WO2002095725A1

WO2002095725A1 - A construction for active sound attenuation

Info

Publication number: WO2002095725A1
Application number: PCT/FI2002/000419
Authority: WO
Inventors: Marko Antila; Hannu NYKÄNEN; Ari Saarinen; Jukka Lekkala
Original assignee: Valtion Teknillinen Tutkimuskeskus
Priority date: 2001-05-21
Filing date: 2002-05-16
Publication date: 2002-11-28
Also published as: FI110896B; FI20011068A0; FI20011068A

Abstract

The invention relates to a construction (P) for active sound attenuation and/or processing by means of an anti-sound (AN) with a opposite phase, to be insta11ed on a sound propagation path. According to the invention, the construction (P) consists of planar and preferably elongated lamellae (L) next to each other, which lamel- lae (L), being substantially parallel to each other in the longitudinal direction (HE), form a Venetian blind type construction, and of which lamellae (L) at least some comprise one or more elements (LS) to generate an anti-sound. The single elements (LS) to produce an anti- sound are preferably flat speaker elements (LS) made of e,g, an electromechanical film, which are arranged on the surface (S1, S2) parallel to the plane of the lamella (L).

Description

A CONSTRUCTION FOR ACTIVE SOUND ATTENUATION

Field of the invention

The invention relates to a construction for active sound attenuation and/or processing according to the preamble of the appended claim 1 , to be installed on a sound propagation path.

Background of the invention and prior art

In this context, sound or sound waves refer to acoustic vibrations propagating in a gaseous medium, typically air, whose frequency may vary from a few herzes to tens of kiloherzes. Consequently, said acoustic vibrations may be at least partly below or above the frequency range of human hearing.

Conventionally, so-called passive methods have been used for the attenuation of acoustic interference or noise. In passive noise attenuation, sound insulating materials or constructions, or sound absorbing or reflecting materials or constructions, are installed on the noise propagation path to influence the propagation of the noise.

Passive, for example sound absorbing constructions and materials are relatively effective, particularly in the attenuation of high-frequency noise. Good attenuation of high-frequency noise can be obtained by using relatively lightweight/thin constructions. However, the effective attenuation of sound waves of a low frequency, for example less than some hundreds of herzes, in a passive way will require relatively massive and/or thick constructions. Therefore, the passive attenuation of low-frequency noise will often also cause considerable costs.

Also, solutions based on so-called active noise control are known from prior art. These include, for example, so-called active absorption, in which the sound absorbing properties of the sound absorbing surface are improved by active methods. Also, the acoustic impedance of the surface can be actively modified, and furthermore, this property can be utilized to improve the absorption properties or sound insulation. In view of the present invention, the closest known prior art relates to active sound control methods based on generating a so-called anti- sound. In these methods, noise is attenuated by producing an anti- sound with a phase opposite to that of the noise. When the noise wave and the anti-sound wave interfere with each other in a destructive way, the noise can be effectively suppressed as the sound waves are "damped" due to their phase difference.

In general, active sound control as compared with passive methods can be considered to have the advantage that in a number of cases, active methods can be used to provide effective noise control focused on a given frequency range without massive and large sound absorbing or other attenuating passive constructions. In particular, active methods are often more suitable than passive methods for the control of low-frequency noise. Below, the brief expression of active noise control will be used to refer primarily to methods based on the active production of an anti-sound, which are relevant in view of the present invention.

US patent 6,023,123 discloses an active noise control system intended for a double-pane window or the like, to prevent the penetration of (low- frequency) noise, for example from the outside, through the window into a building. In this system, vibrations are induced in one or more glass panes by means of a suitable arrangement, for example a piezo- electric element having a mechanical effect on the glass pane. When the glass pane/panes are arranged to vibrate at a suitable frequency, they generate acoustic anti-sound waves which neutralize the noise carried through the window structure to the inside.

