WO2010139951A1

WO2010139951A1 - An acoustic attenuator element and an acoustic attenuator for a ventilation duct

Info

Publication number: WO2010139951A1
Application number: PCT/GB2010/001090
Authority: WO
Inventors: Dos Santos Nunes Jose Paulo Barnfather
Original assignee: Dos Santos Nunes Jose Paulo Barnfather
Priority date: 2009-06-04
Filing date: 2010-06-04
Publication date: 2010-12-09
Also published as: GB2472182A; GB0909558D0

Abstract

An acoustic attenuator for reducing noise levels in a low energy or natural ventilation system/ natural ventilation when placed in a, ventilation channel of a building, the acoustic attenuator comprising: a plurality of acoustic attenuator elements co-operable with one another by means of respective complementary formations to form a self supporting structure having a plurality of channels for the flow of air by means of minimal air pressure characteristic of a low energy or natural ventilation system, the plurality of channels being provided between the acoustic attenuator elements and being defined by the shape of the acoustic attenuator elements; and wherein each acoustic attenuator element is made of acoustic absorbent material for absorbing sound.

Description

AN ACOUSTIC ATTENUATOR ELEMENT AND AN ACOUSTIC ATTENUATOR

FOR A VENTILATION DUCT

Field of the Invention The present invention relates to an acoustic attenuator element for forming an acoustic attenuator for the reduction of noise levels. Particularly, but not exclusively the invention relates to an acoustic splitter element for forming an acoustic attenuator for use in buildings ventilated with low air speeds. Such low air speeds through vents and attenuators are common to low energy and naturally ventilated buildings.

Background of the Invention

Mechanical ventilation systems within conventional buildings use large fans, ducts, etc. to provide ventilation and extraction to cellular and other forms of accommodation. An acoustic attenuator is a device commonly used in ductwork to reduce noise levels from large fans within a buildings air conditioning system or other high velocity systems. The attenuator is placed in the ductwork between the fan and the accommodation to be ventilated. Attenuators work by allowing the passage of air whilst restricting unwanted noise from the fans.

In acoustic attenuators air is passed through paths lined with acoustic absorption material. The absorptive element separating each air way is often referred to as an acoustic splitter. An example of a conventional acoustic attenuator is illustrated in Figure 17. The acoustic attenuator comprises a plurality of acoustic splitters 106 defining air gaps 1.3 within a super structure 1.1. The spacing S between acoustic splitters 1.6 allows airflow while the acoustic absorption material 1.4 incorporated into the acoustic splitters reduces the passage of sound. Since such acoustic attenuators are typically placed in close proximity to large fans, conventional attenuators are commonly built to a very robust standard. Due to the high air speeds within such ventilation systems, there is a need to design attenuators to mitigate a gain in pressure drop across attenuators. This is achieved partly by restricting the minimum gap S between the splitters, which in turn controls and limits the acoustic performance of these attenuators. It is vital that the shapes of the acoustic splitters are not deformed with wind loads, and the rigidity of the splitters ensures that the air gap between each splitter is maintained constant. The splitters are also required to be manufactured such that 5 small pieces and parts of the attenuators do not break off and blow downstream of the attenuator.

Moreover.the nature of the manufacture of such attenuators means that they are produced in standard sizes and shapes. With reference to Figure 17

ID conventionally, splitters are formed from mineral wool or other acoustically absorbent materials held within a metal or rigid enclosure/housing 1.2 or attached to a framing system. These enclosures/frames are then fixed screw, bonded, welded, crimped etc. into a large secondary super structure 1.1. The result is a robust product constructed from many parts, in which each of these parts

I5 undergoes a range of processes during the manufacture of the product.

In low energy buildings, air is conventionally brought into the building via open vents in the building facade. The movement of air is driven through the building as a result of wind and very small pressure changes, often caused by buoyant air0 movements. As a result, low energy buildings typically use large open vents >0.25m² in the building's facade as well as large vents >0.25m² in partitions to allow the flow of air through the building.

This type of ventilation is extremely energy efficient but allows for the passage of5 environmental noise (road, rail and aircraft) into buildings. As such, these types of buildings can only be built on quiet sites away from roads, trains lines and other noise sources. This seriously limits the number of sites available to low energy buildings. 0 Low energy buildings work most effectively when "cross ventilation" is employed. In this case, air is brought in through the building facade and then passes across a given space and out through a partition into another part of the building e.g. corridor, atrium, etc. In the case of cross ventilation, the spread of noise through a partition is a second major limiting factor. The spread of noise across a partition through a ventilation system is known as cross talk.

Buildings only require a minimal level of fresh air to replenish oxygen and other 5 vital requirements. It is therefore often the case for the air within a building to re- circulate. Air recirculation is undertaken in such a way to make use of the existing hot/temper air held in a building. Within some low energy buildings, air is collected at given points, such as top of an atrium, end of a circulation zone, etc. and then pushed back through the building into occupied cellular spaces. To ID reduce energy consumption, it is vital that ventilation passes with low flow resistance are provided between the air collection point, the vented accommodation and vice versa. The drawback of these air paths is that they are large and have the potential to allow the passage of sound.

15 Within a naturally ventilated building, the acoustic requirements needed from attenuators can be much higher, since the attenuators are required to match the performance of the partition. The size of these vents are also typically very large >0.25m2, meaning that the vents can seriously compromise the performance of the partition. Conventional attenuators would need to be impractically long toQ match the performance of the partition between two spaces. Additionally, one or more attenuators are needed per cellular space, hence cost is a primary limiting factor of conventional attenuators. The size of conventional attenuators is also fundamental as they cannot be too big and intrusive as they will be visible from within the room, which is not desirable to architects. 5

Conventional attenuators are therefore not directly suited to the application of low energy buildings, for the following reasons:

• their design objective is to control noise from fans and other industrial noiseD sources, rather than to prevent noise ingress into buildings and the control of noise through ventilation vents in partitions;

• the manufacture of conventional attenuators limits their form to round or rectilinear shapes. The sizes of conventional attenuators are seen to have fixed dimension, ranging by fixed increments. This therefore limits the application of conventional attenuators to be integrated to a specific buildings requirement; • the design of conventional attenuators is limited by a compromise between pressure drop and the acoustic performance of the attenuator; • the high air speeds require the splitters to be robust so as not to deform under wind loads.

