GB2572436A

GB2572436A - A sound-absorbing raft

Info

Publication number: GB2572436A
Application number: GB1805272.0A
Authority: GB
Inventors: Butchard Matthew; Colam Stuart
Original assignee: Sas International Ltd
Current assignee: Sas International Ltd
Priority date: 2018-03-29
Filing date: 2018-03-29
Publication date: 2019-10-02
Also published as: GB201805272D0

Abstract

The sound absorbing raft 2 comprises upper 6 and lower 8 surfaces and a housing arranged to extend in a general horizontal plane. A sound absorbing material is located within the housing. The upper surface of the raft is inclined or sloped at an angle relative to the horizontal to define a ramp for causing sound waves to be absorbed into the sound-absorbing material through the upper surface of the raft. The raft may include ribs including a suspension arrangement. The raft may be perforated. The lower surface may also be slanted or inclined relative to the horizontal. The raft may define a central and peripheral cavities which include sound absorption members made from discrete blocks. Also claimed is an acoustic system comprising at least two rafts arranged in a series

Description

TECHNICAL FIELD

The present invention relates to a sound-absorbing raft, for suspension from a ceiling, to help control acoustic behaviour within a room.

BACKGROUND

The science of acoustics includes designing the sound-absorbing and reflecting properties of the surfaces in a room. Sound absorption within a room is important as its absence can result in excessive reverberation time and loudness which in turn can lead to poor speech intelligibility, for example. In environments where sound-absorbing ceilings are not appropriate, the inclusion of suspended horizontal rafts containing sound-absorbing material can help to control loudness and reverberance.

In large, noisy environments such as open-plan areas, restaurants, shopping centres, school classrooms and other educational establishments etc., the sound-absorbing rafts can be installed close to working areas or other locations where acoustic treatment is needed in order to achieve suitable conditions for communication, concentration or recovery. Sound-absorbing rafts are particularly suitable in, for instance, reception and information counters, refreshment areas, or other large, noisy spaces.

As background, in acoustics, the following definitions apply: 'low frequency' refers to 125Hz and 250Hz octave bands, 'mid frequency' refers to 500Hz and 1kHz octave bands, and 'high frequency' refers to 2kHz and 4kHz octave bands.

It would be highly desirable to improve the efficiency of sound-absorbing rafts, to better control the reverberance and loudness within a room.

The present invention seeks to improve the performance of sound-absorbing rafts of the prior art.

SUMMARY OF THE INVENTION

A sound-absorbing raft for suspension from a ceiling is provided. The raft has:

an upper surface and a lower surface;

a housing arranged to generally extend in a horizontal plane parallel to the ceiling in use; and sound-absorbing material located within the housing, wherein the upper surface of the raft comprises at least one upper inclined surface inclined in relation to the horizontal plane, to define an upper ramp for intersecting and causing sound waves to be absorbed into the sound-absorbing material through the upper surface of the raft.

As sound-waves are intercepted and penetrate through the upper surface and into the sound absorbing material, overall sound absorption is increased. The inclined surface also helps to avoid debris collecting on the upper surface of the raft.

The upper and lower surfaces of the raft may be upper and lower surfaces of the housing. A housing thickness may be defined between the upper and lower surfaces, in a direction generally perpendicular to the horizontal plane, wherein each upper and/or lower inclined surface extends from an area of minimum thickness to an area of maximum thickness.

The housing may be elongate with a central longitudinal axis, the housing comprising a central region, a first peripheral region and a second peripheral region, the central, first peripheral, and second peripheral regions all extending parallel to the longitudinal axis, and the first and second peripheral regions being arranged either side of the central region.

The minimum thickness may be located at a peripheral edge of the housing, the peripheral edge being remote from the central region and extending in a direction parallel to the longitudinal axis.

The thickness of the housing at the area of minimum thickness may be between 10mm and 30mm, preferably between 15mm and 25mm.

This small thickness at the peripheral edge helps to ensure that there is minimal screening of sound to the upper surface of the raft.

