WO2009130685A1

WO2009130685A1 - Sound absorbing device and system

Info

Publication number: WO2009130685A1
Application number: PCT/IB2009/051689
Authority: WO
Inventors: Niels Werner Larsen
Original assignee: Flexacoustics Aps
Priority date: 2008-04-24
Filing date: 2009-04-24
Publication date: 2009-10-29

Abstract

The invention relates to a device for absorbing sound energy over an extended frequency region from a sound field in which the device is placed, the device comprising at least one inflatable body (2) comprising outer wall portions (3, 4) defining one or more inner cavities to be filled with air or another suitable fluid from an air/fluid supply (7, 8), wherein at least one of said outer wall portions is made of a flexible material that can vibrate when exposed to said sound field and wherein said at least one outer wall portion has a thickness in the range 40 μm to 150 μm, whereby the device, when inflated, provides sound absorption at least in a predefined frequency range. The invention also relates to systems of such devices and to rooms provided with such devices or systems. By the invention there is provided a very simple and effective membrane absorber that can absorb acoustic energy over an extended frequency region at least from below 80 Hz to above 5 kHz.

Description

SOUND ABSORBING DEVICE AND SYSTEM

TECHNiCAL FIELD

The present invention relates to devices that can function as sound absorbers of the membrane absorber type comprising one or more inflatable bodies with interna! cavities, where the number of bodies in the device and/or the dimensions of the bodies can be chosen according to specific sound absorption requirements, where the bodies can be brought to an inflated state in which they absorb a substantial amount of sound energy from a sound field in which they are placed and deflated and maybe stored away when no sound absorption is required The present invention furthermore relates to systems comprising such devices. By application of the devices and systems of the invention the reverberation time of a given room in which said devices or systems are applied can be lowered The device or system according to the invention provides either a mobile or stationary sound absorber means, the absorption effect of which can be turned on/off by simply inflating/deflating the sound absorbing bodies in the device/system.

BACKGROUND OF THE INVENTION

A membrane absorber comprising one or more variable cavities has been described in the applicant's own prior international application WO 2006/016321 This document describes a method and corresponding devices and systems for sound absorption and for varying the reverberation time of a room, where the described membrane absorbers, that can be inflated/deflated by the provision of a gas to one or more inner cavities of the membrane absorber, are particularly effective at low frequencies, i.e. at frequencies below approximately 200 Hz, The membrane absorbers described in said document can be supplemented by absorbing means that are effective at higher frequencies to provide sound absorption throughout a broader frequency range.

For many applications it would be advantageous to have access to a sound absorption device that provide substantia! sound absorption not only in the low frequency region but throughout a broader frequency region without having to supplement the absorber with special high frequency absorbing means such as a fabric suspended over the absorber and where said device is very mobile (low weight and volume, when not in use) and flexible (can be turned on and off).

SUMMARY QF THE INVENTION

On the above background it is an object of the present invention to provide a sound absorbing device and corresponding systems of devices that offers a simple means of providing sound absorption over a broadef frequency range, where the design of said devices is such that the devices can easily be tailored (for instance in situ or at the manufacturer) to the dimensions required for a specific application and where the devices after use can easily be removed from a location in which they are used Devices according to the invention can for instance be dismounted and either kept in store at the site of application or returned to the manufacturer, either for storage or for reuse of the material of the device. Since the system is very mobile (low weight and volume, when deflated) it can for instance be brought on a tour with a touring musical orchestra or rented at a venue for a single performance.

Membrane absorbers is a well known way to absorb especially low frequency sound. They usually consist of a stiff plate on a frame structure, although limb/soft materials on a frame has also been tried in practice By the present invention there has been provided a new type of frameless membrane absorbers. This invention builds on this novel construction method.

