panels are particularly well suited for use in hospitals, manufacturing 30 facilities, offices, etc where noise from a variety of sources needs to be absorbed. For example, drilling and cutting equipment used in hospital theatres during surgical procedures can produce considerable levels of noise. By incorporating the panels into the walls of the theatre the noise generated can be absorbed into WO 2009/023900 PCT/AU2008/001185 14 the walls rather than be reflected. Medical staff are thereby able to more easily hear one another during the surgical procedure, minimising the risk of important instructions be misheard. In addition, the panels according to the present invention are advantageously able to be integrated into a wall structure in an 5 aesthetically pleasing manner. Further, the panels can be painted and can be installed utilising the same methods and skills as conventional plasterboard panels. The panels can also be used for other applications, for example as the outer surface of a motor vehicle dashboard. As the present invention may be embodied in several forms without 10 departing from the essential characteristics of the invention it should be understood that the above described embodiments should not be considered to limit the present invention but rather should be construed broadly. Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention. 15 20

Claims

1. A panel including an outer portion and an inner portion, the outer portion including a membrane layer, and the inner portion including a sound absorbing layer having apertures therein, the inner portion further including a support layer 5 having openings therein which, in conjunction with the apertures, define a plurality of passageways extending through the sound absorbing layer and the support layer, wherein sound waves incident on the membrane layer pass therethrough and into the passageways and/or sound absorbing layer.

2. A panel as claimed in claim 1 wherein the support layer is located between 10 the membrane layer and the sound absorbing layer.

3. A panel as claimed in either claim 1 or 2 wherein the apertures in the sound absorbing layer include sidewalls through which sound waves within the passageways may pass.

4. A panel as claimed in any one of the preceding claims wherein the 15 apertures in the sound absorbing layer range between 4mm and 20mm in diameter.

5. A panel as claimed in any one of the preceding claims wherein the sound absorbing layer is made of a fibrous material or a foam material.

6. A panel as claimed in any one of the preceding claims wherein the 20 apertures in the sound absorbing layer cover between 10% and 50% of the surface area of the sound absorbing layer.

7. A panel as claimed in any one of the preceding claims wherein the sound absorbing layer is bonded to the support layer.

8. A panel as claimed in any one of the preceding claims wherein the support 25 layer is made of a rigid material. WO 2009/023900 PCT/AU2008/001185 16

9. A panel as claimed in claim 7 wherein the rigid material is cardboard.

10. A panel as claimed in any one of the preceding claims wherein the openings in the support layer overlie the aperatures in the sound absorbing layer. 5

11. A panel as claimed in any one of the preceding claims wherein the membrane layer is bonded to the support layer.

12. A panel as claimed in any one of the preceding claims wherein regions of the membrane layer which overlie the openings in the support layer and apertures in the sound absorbing layer form a series of diaphragms. 10

13. A panel as claimed in any one of the preceding claims wherein the membrane layer is a polymer film.

14. A panel as claimed in any one of claim 1 to 12 wherein the membrane layer is made of paper.

15. A wall structure including a frame and a wall panel mounted to the frame, 15 wherein the wall panel is a panel as claimed in any one of the preceding claims.

16. A wall structure as claimed in claim 15 wherein a plurality of wall panels are mounted to the frame to thereby provide a continuous wall surface.

17. A wall structure as claimed in claim 16 wherein a multiple number of the wall panels are panels as claimed in any one of claims 1 to 14. 20

18. A wall structure as claimed in any one of claims 15 to 17 wherein the frame includes a plurality of wall studs having sound absorbing material located therebetween.

19. A wall structure as claimed in claim 18 wherein the panels are mounted to the wall studs. WO 2009/023900 PCT/AU2008/001185 17

20. A wall structure as claimed in any one of claims 16 to 19 wherein the membrane layer of each panel lies flush with the wall surface.

21. A wall structure as claimed in any one of claims 15 to 20 wherein the wall structure is part of an interior wall in a building. 5

22. A panel including an outer portion and an inner portion, the outer portion including a membrane layer, and the inner portion including a sound absorbing layer having apertures therein, the inner portion further including a first and second support layer having openings therein which, in conjunction with the apertures, define a plurality of passageways extending through the sound 10 absorbing layer and the support layers, wherein sound waves incident on the membrane layer pass therethrough and into the passageways and/or sound absorbing layer.

23. A panel as claimed in claim 22 wherein the support layers are provided on opposing sides of the sound absorbing layer. 15

24. A panel as claimed in claim 22 or claim 23 wherein the sound absorbing layer is made of a foam material or a fibrous material.

25. A panel including an outer portion and an inner portion, the outer portion including a membrane layer and the inner portion including a sound absorbing layer having apertures therein which define a plurality of passageways extending 20 through the sound absorbing layer, wherein sound waves incident on the membrane layer pass therethrough and into the passageways and/or sound absorbing layer.

26. A panel including an outer portion and an inner portion, the outer portion including a membrane layer and a sound absorbing layer having apertures 25 therein, the inner portion including a support layer having openings therein which, in conjunction with the apertures, define a plurality of passageways extending through the sound absorbing layer and the support layer, wherein WO 2009/023900 PCT/AU2008/001185 18 sound waves incident on the membrane layer pass therethrough and into the passageways and/or sound absorbing layer.