Patent Description:
Acoustic waves may be produced by a large variety of sources. For example, acoustic waves may be produced by people, motor vehicles, airplanes and electronic equipment. For many people, these acoustic waves may be unpleasant and therefore considered noise.

<CIT> discloses an attenuator for attenuating acoustic waves.

One way to reduce noise is to provide a solid wall (consisting of a masonry wall or earthwork for example) between the person and the source of the noise. However, such solid walls may be relatively expensive to construct, require maintenance and have poor drainage for surface water.

Therefore, it would be desirable to provide an alternative attenuator.

The present invention relates to an arrangement comprising a plurality of attenuators as defined in claim <NUM> and to a method for constructing an acoustic barrier as defined in claim <NUM>.

Further details of the invention are set forth in the dependent claims.

For a better understanding of various examples of embodiments of the present invention reference will now be made by way of example only to the accompanying drawings in which:.

<FIG> illustrates a perspective view of an attenuator <NUM> including an elongate body <NUM> that is tubular in shape. The body <NUM> may comprise any suitable material and may comprise, for example, aluminum, brass, copper, diamond, gold, iron, lead, Pyrex glass, rubber or steel. The body <NUM> has a diameter D, a length L, a first end portion <NUM> and a second end portion <NUM> opposite to the first end portion <NUM>.

The body <NUM> defines a cavity <NUM> therein (i.e. the body <NUM> is substantially hollow) and an elongate open aperture <NUM>, having a width W, that extends along the entire length of the body <NUM> from the first end portion <NUM> to the second end portion <NUM>. In this embodiment, the length of the elongate open aperture <NUM> is substantially equal to the length L of the body <NUM>. However, in other embodiments the length of the elongate open aperture may be any substantial portion of the length of the body <NUM> and may be equal to or greater than ninety percent of the length of the body <NUM>.

The elongate open aperture <NUM> is 'open' since it is not covered by a barrier that prevents the flow of fluid (e.g. air) into or out of the cavity <NUM>. Consequently, fluid is able to enter and leave the cavity <NUM> via the elongate open aperture <NUM> without obstruction. In this embodiment, the first and second end portions <NUM>, <NUM> are also open. In other embodiments, the first and second end portions <NUM>, <NUM> may be covered by a barrier which prevents the passage of fluid there through.

The body <NUM> is configured to attenuate incident acoustic waves over a resonant frequency band. In operation, acoustic waves may enter the cavity <NUM> of the body <NUM> through the elongate open aperture <NUM> and through the body <NUM>. The air in the cavity <NUM> resonates if the frequency of the acoustic waves is within the resonant frequency band of the cavity <NUM>. Since the elongate open aperture <NUM> extends across a substantial portion of the body <NUM>, a plurality of standing waves form in the cavity <NUM>, each having a different length to one another. Since each standing wave provides a different resonant frequency, the plurality of standing waves together provide the resonant frequency band of the cavity <NUM>.

The above mentioned resonance reduces the energy of the incident acoustic waves since the energy is transferred from the acoustic waves to the air in the cavity <NUM>. Additionally, the attenuator <NUM> at least partially reflects the acoustic waves back toward their source. Consequently, if an attenuator <NUM> is positioned between an acoustic wave source and an observer, the attenuator <NUM> reduces the amplitude (i.e. volume) of the acoustic wave heard by the observer.

In more detail, when a pressure variation (for example, in the form of a sound wave) interacts with the air in the elongate open aperture <NUM>, the pressure of the air in the cavity <NUM> increases. As the external force is removed, the pressure equalizes and forces air back through the elongate open aperture <NUM>. Due to the inertia of the air in the elongate open aperture <NUM>, a region of low pressure is created in the cavity <NUM>, which in turn causes air to be drawn back into the cavity <NUM>. The air then continues to oscillate and causes attenuation of the incident sound wave.