The upper and/or lower surfaces may be parallel with the horizontal plane in the central region, and inclined to the horizontal plane in the first and second peripheral regions, to define the upper and/or lower inclined surfaces.

The housing may be divided between the central, first and peripheral regions to define a central cavity, a first peripheral cavity, and a second peripheral cavity.

The cavities enable the sound-absorbing material to be easily located.

The central cavity may be further divided to have end portions at its longitudinal ends and a middle portion located between the end portions.

Advantageously, the end portions can locate sound-absorbing material and the middle portion can locate lighting components.

The sound-absorbing material may be a plurality of discrete blocks, each block being shaped and dimensioned to locate in the central cavity, first peripheral cavity, and second peripheral cavity.

This makes it simple to manufacture and install the raft, with a close fit between the housing and the sound-absorbing material, to help ensure maximum sound absorption.

The housing may further comprise at least one rib arranged to extend transversely, perpendicular to the longitudinal axis.

Each rib acts as a structural component to increase the overall strength of the raft.

The rib may comprise a suspension arrangement.

This enables the raft to be easily suspended from a ceiling.

The rib may comprise an interface arrangement to engage with a further rib.

This enables the raft to be hung in series with a further raft, to define a raft system.

The upper and/or the lower inclined surfaces may have a constant angle in relation to the horizontal plane.

The lower surface may be located on a base panel ofthe housing. The upper surface may be located on a cover panel ofthe housing.

This simplifies manufacture and installation, as the two separate parts can be brought together to define the housing and encapsulate the sound-absorbing material.

The cover panel may comprise a first cover portion and a second cover portion, wherein the first and second cover portions each comprise a flange extending downwards perpendicular to the horizontal plane, in the direction ofthe base panel when the housing is assembled, such that when the first and second cover portions are arranged next to one another, a spacing is defined between the flanges.

This spacing is a simple way to divide the housing between the central, first peripheral region and second peripheral region, to define the central, first peripheral and second peripheral cavities.

The cover panel may be perforated, wherein the cover panel is perforated such that from 30% to 60% of the surface area thereof is open, preferably wherein from 25% to 50% of the cover panel is open.

This has been found to be an optimal percentage of perforation for the acoustic performance ofthe raft, whilst maintaining structural integrity and the appearance thereof

The base panel may be perforated, wherein from 10% and 25% ofthe base panel area is open, preferably wherein from 15% to 20% ofthe base panel area is open.

This has been found to be an effective percentage of perforation for the acoustic performance ofthe raft whilst maintaining structural integrity and the appearance thereof.

The sound-absorbing material may be mineral wool, preferably wherein the density of the mineral wool varies across the raft.

The density of the mineral wool may be higher in the first and second peripheral cavities than in the central cavity.

The lower surface of the raft may comprise at least one lower inclined surface inclined in relation to the horizontal plane, to define a lower ramp for directing sound waves to be absorbed into the sound-absorbing material through the lower surface of the raft.

As sound-waves are also intercepted by the lower surface, overall sound absorption is further increased, further increasing the effectiveness of the sound-absorbing raft.

An acoustic system is also provided, comprising at least two sound-absorbing rafts, arranged in series and suspended from a ceiling.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is an isometric view of a sound-absorbing raft;

Figure 2 is a plan view of the sound-absorbing raft of Figure 1, which has been sectioned along the horizontal plane H-H;

Figure 3 is a section view of the sound-absorbing raft of Figure 1, along the plane A-A, as shown in Figure 2;

Figure 4 is an exploded view of the sound-absorbing raft of Figure 1, with lighting components excluded;

Figure 5 is an exploded view of the sound-absorbing raft of Figure 1, with lighting components included;

Figure 6 is an exploded view of an end cap of the sound-absorbing raft of Figure 1;

Figures 7A to 7D are examples of alternative profiles, with each figure showing a crosssection through an alternative sound-absorbing raft, the section being defined by slicing the raft 2 along a vertical plane A-A, in a similar way to the raft 2 of Figure 3;

Figure 8 is an isometric view of an example of a further alternative sound-absorbing raft; and

Figure 9 is a detail view of an interface arrangement for attaching two or more rafts of Figure 1 together, such that they can be hung in series.