This robustness increases the range of manufacturing processes and materials used, which increases cost and limits the shape and size of the attenuators as well as the acoustic performance.

The present invention has been devised with the foregoing in mind.

Summary of the Invention

According to a first aspect of the invention there is provided an acoustic attenuator element for forming an acoustic attenuator for reducing noise levels and enabling the flow of air when placed in a ventilation channel of a low energy or naturally ventilated building, wherein the acoustic attenuator element is made of acoustic absorbent material for absorbing sound and is provided with shaped formations which co-operate with complementary shaped formations of at least one further acoustic attenuator element, according to claim 1 , to form a self supporting acoustic attenuator structure and to define a plurality of channels between the acoustic attenuator elements for the flow of air by natural or low energy ventilation within the self supporting structure.

The acoustic attenuator may be placed in a ventilation channel between a cellular space, such a room, and an air circulation space, or in an external facade wall between a cellular space and the outdoors, or between two cellular spaces for example.

In embodiments of the invention: • the plurality of channels may be shaped to define flow restrictive and torturous acoustic paths for the flow of air without a prohibitive restraint on the attenuator pressure drop.

• the acoustic element may be formed in a planar shape and is provided with 5 a pair of parallel channels arranged in a longitudinal direction at the lateral side regions of the acoustic attenuator element, the channels being configured such that the lateral side regions of the acoustic attenuator element can be folded from a position parallel to the main planar surface of the attenuator element to form a pair of walls generally perpendicular to theO planar surface of the acoustic attenuator element, the pair of walls forming the shaped formations.

• the acoustic element may be formed in a repetitive shape providing an increased surface area of the acoustic element defining the shaped elements and the plurality of channels. 5 • the acoustic element may be formed in a zig-zag shape

• the acoustic element may be formed in a shape such that the resulting acoustic attenuator has a tessellated structure defining a plurality of channels.

• the acoustic attenuator element may be made of an extruded materialD • the acoustic attenuator element may be made out of at least one of a fibrous, an open-cell or a porous material. For example it may be made out of foam. It may also be made out of thermo set materials or malleable acoustic absorbers.

• the acoustic attenuator element can be arranged to co-operate with the5 further acoustic attenuator element to form baffles within the attenuator structure

• the material constituting the acoustic element can be varied to frequency tune the attenuator structure.

• the shaped formations of the acoustic element may be co-operable with theD complementary shaped formations of the further acoustic element by an abutting engagement to form a stack, to interlock with one another, or to form a tessellated structure A second aspect of the invention provides an acoustic attenuator for reducing noise levels in a low energy or natural ventilation system when placed in a, ventilation channel of a building, the acoustic attenuator comprising: a plurality of acoustic attenuator elements co-operable with one another by means of

5 respective complementary formations to form a self supporting structure having a plurality of channels for the flow of air by means of minimal air pressure characteristic of a low energy or natural ventilation system, the plurality of channels being provided between the acoustic attenuator elements and being defined by the shape of the acoustic attenuator elements; and wherein each

ID acoustic attenuator element is made of acoustic absorbent material for absorbing sound.

In embodiments of the invention:

• the plurality of channels may be shaped to define flow restrictive and

15 torturous acoustic paths without a prohibitive restraint on the attenuator pressure drop.

• the speed of air flow in the ventilation channel is ≥4m/s

• each acoustic element may be formed in a planar shape and is provided with a pair of parallel shaped channels arranged in a D longitudinal direction at the lateral side regions of the acoustic attenuator element, the parallel channels being arranged such that the lateral sides regions of the acoustic attenuator element can be folded to a position generally perpendicular with respect to the rest of the acoustic attenuator element. 5 • each acoustic element may be formed in a repetitive shape forming an acoustic attenuator of a tessellated shape defining the plurality of channels. For example each acoustic element may be formed in a zigzag shape

• each acoustic attenuator element may be made of an extruded D material

• each acoustic attenuator element may be made out of at least one of a fibrous, an open-cell or a porous material. • the acoustic attenuator elements may be arranged to co-operate with each other to form baffles within the attenuator structure

• the acoustic attenuator elements may be arranged such that the 5 complementary shaped formations engage with each other by an abutting engagement to from a stack for packing.

• wherein the acoustic attenuator elements may be configured with respect to one another to form reactive acoustic components of air masses within the attenuator structure enabling the acoustic

ID performance of the acoustic attenuator to be tuned.

• The acoustic attenuator may further comprise solid elements of higher density than the material of the acoustic attenuator elements within one or more of the acoustic elements to further improve acoustic performance.

15 • wherein the cross sectional size of the channels may be formed between the acoustic attenuator elements can be varied to tune the frequency response of the attenuator.

• the attenuator elements forming the acoustic attenuator may have different material densities to tune the frequency response of the0 attenuator.

