WO1998058127A1

WO1998058127A1 - Acoustic barrier

Info

Publication number: WO1998058127A1
Application number: PCT/AU1998/000458
Authority: WO
Inventors: Richard Laurance Lewellin
Original assignee: Richard Laurance Lewellin
Priority date: 1997-06-13
Filing date: 1998-06-15
Publication date: 1998-12-23
Also published as: AUPO735197A0

Abstract

The acoustic barrier (10) includes an acoustic insulation body (20) composed of a substantial proportion of uncomminuted rice hulls and a casing (13) enclosing the body of rice hulls. The casing (13) provides strength, permeability to sound waves, and inhibits access of vermin and birds to the body (20). The rice hulls may be bonded together or not. The density of the body (20) can be chosen to attenuate expected noise frequencies. Multiple layers of different densities are possible. Perforations (17) in the casing faces (11, 12) pass sound to the body (20) and impede bird and vermin access. An air gap (22) between the casing (13) and body (20), and an intervening screen or membrane can be provided. A method of noise reduction is also provided.

Description

ACOUSTIC BARRIER This invention relates to acoustic barriers for providing acoustic insulation or barriers

against offensive noise, particularly barriers provided along the sides of roadways, although the invention is applicable to other situations such as acoustic barriers used in industrial situations, including sound enclosures and industrial silencers The invention also relates to

methods of reducing noise by using acoustic barriers

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 structural 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, 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 galvanised 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 1 1, 12

In Fig 2, the face panels 1 1, 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 1 1, 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 1 1, 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 1 1 , 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 by

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 constaicted 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 5 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

10 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

15 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 1 1, 12 and the rice hulls body 20 can help to spread the sound passing through the apertures 17 of the face panel across the

20 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

5 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

10 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

15 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

0 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.

Claims

1 An acoustic barrier (10) including an acoustic insulation body (20) composed of a substantial proportion of uncomminuted rice hulls and a casing (13) enclosing the body of rice hulls, the casing (13) 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

(20), and (c) inhibiting access of vermin and birds to the body (20) containing rice hulls

2 A barrier as claimed in claim 1 wherein the acoustic insulation body (20) includes rice

hulls which are bonded together so that the body has at least self-supporting structural

integrity 3 A barrier as claimed in claim 1 wherein the acoustic insulation body (20) includes rice

hulls which are not bonded together or which are bonded together with insufficient strength

to provide self-supporting structural integrity, the acoustic insulation body (20) having a

shape defined by confining walls (1 1, 12) which confine the material of which the body is

composed

4 A barrier as claimed in any one of the preceding claims wherein the material including

uncomminuted rice hulls of which the acoustic insulation body (20) is composed is

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

5 A barrier as claimed in claim 4 wherein the acoustic insulation body (20) has zones (26, 27) of differing densities through the thickness of the body (20) so as to provide in the

different density zones (26, 27) effective attenuation of different expected frequencies or frequency ranges 6 A barrier as claimed in any one of the preceding claims wherein the casing (13) enclosing the acoustic insulation body (20) provides sufficient strength to the barrier (10) so

that the barrier is of at least self-supporting structural strength

7 A barrier as claimed in claim 6, the barrier (10) being for use as a roadside noise barrier, the casing (13), in conjunction with any stmctural strength provided by the acoustic

insulation body (20), being of sufficient strength and rigidity to withstand wind and storm

loadings to which the barrier will be exposed in use

8 A barrier as claimed in any one of the preceding claims wherein the casing (13) is

provided with passages or perforations (17) 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 (20)

9 A barrier as claimed in claim 8 wherein the barrier (10) has the configuration of a

panel having opposed broad faces, the casing including spaced face panels (11, 12) providing

the opposed broad faces of the barrier panel

10 A barrier as claimed in claim 9 wherein the total area of the perforations (17) provided

in at least one of the face panels (11, 12) providing the opposed broad faces of the barrier

panel is in the range of 30 to 70% of the total area of the respective broad face of the panel

11 A barrier as claimed in any one of the preceding claims wherein the casing (13) is

spaced from the acoustic insulation body (20) so as to leave an air gap (22) between the body (20) and the casing (13)

12 A barrier as claimed in claim 11 wherein the casing (13) includes a (11, 12) surface sheet provided with apertures (17), the apertures (17) acting as sound wave sources from

which sound waves radiate towards the acoustic insulation body (20) upon sound waves

impinging on the surface sheet of the casing, the air gap (22) between the surface sheet (1 1, 12) and the body (20) being of sufficient width to enable incident sound passing through the apertures (17) to spread across substantially the full surface area of the body (20) facing the

apertured surface sheet (11, 12)

13 A barrier as claimed in claim 1 1 or 12 wherein the surface of the body (20) located behind and spaced from the casing (13) by the air gap (22) is non-planar having regular or

irregular surface indentations and/or protrusions and/or convolutions

14 A barrier as claimed in any one of claims 1 to 10 wherein the casing (13) is located in

contact with or closely adjacent the acoustic insulation body (20)

15 A barrier as claimed in any one of claims 1 1 to 14 wherein there is further provided a

screen or membrane (25) interposed between the casing (13) and the respective adjacent or

facing surface of the acoustic insulation body (20), the screen or membrane (25) inhibiting

access to the surface of the body (20) by birds, vermin, insects, and/or water

16 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 (10) as claimed in any one of the preceding claims in a position interposed

between the source of noise and the nearby area whereby the noise is attenuated by the barrier

17 A method as claimed in claim 16 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 including erecting multiple acoustic barriers

(10) each of which is constructed as claimed in any one of claims 1 to 15, 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