DETAILED DESCRIPTION

Figure 1 shows a sound-absorbing raft 2. The sound-absorbing raft 2 is intended for suspension from a ceiling (also known in the art as a slab), to help control acoustic behaviour within a room. The raft 2 generally comprises a housing 4 and sound-absorbing material 10, which is located within the housing 4. The housing 4 is arranged to generally extend along a horizontal plane H-H, which is intended to be parallel to the ceiling in use. The housing 4 is generally made up of two parts that are brought together to form the housing 4; an upper surface 6 and a lower surface 8.

Figure 2 shows a plan view of a section of the raft 2, the section defined by slicing the raft 2 along the horizontal plane H-H. The sound-absorbing material 10 is represented by the cross-hatching pattern It can be seen from Figure 2 that the housing 4 is generally elongate with a central longitudinal axis X-X. In this embodiment, the housing 4 is around 2500mm in length and 800mm in width.

The housing 4 has three regions that extend parallel to the longitudinal axis X-X. A central region 12 is located generally in line with the longitudinal axis X-X. First and second peripheral regions 14, 16 are located either side of the central region 12. The housing 4 is divided to define a central cavity 18 corresponding to the central region 12, a first peripheral cavity 20 corresponding to the first peripheral region 14 and a second peripheral cavity 22 corresponding to the second peripheral region 16. The cavities 18, 20, 22 locate the sound-absorbing material 10. Each cavity 18, 20, 22 is further divided (for example by structural ribs 30, as described in more detail below) in a transverse direction perpendicular to the longitudinal axis X-X, to define three separate portions. Each of the central cavity 18, the first peripheral cavity 20 and the second peripheral cavity 22 have a first end portion at one longitudinal end and a second end portion at the other longitudinal end, with a middle portion being located between the end portions.

Therefore, the housing 4 is divided in total into nine different portions. The middle portions of the first peripheral cavity, the second peripheral cavity and the central cavity are around 1200mm in length. The middle portions of the first peripheral cavity and the second peripheral cavity are around 370mm in width, whereas the middle portion of the central cavity is about 60mm in width.

In this embodiment, the first and second end portions of the first peripheral cavity, the second peripheral cavity and the central cavity all locate sound-absorbing material 10. The middle portions of the first peripheral cavity and the second peripheral cavity also locate sound-absorbing material 10. The middle portion of the central cavity, however, locates lighting components (an example of which is described in more detail below).

In this embodiment, the housing 4 is divided in the longitudinal direction into the cavities 18, 20, 22 by flanges 42 of the upper surface 6 of the housing 4, which extend the entire length of the housing 4. The structure of the flanges 42 will be described in more detail below. In this embodiment the cavities 18, 20, 22 are divided in the transverse direction by structural ribs 30, which extend the entire width of the housing 4. The structure of the ribs 30 will be described in more detail below.

Figure 3 shows a cross-section through the raft 2, the section defined by slicing the raft 2 along the vertical plane A-A, as shown in Figure 2. As in Figure 2, the sound-absorbing material 10 is represented by the cross-hatching pattern. The view of Figure 3 most clearly shows the profile of the housing 4, which significantly contributes to the improved performance of the sound-absorbing raft 2, compared to sound-absorbing rafts of the prior art. It can be seen that a housing thickness t is defined between the upper and lower surfaces 6, 8 of the housing 4. The thickness t is in a direction generally perpendicular to the horizontal plane H-H. The upper surface 6 includes first and second upper inclined surfaces 24, 25. The first upper inclined surface 24 generally corresponds to the first peripheral region 14 and the second upper inclined surface 25 generally corresponds to the second peripheral region 16. The first and second upper inclined surfaces 24, 25 are inclined in relation to the horizontal plane H-H, to define upper ramps for intercepting sound waves and causing the sound waves to be absorbed into the sound-absorbing material 10 through the upper surface 6 of the housing 4. The inclined surfaces are particularly beneficial to help intercept any sound waves that are travelling in a direction generally parallel to the horizontal plane H-H. In contrast to the planar upper surfaces of rafts of the prior art, where horizontal sound waves often just 'graze' along the upper surface of the raft with minimal absorption, the inclined surfaces 24, 25 intercept the sound waves along their path, greatly increasing overall sound-absorption. In this embodiment, the angle between each inclined surface and the horizontal plane H-H is around 5 degrees. The advantageous effect of directing sounds waves can be achieved by any angle up to around 15-20 degrees. Any higher than this and the dimensions of the raft are likely to be compromised; it will be too thick to be satisfactory in an aesthetic sense, and would have to be hung very low from the ceiling, reducing useful space within a room. As sound waves are intercepted by the upper inclined surfaces 24, 25, they are then directed through the upper surface 6 and into the sound-absorbing material 10. This is generally shown in Figure 3, which schematically shows sound waves S, as an illustration of how they may be directed by the first and second upper inclined surfaces 24, 25.