A third aspect of the invention provides a method of making an acoustic attenuator for reducing noises level in a low energy or natural ventilation system when placed in a ventilation channel of said ventilation system, the5 method comprising: cutting a block of acoustic attenuator material into a plurality of acoustic attenuator elements; defining a pair of longitudinal parallel channels in the lateral side regions of each acoustic attenuator element folding each acoustic attenuator element along the pair of longitudinal parallel channels to from a pair of walls generally perpendicular to the planar surface ofD the acoustic attenuator element; placing the acoustic attenuator elements adjacent to one another to form a self supporting acoustic attenuator structure such that an air channel is formed between adjacent acoustic attenuator elements for the flow of air by natural or low energy ventilation, an air channel being defined by the walls and planar surface of a first acoustic attenuator element and the opposing planar surface of a second adjacent acoustic attenuator element.

A fourth aspect of the invention provides a method of making an acoustic 5 attenuator for reducing noises level in a low energy or natural ventilation system when placed in a ventilation channel of said ventilation system, the method comprising: cutting a block of acoustic attenuator material into a plurality of acoustic attenuator elements having a repetitive angular shape; separating the acoustic attenuator elements a distance from one another; ID turning every other acoustic attenuator element through a angle of 180 to form a self supporting acoustic attenuator structure having a tessellated structure defining a plurality of air channels between adjacent acoustic attenuator elements for the flow of air by natural or low energy ventilation, an air channel being defined by the angular shape of adjacent acoustic elements with respect I5 to one another.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, andQ with reference to the following drawings in which:-

Figures 1 A to 1C are perspective views of an acoustic attenuator element according to a first embodiment of the invention;

Figure 2 is a perspective view of an acoustic attenuator according to a first5 embodiment of the invention;

Figure 3 is a perspective view of an acoustic attenuator element according to a second embodiment of the invention;

Figure 4 is a perspective view of an acoustic attenuator according to the second embodiment of the invention; D Figure 5 is a schematic view of an acoustic attenuator according to an embodiment of the invention being used in cross ventilation applications.

Figure 6.A is a schematic view of an acoustic attenuator according to an embodiment of the invention being used in cross ventilation applications. Figure 6.B is a schematic view of an acoustic attenuator according to an embodiment of the invention being used in cross ventilation applications. Figures 7A to 7D are schematic views of an acoustic attenuator according to embodiments of the invention being used in cross ventilation applications between

5 two cellular spaces or between a cellular spaces and circulation spaces and in external facades.

Figures 8A to 8C are schematic view of an acoustic attenuator according to embodiments of the invention being used in cross ventilation applications between a cellular space and a circulation space/zone.

ID Figures 9A to 9C are perspective views of acoustic attenuators according to different embodiments of the invention;

Figures 1OA to 1OE are perspective views of the manufacture of a plurality of acoustic attenuator elements according to an embodiment of the invention for the construction of an acoustic attenuator;

I5 Figures 11 A to 11 E are perspective views of the manufacture of a plurality of acoustic attenuator elements according to an alternative embodiment of the invention for the construction of an acoustic attenuator; Figures 12A to 12C are perspective views of the manufacture of a plurality of acoustic attenuator elements being according to embodiments of the invention forD the construction of an acoustic attenuator;

Figure 13 presents schematic views of examples of tessellated shapes for an acoustic splitter element according to embodiments of the invention; Figure 14 is a schematic view of examples of reactive components for acoustic attenuators according to some embodiments of the invention; and 5 Figure 15 is an acoustic attenuator according to the first embodiment of the invention within an additional super structure

Figure 16 is an acoustic attenuator according to the second embodiment of the invention without and within an additional super structure Figure 17 is a perspective view of a conventional acoustic attenuator. 0 DETAILED DESCRIPTION

Figure 1 A is a perspective view of a first embodiment of an acoustic attenuator element according to a first embodiment of the invention. The acoustic attenuator 5 elements forms an acoustic splitter element 100 and constitutes a constitutional element of an acoustic attenuator made of a plurality of such acoustic splitter elements and being designed for reducing noise levels and enabling air flow when placed in the ventilation channel of a low energy or naturally ventilated building.

ID The acoustic splitter element 100 is made of an acoustic absorbent material. Examples of such acoustic absorbent materials include fibrous materials which absorb sound energy by the transfer of kinetic energy to the fibres of the fibrous material thereby converting the energy to heat energy through their movement as well as open cell structure materials or porous materials that dissipate sound

I5 energy by the resistive paths through the material. Suitable fibrous materials may include mineral wool, synthetic wool, animal wool, and materials made from paper fibres. Suitable open cell materials may include foam, or reconstituted particles bonded in a way to create an open cell structure. O In the first embodiment of the invention the acoustic splitter element 100 is formed in a planar shape and is provided on one planar surface with a pair of parallel V shaped channels 101, shaped to increase surface area of the acoustic splitter element 100. The V shaped channels 101 are arranged in a longitudinal direction at the lateral side regions of the acoustic splitter element 100 and are configured5 such that the lateral sides 102 of the acoustic splitter element 100 located between the channels 101 and the lateral edges of the acoustic splitter element 100 can be folded as illustrated in Figure 1B to a position generally perpendicular to the planar surface of the acoustic splitter element 100 forming a pair of lateral walls 102 facing parallel to one another as illustrated in Figure 1C. While in this0 embodiment of the invention the channels 101 are generally V shaped it will be appreciated that in other embodiments of the invention any suitably shaped channels may be provided such as square, rectangle, trapezoidal, hexagon, circular shaped channels.

ID In this way a plurality of acoustic splitter elements 100 can be packed flat one on top of the as shown in Figure 10B, for example, when the lateral walls 102 are positioned parallel to the planar surface of the acoustic splitter element 100 or stacked one on top of the other when the walls 102 are positioned generally 5 perpendicular to the planar surface to form a self supporting structure forming an acoustic attenuator 1000 as illustrated in Figure 2 or Figure 10E, for example.