US patent 5,315,661 discloses an actively sound controlling sheet-like panel construction which consists of a number of cubic elements, so- called cells, arranged in the form of an array to generate an anti-sound. The side walls of adjacent cells are arranged against each other, and the front and back walls of the cells form the front and back surfaces of said panel construction, respectively. The front and back walls of the single cells consist of plates, and each cell is provided with an actuator, for example a piezoceramic means, to generate acoustic vibrations in the front and back walls of the cell. Each cell also contains one or more sound detecting sensors. On the basis of the signal from the sensors, it is possible to control the anti-sound generated by said cell by controlling the operation of the actuator generating vibrations in the cell. Noise carried through the panel to be placed transversely to the direction of noise propagation, i.e. through the front and back walls of the single cells, can now be actively controlled by controlling the operation of each cell individually, if necessary.

Comparing the solutions presented in said patents US 6,023,123 and US 5,315,661 with each other in principle, the solution disclosed in US patent 6,023,123 can be considered to comprise only one cell to generate the anti-sound, whereas in US patent 5,315,661 the anti- sound is generated by means of an array, or panel construction, con- sisting of several cells. It is obvious that an array construction which based on several sources of the anti-sound which can be controlled individually if necessary, or in this case cells, and which has a more complex structure and implementation, will, in return, also make it possible to control noise more efficiently and use the method at a wider frequency range.

However, a significant problem of the panel construction presented in US patent 5,315,661 is the fact that it is very difficult to implement the panel as a transparent construction. This limitation significantly pre- vents the use of said solution for example in connection with a window or a corresponding opening.

Furthermore, the solutions disclosed in US patents 5,315,661 and 6,023,123 and other similar solutions cannot be applied in a situation of preventing the propagation of noise through such an opening, channel or similar space, through which an exchange of air or other gases takes place. In other words, the above-presented solutions of prior art are not suitable for use, for example, in ventilation ducts, ventilation holes or the like, because their structure will either effectively prevent all gas exchange through the structure or at least cause a considerable increase in the flow resistance. Further, said flow resistance can, due to the interference (turbulence) caused by itself in the flow, produce more noise.

In practice, however, there are a number of situations, in which noise is to be controlled on its propagation path particularly in such a way that a visual contact and/or a possibility for ventilation or other gas exchange is to be maintained on said propagation path. The constructions to be used in active noise control should also be as simple, light-weight and easily modifiable as possible, with respect to their size as well as other properties. Also in these respects, there are clear disadvantages in the prior art solutions based on the generation of an anti-sound.

Basic principle and most important advantages of the invention

It is the main aim of the present invention to provide a novel construction which is to be installed on a sound propagation path and which actively controls sound by means of an anti-sound, and/or another construction for sound processing, to avoid the restrictions of the above-presented solutions of prior art.

Thus, the primary aim of the invention is to provide a structure which attenuates sound actively and also passively, if necessary, and which enables the maintenance of a visual contact as well as gas exchange, such as ventilation, through said structure. Furthermore, it is an aim of the invention to provide a construction which has a simple structure and whose properties can be easily modified and which is thereby suitable for various uses.

To attain these purposes, the construction according to the invention is primarily characterized in what will be presented in the characterizing part of the independent claim 1.

The other, dependent claims will present some preferred embodiments of the invention.

The basic idea of the invention is that the elements to be used for generating the anti-sound are placed in lamellae, which preferably thin lamellae, placed next to each other in the vertical or horizontal direction, further constitute a construction similar to a Venetian blind.

According to the invention, a single plate-like and/or strip-like lamella comprises one or more preferably flat speaker elements arranged on a surface or surfaces parallel to the plane of the lamella to produce an anti-sound. In a corresponding manner, the same lamella can also be provided with one or more sound detecting sensors. On the basis of the signal from these sensors, the anti-sound produced by said lamella can be controlled by controlling the operation of the speaker elements placed in the lamella.