The attenuation associated with the attenuator <NUM> is substantially provided by the resonance of the air in the cavity <NUM> and not by the mechanical resonance of the body <NUM> itself. Consequently, the desirable resonant frequency band of the body <NUM> is substantially independent of the material of the body <NUM>. Additionally, it has been observed that the magnitude of attenuation provided by the attenuator <NUM> is substantially unaffected by the orientation of the attenuator <NUM> (and hence the orientation of the elongate open aperture <NUM>) relative to the source of acoustic waves.

It should be appreciated that the dimensions of the body <NUM> and the elongate open aperture <NUM> determine the resonant frequency band of the attenuator <NUM>. This will now be explained in detail in the following paragraphs with reference to <FIG>, <FIG> and <FIG>.

<FIG> illustrates a graph of frequency versus pressure for two attenuators <NUM> having different diameters D (and therefore different volumes). The graph includes an X axis <NUM> for frequency (in kilohertz), a Y axis <NUM> for pressure (in dB), a solid line <NUM> representing an attenuator having a diameter D of <NUM> and a dotted line <NUM> representing an attenuator having a diameter D of <NUM>.

With reference to the solid line <NUM>, the pressure increases from approximately <NUM> dB at <NUM> to approximately <NUM> dB at <NUM>. In the region of the resonance band gap at <NUM>, the pressure decreases and reaches a minimum of <NUM> dB at approximately <NUM>. After <NUM>, the pressure increases and is approximately <NUM> dB at <NUM>. After <NUM>, the pressure remains substantially constant at <NUM> dB.

With reference to the dotted line <NUM>, the pressure increases from approximately <NUM> dB at <NUM> to approximately <NUM> dB at <NUM> and remains constant until <NUM>. In the region of the resonance band gap at <NUM>, the pressure decreases and reaches a minimum of <NUM> dB at approximately <NUM>. After <NUM>, the pressure increases and is approximately <NUM> dB at <NUM>. After <NUM>, the pressure remains substantially constant at <NUM> dB.

From the above paragraphs, it should be appreciated that an increase in the diameter D (and hence volume) of the body <NUM> of an attenuator <NUM> lowers the position of the resonant frequency band of the body <NUM> on the frequency axis <NUM>.

<FIG> illustrates a graph of frequency versus pressure for two attenuators <NUM> having elongate open apertures <NUM> with different widths W. The graph includes an X axis <NUM> for frequency (in kilohertz), a Y axis <NUM> for pressure (in dB), a solid line <NUM> representing an attenuator having an elongate open aperture with a width of <NUM> and a dotted line <NUM> representing an attenuator having an elongate open aperture with a width of <NUM>.

With reference to the solid line <NUM>, the pressure is substantially constant at <NUM> dB between the frequencies of <NUM> and <NUM>. In the region of the resonance band gap at <NUM>, the pressure decreases and reaches a minima of <NUM> dB at approximately <NUM>. After <NUM>, the pressure increases and is approximately <NUM> dB at <NUM>. After <NUM>, the pressure remains substantially constant at <NUM> dB.

With reference to the dotted line <NUM>, the pressure is substantially constant at <NUM> dB between the frequencies of <NUM> and <NUM>. In the region of the resonance band gap at <NUM>, the pressure decreases and reaches a minimum of <NUM> dB at approximately <NUM>. After <NUM>, the pressure increases and is approximately <NUM> dB at <NUM>. After <NUM>, the pressure remains substantially constant at <NUM> dB.

From the above paragraphs, it should be appreciated that an increase in the width W of an elongate open aperture moves the location of the resonant frequency band of the body <NUM> to higher frequencies.

<FIG> illustrates a perspective view of another attenuator <NUM> according to various embodiments of the invention. The attenuator <NUM> is similar to the attenuator <NUM> illustrated in <FIG> and where the features are similar, the same reference numerals are used. The attenuator <NUM> is configured to attenuate acoustic waves in a similar manner to the attenuator <NUM> illustrated in <FIG>.