Figure 2 is a perspective view of an acoustic attenuator according to the first embodiment of the invention. The acoustic attenuator 1000 is made up of a

ID plurality of attenuator splitter elements 100_1 to 100_4 stacked on top of one another to form a self supporting structure. While in this embodiment the acoustic attenuator is made up of 4 acoustic splitter elements, it will be appreciated that in alternative embodiments of the invention the acoustic attenuator may be made up of any number of acoustic splitter elements.

I5

The top surface 102a of lateral walls 102 of acoustic splitter element 100_2 form an abutting engagement with the underside planar surface 103 of acoustic splitter element 100_1 which is placed above it. Air flow channels 104 are formed between adjacent acoustic splitter elements. The air flow channels 104 are0 defined by the lateral walls 102 and top surface of acoustic splitter element 10O i and the under surface of adjacent acoustic splitter element 100_i-1. For example, an air flow channel 104 is defined by the lateral walls 102 and top surface of acoustic splitter element 100_2 and the under surface of adjacent acoustic splitter element 100_1. The air flow channels 104 formed thereby are suitable for the flow5 of air by natural or low energy ventilation when placed in a ventilation channel. The air flow channels in some embodiments of the invention may be shaped to define flow restrictive and torturous acoustic paths without a prohibitive restraint on the attenuator pressure drop. D Figure 3 is a perspective view of an acoustic splitter element according to a second embodiment of the invention. The acoustic splitter element 200 constitutes a constitutional element of an acoustic attenuator made of a plurality of such acoustic splitter elements and being designed for reducing noise levels and enabling air flow when placed in the ventilation channel of a low energy or naturally ventilated building.

The acoustic splitter element 200 is made of an acoustic absorbent material similar to the acoustic absorbent material of the first embodiment of the invention. In the second embodiment of the invention the acoustic splitter element 200 is formed in a repetitive zig-zag shape of troughs and peaks defining a plurality of channels 204.

Figure 4 is a perspective view of an acoustic attenuator according to the second embodiment of the invention. The acoustic attenuator 2000 is made up of a plurality of attenuator splitter elements 200_1 to 200_4 according to the second embodiment of the invention stacked on top of one another to form a self supporting structure. While in this embodiment the acoustic attenuator is made up of 4 acoustic splitter elements, it will be appreciated that in alternative embodiments of the invention the acoustic attenuator may be made up of any number of acoustic splitter elements. The stacked acoustic splitter elements 200_1 to 200_4 forms a self supporting tessellated or honey comb structure

The top surface 204a of the peaks of acoustic splitter element 200_2 form an abutting engagement with the underside surface 204b the troughs of acoustic splitter element 200_1 which is placed above it. Air flow channels 204 defined by the shaped formations are thereby formed between adjacent acoustic splitter elements 200_i and 200_i+1 and 200_i and 200_i-1. The air flow channels 204 formed are suitable for the flow of air by natural or low energy ventilation. The air flow channels 204 may in some embodiments of the invention be shaped to define flow restrictive and torturous acoustic paths without a prohibitive restraint on the attenuator pressure drop.

Since the acoustic attenuator structures formed by the embodiments of the invention are self-supporting, the need for an additional a supporting housing or super structure can be eliminated. Eliminating the housing or super structure 1.1 of a conventional attenuator as illustrated in Figure 17, as well as supporting elements - metal housing 1.2 and the robust bull nose 1.5, enables the

IZ manufacturing process used to form an attenuator to be adapted. Processing semi rigid and rigid acoustically absorbent materials forming the acoustic splitter element 100 enables acoustic splitter elements to be formed as a single part. One of the principle innovative steps of the invention is therefore the formation of an 5 absorbent, standalone structure from a repeated pattern of acoustic splitter elements or building blocks for low energy buildings.

The shape, form and properties of the acoustic splitter elements can be designed to facilitate the construction of the attenuators. The single components forming ID the acoustic attenuators according to the invention are designed and shaped such that each acoustic splitter element can interlock, rest against, stack, form a layer, fit against another acoustic splitter element to form a self supporting acoustic attenuator structure.

I5 Embodiments of the invention enable an entire acoustic attenuator structure to be formed from acoustic splitter element building blocks. The acoustic splitter elements can be shaped and sized such that air ways and splitters formed within the acoustic attenuators will be self supporting. This eliminates the requirements for shelves, brakes, housing and other structural supports when forming such0 attenuators. The shape of the building blocks can be selected in order to minimize waste.

Attenuator acoustic elements according to some embodiments of the invention can be cut from a block of raw materials which may be granulated, liquid or semi5 rigid by a process of pressing, heating, extruding, or using chemical means. Working with raw materials allows greater flexibility in terms of size. Raw materials can easily be cut, shaped or extruded into non standardized sizes (any size). An example of such a procedure is illustrated in Figures 10A to 10E for the manufacture of acoustic attenuator elements and construction of an acousticD attenuator according to the first embodiment of the invention. In Figure 10A a block of raw acoustic absorbent material 500 is cut, a pair of parallel channels 101 are cut in the material for each acoustic splitter element 100. Waste material is removed in Fig 10B. As illustrated in Fig 10C, the side walls 102 of each acoustic splitter element 100 are folded inwards to form lateral walls generally

I3 perpendicular to the planar surface as illustrated in Fig 1OD. The acoustic splitter elements 100J are stacked on top of one another as illustrated in Fig 1OE the formed acoustic attenuator 1000 can be placed directly in the ventilation duct of a building or, if desired, inside a super structure.