When the Venetian blind like attenuator construction formed by the lamellae is placed on a noise propagation path in such a way that the lamellae, which are substantially parallel in the longitudinal direction, are arranged in a mutual position in which the planes of the single lamellae are substantially transverse to the plane of the Venetian blind construction, in other words, the Venetian blind construction is "open", both the visible contact and the possibility for gas exchange are main- tained through the Venetian blind construction, while the noise propagating through the plane formed by the Venetian blind construction can be effectively attenuated by the anti-sound generated by the lamellae. For the gas exchange, the Venetian blind like construction in the "open" position will cause only an insignificant flow resistance to the flow through it.

In an advantageous embodiment of the invention, the elements placed in the lamellae to generate an anti-sound, and/or the sound sensors used in the control, are implemented on the basis of an electrically charged electromechanical film (EMFi). The EMFi makes it possible to implement very flat and light-weight speaker and microphone elements and thereby a light-weight and simple active attenuator construction.

In an embodiment of the invention, the lamellae may, in addition to the active attenuator elements, also contain elements suitable for passive noise attenuation, such as surfaces made of a sound absorbing material. In this way, it is possible e.g. to improve the basic acoustic proper- ties of the construction to facilitate the operation of the control system used for generating the anti-sound. The design and/or disposition of the lamellae can, as such, also be arranged to attenuate sound passively.

The advantages of the invention include not only the transparency of the construction and the possibility of gas exchange through the construction but also, for example, the possibility to use the construction as a conventional Venetian blind. In other words, when the lamellae included in the Venetian blind construction are "closed", the construction for sound attenuation according to the invention can, if desired, also be used as a visual obstruction or to prevent the flow of air or other gases.

The attenuator construction according to the invention can be easily installed afterwards in front of, for example, a window or a corresponding opening, and it does not necessarily require modifications in the original construction of e.g. a window, as in solutions of prior art. The attenuator construction according to the invention is suitable to be installed not only in a window or an opening but also, for example, in a ventilation duct or the like, to attenuate noise caused by a fan or the like in the duct.

The size of the attenuator construction according to the invention can be easily adapted to the size of the opening or the space, through which the acoustic interference to be attenuated propagates. It is possible to add lamellae in or remove them from the Venetian blind construction to change the size of the construction. Thus, when vertical lamellae are used, the Venetian blind construction is suitable for use, for example, as a partition wall between rooms, which can be used either in the "open" or "closed" position of the lamellae and which can, if necessary, be easily moved aside, thanks to its collapsible lamella structure.

As the attenuator construction according to the invention preferably consists of several anti-sound sources which are separate from each other and which can also be controlled separately, if necessary, the invention can be applied in active noise control in a very versatile way. Said structure also makes it possible to implement very large attenuator constructions effective under varying noise conditions. Furthermore, the invention makes it possible not only to reduce noise but also to control sound actively in rooms, because the same construction is capable of attenuating noise by an anti-sound and simultaneously also generating an effective sound, for example to improve the acoustics of the room.

Brief description of the drawings:

In the following, the invention will be described in more detail by means of examples and with reference to the appended drawings, in which

Fig. 1 shows, in a perspective view in principle, a construction according to the invention, consisting of lamellae and controlling sound actively by means of an anti-sound, to be installed on a noise propagation path,

Fig. 2 shows, in a cross-sectional view in principle, a construction according to the invention seen from above, in the direction of the longitudinal axis of the lamellae,

Fig. 3 shows the construction of Fig. 2 seen directly from the front, in the direction of propagation of the noise,

Figs. 4A to 4H show, in principle, alternative embodiments of a single lamella,

Fig. 5 shows, in principle, the use of a feedforward control system in controlling the generation of an anti-sound,

Fig. 6 shows, in principle, the use of a feedback control system in controlling the generation of an anti-sound, Fig. 7 shows, in a cross-sectional view in principle and seen in the direction of the longitudinal axis of the lamella, the operation of a single lamella as a monopole source, and

Fig. 8 shows, in a way corresponding to Fig. 7, the operation of a single lamella as a dipole source.

Detailed description of the invention

Attenuator construction consisting of lamellae

Figure 1 shows, in a perspective view in principle, a Venetian blind type construction P according to the invention, consisting of adjacent lamellae L and actively attenuating and/or processing sound.