It has surprisingly been realised that significant sound absorption can be obtained over a broad frequency region with a sound absorber of the membrane absorber type simply consisting of a hollow inflated body with very thin walls, these walls being brought in contact with a sound field from which sound energy is to be absorbed, it has furthermore been realised that providing such bodies with shapes that lead to diffusion of the sound filed in which such bodies are located this leads to increased sound absorption from the sound field

Based on these findings the above and further objects and advantages are according to a first aspect obtained by the provision of a device for absorbing sound energy from a sound field in which the device is placed, the device comprising at least one inflatable body comprising outer wall portions defining one or more inner cavities to be filled with air or another suitable fluid from an air/fluid supply, wherein at least one of said outer wall portions is made of a flexible/resilient material that can vibrate when exposed to said sound field, i e be excited by a sound field in which the body is placed, and wherein said at least one outer wall portion has a thickness of less than 300 μm (corresponding to a weight per unit area of 0 2 kg/m² for a low density polyethylene material) and preferably a thickness in the range 40 μm to 150 μm, whereby the device, when inflated, provides sound absorption at least in a predefined frequency range However, even thinner material may be used, the lower limit being primarily set by handling and robustness requirements The material used in the devices/systems of the present invention has a thickness (thickness of the walls of the absorbing bodies) that is substantiaSiy thinner than that of other inflatables, which normally has a thickness corresponding to a weight per unit area above 0 5 kg/m²

A device according to the invention for absorbing sound energy from a sound field in which the device is placed comprises at least one inflatable body comprising outer wall portions defining one or more inner cavities to be filled with air or another suitable fluid from an air/fluid supply, wherein at least one of said outer wall portions is made of a flexible/resilient material that can vibrate when exposed to said sound field and wherein the shape of the device and/or the thickness of at least one outer wall portion ensures a sound absorption coefficient of at least 0 2 from 80 Hz to 3 kHz

The use of thicker material will result in greater stiffness of the absorber, which will again lead to altered (not desirable) absorption properties

Typically the weight per unit area of the material of the bodies is approximately 0. t kg/m², but this is only to be considered as a typical and not limiting example

In principle any shape of such bodies can be used, but some typical shapes will be defined and described below and in the detailed description of the invention Generally, however, the shape of the sound absorbing bodies used in the devices and system of the present invention are defined by an outer surface OS(x, y, z) that can be brought in contact with the sound field from which sound energy is to be absorbed, wherein the outer surface is a function of all three space coordinates x, y and z it is thus to be noted that even though the various embodiments of the invention shown and described in this specification are generally of an elongated shape, i e. substantially extending along a given longitudinal axis and even though that bodies that are essentially bodies of revolution have been chosen to illustrate the practical implementations of the inventive principles, this is not to be regarded as a limitation of the present invention The invention comprises one or more bodies defined by the above mentioned generalised outer surface OS(x, y, z) as apparent from the independent claim, in which no reference to any specific shape of the sound absorbing bodies has been made

Thus, according to an embodiment of the invention there is provided a device of the membrane absorber type comprising at least one body with a maximum length L and a maximum width W or maximum diameter D, maximum cross sectional area S_MAχ, a width w(x) or diameter d(x) and a cross section S(x), where said body is defined by a longitudinal axis X through the body and where x is the coordinate along the X-axis. The width or diameter of the body may thus either be constant throughout the entire length of the body, but the one or more bodies of the device according to the invention may also change its shape along the longitudinal axis, i.e the width w, the diameter d or the cross sectional area S of the body may be functions of the coordinate x on the longitudinal axis For instance, the shape of the body may resemble that of well known brands of bottles, such as Coca Cola bottles, whereby the body and generally the devices and systems of devices according to the invention may be used for advertising purposes in addition to their sound absorbing effect Such devices, and indeed any of the devices according to the invention, may be oriented in any direction relative to the room in which they are used. For instance, the bottle shaped bodies or cylindrical bodies mentioned above may be oriented vertically in the room

According to a specific embodiment said at least one body is a body of revolution defined by the longitudinal axis X

Specifically said body could be substantially cylindrical, with a diameter D and specifically the body could be elongated

Generally, the resonance frequency f₀ where maximum absorption will be expected depends on the mass per unit area of the material used for the walls of the sound absorbing bodies, which mass per unit area for a given material will be inversely proportional to the thickness t of the walls of the bodies. Furthermore the resonance frequency of the absorber depends on the volume of air/fluid in the absorber, i e on the dimensions of the absorber Preferably the maximum width or diameter of the individual bodies should be large and it has been found that a maximum width W or diameter D in the range 0.3 to 1 meter yields good results in practice (For a wall thickness below 200μm), although both smaller and larger dimensions may be used in practice (dependent on the actual wall thickness and material of the bodies).