5

A further example of a procedure for the manufacture of acoustic attenuator elements and construction of an acoustic attenuator according to the first embodiment of the invention is illustrated in Figures 11A to 11 E. In Figure 11A a block of raw acoustic absorbent material 600 is cut and divided into acoustic

ID attenuator elements 200. Waste material is removed in Fig 11 B and the acoustic attenuator elements 200 are separated from one another as illustrated in Fig 11C. As illustrated in Fig 11D, the every other acoustic attenuator is rotated by an angle of 180° so that the peak of one acoustic attenuator element 200_i is facing towards the trough of an adjacent other acoustic attenuator element 200_i+1 and

I5 200_i-1. A tessellated honeycomb structure is thereby provided defining channels 204 between adjacent acoustic splitter elements providing an acoustic attenuator 2000 as illustrated in Fig 11E which can be placed directly in the ventilation duct of a building or, if desired, within a super structure. D Figures 12A to 12C illustrate the extruded material 1200 for the acoustic splitter elements according to some embodiments of the invention being extruded through an extrusion die 1210. in Fig 12B the extruded material 1200 is cut into sections, each section forming an acoustic splitter element 100 with walls similar to the first embodiment of the invention. The acoustic splitter elements 100 are stacked on5 top of one another as illustrated in Fig 12C to form an acoustic attenuator 1000.

The shapes of the acoustic splitter elements according to different embodiments of the invention can be selected such to increase and tune the acoustic performance of the attenuator, as well as reduce manufacturing times and aid with0 air flow through the attenuator

The level of attenuation provided by an acoustic attenuator has a strong correlation with the level of acoustic absorption provided by the materials used to form the attenuator. Levels of acoustic absorption will have an effect on both the

I4 magnitude and frequency characteristics of the attenuator - the higher the level of absorption, the better the performance of the attenuator. There is therefore a desire to increase the performance of the attenuator as much as possible by means of material selection.

5

The density of the materials used for the acoustic splitter elements forming the acoustic attenuator is important. A low density material offers a higher level of acoustic absorption, which in turn provides high levels of acoustic attenuation through the air path of the attenuator structure. However, the passage of sound

ID directly through a light material is greater than that of a denser material.

Therefore, the selection of light weight materials can compromise the performance of the attenuators by allowing the passage of sound through the solid section of the attenuator, noting that the levels of acoustic attenuation through the air path of the attenuator and the propagation of sound waves through solid components

15 making up the splitters is frequency dependant. Where dense materials are used to form the splitters, the low frequency performance of the attenuator is increased. On the other hand, the overall performance of the attenuator is compromised as a result of reduced levels of acoustic absorption. In order to address such issues, it is proposed to use materials with different densities within the construction of theD attenuator structure. These denser materials could be used to form splitters in their own right or combined within or around splitters such to increase the density of the splitter. The density of the materials is therefore a known factor in the performance of these products. It is also known that combining materials of different densities can affect the performance and frequency performance of the5 product.

In embodiments of the invention materials having a density in the range of 20kg/m³ - 200kg/m³ may be used. D Figure 13 illustrates an example of a tessellated shape acoustic attenuator element according to a further embodiment of the invention formed by cutting. A block of raw material 1300is cut - 13.1 to form acoustic attenuator elements having a repetitive tessellated shaped. The acoustic attenuator elements formed thereby are separated - 13.2. A tessellated flow path 13.3 is formed between two

I5 acoustic attenuator elements wherein the air coming in from an inlet at the side follows the tessellated path of troughs and peaks to the output. Sections of denser material 13.41 can be placed between sections of less dense material 13.42. The denser material may be of the same material as the less dense material but of a

5 higher density or may be of a different material of a higher density. The acoustic performance of the acoustic attenuator may thereby be tuned by adapting the density of the material or materials of the acoustic attenuator elements. Moreover acoustic elements of different densities may be used to build an attenuator structure, the selection of the densities of the materials being used to tune the

ID acoustic performance of the acoustic attenuator.

Fig 9A to 9C for example show attenuator elements made of different material. In Fig 9A the material is conventional acoustic material, in FIG 9A the material is fire resistance -fire class O material, in Fig 9C the material is recycled material and I5 FIG 9D illustrates a thermal damper structure.

In some embodiments of the invention, as illustrated in Figure 13, the acoustic splitter elements can be combined with solid elements 13.5 in order to boost the acoustic performance of the splitters and attenuator. The material used for theD solid elements may include, for example, MDF, timber, metal, or other materials having a greater density than that used for the acoustic splitter element.

The rigidity of the materials selected to form the acoustic splitter elements in embodiments of the invention can be such that splitters and other elements5 forming the acoustic attenuator will be self supporting and will not deform or sag over time or under wind loads.

Since in embodiments of the invention the attenuators will be used within ventilation systems, the airway size and migration path of these airway gaps willD therefore be considered.

In the case where fire resistance is required, material selection when forming the attenuator will be considered. Appropriate materials may include mineral wool or other materials with the addition of a fire retardant additive.

IG In some embodiments of the invention recycled materials may be used. Such materials may include car dashboards, newspapers, tyres, carpet, foam, cloth, glass, plastics, etc. Any suitable material that is fibrous or can be bonded such 5 that it has an open cell structure or porous structure may be used.

The surface finish and shape of the materials used to form the acoustic attenuator elements may be designed to mitigate against pressure drops as a result of roughness, consequential boundary layer effects and the recirculation of air.

ID

The slow air speed used to ventilate low energy buildings allows for the gap between the acoustic attenuator elements forming splitters to be reduced, allowing the performance of the acoustic attenuator to be increased and tuned to a specific requirement. These changes to increase the performance of the acoustic

15 attenuator of embodiments of the invention, are made possible due to the low air speed associated with low energy buildings and the fact the splitters can be formed from pre-fabricated blocks.