The attenuator <NUM> differs from the attenuator <NUM> in that the body <NUM> defines a first elongate open aperture <NUM><NUM>, a second elongate open aperture <NUM><NUM>, a third elongate open aperture <NUM><NUM> and a fourth elongate open aperture <NUM><NUM> that extend in series along the length L of the body <NUM>. The open apertures <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM> are separate from one another and have portions of the body <NUM> there between (in other words, the open apertures <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM> are distinct from one another and do not join up). The first elongate open aperture <NUM><NUM> is defined adjacent the second end portion <NUM> so that a portion of the body <NUM> is provided between the first elongate open aperture <NUM><NUM> and the second end portion <NUM>. The fourth elongate open aperture <NUM><NUM> is defined adjacent the first end portion <NUM> so that a portion of the body <NUM> is provided between the fourth elongate open aperture <NUM><NUM> and the first end portion <NUM>.

In some examples, the open apertures <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM> may not be elongate and may have a length that is substantially equal to their width. Furthermore, in other examples, the body <NUM> may define any number of open apertures <NUM>. Additionally, in some examples, the first elongate open aperture <NUM><NUM> and/or the fourth elongate open aperture <NUM><NUM> may join with the second end portion <NUM> and/or the first end portion <NUM> respectively (i.e. there is no portion of the body <NUM> between the open apertures and the end portions of the body).

Embodiments of the present invention provide an advantage in that the body <NUM> of the attenuator <NUM> may be configured to attenuate a particular frequency band of interest (for example, to attenuate noise over a particular frequency range). For example, if it is desired to attenuate acoustic waves having a frequency of between <NUM> and <NUM>, the diameter D of the body <NUM> and the width W of the elongate open aperture <NUM> may be chosen to obtain optimum attenuation at those frequencies.

Furthermore, another advantage provided by embodiments of the present invention is that the material of the body <NUM> can be freely selected for any application since the resonant frequency band of the body <NUM> is substantially independent of the material of the body <NUM>. For example, if it is desired to reduce the visibility of the attenuator <NUM>, the body <NUM> may comprise Pyrex glass. Alternatively, if it is desired to increase the visibility of the attenuator <NUM> (e.g. for decorative purposes), the body <NUM> may comprise diamond or gold.

Additionally, the attenuator <NUM> may advantageously have increased structural rigidity (relative to the attenuator <NUM> illustrated in <FIG> for example) and may require less manufacturing time for the open apertures to be cut out of the body <NUM>. Additionally, the increased rigidity of the attenuator <NUM> may result in an increased accuracy when machining the open apertures.

<FIG> illustrates a perspective view of another attenuator <NUM> according to various embodiments of the present invention. The attenuator <NUM> is similar to the attenuators <NUM>, <NUM> illustrated in <FIG> and <FIG> and is configured to attenuate acoustic waves in a similar manner. The attenuator <NUM> includes a first body <NUM> defining a cavity <NUM> therein and an elongate open aperture <NUM> that extends across a substantial portion of the body <NUM>. The attenuator <NUM> also includes a second body <NUM> that is positioned within the cavity <NUM> of the first body <NUM>. The second body <NUM> also defines a cavity <NUM> therein and an elongate open aperture <NUM> that extends across a substantial portion of the second body <NUM>. In this example, the first body <NUM> and the second body <NUM> are concentric (that is, the first body <NUM> and the second body <NUM> have a common center). In other examples, the first body <NUM> and the second body <NUM> may be in a non-concentric arrangement (that is, the first body <NUM> and the second body <NUM> do not have a common center).

The first body <NUM> and the second body <NUM> are configured to attenuate acoustic waves over different resonant frequency bands. For example, the first body may be configured to attenuate acoustic waves in the frequency range of <NUM> to <NUM> and the second body may be configured to attenuate acoustic waves in the frequency range of <NUM> to <NUM>.

In other examples, the first body <NUM> and/or the second body <NUM> may define a plurality of open apertures as illustrated in <FIG> and as described in the preceding paragraphs.

The attenuator <NUM> illustrated in <FIG> may provide an advantage in that it may be able to attenuate acoustic waves over a greater range of frequencies (when compared to the attenuator <NUM> illustrated in <FIG>). Furthermore, the attenuator <NUM> may not require any more space than the attenuator <NUM> illustrated in <FIG> since the second body <NUM> is positioned within the cavity <NUM> of the first body <NUM>.