In this embodiment, the lower surface 8 comprises first and second lower inclined surfaces 26, 27. The first lower inclined surface 26 generally corresponds to the first peripheral region 14 and the second lower inclined surface 27 generally corresponds to the second peripheral region 16. The first and second lower inclined surfaces 26, 27 are inclined in relation to the horizontal plane H-H. This further increases the thickness of the raft at the centre, which may enhance low-frequency sound absorption. The lower inclined surfaces 26, 27 achieve this without compromising the aesthetic properties of the raft, by emphasising the central region 12 ofthe raft 2, and maintaining its symmetry.

It can also be seen from Figure 3 that the first and second upper and lower inclined surfaces 24, 25, 26, 27 extend from an area of minimum thickness tmin, to an area of maximum thickness tmax·

In this embodiment, the areas of minimum thickness tmin are located at peripheral edges 28 of the housing 4. This can be seen most clearly in Figure 2, which shows that the peripheral edges 28 ofthe housing 4 extend in a direction parallel to the longitudinal axis X-X ofthe housing 4. The peripheral edges 28 are remote from the central region 12. The area of maximum thickness tmax generally corresponds to the central region 12. The maximum thickness tmax is around 80mm. The minimum thickness tmin is between 10mm and 30mm, preferably between 15mm and 25mm. In this embodiment, the minimum thickness tmin is 20mm. This small thickness at the peripheral edge helps to ensure that there is minimal screening of sound to the upper surface 6 of the raft 2, i.e. the edge does not act as a barrier, creating a shadow that would prevent sound waves from reaching, and therefore being absorbed by, the upper surface 6. Finally, compared to rafts ofthe prior art, the central region 12 can be made thicker while still preserving the aesthetic properties of the raft 2 (because it is less noticeable if the raft 2 is thin at the peripheral edge). This helps to ensure good low-frequency absorption of sound waves. In an alternative embodiment, the thickness tmin at the peripheral edge could be zero, i.e. the raft 2 could taper to a point at the peripheral edge.

In this embodiment, the first and second upper and lower inclined surfaces 24, 25, 26, 27 have a constant angle in relation to the horizontal plane H-H. This creates a constant taper between the peripheral edges 28 to the central region 12 ofthe housing 4, to encourage consistent absorption of sound waves. As can be seen from Figure 3, the profile on either side of the raft 2 is generally wedge-shaped, but with a truncated end at each peripheral edge 28.

In this embodiment, the upper and lower surfaces 6, 8 are parallel with the horizontal plane H-H in the central region 12.

Figure 4 is an exploded view of the raft 2, which illustrates how the housing 4, soundabsorbing material 10 and ribs 30 fit together to define the raft 2. The housing 4 is made up of a base panel 36 and a cover panel 37. The cover panel 37 is made up of a first cover portion 38 and a second cover portion 40. Each ofthe first and second cover portions 38, 40 include a flange 42. The flanges 42 extend, in use, in a downward direction, away from the ceiling and perpendicular to the horizontal plane H-H in the direction ofthe base panel

36. When the first and second cover portions 38, 40 are arranged next to one another to define the cover panel 37 of the housing 4, a spacing is defined between the flanges 42. This spacing defines the central cavity 18, as well as the first and second peripheral cavities 20, 22, which are located either side of the central cavity 18. This, in effect, encapsulates the sound-absorbing material, to help avoid particular migration, as well as provide an easy-to-clean top surface for user convenience.