Generally the total outer surface area, i.e the total area in contact with the sound Filed should be made as large as possible if maximum sound absorption is required This requirement may be futfilSed according to the invention by using individual bodies of large dimensions or by using devices/systems of such bodies of smaller dimensions, the total contact area of the devices with the sound field however being large due to a large number of bodies.

According to a specific embodiment at least one of the inflatable bodies may comprise outer wall portions with a cross sectional area Si(x) that are reduced compared to said maximum cross sectionai area S_MAX.

It is preferable according to the invention to be able to control the air/fluid pressure within the cavities in the bodies, such that this pressure can be adjusted to obtain a maximum value of sound absorption from the sound field in which the device is placed Generally, the air/fluid pressure inside the bodies will affect both the overali size of the bodies and thereby the absorption area of the bodies and also the stiffness of the bodies and thereby the resonance frequency and bandwidth at/within which sound absorption of the bodies will be as large as possible Also, during actual use of the devices according to the invention the air temperature of the room in which the device is located may change (typically increase for instance during a live musical performance in a hall with a large audience) and also for this reason it can be advantageous to be able automatically to control air/fluid pressure within the bodies in order to keep their sound absorbing properties constant

The bodies used in the devices or systems of the invention are made of a resilient material, preferably a plastic materia! It has turned out in practice that iow density polyethylene (PE LD) can be used with good results, but other materials may also be used Preferably, or due to local regulations, the material of the at least one body should be fire retardant Sound absorption is characterised by the sound absorption coefficient, the centre or resonance frequency of the absorber and its bandwidth With the devices or systems according to the invention a sound absorption coefficient of at least 0.4 can typically be obtained over a broad frequency range such as for instance approximately 80 Hz to 3 kHz, whereby the device is a broadband sound absorber Considerably higher absorption coefficients may however be obtained at specific frequencies, for instance in the lower frequency end of the absorption range. {It is noted that whenever specific vaiues of absorption coefficients are mentioned in the present specification measurement conditions follow the ISO 354 (1985) standards and the air-filled absorbers are placed next to each other lying on the floor

Although the device according to the invention may comprise only a single body as described above the device may also comprise a plurality of inflatable bodies, wherein each of said bodies is attached either directly or through an intermediate portion to at least one other of the bodies, whereby the plurality of bodies, when inflated, will form a three-dimensional structure of bodies that can be placed in the sound field

The individual bodies of this multi body structure is or can be is in fluid communication with at least one other of the bodies.

The intermediate portions that optionally are formed between adjacent bodies can separate adjacent bodies from each other by a minimum distance (d), which distance (d) optionally can be substantially equal to zero, Whether such intermediate portions are present or not - and generally how adjacent bodies are attached to each other in a multi body structure - depends on the actual design and assembling technique used in a given application. A specific embodiment of the device according to the invention comprising multiple bodies separated by intermediate portions is described in the detailed description of the invention.

The length of the bodies used in the invention may be chosen according to specific requirements and may be tailored specifically to for instance a room in which the device or systems of devices according to the invention is used.

As mentioned above, the devices according to the invention may apart from their sound absorbing effect additionally be used for other purposes Thus according to the invention the overall appearance of the bodies of the devices could be chosen according to specific desires and it is even possible to change this appearance during actual use of the devices according to the invention Thus, according to specific embodiments the at least one body and/or at least one intermediate portion (if present) can be provided with graphical items affecting the appearance of the device or conveying information (advertisements for instance) to an audience in a hall