Since in embodiments of the invention the gap G between splitters forming airD channels 104 or 204 illustrated in Figures 2 and 4, is reduced, the acoustic performance of the acoustic attenuator tends to improve. Likewise, the pressure drop across the acoustic attenuator increases. The low air speeds within low energy buildings allows for a significantly greater variation in gap size G, due to the reduced air speeds and subsequent reduced pressure drop across the 5 attenuator. This allows the acoustic performance of the attenuator to be increased. The frequency response of the attenuator is also known to be a function of the gap size G. Consequently the gap size G can be varied in order to tune the frequency response and performance of the attenuator. This allows acoustic attenuators according to embodiments of the invention to be designed to specifically mitigate0 against road noise, air craft noise, train noise, speech and any other noise type within a defined or semi defined characteristic.

The acoustic performance of an attenuator is a function of the surface area of the acoustic splitter elements. The shape, cross section and layout of the acoustic

I7 elements within the acoustic attenuator have a significant impact upon its acoustic performance. In conventional acoustic attenuators due to high air speeds, it is typical to use straight, rectangular splitters, with or without shaped bull noses to reduce the pressure drop.

5

The low air speed of low energy or natural ventilation enables alternative splitter shapes to be used. The surface area of the acoustic splitter elements according to embodiments of the invention can increase the effective area of the splitter by 5% percent or more, comparing for example, the acoustic attenuator structures of

ID Fig 1OE and Fig 11E. This may be achieved by moving away from the standard rectilinear of the chevron shape.

Removing elements such as metal housing 1.2 and robust bull noses 1.5 used for structure and robustness of the acoustic splitter in conventional acoustic I5 attenuators such as that as illustrated in Figure 17 can also be used to increase in the surface area of the acoustic splitter elements significantly.

Forcing the ventilating air and sound to pass through bends, chevrons and other torturous elements forming the attenuator structure according to embodiments ofD the invention will increase the performance of the acoustic attenuator. An example of such a tortuous acoustic path 13.3 is illustrated in Figure 13. These techniques can therefore be used to enhance the acoustic performance of the attenuator when air speeds are low. 5 Reducing the line of sight through attenuators can be used to increase the acoustic performance of the attenuator. One method of reducing the line of sight of air or sound waves through the attenuator is to use sound baffles. Again, sound baffles are not typically used in conventional acoustic attenuators due to the pressure drop through attenuators. D

In embodiments of the invention reactive components can be used to reduce noise levels within ducts containing gas flow. The pressure drop through these systems is typically high and therefore this type of noise attenuation is often used to control noise from combustion engines. The key advantage of reactive

I8 components is their high level of attenuation and the capacity to frequency tune the performance of the attenuator.

In the case of attenuators for low energy buildings, the air flow rate through the 5 attenuator is low and therefore the addition of reactive components on pressure drops is seen to be acceptable. In order to tune and enhance the performance of these attenuators, reactive components are proposed. The use of reactive components can increase the acoustic resistance of the attenuator, as well as reduce the required levels of material within the attenuator to provide a given level ID of acoustic performance.

Two types of reactive components are illustrated in Figure 14. The first type of reactive components referenced as 14.1 , 14.3, act as a mass as a result of the sound waves forcing the air to move between the acoustic splitter elements 100.

I5 In the first type of mass element the centre of gravity of a slug of gas or air is moved or oscillates as a result of the partial movement of sound. The slug of gas has an effective mass and therefore has a reluctance to oscillate movement, which in turn results in a reactive component. Air mass 14.1 is different to air mass 14.3 since the gaps between the attenuator elements forming the air0 channels are different. G1 the gap formed by acoustic attenuators configuring air mass 14.1 is greater than G2 the gap formed by acoustic attenuators configuring air mass 14.3. The second potential reactive component is a spring/capacitive element 14.2. Here, the partial movement of sound compresses a volume of gas 14.2, the centre of gravity of this volume remains constant. As a result of the air5 being compressed and expanded, a reactive component is formed. In essence this type of reactive component acts as a spring since the air is compressed within this zone.

The shape, angle, edge details and other factors within the design of the acousticD attenuator elements and attenuators, all affect the air resistance of the resulting attenuator structure. It is therefore proposed to shape splitters by means of sweep and round air paths, in order to mitigate against turbulent flow and increased levels of pressure drop through the attenuator. These sweeps can be formed by cutting, pressing, extruding heating materials.

I9 Depending upon the function and location of the attenuator structure within a building, the attenuator may be combined with other elements such as fire dampers, air flow dampers, thermal air flow dampers and other elements.

5

Embodiments of the invention propose a new design of an acoustic attenuator resulting in an enhanced acoustic performance and manufacturing process for attenuators. In particular, embodiments of the invention can be used in low energy buildings for low energy or natural ventilation system and aim to overcome the

ID clashes between natural ventilation and acoustics. Acoustic attenuators according to embodiments of the invention can be incorporated into the facade of a building to reduce noise ingress, as well as being incorporated above a partition to control noise transfer between partitioned spaces, whilst allowing the passage of air through the building. The innovative concepts within this product, enables the

15 performance of the attenuator to be specifically designed to the acoustic requirements of a given building, a buildings applications needs and the building construction process.

Acoustic attenuators according to embodiments of the invention may be used inD the control of the spread of noise/speech through ventilation systems for low energy buildings as illustrated in Figures 5 to 8.

Figure 5 illustrates an example of cross ventilation in which an acoustic attenuator

4.1 according to embodiments of the invention is installed in a ventilation channel5 within a partition 4.3 to a circulation space 4.2 between an inlet 4.4 and outlet of air 4.5. In this example to ventilate spaces within the building air is drawn through the external facade 4.4 of the building though the cellular spaces or rooms 4.0 to be ventilated and exits through the roof of the building 4.5 via the circulation space

4.2 The acoustic attenuator can be used to maintain the sound installation of thisD partition 4.3 while allowing a cross flow through the space 4.0 to be ventilated and other cellular spaces.

Figure 6A illustrates how an acoustic attenuator 6.1 according to an embodiment of the invention can be installed in a partition 6.3 where steel 6.4 has been placed.