Figure 2 shows a possible construction according to the invention in a cross-sectional view seen from above, in the longitudinal direction of the elongated lamellae L. Noise waves N, attempting to propagate from a side A of the attenuator construction P through the attenuator con- struction to the opposite side B, are attenuated when they interfere destructively with anti-sound waves AN with an opposite phase, produced by means of the lamellae L.

To generate the anti-sound waves AN, surfaces S1 , S2 in the direction of the plane of a single lamella L are provided with one or more speaker elements which produce the anti-sound and are preferably as flat as possible. In a corresponding manner, the same lamella which comprises the speaker elements can also be provided with one or more sound detecting sensors. On the basis of the signal generated by these sensors, the anti-sound produced by said lamella can be controlled by controlling the operation of the speaker elements placed in the lamella.

Figure 3 shows the construction P of Fig. 2 seen directly from the front. The single vertical lamellae L are suspended at their upper end to a suspension means H in such a way that an air gap G is left between adjacent lamellae when the Venetian blind construction formed by the lamellae L is in the "open" position. The wiring required by the active sound generating and/or sound detecting means in the lamellae L is preferably arranged inside the structure of the suspending means H, wherein there is no wiring visible outside the attenuator construction P. In addition to the mere wiring, the suspension means H preferably also contains electronics required in the system, such as for example amplifiers required for speaker input. The suspension means H can be arranged to be such that the lamellae L can, if necessary, be bundled up to the right or left hand side in Fig. 3, wherein the attenuator construction P installed, for example, in front of a window can thus be easily moved aside like a Venetian blind, if necessary.

It is obvious that instead of installing the lamellae L upright in their longitudinal direction, they can also be installed in the horizontal direction or, if necessary, in any other position suitable for the application in question. If necessary, the lamellae can be supported at both ends and in the middle, or the support of the lamellae can also be arranged in any other way obvious for a person skilled in the art. Also, the electrical couplings to be made in the lamellae can be arranged in any suitable way which is obvious as such for a person skilled in the art.

The structure of a single lamella

Figures 4A to 4H show, in principle, some alternative structures of a single lamella L seen in the direction of the surface S1 and/or S2 parallel to the plane of the plate-like lamella.

In Fig. 4A, the surface S1 , S2 of the elongated lamella L (length HE > width Wl) consists, substantially over its whole area, of a speaker ele- ment LS suitable for generating an anti-sound. Preferably, the speaker LS is implemented by using an electromechanical film (EMFi). The use of an electromechanical film in speakers is known as such, and it makes it possible to implement very flat and light-weight speaker elements, which is very advantageous in view of the present invention. The speaker element LS can also be implemented by using other solutions known as such and based, for example, on the electrostatic principle of operation. In Fig. 4B, the surface S1 , S2 of the lamella L is divided into a number of separate blocks, a separate speaker element LS being placed in each block. The more complex structure of this embodiment is compensated for by the possibility to control the speaker elements LS placed in different blocks separately from each other. In this way, the anti-sound can be generated, if necessary, in different ways in different areas of the lamella, in the most suitable way in the situation (acoustic interference field) prevailing in each location.

Figure 4C shows the speaker elements LS as well as the sound detecting sensors, i.e. microphones M, alternating in different blocks on the surface S1 , S2 of the lamella L. The use of the microphones M for controlling the generation of the anti-sound will be described in more detail below, in connection with the description of feedforward and feedback control systems with reference to Figs. 5 and 6. The use of several microphone elements M will naturally make it possible to generate a more precise anti-sound locally; in other words, for example the signal from a given microphone M is used to control only a specific speaker element LS located in the vicinity.

As shown in Figs. 4D and 4E, the surface S1 , S2 of a single lamella L may also consist of only one or more microphone elements M.