Furthermore, the at least one body and/or at least one intermediate portion (if present) could be provided with light emitting means for illumination of at least chosen portions of the device, which may make it possible also to change appearance during actual use of the devices according to the invention The light emitting means could either be placed outside of the bodies or inside of these and illuminate the outer wall portions of the bodies of the devices, which illumination may even be controlled during use for example related to actions of performers on a stage or the according to content, loudness or rhythm of music played at a live performance in the room It would even be possible to use the material of which the bodies are made as an optical fibre for providing illumination effects of the bodies

The at least one body and/or at least one intermediate portions (if present) could according to the invention even be provided with sound emitting means used for public address purposes or as a supplement to other such means used during actual performances in a room

According to a second aspect the present invention also relates to a system for absorbing sound energy from a sound field within which the system is placed, the system comprising a plurality of devices according to the invention as described above.

A system of devices may according to the invention be designed specifically to the room in which it is to be applied both regarding the absorption properties of the bodies used in the devices according to the invention, the number of such bodies in each individual device making up the entire system and the dimensions of the bodies in the devices. Furthermore a system according to the invention may comprise means for controlling the air/fluid pressure in the bodies, means for controlling illumination of said bodies and/or intermediate portions and means for controlling sound emission from sound emitters placed in/or said bodies and/or intermediate portions illustrative examples of systems of devices according to the present invention are described in the detailed description of the invention, but numerous other configurations of systems according to the invention could also be envisaged without departing from the scope of the invention Thus, for instance, in a room with a plane ceiling it may be possible to apply only a single layer of bodies (i e. each device comprising only a single body) or devices comprising two or more such bodies.

According to a preferred embodiment the system according to the present invention comprises a plurality of devices, the parameters of which is chosen such that it reduces the reverberation time (measured T30) of the room in which it is applied by at least 0.1 second.

According to a third aspect the present invention also relates to a room (such as, but not limited to, a sports arena, a multi-purpose room, a room for live performances of music or drama, wherein in certain situations a very "live" acoustic, i e a relatively long reverberation time, is advantageous, whereas in other situations relatively "dry" acoustics, i.e a relatively short reverberation time, is desired) provided with devices according to the present invention and/or systems according to the present invention, such that the reverberation time of the room can be reduced dependent on the number, dimensions and placement of the devices or systems of the invention within the room, whereby the reverberation time of the room can be changed - upon inflation of the bodies of the devices or placement of such inflated bodies in the room - from a relatively long to a relatively short value. It is even possible applying the principles of the invention to vary the resultant reverberation time dependant on the number of inflated bodies in the devices or systems thereby obtaining absorption coefficients that are less than the maximum absorption that can be obtained with the devices and systems of the invention.

According to a specific embodiment that is described in more detail in the detailed description of the invention the present invention relates to a sound absorbing device comprising a number N of bodies that can be inflated by the supply of a fluid such as air, said bodies comprising outer wall portions that during application are in contact with a surrounding sound field, said outer wall portions defining one or more inner cavities in each of said bodies, which one or more cavities are supplied with said fluid, whereby the bodies become inflated to a state where they can absorb acoustic energy from said sound field. Adjacent bodies are connected to each other by intermediate portions that are advantageously made from the same material as said bodies. The supply of fluid such as air to the internal cavity/cavities of said bodies can according to a specific embodiment of the invention take place by supply of fluid/air to one of said bodies from which the fluid/air can be provided to the remaining bodies through passages between adjacent bodies. This specific embodiment is shown and described in the detailed description of the invention The supply of fluid/air to the individual bodies could alternatively take place at each individual body or subgroups of individual bodies out of the total number N of bodies could be interconnected with passages for fluid/air communication between the individual bodies of each subgroup

Once the bodies have been suitably inflated by the supply of said fluid/air to the internal cavity/cavities of the bodies the supply of fluid/air can be halted, but it is alternatively possible to keep the supply means for fluid/air in an active state for maintaining a given fluid/air pressure within the bodies, even at the presence of (unintentional) minor apertures in the walls of the bodies The supply means can for instance be designed and controlled for providing a large flow of fluid/air into the bodies during inflation and for providing a reduced flow of fluid/air when the bodies are inflated for keeping the fluid/air pressure in the bodies within acceptable limits during application of the sound-absorbing device.