The first body <NUM> and the second body <NUM> are not connected to one another (that is, the attenuator <NUM> includes no connectors between the first body <NUM> and the second body <NUM>). This may provide an advantage in that the attenuator <NUM> may be relatively easy to manufacture. Additionally, if a change in the resonant frequency bands of the attenuator <NUM> is desired, the first body <NUM> or second body <NUM> may be replaced with other bodies that have different resonant frequency bands to the first body <NUM> and the second body <NUM>. For example, the second body <NUM> may be replaced with another body (not illustrated) that has a different resonant frequency band to the resonant frequency bands of the first body <NUM> and the second body <NUM>.

It should be appreciated that the attenuator <NUM> may include a third body (not illustrated for clarity purposes) positioned within the cavity <NUM> of the second body <NUM>, and a fourth body (not illustrated for clarity purposes) positioned within the cavity of the third body and so on (each body being configured to attenuate acoustic waves over different resonant frequency bands). Alternatively, if the diameter of the first body <NUM> is relatively large, the cavity <NUM> may include a plurality of bodies which are not positioned inside one another, each of which being configured to attenuate acoustic waves over different resonant frequency bands. In both of these embodiments, the plurality of bodies may not be connected to one another. These embodiments may provide an advantage in that they may attenuate acoustic waves over a very broad frequency range.

<FIG> illustrates a cross sectional plan view of a further attenuator <NUM> and <FIG> illustrates a perspective view of the attenuator <NUM>. The attenuator <NUM> includes an elongate body <NUM> that is substantially tubular in shape. The body <NUM> may comprise any suitable material and may comprise, for example, aluminum, brass, copper, diamond, gold, iron, lead, Pyrex glass, rubber or steel. The body <NUM> has a diameter D, a length L, a first end portion <NUM> and a second end portion <NUM> opposite to the first end portion <NUM>.

When viewed in cross section, the body <NUM> has a spiral shape (i.e. the body <NUM> curves from a central point and continuously increases in radius). The body <NUM> defines a cavity <NUM> therein (i.e. the body <NUM> is substantially hollow) and the cavity <NUM> also has a spiral shape when viewed in cross section. Additionally, the body <NUM> defines an elongate open aperture <NUM>, having a width W, that extends along the entire length of the body <NUM> from the first end portion <NUM> to the second end portion <NUM>. In this embodiment, the length of the elongate open aperture <NUM> is substantially equal to the length L of the body <NUM>. However, in other embodiments the length of the elongate open aperture <NUM> may be any substantial portion of the length of the body <NUM> and may be equal to or greater than ninety percent of the length of the body <NUM>.

The body <NUM> is configured to attenuate incident acoustic waves over a resonant frequency band. It should be appreciated that the spiral shaped cavity <NUM> has a length that extends between the opening of the elongate aperture <NUM> to the centre of the body <NUM>. The path length of the cavity <NUM> is substantially equal to a quarter of the wavelength of the acoustic waves that are to be attenuated.

As an acoustic wave is incident upon the attenuator <NUM>, part of the acoustic wave enters the cavity <NUM> and part of the acoustic wave is reflected. In the time the acoustic wave takes to travel down the cavity <NUM> and back to the elongate open aperture <NUM>, the acoustic wave outside of the attenuator <NUM> has shifted half a wavelength, and the two waves interfere destructively causing attenuation of the acoustic wave.

The attenuator <NUM> may provide a number of advantages. Since the length of the cavity <NUM> is relatively long for the size of the attenuator <NUM>, the attenuator <NUM> may advantageously attenuate acoustic waves having a relatively large wavelength / relatively low frequency for its given size. Additionally, attenuation of acoustic waves may occur where the acoustic wave has a frequency that is a harmonic of the fundamental frequency of the attenuator <NUM>.

