Acoustic or noise barriers provided along the sides of roadways, such as along freeways to absorb and deflect road noise away from adjacent properties, particularly domestic properties, are well known. There are a number of forms of such noise or acoustic barriers. One type comprises stone, masonry, or concrete formations which are designed to reflect noise and thus shield properties beyond the barriers. Such hard dense materials do not absorb sound particularly efficiently although particular geometries may be used to assist absorption and diffusely deflect the incident sound waves.

Another known kind of roadside sound or noise barrier comprises timber panels, e. g. made of chemically treated pine so as to resist premature rotting by fungal decay. However, it is believed that such timber noise barriers will nevertheless have an uneconomically short useful life since such structures show substantial structural deterioration after 10 years.

Some standards or specifications for such noise barriers require a 40 year life so that it is extremely doubtful that timber sound barriers will achieve such a life.

It is an object of the present invention to provide an acoustic or noise barrier which is effective in use to substantially attenuate incident sound, particularly noise from road traffic and/or industrial noise.

It is a further object to provide an acoustic or noise barrier which can be suitable for external installation and which can have a substantial effective period of use.

It is an object of a second aspect of the invention to provide a method of effectively reducing noise reaching an area nearby to the source of noise.

According to a first aspect of the present invention there is provided an acoustic barrier including an acoustic insulation body composed of a substantial proportion of uncomminuted rice hulls and a casing enclosing the body of rice hulls, the casing providing the properties of (a) strength to the barrier, (b) at least partial permeability to sound waves so as to pass incident sound waves to the insulation body, and (c) inhibiting access of vermin and birds to the body containing rice hulls.

In one embodiment, the acoustic insulation body includes rice hulls which are bonded together so that the body has at least self-supporting structural integrity. However, it is possible in an alternative embodiment to provide rice hulls which are not bonded together or which are bonded together with insufficient strength to provide self-supporting sttuctural integrity, the acoustic insulation body having a shape defined by confining walls which confine the material of which the body is composed.

The material including uncomminuted rice hulls of which the acoustic insulation body is composed may be compressed to provide a density and thickness of the body to effectively attenuate sound frequencies which are expected to be encountered and attenuated by the barrier. If desired, the acoustic insulation body may have zones of differing densities through the thickness of the body so as to provide in the different density zones effective attenuation of different expected frequencies or frequency ranges.

Preferably the casing enclosing the acoustic insulation body provides sufficient strength to the barrier so that the barrier is of at least self-supporting structural strength. In the case of the barrier being for use as a roadside noise barrier, the casing in conjunction with any structural strength provided by the acoustic insulation body, would be of sufficient

strength and rigidity to withstand wind and storm loadings to which the barrier will be exposed in use.

The casing may be provided with passages or perforations so as to provide the property of at least a partial permeability to sound waves thereby enabling the sound waves to pass the casing and reach the acoustic insulation body. For example, the barrier may have the configuration of a panel having opposed broad faces, the casing including spaced face panels providing the opposed broad faces of the barrier panel. The total area of the perforations provided in at least one of the face panels providing the opposed broad faces of the barrier panel preferably is in the range of 30 to 70% of the total area of the respective broad face of the panel.

The casing may be spaced from the acoustic insulation body so as to leave an air gap between the body and the casing. Where the casing includes a surface sheet provided with apertures, the apertures can act as sound wave sources from which sound waves radiate towards the acoustic insulation body upon sound waves impinging on the surface sheet of the casing, the air gap between the surface sheet and the body preferably being of sufficient width to enable incident sound passing through the apertures to spread across substantially the full surface area of the body facing the apertured surface sheet. The surface of the body located behind and spaced from the casing by the air gap may be non-planar having regular or irregular surface indentations and/or protrusions and/or convolutions.

In an alternative embodiment to that providing an air gap, the casing may be located in contact with or closely adjacent the acoustic insulation body. In either embodiment, the barrier may further include a screen or membrane interposed between the casing and the respective adjacent or facing surface of the acoustic insulation body, the screen or membrane inhibiting access to the surface of the body by birds, vermin, insects, and/or water.