A number of devices according to the invention can be provided in a given room according to the specific requirements, for instance hung from the ceiling of the room The detailed description of the invention shows examples of such arrangements.

An important characteristic of the sound absorbing devices according to the present invention is that these devices in the deflated state, for instance prior to installation and inflation a given room, are extremely flexible, such that the device in the deflated state essentially constitutes a thin sheet structure that can be stored in rolls that can be delivered to the end user This is illustrated in the detailed description of the invention The device according to the invention can easily be tailored either in-situ or at the manufacturer to those dimensions that are required in each specific situation. Such tailoring merely requires cutting the rolSed-up devices to the required length and forming said internal cavities of the bodies for instance by hot welding or binding a knot etc. After use the deflated devices can easily be dismantled and either kept in store at the end user or returned to the manufacturer for storage or for re-cycling of the material. According to the above embodiment of the invention the sound absorbing device comprises a number, for instance five, substantially cylindrical bodies made from a thin plastic material, each body defining an inner cavity formed by the circumferential wall portion of the cylinder and the end surface of the cylinder Said cylindrical bodies can have a diameter of approximately 0 8 meter and a length of for instance up to approximately 50 meter It is however understood that these and any other numerical values are merely to be regarded as examples and that the invention is not limited by these numerical values. Said cylindrical bodies extend substantially parallel to each other (i.e. their individual longitudinal axes extend substantially parallel to each other) and the shortest distance between adjacent cylindrical bodies is according to this embodiment approximately 0.1 meters. The space between adjacent cylindrical bodies can be provided with connecting portions connecting said adjacent cylindrical bodies with each other and through which portions there may be provided said interconnecting passages for fluid/air communication between adjacent cylindrical bodies At least on of the cylindrical bodies is provided with means for fluid/air communication with fluid/air supply means, such as a controllable pump At least one of the cylindrical bodies can furthermore be provided with suspension means for suspending the device from for instance a ceiling of a room

By the present invention there is provided devices and/or systems that can provide significant sound absorption over a broad frequency range. Said absorption can by simple means (inflating/deflating the sound absorbing bodies used in the device or system) be "turned either ON or OFF". The devices and system of devices according to the invention is extremely flexible and can easily be installed in a room or removed from the room Due to the very thin materia! of the sound absorbing bodies used according to the invention the weight of the devices or systems is very limited even for large systems and deflated devices or systems can easily be transported from one place to another and/or stored at a given location or for instance in a truck during transportation within a relatively limited space even in case of very large systems. The system according to the invention is hence very mobile

BRIEF DESCRIPTION OF THE DRAWINGS The invention wil! be better understood with reference to the following detailed description of a specific embodiment of the invention in conjunction with the drawing, where:

figure 1 shows a schematic perspective view of an embodiment of a sound absorbing device according to the invention;

figure 2a shows a schematic perspective view of the embodiment of the invention shown in figure 1 in a deflated state in which it can be stored or supplied on a roller;

figure 2b shows a side view of a portions of the edge region of the deflated device;

figure 3 shows an illustration of an arena provided with a first embodiment of a system of sound absorbing devices according to the invention hung from the ceiling of the auditorium;

figure 4 shows a further illustration of an arena provided with the first embodiment of the system of sound absorbing devices according to the invention hung from the ceiling of the auditorium;

figure 5{a) shows an illustration of an arena provided with a second embodiment of a system of sound absorbing devices according to the invention hung from the ceiling of an auditorium;

figure 5(b) shows a specific configuration of sound absorbing devices used in the system shown in figure 4(a};

figure 5(c) shows a schematic longitudinal cross sectional view through a hall in which an embodiment of a system according to the invention is hung from the ceiiing and where different lengths of tubes are applied in order to provide an uninterrupted view of the stage from the back seats of the auditorium;

figure 6 shows a plot of a sound absorption coefficient as a function of frequency that can be obtained with sound absorbing devices according to the invention; and figure 7 shows a specific embodiment of a sound absorbing body used in the devices/system of the invention, wherein a generally cylindrical body is subdivided in sections by a number of contractions