By way of example, the body <NUM> may define a Bernoulli type spiral with an external radius of <NUM> and decay per <NUM>° of <NUM>% with <NUM> turns. This spiral has a characteristic path length of <NUM> and a corresponding fundamental frequency of <NUM>. The resonant frequency band gap of this attenuator is <NUM> to <NUM> with <NUM> dB of attenuation. A higher order harmonic also exists at double the fundamental frequency at <NUM> with similar levels of attenuation.

It should be appreciated that an attenuator according to embodiments of the invention may have a body that defines any meandering or labyrinth cavity that causes attenuation of acoustic waves as described in the above paragraphs with reference to <FIG>.

<FIG> illustrates a cross sectional plan view of another attenuator <NUM> according to various embodiments of the present invention. The attenuator <NUM> is similar to the attenuator <NUM> illustrated in <FIG> and where the features are similar, the same reference numerals are used. The attenuator <NUM> differs from the attenuator <NUM> in that the body <NUM> includes a plurality of walls <NUM> within the cavity <NUM>. The walls <NUM> divide the cavity <NUM> into a plurality of compartments <NUM> and in this embodiment, the walls <NUM> extend radially between adjacent portions of the body <NUM> and define open elongate apertures <NUM> that extend for at least a substantially length of the body <NUM>. The compartments <NUM> and open elongate apertures <NUM> are configured to attenuate acoustic waves within frequency bands in the same way as the attenuator <NUM> illustrated in <FIG>.

<FIG> illustrates a cross sectional plan view of another attenuator <NUM> according to various embodiments of the present invention. The attenuator <NUM> is similar to the attenuator <NUM> illustrated in <FIG> and where the features are similar, the same reference numerals are used. The attenuator <NUM> differs from the attenuator <NUM> in that the plurality of walls <NUM> do not define open elongate apertures and instead, the body <NUM> defines a plurality of open elongate apertures <NUM> (in this example, one elongate open aperture <NUM> per compartment <NUM>). The compartments <NUM> and open elongate apertures <NUM> are configured to attenuate acoustic waves within frequency bands in the same way as the attenuator <NUM> illustrated in <FIG>.

<FIG> illustrates a plan view of an arrangement <NUM> including a plurality of attenuators not forming part of the present invention. The attenuators illustrated in <FIG> are similar to the attenuator <NUM> illustrated in <FIG> and attenuate acoustic waves in a similar manner. In other embodiments, the arrangement <NUM> may include at least some attenuators which are similar to the attenuators <NUM>, <NUM>, <NUM>, <NUM>, <NUM> illustrated in <FIG>, <FIG>, <FIG>.

The arrangement <NUM> includes a first subset of attenuators <NUM> (which are relatively large), a second subset of attenuators <NUM> (which are medium sized) and a third subset of attenuators <NUM> (which are relatively small). The attenuators <NUM> in the first subset are configured to attenuate acoustic waves over a first resonant frequency band (e.g. <NUM> to <NUM>). The attenuators <NUM> in the second subset are configured to attenuate acoustic waves over a second resonant frequency band (e.g. <NUM> to <NUM>). The attenuators <NUM> in the third subset are configured to attenuate acoustic waves over a third resonant frequency band (e.g. <NUM> to <NUM>). Consequently, the arrangement <NUM> is configured to attenuate acoustic waves in the frequency range of <NUM> to <NUM>.

The attenuators <NUM>, <NUM>, <NUM> are spaced apart from one another and the arrangement <NUM> does not include any members that connect the attenuators <NUM>, <NUM>, <NUM> to one another. Consequently, the attenuators <NUM>, <NUM>, <NUM> may be arranged randomly in a square formation around a square space that includes a source <NUM> of acoustic waves but does not include any attenuators. It has been observed that the distribution of the attenuators <NUM>, <NUM>, <NUM> does not substantially effect the attenuation provided by the arrangement <NUM>.

The square formation includes a first wall <NUM>, a second wall <NUM>, a third wall <NUM> and a fourth wall <NUM>. The first, second and third walls <NUM>, <NUM> and <NUM> include three layers of attenuators (i.e. they are three attenuators deep). The fourth wall <NUM> includes two layers of attenuators (i.e. they are two attenuators deep).