According to a second aspect of the invention there is provided a method of attenuating noise arising from a source of noise and radiating towards a nearby area to be screened from the noise, the method comprising erecting at least one acoustic barrier according to the first aspect of the invention in a position interposed between the source of noise and the nearby area whereby the noise is attenuated by the barrier.

In the method according to the invention wherein the noise source comprises a roadway carrying motor vehicle traffic which generates the noise and the nearby area comprises land or property adjacent the roadway, the method preferably includes erecting multiple acoustic barriers each of which is constructed according to the first aspect of the invention, the barriers being erected so as to be substantially contiguous with each other along at least a section of the roadway at one side thereof so that noise from the motor vehicle traffic on the roadway is incident upon and is attenuated by the acoustic barriers.

Possible and preferred features of the present invention will now be described with particular reference to the accompanying drawings. However it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention. In the drawings : Fig. 1 shows a sectioned panel suitable for use as a roadside acoustic barrier according to an embodiment of the present invention; Fig. 2 shows a sectioned view of an alternative panel construction for use as a roadside acoustic barrier ; Fig. 3 shows a front elevation of a wall functioning as a noise barrier, in accordance with an embodiment of the present invention; Fig. 4 is a top plan view of the wall shown in Fig. 3 ; and Fig. 5 is a top plan view of an alternative construction of the wall shown in Fig. 3.

The acoustic or noise barrier 10 in Fig. 1 includes an acoustic insulation body 20 composed of a substantial proportion of uncomminuted rice hulls and a casing enclosing the body of rice hulls. The casing provides the properties of strength to the barrier, at least partial permeability to sound waves so as to pass the sound waves to the insulation body 20, and inhibiting access of vermin and birds to the body 20 of rice hulls.

The acoustic insulation body 20 may be composed of rice hulls, with or without other materials providing the bulk of the body, which are bonded together so that the body has at least self supporting structural integrity. The rice hulls may be bonded to form the body 20 by any suitable binder such as a resin binder (e. g. urea formaldehyde resin, phenol formaldehyde resin, melamine binder such as MUPF, or other natural or synthetic resin binders).

The uncomminuted rice hulls may be raw rice hulls, i. e. rice hulls derived directly from the process which recovers the edible rice grains. Such rice hulls are mostly a waste product. However, their concave shape, and resistance to decay by rotting (due to high silica content and waxy surface) can make them an effective acoustic absorbent material.

Rice hulls can be mixed with a suitable binder and compressed to any required density. The density, as well as the thickness, of a panel formed of bonded rice hulls will determine the sound frequencies which the panel will most effectively attenuate. Hence for an acoustic or noise barrier for location alongside a road way where particular frequencies of sound are expected, the density as well as the thickness of the body 20 of rice hulls can be determined, e. g. empirically, to most efficiently attenuate those frequencies. It is also possible (see Fig.

2) to provide the acoustic insulation body 20 having multiple zones 26,27 of different densities throughout the thickness of the body, for example two or more individual layers 26, 27 of bonded rice hulls may be provided as a laminate or simply superimposed individual

layers, the different densities being chosen to attenuate different expected frequencies or frequency ranges.

It will be appreciated that materials other than rice hulls may be included if desired to impart additional properties or to assist in the acoustic insulating properties of the body 20.

For example comminuted rice hulls having ranges of particle sizes down to essentially powder or individual fibre sizes may be incorporated particularly if a denser body or a denser layer of the body is desired.

In addition to other materials contributing to the bulk or to the acoustic properties, other materials to contribute other desirable properties may be incorporated. For example materials to inhibit or deter microbial or insect attack can be incorporated. A suitable insect deterrent which can be incorporated in the composition from which the acoustic insulated body is composed is manufactured by Orica Limited (formerly ICI) and supplied under the trade mark"Perigen". In Fig. 1 some reinforcing material 21 is incorporated into the body 20 composed of or including rice hulls. For example fibrous materials or mesh 21 may be incorporated to provide additional structural integrity or strength. Such additional components may also be made of materials and have a geometry or configuration to contribute to the sound attenuation and/or reflection of sound which has entered the body.