Figure 4 also shows the structural ribs 30, which are arranged transversely on the base panel 36, when the raft 2 is assembled. The cover portions 38, 40 comprise a plurality of transverse channels 39, for locating the ribs 30.

The ribs 30, as well as dividing the cavities 18, 20, 22 into multiple regions, also act as structural components to help increase the overall strength of the raft 2. In this embodiment, each rib 30 also includes a suspension arrangement to enable the raft 2 to be easily suspended from a ceiling. In this embodiment, each rib 30 includes a keyhole arrangement, configured to accept a standard fitting to enable wire to be attached, to suspend the raft 2 from the ceiling. An example of how the raft 2 can be suspended from the ceiling is shown schematically in Figure 3. Wires 3 are shown, connected to the raft 2 as well as to a ceiling 1, to suspend the raft 2 from the ceiling 1 under gravity. In this embodiment, the wires 3 are only connected to ribs 30 that are located adjacent the longitudinal ends of the raft. Alternatively, instead of wires, solid rods could be used, or some other suitable arrangement for suspending the raft 2 from the ceiling 1. Each rib 30 also includes an interface arrangement to enable each rib 30 to engage with a further rib.

The interface arrangement is shown in more detail in Figure 9, which shows two rafts 30 hung in series. The ribs 30 of each raft 2 are 'spliced' together with the interface arrangement. In this embodiment, the end of each raft 2 includes square shaped cut-away portions 60 in the upper surface 6, at each peripheral edge of the raft 2, to expose the rib 30 that is beneath. Each rib 30 comprises apertures 62 at a point that is generally in line with the centre-point of each cut-away portion 60. A link portion 64 has a U-shape in cross section, and is arranged to locate over the top surface of a first rib 30 and a second rib 30. The link portion 64 has, in this embodiment, two apertures 66 in its top surface that correspond to the apertures 62 in the top surface of the first and second ribs 30. As can be seen from Figure 6, the corresponding apertures of these components line-up when the components are fitted together, so fastening members can be inserted to fix the two ribs 30 together, and 'splice' multiple rafts 2 in series.

As shown in Figure 6, in the case of the ribs 30 located at the longitudinal ends of the raft 2, these ribs 30 also include an end cap arrangement 32. The end cap arrangement 32 covers the ends of the ribs 30. The components of this end cap arrangement 32 are shown in more detail in Figure 6. Figure 6 shows a rib 30 and an end plate 34 for locating over the rib 30. The end plate 34 has a surface arranged to be generally parallel to the major surface of the rib 30 and a flange 37 extending at 90 degrees from the surface, for engaging a top surface of the rib 30. The flange 37 and the top surface of the rib 30 have corresponding apertures that line up when the end plate 34 is located on the rib 30. In other embodiments, the end cap arrangement 32 could be a different shape or even extended into an end wing to continue the aesthetic lines of the raft 2.

The base panel 36 and first and second cover portions 38, 40 are perforated. In this embodiment, the perforations are a plurality of apertures with a diameter of approximately 1.5mm on the base panel 36 and approximately 4mm on the first and second cover portions 38, 40 (not shown in the figures), but it will be appreciated that this can be varied as desired. In this embodiment, the base panel 36 has approximately 15 percent of its surface area perforated, i.e. 15% of the lower surface 8. In this embodiment, the first and second cover portions 38, 40 have approximately 50 percent of their surface area perforated, i.e. 50% of the upper surface 6. These perforation percentages have been found to be optimum values to help ensure good acoustic performance of the raft 2, whilst maintaining structural integrity and a good visual appearance. It will, however, be appreciated that the exact percentage each surface is perforated can be varied, and the technical effect of the invention still achieved. In practice, a range of 10 to 25 % would be a suitable range for the percentage of perforation of the surface area of the base panel 36, to achieve the technical effect. A range of 30 to 60% would be an acceptable range for the percentage of perforation of the surface area of the cover portions 38, 40, to achieve the technical effect. In an alternative embodiment (not shown), the raft could be entirely open at the top. In other words, instead of the cover portions 38, 40, the soundabsorbing material 10 could be seated on the base panel 36 with no cover portions 38, 40 to encapsulate the sound-absorbing material 10. In this case, the sound-absorbing material 10 could be shaped such that the upper inclined surfaces 24, 25 are defined only by the shape of the sound-absorbing material 10, i.e. the sound-absorbing material 10 could have surfaces inclined to the horizontal plane H-H, so that the technical effect of guiding sound waves into the sound-absorbing material is still achieved.