DETAILED DESCRIPTION QF THE INVENTION

In the following a detailed description of an embodiment of the present invention will be given, but it is understood that a person skilled in the art may design alternative embodiments of the present invention and that such alternative embodiments will also fail within the scope of the present invention as defined by at appended claims

Referring to figure 1 there is shown a schematic perspective view of an embodiment of a sound absorbing device according to the invention, comprising a plurality of elongated cylindrical sound absorbing inflatable bodies 2, each body having circumferential wall portions 4 and substantially circular end walls 3, although particularly the end walls may have other shapes according to the particular method used for forming the cylindrical bodies The longitudinal axes of the cylindrical bodies 2 extend substantially parallel to each other leaving an intermediate portion 5 of approximately 0 1 meters between adjacent cylindrical bodies A pump 7 is in fluid communication 8 with the uppermost body that is suspended 9 from the ceiling 1 of the room. As explained above adjacent bodies {i e. the internal cavity defined by the walls 3 and 4 of the body) can be in fluid communication with each other through passageways 6 in the intermediate portions 5. Typical, but not limiting, dimensions are shown in the figure, but it is understood that other dimensions as well as other numbers of bodies and even other shapes and relative orientation of the individual bodies to other bodies of the device can be envisaged and such alternative embodiments will also fall within the scope of the present invention

Referring to figure 2a there is shown a schematic perspective view of the embodiment of the invention shown in figure 1 in a deflated state in which it can be stored or supplied for instance on a roller 1 1 or can be rolled up to form a roll. Particularly with reference to figure 2b showing a portion of the edge region of the deflated device it san be seen that the shown embodiment of the invention can implemented by a sandwich structure of two layers 10' and 10" of thin plastic material that are not attached to each other in those regions 10 of the sandwich structure where the cylindrical bodies will be formed by inflating the structure as described, but where the two layers 10' and 10" are attached to each other - by hot welding, adhesives or any other suitable means - at the intermediate portions 5 of the device These portions are indicated by reference numeral 12 in figure 2b, where a small gap between the layers is visible in the figure, merely for indicating the presence of two separate, superimposed layers in the regions.

Referring to figure 3 there is shown an illustration of an arena provided with a first embodiment of a system of sound absorbing devices according to the invention hung from the ceiling of the auditorium.

Referring to figure 4 there is shown a further illustration of an auditorium provided with sound absorbing devices according to the invention hung from the ceiling of the auditorium

Referring to figure 5(a) there is shown an illustration of an auditorium provided with a second embodiment of a system of sound absorbing devices (these devices being actually shown Sn figure 5(b)) according to the invention hung from the ceiling 15 of an auditorium by means of suitable suspensions means 14 Figure 5(a) is an example of the view from the stage in a typical arena that is also used for amplified music concerts, The numbers I, I! and II! in figure 5(a) correspond to the numbers in figure 5(b) and explains that a different number of absorbing bodies (2) can be mounted underneath each other, Thus, figure 5(b) shows a specific configuration of sound absorbing devices used in the system shown in figure 4(a) that is adapted to the particular shape of the auditorium The system comprises three embodiments of devices according to the invention, the first of these 15 comprising only a single body (2), the second 16 comprising three bodies and the third 17 comprising four bodies (2) The specific configuration of the devices (i.e in this case the number of bodies) can be chosen such that the bodies will not obstruct the line of sight of any member of the audience in the hall, This is made even more apparent with reference to figure 5(c) that shows a schematic longitudinal cross sectional view through the middle of a hall 19 in which an embodiment of a system according to the invention is hung from the ceiling 18 and where different lengths of tubes are applied in order to provide an uninterrupted view of the stage from the back seats of the auditorium As shown in figures 4{a) and (b) the number of bodies is in this cross section through the hall equal to four It appears also from figure 5(c) that the length L of each individual body (2', 2", 2'" and 2"") can be tailored in order to avoid obstruction of visual contact between audience 21 and stage 22

The devices according to the invention are preferably mounted where the level of sound energy is high !f the ceiling is not very high above the floor the sound absorbing devices can preferably be mounted perpendicular to the stage front or to the direction of sound emission from loudspeakers on the stage in order to avoid obstruction the sound emission from the loudspeakers on the stage significantly This direction, i e, the direction of the longitudinal axis through the bodies of the sound absorbing devices, is in fact shown in figures 5(a), (b) and (c) If the sound absorbing devices can be mounted much higher than loudspeakers on the stage this becomes less important Orientation of the devices according to the invention in a substantially transversal direction, i e parallel with the stage front, is illustrated in figures 3{a) and (b).