The source <NUM> produces acoustic waves <NUM> that have relatively high amplitudes (e.g. <NUM> dB) and have frequencies in the range of <NUM> to <NUM>. The arrangement <NUM> of attenuators <NUM>, <NUM>, <NUM> provides an acoustic barrier <NUM> which attenuates the acoustic waves <NUM> since the frequencies of the acoustic waves <NUM> fall within the resonant frequency band of the arrangement <NUM>. Acoustic waves <NUM> that leave the arrangement <NUM> have significantly lower amplitudes (e.g. <NUM> dB) than the acoustic waves <NUM> produced by the source <NUM>.

Embodiments of the present invention provide an advantage in that an arrangement of attenuators having different dimensions may attenuate acoustic waves over a relatively broad range of frequencies (<NUM> to <NUM> in the above example). Furthermore, relatively significant attenuation of acoustic waves may be achieved by arranging the attenuators into layers and by increasing the number of the attenuators in a given volume in the arrangement.

Furthermore, since the attenuator in the arrangement may not be connected to one another, the arrangement may be formed into any shape and with any spacing between the attenuators. This may advantageously enable the creation of an acoustic barrier for any frequency to be attenuated.

<FIG> illustrates a plan view of another arrangement <NUM> of attenuators <NUM> not forming part of the present invention. The attenuators <NUM> may be any suitable attenuators according to embodiments of the present invention and may be, for example, any of the attenuators <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> (including any combination of these attenuators). In this example, the attenuators <NUM> are similar to the attenuator <NUM> illustrated in <FIG>.

The attenuators <NUM> are arranged periodically into four rows and five columns. It should be appreciated that this number of rows and columns is provided as an example and the arrangement <NUM> may have any number of rows and columns. Furthermore, it should be appreciated that the attenuators <NUM> may be arranged in any periodic arrangement. Each row of attenuators <NUM> is spaced apart from adjacent rows by a distance d<NUM> and each column of attenuators <NUM> is spaced apart from adjacent columns by a distance d<NUM>. In this example, the distance d<NUM> is substantially equal to the distance d<NUM>. In other embodiments, the distance d<NUM> may be different to the distance d<NUM>.

In operation, an acoustic wave <NUM> is incident upon the arrangement <NUM>. As described in the preceding paragraphs, the attenuators <NUM> attenuate the acoustic wave <NUM> in each of their individual resonant frequency bands. Additionally, the collective arrangement of the attenuators also attenuates the acoustic wave <NUM> in a further resonant frequency band due to the acoustic wave <NUM> being reflected off of the attenuators <NUM> and causing destructive interference in accordance with Braggs law. The wavelength at which the acoustic wave <NUM> is attenuated is given by: <MAT>.

Where d is the distance between the rows or columns and θ is the angle of incidence of the acoustic wave relative to the row/column. From equation <NUM> it should be appreciated that the further resonant frequency band of the arrangement <NUM> is dependent upon the distances d<NUM> and d<NUM> between the attenuators <NUM>.

<FIG> illustrates a graph of frequency versus pressure for an acoustic wave <NUM> (please see <FIG>) attenuated by the arrangement <NUM> of attenuators <NUM> illustrated in <FIG>. The graph includes an X axis <NUM> for frequency, a Y axis <NUM> for pressure and a solid line <NUM> representing the attenuated acoustic wave <NUM>.

The line <NUM> includes a first minimum <NUM> in pressure in a first frequency band and a second minimum <NUM> in pressure in a second frequency band. The second frequency band is at higher frequencies than the first frequency band. The first minimum <NUM> is caused by attenuation by the individual attenuators <NUM> and the second minimum <NUM> is caused by attenuation by the collective arrangement of attenuators <NUM> as described above.

The arrangement <NUM> illustrated in <FIG> may provide an advantage in that the attenuation frequency band of the collective arrangement <NUM> of attenuators <NUM> may be tuned to desired frequencies by changing the distance between the rows/columns of attenuators <NUM>. For example, if a particularly wide attenuation frequency band is desired, the distance between the rows and columns may be selected so that the first minimum <NUM> and the second minimum at least partially overlap one another.