In this embodiment, the base panel 36, first cover portion 38 and second cover portion 40 are each manufactured as a single piece of powder coated galvanised steel, but it will be appreciated that any suitable material could be used. The base panel 36, first cover portion 38 and second cover portion 40 also have a plurality of cut-outs, as required, to accept lighting components, cable routes and structural rib fixing points.

As can be seen, in this embodiment, the sound-absorbing material 10 is provided as a plurality of discrete blocks. Each block is shaped and dimensioned such that it can be located in the relevant cavity. In other words, the blocks of sound-absorbing material 10 that intended to locate in the first or second peripheral cavities 20, 22 are generally wedgeshaped. The blocks of sound-absorbing material 10 that are intended to locate in the central cavity 18 is generally cuboid in shape. In alternative embodiments, the blocks of sound-absorbing material 10 that are intended to locate in the central cavity 18 are dimensioned such that they do not fill the entire first and second end portions of the central cavity 18, and instead space is defined for locating further components, such as a speaker or a movement sensor, to further increase the functionality of the raft 2.

In this embodiment, the sound-absorbing material 10 is mineral wool. An example of this is Rockwool®, as manufactured by Rockwool Limited. In this embodiment, the mineral wool has a density of 80kg/m³, but it will be appreciated that this can be varied as required, depending on the particular requirements. For example, the sound-absorbing material 10 in the first and second peripheral cavities 20, 22 could be of a higher density than the sound-absorbing material 10 in the central cavity 18. This would help ensure that the sound absorption is consistent across the entire raft 2.

To achieve this, a mass of 4kg of Rockwool per m², has been found to be suitable. Therefore, in areas where there is less depth available to accommodate sound-absorbing material 10 (towards the peripheral edges 28), and where a particularly high performance is required, it may be advantageous to provide sound-absorbing material 10 of an increased density, to result in the overall mass per unit area being at or above this level.

In this embodiment, the base panel 36, first cover portion 38 and second cover portion 40 are each backed with ironed-in fleece, such as Royalin R6/40 FF, i.e. the internal surfaces in contact with the sound-absorbing material 10 have a coating of 0.3mm thick non-woven glass tissue. The inclusion of fleece improves the low frequency absorption of the raft 2, without it being necessary to increase the density of the sound-absorbing material. The fleece also helps to prevent fibre migration when mineral wool is used. The fleece is typically around 0.2-0.5mm thick and exhibits a density of around 300kg/m³, significantly more than the mineral wool; around four times as much. Installation is very simple; for example, the fleece can simply be heated with an iron or heat lamp, to bond it to the material below. In alternative embodiments, where there is no ironed-in fleece, the mineral wool is wrapped in tissue, to help prevent fibre migration.

Providing the sound-absorbing material 10 in the form of discrete blocks makes it simple to manufacture the raft 2 as well as install the sound-absorbing material 10 within the housing 4. The shape and dimensions help to ensure a close fit between the soundabsorbing material 10 and the housing 4, to help ensure maximum sound absorption. In alternative embodiments, all the sound-absorbing 10 material could be provided in cuboid shaped blocks, and compressed into the tapered peripheral cavities. This compression can increase the density of the sound-absorbing material 10 in these areas, to result in the density varying across the raft 2, which can be advantageous, as discussed above.