Referring to figure 6 there is shown a plot of a sound absorption coefficient a(f) as a function of frequency that can be obtained with a device according to the invention It appears from figure 4 that substantial sound absorption can be attained over a broad frequency range, in the shown example from well below 125 Hz to above 4 kHz

Referring to figure 7 there is shown a specific embodiment of a sound absorbing body used in the devices/system of the invention, wherein a generally cylindrical body 22 is subdivided in sections 23 by a number of contractions 24, This embodiment leads to increased diffusion of the sound field and hence increased sound absorption In the shown embodiment three sections 23 are provided, but any other number of sections could be provided- In a practical design the individual length I of the sections may be approximately 1 meter, but this numerical value is only exemplary and non-limiting A plurality of such bodies may in an embodiment of a system according to the invention be hung from the ceiling of a room or from a suitable suspension structure for instance with the X-axis oriented substantially vertically Other orientations are of cause also possible It is even possible according to an embodiment of a system according to the invention to orient the X-axes of different bodies in a multi-body system differently either according to a given pattern or randomly Also the distance between adjacent bodies may be chosen by the user, and the distance between adjacent bodies could be either substantially equal or varying according to a chosen pattern or even varying at random. It is understood that the embodiment shown in figure 7 is only one example of the more general shape of the absorbing bodies used according to the invention that has previously been defines in the summary of the invention as a body with a width w, diameter d and cross-sectional area S that depends on the coordinate x on the X-axis The contractions 24 provide diffusion of the sound field Typically the length (longitudinal extension) I₁ of the contractions is in the range 0 2 to 04 meter, but other lengths of the contractions couid be used including different lengths for different contractions.

Claims

1. A device for absorbing sound energy from a sound field in which the device is piaced, the device comprising at least one inflatable body (2) comprising outer wall portions (3, 4) defining one or more inner cavities to be filled with air or another suitable fluid from an air/fiuid supply {7, 8), wherein at least one of said outer wall portions is made of a flexible/resilient material that can vibrate when exposed to said sound field and wherein the shape of the device and/or the thickness of at least one outer wall portion ensures a sound absorption coefficient of at least 0.2 from 80 Hz to 3 kHz

2 A device according to claim 1 , wherein said thickness is below 300μm, preferable below 150μm.

3 A device according to claim 1, wherein said thickness is in the range 30 μm to 150 μm

4. A device according to claim 1, 2 or 3, wherein said at least one body (2) is a body with a maximum length L and a maximum width W or maximum diameter D, maximum cross sectional area S_MAχ. a width w{x) or diameter d(x) and a cross section S(x), where said body is defined by a longitudinal axis X through the body and where x is the coordinate along the X-axis

5 A device according to claim 4, wherein said at least one body (2) is a body of revolution defined by the longitudinal axis X.

6. A device according to claim 4, wherein said elongated body is substantially cylindrical, with a diameter D

7. A device according to claim 4, 5 or 6, wherein the maximum width W or diameter D is in the range 0.3 to 1 meter

8. A device according to any of the preceding claims, wherein said at least one inflatable body (2) comprises outer wall portions with a cross sectional area S|(x) that are reduced compared to said maximum cross sectional area S_MAχ-

9 A device according to any of the preceding claims, wherein the air/fluid pressure within the cavities can be adjusted such that a substantia! value of sound absorption from the sound field in which the device Is placed is obtained

10 A device according to any of the preceding claims, wherein the material of the at least one body is low density polyethylene (PE LD)