2D The presence of the steel 6.4 restricts the use of a conventional acoustic attenuator. However in this embodiment the acoustic attenuator 6.1 has been configured in combination with the steel to provide air channels so that the ventilating air passes through the steel. In an alternative design illustrated in 5 Figure 6B the acoustic attenuator 6.2 is shaped around the steel 6.4.

Figure 7A illustrates another example of cross ventilation where acoustic attenuators 7.1 according to an embodiment of the invention is used to maintain the sound insulation of the partition 7.30between a cellular space 7.0 and a ID circulation space 7.4. Figure 7A also illustrates acoustic attenuators 7.2 according to embodiments of the invention being placed in the facade 7.5 to boost the acoustic absorption performance of the facade.

Figure 7B illustrates a simple operable window 7.8 allowing the inflow of I5 ventilating air which provides only a limited level of acoustic resistance. In Figure 7C an acoustic attenuator 7.30 is modelled into the facade of the building below the window thereby increasing its acoustic resistance while allowing the flow of air through the facade. In Figure 7D a first acoustic attenuator 7.4 is modelled into the facade 7.5 of the building below the window and a second acoustic attenuatorD 7.4 is modelled into the facade 7.5 of the building above the window thereby increasing the flow of ventilating air through the facade 7.5 while still providing acoustic resistance.

Since the acoustic attenuator structure may be incorporated into the facade of a5 building the acoustic resistance of the facade is improved thereby increasing the number of geographical sites available to natural ventilation.

In Figures 8A to 8C an acoustic attenuator 8.0 according to an embodiment of the invention, is installed into a partition between a cellular space 8.5 and a circulationD zone 8.6 . A ventilation flap 8.1 may be added to open or close the ventilation channel in which the acoustic attenuator is placed. A protective grill 8.3 may be placed at an end of the ventilation channel.

a The low air speeds (<4m/s) common to low energy ventilation systems, allow for rigid and semi rigid materials to form a diverse range of attenuators Rigid and semi rigid materials are processed into attenuator building blocks to generate self supporting or tessellating structures, to create the building blocks to form the acoustic attenuator splitters or the entire attenuator structure. Since these building blocks can be processed from a single element by; cutting, heating, extruding, etc raw materials the need to standardize the size of the attenuator is removed. The attenuators can also be designed to fit into unconventional locations and gaps.

The acoustic attenuator of embodiments of the invention is aimed at improving the acoustics of naturally ventilated, low energy buildings, and in particular outside of the residential sector. The ventilation rates to these buildings are very much dependent on the heat gain and ventilation requirements. The acoustic attenuator of embodiments of the invention can be used to ventilate spaces which require ventilation openings with a free area of at least 0.5% of the ventilated spaces floor area.

The size of the unit is dependent upon the ventilation rate and free area requirements of specific buildings. The overall dimension of the acoustic attenuator structure is also proportional to where the installation of the acoustic attenuator structure occurs within the building. In some embodiments of the invention the acoustic attenuator can have a minimum overall cross sectional surface area of <0.25m², the free area for the passage being at least 0.125m². Typically the air speed through the attenuator structure will be less than 4 ms^"1. In some cases less than 1 ms^"1 . The acoustic performance of the acoustic attenuator according to embodiments of the invention depends upon the required level of separation required across this device. 5-45 dB D_new D™ (where new= normalised element weighted and iw=insertion weighted acoustic values).

The low air speed through the acoustic attenuators according to embodiments of the invention means that pressure drops across these units do not increase dramatically when changes are made to the standard rectilinear or chevrons design, thus still allowing a required volumetric rate of air to ventilate a space with said requirement by forces associated with natural ventilation. As such, there is considerably more design flexibility in terms of the air path through the attenuator, which in turn results in considerable benefits to the acoustic performance of the attenuator.

The low air speeds through the acoustic attenuators according to embodiments of the invention also mean that alternative forms of construction can be used. The low air speed considerably reduces wind load on the splitters. It is therefore possible to use rigid and semi rigid materials to form single component splitters. The use of rigid and semi rigid materials enables splitters to be formed as the building blocks prior to the construction of the attenuators by cutting, extrusion, heating, etc. These building blocks can then be fixed, interlocked, sandwiched, layered, tessellated together to form a structure, self supporting structure or part of a super structure resulting in an acoustic attenuator structure.

Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

1. An acoustic attenuator element for forming an acoustic attenuator for reducing noise levels and enabling the flow of air when placed in a 5 ventilation channel of a low energy or naturally ventilated building, wherein the acoustic attenuator element is made of acoustic absorbent material for absorbing sound and is provided with shaped formations which co-operate with complementary shaped formations of at least one further acoustic attenuator element, according to claim 1 , to ID form a self supporting acoustic attenuator structure and to define a plurality of channels between the acoustic attenuator elements for the flow of air by natural or low energy ventilation within the self supporting structure.

I5 2. An acoustic attenuator element according to claim 1 wherein the plurality of channels are shaped to define flow restrictive and torturous acoustic paths for the flow of air without a prohibitive restraint on the attenuator pressure drop.

ZD 3. An acoustic attenuator element according to claim 1 or 2 wherein the acoustic element is formed in a planar shape and is provided with a pair of parallel channels arranged in a longitudinal direction at the lateral side regions of the acoustic attenuator element, the channels being configured such that the lateral side regions of the acoustic attenuator element can be

25 folded from a position parallel to the main planar surface of the attenuator element to form a pair of walls generally perpendicular to the planar surface of the acoustic attenuator element, the pair of walls forming the shaped formations.

3D 4. An acoustic attenuator element according to any one of the preceding claims wherein the acoustic element is formed in a repetitive shape providing an increased surface area of the acoustic element defining the shaped elements and the plurality of channels.