The table below shows test data that illustrates the sound absorption for the raft. The absorption is quantified in terms of Sabins per m². Values close to 2 indicate that both sides of the raft are providing unity absorption.

	Octave band centre frequency (Hz)
125	250	500	Ik	2k	4k
Sound absorption (Sabins per m²)	0.46	1.32	1.81	2.02	2.12	2.00

As can be seen, the sound absorption is relatively consistent for different frequencies of sound, particularly at mid and high frequencies. A Sabin (or Sabine) is a unit of sound absorption and, as can be seen from this test data, it has been found that an average value across the raft of around 1.65 Sabins per m² can be achieved with the design, which is a substantial improvement over conventional rafts.

Figure 5 shows an example of a lighting arrangement that can be installed in the central cavity 18. An upper lighting arrangement 44 is shown, as well as a lower lighting arrangement 46. The upper lighting arrangement 44 includes an upper lighting housing 48, which is intended to sit flush with the upper surface 6 of the housing 4. The top surface of the upper lighting housing is intended to seat an up-lighter 50. The upper lighting housing 48 also locates lighting electrical components 52. The upper lighting housing 48 is located on a mounting tray 54. The mounting tray 54 locates downlights, LED boards 56 and a diffuser 58. The diffuser 58 has end caps at its longitudinal ends. In use, the LED boards 56 project light in a downward direction which is diffused by the diffuser 58. It will be appreciated however, that this is just an example and the particular lighting arrangement can be varied. For example, a sensor component could be included.

It will be appreciated that numerous changes may be made within the scope of the present invention. For example, the cross-sectional profile of the raft 2 could be varied in ways that would still achieve the technical effect.

Figures 7A-7D show examples of alternative profiles. Each of Figures 7A-7D shows a crosssection through a raft 102, 202, 302, and 402, the section being defined by slicing the raft 2 along a vertical plane A-A, in a similar way to the raft 2 of Figure 3. Similar features to those ofthe raft 2 have the same reference numeral, but with the prefix 1, 2, 3 or 4

Figure 7A shows a profile where inclined upper inclined surfaces 124, 125 are provided, in a similar way to the raft 2 of Figure 3, but no lower inclined surfaces are provided; the bottom surface 108 ofthe housing is planar.

Figure 7B shows a profile where only a single inclined upper inclined surface 224 is provided, and only a single lower inclined surface 226 is provided. This profile is, in effect, the profile of Figure 3 but split through a plane that passes through the longitudinal axis of the raft 202 and is perpendicular to the horizontal plane H-H.

Figure 7C shows a profile that is similar to Figure 7B, with a single inclined upper inclined surface 324, but no lower inclined surfaces; the bottom surface 308 of the housing is planar.

Figure 7D shows a profile that is similar to Figure 7A, where inclined upper inclined surfaces 424, 425 are provided, but no lower inclined surfaces are provided; the bottom surface 408 of the housing is planar. Further, however, at the peripheral edges 428 there is no truncation; the profile tapers to a point. There is also no planar section ofthe upper surface 406; the inclined upper inclined surfaces 424, 425 meet at a point.

It will be appreciated that further variations to the profile of the raft are possible, as desired.

In a further alternative, inclined upper and/or lower inclined surfaces could also be provided that extend from the longitudinal edges ofthe housing 4, i.e. extending parallel to the longitudinal axis X-X, rather than, or in addition to, the upper and lower inclined surfaces that extend from the peripheral edges 28. One example of this is shown visually in the isometric view of a raft 502 in Figure 8. As can be seen, in this example, the alternative profile is achieved by attaching an alternative end cap arrangement 532 to the rib 530 of the raft 502.

Rather than the raft 2 being substantially rectangular, like the embodiments shown in the Figures, in alternative embodiments, the raft 2 could be a different shape such as square, hexagonal, triangular, etc. The minimum thickness tmin and the maximum thickness tmax could be varied as required to alter the acoustic behaviour of a room, as desired.