1 1 A device according to any of the preceding claims, wherein the material of the at least one body is fire retardant

12. A device according to claim 10 or 11 , wherein the weight of said material is approximately 0 03 to 0 3 kg/m².

13 A device according to any of the preceding claims, wherein a sound absorption coefficient of at least 0 4 is obtained over a frequency range of approximately 80 Hz to 3 kHz, whereby the device can be used as a broadband sound absorber

14. A device according to any of the preceding claims, the device comprising a plurality of said inflatable bodies (2), wherein each of said bodies (2) is attached either directly or through an intermediate portion (5) to at least one other of said bodies (2), whereby said plurality of bodies (2) when inflated form a three-dimensional structure that can be placed in the sound field

15, A device according to claim 14, wherein each of said bodies (2) is in fluid communication (6) with at least one other of said bodies (2).

16 A device according to claim 14 or 15, wherein intermediate portions (5) are formed between adjacent bodies (2), whereby adjacent bodies (2) can be separated from each other by a minimum distance (d), which distance (d) optionally can be substantially equal to zero

17. A device according to claim 14, 15 or 16, wherein the device is formed as a sandwich structure comprising two superimposed layers (10', 10") of material attached to each other in those portions of the structure that forms said intermediate portions (5), but not attached to each other in those portions of the structure that upon inflation form said outer circumferential wall portions (4) of said bodies (2)

18 A device according to claim 17, comprising passageways (6) for fluid communication between inner cavities of adjacent bodies (2), whereby fluid/air can flow from the inner cavity of a given body to inner cavities of other bodies of the device during inflation/deflation of the bodies

19 A device according to any preceding claims, wherein the inner cavity of one of said bodies (2) is supplied (7, 8) with said fluid/air and the inner cavities of the remaining bodies are supplied with fluid/air via said passageways (6)

20 A device according to any of the preceding claims, wherein at least one body (2) and/or at feast one intermediate portion (5) (if present) is provided with graphical items, such as commercials, affecting the appearance of the device

21 , A device according to any of the preceding claims, wherein at least one body (2) and/or at least one intermediate portion (5) (if present) is provided with light emitting means for illumination of at least chosen portions of the device

22 A device according to any of the preceding claims, wherein at least one body (2) and/or at least one intermediate portion (5) (if present) is provided with sound emitting means

23 A device according to any of the preceding claims, wherein the material of which the bodies is made is used as an optical fibre for providing illumination effects of the bodies

24 A system for absorbing sound energy from a sound field within which the system is placed, the system comprising a plurality of devices according to any of the preceding claims 1 to 23

25 A system according to claim 24, wherein said plurality of devices is of such a nature that it reduces the reverberation time (measured T30) of the room in which it is applied by at least 0 1 second

26 A system according to claim 24, wherein the individual devices of said plurality of devices are oriented substantially in the same direction

27 A system according to claim 24 comprising sub-groups of devices the orientation of which differs from the orientation of other sub-groups of devices

28 A system according to claim 24, wherein the individual devices of said plurality of devices are oriented at random

29 A system according to an of the preceding claims claim 24 to 28 comprising means for controlling the air/fiuid pressure in the bodies (2)

30 A system according to claim 24 to 29 comprising means for controlling illumination of said bodies (2) and/or intermediate portions (5)

31 A system according to any of the preceding claims 24 to 30 comprising means for controlling sound emission from sound emitters placed in/or said bodies (2) and/or intermediate portions (5).

32 A room provided with devices according to any of the claims 1 to 23 and/or systems according to any of the claims 24 to 31 , such that the reverberation time of the room can be reduced dependent on the number, dimensions and placement of the devices or systems within the room, whereby an unsatisfactorily long reverberation time of the room can be reduced according to specific requirements dependent on the actual use of the room

33. A room according to claim 32, wherein the configuration and placement of the devices and/or system of devices are chosen such that the view of a stage area in the room from the audience is not obstructed by the devices and or system

34 A room according to claim 33, wherein the devices are oriented substantially perpendicularly to the stage front

35 A room according to claim 33, wherein the devices are oriented substantially parallel with the stage front