5. An acoustic attenuator element according to any one of the preceding claims wherein the acoustic element is formed in a zig-zag shape

6. An acoustic attenuator element according to any one of the

5 preceding claims wherein the acoustic element is formed in a shape such that the resulting acoustic attenuator has a tessellated structure defining a plurality of channels.

7. An acoustic attenuator element according to any one of the

IO preceding claims wherein the acoustic attenuator element is made of an extruded material

8. An acoustic attenuator element according to any one of the preceding claims wherein the acoustic attenuator element is made out of at

15 least one of a fibrous, an open-cell or a porous material.

9. An acoustic attenuator according to any one of the preceding claims made out of thermo set materials or malleable acoustic absorbers.

ZD 10. An acoustic attenuator element according to any one of the preceding claims wherein the acoustic attenuator element can be arranged to co-operate with the further acoustic attenuator element to form baffles within the attenuator structure

25 11. An acoustic attenuator element according to any one of the preceding claims wherein the material of the acoustic element can be varied to frequency tune the attenuator structure.

12. An acoustic attenuator element according to any one of the

3D preceding claims wherein the shaped formations of the acoustic element are co-operable with the complementary shaped formations of the further acoustic element by an abutting engagement to form a stack, to interlock with one another, or to form a tessellated structure

13. An acoustic attenuator for reducing noise levels in a low energy or natural ventilation system when placed in a, ventilation channel of a building, the acoustic attenuator comprising: a plurality of acoustic attenuator elements co-operable with one

5 another by means of respective complementary formations to form a self supporting structure having a plurality of channels for the flow of air by means of minimal air pressure characteristic of a low energy or natural ventilation system, the plurality of channels being provided between the acoustic attenuator elements and being defined by the shape of the acoustic attenuator

ID elements; and wherein each acoustic attenuator element is made of acoustic absorbent material for absorbing sound.

14. An acoustic attenuator according to claim 13 wherein the plurality of channels are shaped to define flow restrictive and torturous acoustic paths

I5 without a prohibitive restraint on the attenuator pressure drop.

15. An acoustic attenuator according to claim 13 or 14, wherein the speed of air flow in the ventilation channel is >4m/s D

16. An acoustic attenuator according to any one of claims 13 to 15 wherein each acoustic element is formed in a planar shape and is provided with a pair of parallel shaped channels arranged in a longitudinal direction at the lateral side regions of the acoustic attenuator element, the parallel channels being arranged such that the lateral sides regions of the acoustic5 attenuator element can be folded to a position generally perpendicular with respect to the rest of the acoustic attenuator element.

17. An acoustic attenuator according to any one claims 13 to 16 wherein each acoustic element is formed in a repetitive shape forming an acousticD attenuator of a tessellated shape defining the plurality of channels.

18. An acoustic attenuator according to any one claims 13 to 17, wherein each acoustic element is formed in a zig-zag shape

2G

19. An acoustic attenuator according to any one of claims 13 to 18 wherein each acoustic attenuator element is made of an extruded material

5 20. An acoustic attenuator according to any one of claims 13 to 19, wherein each acoustic attenuator element is made out of at least one of a fibrous, an open-cell or a porous material.

21. An acoustic attenuator according to any one of claims 13 to 20

ID wherein the acoustic attenuator elements are arranged to co-operate with each other to form baffles within the attenuator structure

22. An acoustic attenuator according to any one of claims 13 to 21 wherein the acoustic attenuator elements are arranged such that the

I5 complementary shaped formations engage with each other by an abutting engagement to from a stack for packing.

23. An acoustic attenuator according to any one of claims 13 to 22, wherein the acoustic attenuator elements are configured with respect to one0 another to form reactive acoustic components of air masses within the attenuator structure enabling the acoustic performance of the acoustic attenuator to be tuned.

24. An acoustic attenuator according to any one of claims 13 to 23,5 further comprising solid elements within one or more of the acoustic elements to further improve acoustic performance.

25. An acoustic attenuator according to any one of claims 13 to 24, wherein the cross sectional size of the channels formed between the acousticD attenuator elements can be varied to tune the frequency response of the attenuator.

26. An acoustic attenuator according to any one of claims 13 to 25, wherein, the attenuator elements forming the acoustic attenuator may have different material densities to tune the frequency response of the attenuator.

5 27. A method of making an acoustic attenuator for reducing noises level in a low energy or natural ventilation system when placed in a ventilation channel of said ventilation system, the method comprising cutting a block of acoustic attenuator material into a plurality of acoustic attenuator elements;

IO defining a pair of longitudinal parallel channels in the lateral side regions of each acoustic attenuator element folding each acoustic attenuator element along the pair of longitudinal parallel channels to from a pair of walls generally perpendicular to the planar surface of the acoustic attenuator element;

I5 placing the acoustic attenuator elements adjacent to one another to form a self supporting acoustic attenuator structure such that an air channel is formed between adjacent acoustic attenuator elements for the flow of air by natural or low energy ventilation, an air channel being defined by the walls and planar surface of a first acoustic attenuator element and the opposing planar surfaceD of a second adjacent acoustic attenuator element.

28. A method of making an acoustic attenuator for reducing noises level in a low energy or natural ventilation system when placed in a ventilation channel of said ventilation system, the method comprising 5 cutting a block of acoustic attenuator material into a plurality of acoustic attenuator elements having a repetitive angular shape; separating the acoustic attenuator elements a distance from one another turning every other acoustic attenuator element through a angle of 180 to form a self supporting acoustic attenuator structure having a tessellatedD structure defining a plurality of air channels between adjacent acoustic attenuator elements for the flow of air by natural or low energy ventilation, an air channel being defined by the angular shape of adjacent acoustic elements with respect to one another.