In the case of a body composed of substantially uncomminuted rice hulls, reference may be made to patent specifications AU 48947/93 (patent No. 651285) and AU 70802/96 (and its equivalent PCT/AU96/00626) which describe in some detail the construction and manufacture of panels composed of rice hulls bonded together with a thermo setting resin binder. The contents of those patent specifications are incorporated herein by reference to enable understanding of suitable methods of manufacturing a body 20 for use in the present invention.

The casing 13 enclosing the acoustic insulation body 20 provides strength to the barrier so that the barrier as a whole is of at least self-supporting structural strength. In particular, for use in roadside noise barriers, the barrier must be of sufficient strength and rigidity to withstand not only forces normally encountered during the installation process but also wind and storm loadings which can be substantial at some sites on an open road or freeway. The casing 13 for example may be a metal panel and may, for example, comprise an aluminium panel, a cheaper type of stainless steel, a galvanise or powder coated mild steel panel, or the like.

To prevent vermin and/or birds from causing any significant damage to the body 20 composed of rice hulls, the casing 13 covers at least the totally exposed surfaces or faces of the barrier (when installed in use). For example, if the barrier is to be installed at the side of a roadway generally in the form of a fence, both broad faces of the insulation body 20 composed of rice hulls are entirely covered by spaced face panels 11,12.

In Fig. 2, the face panels 11,12 define confining walls which confine therein the material including rice hulls of which the body 20 is composed. In this embodiment, the rice hulls need not be bonded together, or may be bonded with insufficient strength to provide self-supporting structural integrity to the body 20. Some minimal amount of binder may be desirable to inhibit settling of the rice hulls over time, possibly measured over several decades. A screen or membrane 25 is interposed between the face panel 11 and the body 20 so as to inhibit access to the surface of the body 20 by birds, vermin, insects, and/or water.

Although illustrated adjacent face panel 11 only, the screen or membrane 25 may also be provided adjacent face panel 12, and may also be provided in the air gaps 22 in the embodiment of Fig. 1. In the case of rice hulls being loosely filled into the casing 13 and remaining unbound, or relatively weakly bound together, the rice hulls may be rammed or

otherwise compressed to the required density. The screen or membrane 25 helps to confine the material against projecting or passing through the perforations 17.

The other function of the casing 13, namely to pass sound waves into the insulation body 20 of rice hulls is preferably achieved by providing passages or perforations 17 in the casing 13. For example, each face panel 11,12 may be defined by a metal panel having perforations 17, the total area of the perforations being a substantial proportion of the total surface area of the relevant face panel 11, 12 of the barrier. For example, the total area of the perforations 17 may be in the range of 30 to 70% of the area of the face panel 1l, 12.

However, to provide a barrier to vermin and birds, the individual perforations 17 can be of a suitable size for this purpose. If the barrier is to function primarily as a reflector of the incident sound, a lower surface area of the perforations 17 can be provided, (or none at all) i. e. a greater area of"solid"reflective surface area can be provided. However, if the barrier is primarily intended to absorb incident sound, a greater perforation total area can be provided.

For roadside noise barriers, the product of the present invention may be in the form of a panel which can be prefabricated off site and installed on site. The panel may have the acoustic insulation body 20 composed of rice hulls forming a core and a casing 13 on both major faces of the panel and preferably also at respective opposite sides and/or respective opposite ends of the panel. One particular suitable form of panel having a metal casing enclosing the opposite broad faces and at least two opposite edges is described and illustrated in patent specification No. AU-20952/88 (patent No. 595130), and its equivalent US 4,941,304, and the contents of those patent specifications are incorporated herein bv cross reference to enable full understanding of a suitable form of casing (although the patent invention is not to be limited to casings as shown in those specifications). In those patent

specifications there is described and illustrated a panel having a female edge formation 15 and a complementary male edge formation 16 which can interlock or interfit with similarly constructed adjacent panels. Such panels when used according to the present invention as acoustic or noise barriers can be interfitted with each other to provide an acoustic or noise barrier wall, e. g. at the side of a roadway. Such individual panels can be for example formed as individual planks which can be built up to form a wall, the planks being laid on top of one another and extending between spaced upright posts. This is described later with reference to Figs. 3 to 5. However, it will be appreciated that it is also possible to provide individual panels having a substantial surface area and which are mounted side by side to form an acoustic barrier or a noise reflecting or noise attenuating wall.