<FIG> illustrates a plan view of another arrangement <NUM> of attenuators <NUM> according to various embodiments of the present invention. The attenuators <NUM> may be any suitable attenuators according to embodiments of the present invention and may be, for example, any of the attenuators <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> (including any combination of these attenuators).

The attenuators <NUM> are arranged into a first column <NUM>, a second column <NUM> and a third column <NUM>. It should be appreciated that the number of columns is provided as an example and the arrangement <NUM> may have any number of columns. Each row of attenuators <NUM> is spaced apart from adjacent rows by a distance d<NUM> and each column of attenuators <NUM> is spaced apart from adjacent columns by a distance d<NUM>.

In the first column <NUM> and the third column <NUM>, the distance d<NUM> between adjacent attenuators <NUM> is greater than zero. In the second column <NUM>, the distance d<NUM> between adjacent attenuators is equal to zero. Consequently, the attenuators <NUM> in the second column <NUM> abut one another and may be connected to one another in some examples. For example, the attenuators <NUM> in the second column <NUM> may be joined by gluing or welding them together, or may be clamped together along the top and bottom end portions <NUM>, <NUM> with fasters such as bolts or rivets. Alternatively, the attenuators <NUM> in the second column <NUM> may be coupled together via a frame. In other examples, the attenuators <NUM> in the second column <NUM> may be molded to form a unitary panel (i.e. they form a seamless piece/panel). A molded panel may be advantageous in that such a panel may be structurally strong and may not require a supporting frame and may thus be less costly to manufacture.

In other embodiments, the arrangement <NUM> may include any number of columns where the distance d<NUM> between adjacent attenuators is equal to zero.

The arrangement <NUM> may be advantageous in that the second column <NUM> may provide an air tight seal and prevent the flow of a fluid (such as air or water) there through. Additionally, the arrangement <NUM> is advantageous in that the second column <NUM> increases the acoustic performance (that is, the attenuation) of the arrangement <NUM> due to an increased density of attenuators <NUM> in a given area. This in turn results in a higher interaction parameter between each attenuator <NUM> in the array which increases the overall attenuation level. It has been found that the performance of an individual attenuator <NUM> is enhanced when it is positioned in relatively close proximity to a similar attenuator <NUM> such that the closer they are positioned to one another, the better the resonance as the individual resonance bands coalesce to form a large attenuation band.

The attenuators <NUM> are arranged into a plurality of columns and a plurality of rows. Each row of attenuators <NUM> is spaced apart from adjacent rows by a distance d<NUM> and each column of attenuators <NUM> is spaced apart from adjacent columns by a distance d<NUM>. In this example, the distance d<NUM> between adjacent attenuators <NUM> is equal to zero and consequently, adjacent rows of attenuators <NUM> in the arrangement <NUM> abut one another.

<FIG> illustrates a plan view of another arrangement <NUM> of attenuators <NUM> not forming part of the present invention. The attenuators <NUM> may be any suitable attenuators according to embodiments of the present invention and may be, for example, any of the attenuators <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> (including any combination of these attenuators).

The attenuators <NUM> are arranged into a single column and are spaced apart from one another by a distance d. The distance d<NUM> between adjacent attenuators <NUM> may have any suitable value and may be equal to zero or may be greater than zero.

The arrangement <NUM> includes a first subset <NUM> of attenuators (which are relatively small), and a second subset <NUM> of attenuators (which are relatively large). The attenuators <NUM> in the first subset <NUM> are configured to attenuate acoustic waves over a first resonant frequency band. The attenuators <NUM> in the second subset <NUM> are configured to attenuate acoustic waves over a second (different) resonant frequency band. In other examples, the arrangement <NUM> may have any number of subsets of attenuators which are configured to attenuate acoustic waves over a plurality of different frequency bands.

The arrangement <NUM> may be advantageous where depth or size restrictions for the arrangement <NUM> apply. In particular, the arrangement <NUM> may be provided where the cost of land is relatively expensive and only a relatively small surface area may be dedicated to an arrangement of attenuators.