Claims

1. A sound-absorbing raft for suspension from a ceiling, the raft comprising:

an upper surface and a lower surface;

2. The sound-absorbing raft of claim 1, wherein the upper and lower surfaces of the raft are upper and lower surfaces of the housing, and a housing thickness is defined between the upper and lower surfaces, in a direction generally perpendicular to the horizontal plane, wherein each upper and/or lower inclined surface extends from an area of minimum thickness to an area of maximum thickness.

3. The sound-absorbing raft of claim 2, wherein the housing is elongate with a central longitudinal axis, the housing comprising a central region, a first peripheral region and a second peripheral region, the central, first peripheral, and second peripheral regions all extending parallel to the longitudinal axis, and the first and second peripheral regions being arranged either side of the central region.

4. The sound-absorbing raft of claim 3, wherein the minimum thickness is located at a peripheral edge of the housing, the peripheral edge being remote from the central region and extending in a direction parallel to the longitudinal axis.

5. The sound-absorbing raft of claim 4, wherein the thickness of the housing at the area of minimum thickness is between 10mm and 30mm, preferably between 15mm and 25mm.

6. The sound-absorbing raft of claim 4 or claim 5, wherein the upper and/or lower surfaces are parallel with the horizontal plane in the central region, and inclined to the horizontal plane in the first and second peripheral regions, to define the upper and/or lower inclined surfaces.

7. The sound-absorbing raft of any of claims 4 to 6, wherein the housing is divided between the central, first and peripheral regions to define a central cavity, a first peripheral cavity, and a second peripheral cavity.

8. The sound-absorbing raft of claim 7, wherein the central cavity is further divided to have end portions at its longitudinal ends and a middle portion located between the end portions.

9. The sound-absorbing raft of claim 7 or claim 8, wherein the sound-absorbing material is a plurality of discrete blocks, each block being shaped and dimensioned to locate in the central cavity, first peripheral cavity, and second peripheral cavity.

10. The sound-absorbing raft of any of claims 4 to 9, wherein the housing further comprises at least one rib arranged to extend transversely, perpendicular to the longitudinal axis.

11. The sound-absorbing raft of claim 10, wherein the rib comprises a suspension arrangement.

12. The sound-absorbing raft of claim 10 or claim 11, wherein the rib comprises an interface arrangement to engage with a further rib.

13. The sound-absorbing raft of any of claims 4 to 12, wherein the upper and/or the lower inclined surfaces have a constant angle in relation to the horizontal plane.

14. The sound-absorbing raft of any previous claim, wherein the lower surface is located on a base panel of the housing and the upper surface is located on a cover panel of the housing.

15. The sound-absorbing raft of claim 14 when dependent on claim 7, wherein the cover panel comprises a first cover portion and a second cover portion, wherein the first and second cover portions each comprise a flange extending downwards perpendicular to the horizontal plane, in the direction of the base panel when the housing is assembled, such that when the first and second cover portions are arranged next to one another, a spacing is defined between the flanges.

16. The sound-absorbing raft of claim 14 or claim 15, wherein the cover panel is perforated, wherein the cover panel is perforated such that from 30% to 60% of the surface area thereof is open, preferably wherein from 25% to 50% of the cover panel is open.

17. The sound-absorbing raft of any of claims 14 to 16, wherein the base panel is perforated, wherein from 10% and 25% of the base panel area is open, preferably wherein from 15% to 20% of the base panel area is open.

18. The sound-absorbing raft of any previous claim, wherein the sound-absorbing material is mineral wool, preferably wherein the density of the mineral wool varies across the raft.

19. The sound-absorbing raft of clam 18 when dependent on claim 7, wherein the density of the mineral wool is higher in the first and second peripheral cavities than in the central cavity.

20. The sound-absorbing raft of any previous claim, wherein the lower surface of the raft comprises at least one lower inclined surface inclined in relation to the horizontal plane, to define a lower ramp for directing sound waves to be absorbed into the soundabsorbing material through the lower surface of the raft.

21. An acoustic system comprising at least two sound-absorbing rafts according to any of claims 1 to 20, arranged in series and suspended from a ceiling.