In the embodiment in Fig. 1, the barrier comprises the acoustic insulation body 20 composed of a substantial proportion of uncomminuted rice hulls and an enclosing casing 13 which is spaced from the body of rice hulls so as to leave an air gap 22 between the body 20 and the casing 13. The air gap 22 can provide a number of useful functions. Firstly, the gap 22 can help with the acoustic attenuation properties of the barrier. Since individual apertures 17 provided in the casing 13 can act as effective sound wave sources from which sound waves radiate towards the body 20 composed of at least a proportion of rice hulls, the provision of the air space or gap 22 between the face panel 11,12 and the rice hulls body 20 can help to spread the sound passing through the apertures 17 of the face panel across the full surface area of the rice hulls body 20. Furthermore, the provision of the air gap 22 can enable the surface 28 of the rice hulls body located behind the casing 13 to be of irregular or convoluted shape so as to further enhance sound attenuation. That is, the body 20 of bound rice hulls located in the panel casing, may have a face 28 which is non-planar, e. g. being rippled or having regular or irregular indentations and/or protrusions and/or convolutions.

Such irregular shapes can be manufactured into the surface 28 of the rice hulls body 20 at the time of bonding of the rice hulls together or can be impressed, machined or otherwise formed in the surface after the rice hulls are bonded into a self-supporting body.

A further advantage of the provision of an air gap 22 is to make it more difficult for birds to reach through perforations 17 in the casing to damage the rice hulls body 20 by pecking. A yet further advantage of the air gap 22 is to provide an air space to inhibit water entering and passing directly into the rice hulls body 20, and when there is some moisture or dampness, to assist drying.

The preferred method of attenuating noise from a source of noise before reaching a nearby area comprises erecting multiple acoustic barriers, such as the barriers illustrated in Figs. 1 and 2, between the source of noise and the nearby area. This can be achieved using structures as illustrated in Figs. 3 to 5.

In Fig. 3, the acoustic barrier wall 30 is composed of a number of spaced uprights 31 and, in between consecutive uprights 31 there are provided a number of individual barriers 32 in the form of individual planks or panels. The barriers can be constructed as shown in Fig. 1 with the male and female formations 15,16 interfitting along the join lines 33. It will be seen that the join lines 33 are inclined to the horizontal and this may be achieved by making the individual barriers or panels 22 of parallelogram shape with specially constructed top and bottom barriers of triangular shape. The purpose of the inclined joining of the individual barriers 32 is to facilitate drainage of water passing through the face panels of individual barriers down to the lower edge of each barrier or panel 22 where it can be drained to the ground, although this angle of incline could be varied from horizontal up to vertical.

As shown in Fig. 4, the uprights 31 can be generally S or Z shaped in cross section with oppositely facing sockets 35,36 for receiving the ends of the barriers or panels 22.

The alternative arrangement shown in Fig. 5 provides uprights which are H shaped in section so as to provide oppositely facing sockets 45,46 for receiving the barriers 42 thereby forming a substantially planar continuous wall.

It will be seen that the acoustic or noise barrier according to the present invention can be effective in operation. In particular, the acoustic absorbing or dissipating properties of panels or bodies formed of rice hulls can be utilised and, indeed, the particular acoustic properties of the barrier can be tailored to suit the expected sound or noise to be encountered in use. In particular, this variability of the acoustic properties can be provided by manipulating: (a) the materials of the rice hulls body, (b) the density of the rice hulls body, (c) the variations in density throughout the thickness of the rice hulls body, (d) the air gap between the rice hulls body and the casing, (e) the configuration of apertures and the percentage of the surface area provided by the apertures in the casing.

These variables can be optimised for a particular installation where the barriers are to be used.

The ability to use the relatively low density of rice hulls through medium to high densities of rice hulls (approaching natural timber) can provide significantly better sound absorbent properties than stone, masonry and concrete and also better than the relatively high density natural timber.

The potentially limiting structural strength or integrity of bonded rice hull panels, and/or susceptibility to vermin or bird attack, is alleviated by the casing, but the combination can also provide significant enhancements of the properties of the barrier as a whole by making use of the particular properties of the casing materials as well as the rice hulls body as well as, in the preferred embodiment, the air gap between the two.