<FIG> illustrates a plan view of another arrangement <NUM> of attenuators <NUM> not forming part of the present invention. The attenuators <NUM> comprise a plurality of the attenuators <NUM> as illustrated in <FIG>. The attenuators <NUM> may have the same dimensions as one another, or may have different dimensions as illustrated in <FIG> for example.

The attenuators <NUM> may be clamped to a frame along the top and bottom end portions of the attenuators <NUM>, or may be joined by bolts and/or rivets with spacers internally. Alternatively, the attenuators <NUM> may be molded as a single piece or panel and have a connecting base plate.

The arrangement <NUM> may advantageously have a relatively high density of attenuators <NUM> (since the attenuators <NUM> include at least a first body and a second body as illustrated in <FIG>) which improves attenuation performance. Furthermore, the arrangement <NUM> may allow for a greater variety of differing sizes of attenuator, whilst reducing the overall footprint of the arrangement <NUM>. It should be appreciated that the overall footprint of an arrangement can add substantial cost as in most applications, installation space is at a premium, and in the case for highways and railways, the land has to be purchased to install an arrangement, thus more land required gives rise to increased costs.

An arrangement of attenuators according to embodiments of the present invention may be formed into one or more acoustic barriers for a variety of different applications.

One such application is to arrange a plurality of attenuators into a fence-like acoustic barrier around a property (e.g. a house or an office) to reduce noise received at the property. Embodiments of the present invention provide several advantages in this application. For example, the acoustic barrier may allow drainage of surface water and flow of fresh air since the attenuators in the acoustic barrier are spaced apart from one another and may not be connected to one another. Additionally, the acoustic barrier may be made from opaque or transparent materials depending on the location of the property (e.g. urban or rural). For example, if the property is located in an urban area, the acoustic barrier may be made from opaque materials in order to increase privacy. If the property is located in a rural area, the acoustic barrier may be made from transparent materials in order to improve the view from the property.

Another application is to install a plurality of attenuators according to embodiments of the present invention into the wall cavity and/or into the roofing space of a property to form an acoustic barrier which reduces noise entering the property.

A further application is to install a plurality of attenuators according to embodiments of the present invention alongside a road, train track or airport runway to reduce the noise from the road, train track or runway. As mentioned above, such an acoustic barrier provides an advantage in that it allows drainage of surface water and flow of fresh air and may be formed from opaque or transparent materials depending on the location.

Another application is to form a plurality of attenuators according to embodiments of the invention into an acoustic barrier blind for a window which reduces noise received from outside the window and also allows the window to remain open and allow the passage of fresh air there through.

The above described acoustic barriers provide several advantages for a person due to the reduction of noise. These advantages include lessened sleep disturbance, improved ability to enjoy outdoor life, reduced speech interference, stress reduction, reduced risk of hearing impairment and reduction in blood pressure (improved cardiovascular health).

Claim 1:
An arrangement (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising a plurality of attenuators (<NUM>, <NUM>, <NUM>) for attenuating acoustic waves, each attenuator (<NUM>, <NUM>, <NUM>) of the plurality of attenuators (<NUM>, <NUM>, <NUM>) comprising:
a first body (<NUM>, <NUM>) defining a cavity (<NUM>, <NUM>) therein and at least one elongate open aperture (<NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM>) extending across a substantial portion of the first body (<NUM>, <NUM>), the first body (<NUM>, <NUM>) being configured to attenuate acoustic waves over a resonant frequency band,
wherein the arrangement (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is configured so that acoustic waves incident upon an attenuator of the plurality of attenuators, enter the cavity (<NUM>, <NUM>) through the open aperture (<NUM>, <NUM><NUM>, <NUM><NUM>, <NUM>, <NUM><NUM>, <NUM>) and air in the cavity (<NUM>, <NUM>) resonates to thereby attenuate said incident acoustic waves when a frequency of the acoustic waves is within the resonant frequency band of the cavity (<NUM>),
characterised in that the at least some of the plurality of attenuators form a row, wherein adjacent attenuators in the row of attenuators abut one another.