In Fig. 4F, the lamella L is arranged to be sound absorbing, in other words passively sound attenuating, substantially over its whole surface area. A passively sound attenuating construction SA can be provided, for example, by coating the lamella with a suitable sound absorbing material or by making the whole lamella L of a sound absorbing mate- rial. By the suitable use of passively sound attenuating constructions in the lamellae L, it is possible, for example, to improve the basic acoustic properties of the blind construction P, which will facilitate the operation of the control system to be used for generating the anti-sound.

In Fig. 4G, a single elongated lamella L comprises a speaker element LS, a passively sound attenuating construction SA, and a microphone M. In the embodiments presented above in Figs. 4A to 4G, the elongated lamella L comprises, in its width direction Wl, only one element LS, M, SA with an effect on sound. In the direction of the plane of the surface S1 , S2, the shape of the lamella L can, however, differ from the above- presented elongated rectangle, for example in the way shown in Fig. 4H.

Figure 4H shows a rectangular lamella L which comprises, both in the longitudinal direction HE and in the width direction Wl, several components LS, M, SA, forming a matrix-like structure.

In Figs. 4A to 4H, the above-presented structures can be used on only one side S1 (or S2) of a single lamella or also on both sides S1 and S2 of the single lamella. The opposite surfaces S1 and S2 of the same lamella may have structures similar to each other or also different from each other. For example, it is possible that one side S1 of the single lamella L has the structure of Fig. 4C, comprising speaker elements LS and microphones M in an alternating way, and the opposite surface S2 of the same lamella has the passively sound attenuating structure SA of Fig. 4F.

The attenuator construction P consisting of lamellae L can also be such that some of the lamellae L are totally passive, and only some of the lamellae, for example every second lamella, comprises active elements LS, M.

Differring from Figs. 4A to 4H, the size, number and position of the active elements LS, M and the passive elements SA on the surface S1, S2 of the lamella may freely vary according to each use. It is also possible that a part of the surface S1, S2 of the lamella L does not function as a particularly active LS, M or passive SA element affecting on sound.

In the plane of the surface S1 , S2 of the lamella L, the cross-sectional shape of the lamella is preferably the elongated rectangle as shown in Figs. 4A to 4H (HE > Wl) but, if necessary, said cross-sectional shape of the lamella L can also vary from the rectangular shape to a square (HE = Wl) or another shape according to each application. It is also possible that the width Wl of the lamella is greater than the length HE of the lamella in the direction of propagation of the noise.

Particularly in the use of elements based on an electromechanical film, it is also possible that the same area on the surface S1 , S2 of the lamella L is used both as a means to generate an anti-sound, i.e. as a speaker M, and simultaneously as a microphone M measuring the sound waves hitting the surface. In this case, the control system based on the signal from said microphone can supply a signal to the electromechanical film to generate a suitable anti-sound and to attenuate the noise. This embodiment has the significant advantage that the structure of the lamella becomes simpler, because there will be no need to use separate elements for sound generation and measuring.

The single lamella L has typically a thickness of, for example, 2 to 15 mm and a width of, for example, 5 to 70 cm. Depending on the application, the thickness and width Wl of the lamellae may also differ from those presented above. The length HE of the lamella can be fitted to suit each case, and it may vary, for example, from some tens of centimetres to several metres. As the material for the body of the lamella L, it is possible to use, for example, wood, plastic or another suitable material, or also a composite structure consisting of several different materials, to yield a structure with a light weight and a sufficient rigidity.

Differing from purely planar sheets, the shape of the single lamellae L may also be curved to some extent.

Control system

The attenuator system according to the invention can be used in connection with control systems of both the feedforward and the feedback type. Figure 5 shows, in principle, the use of a feedforward control system FF in controlling the generation of an anti-sound. Noise caused by a noise source NS is measured with a reference sensor (microphone) RM generating a signal which is used by a signal processing unit CPU to control the generation of an anti-sound in the lamellae L. In a purely feedforward system, the control is based on the use of a reference sensor / reference sensors RM only.

However, the feedforward control system preferably also comprises a difference sensor EM to monitor the remaining noise which has penetrated the attenuator construction P. The signal of the difference sensor EM is input as feedback to the signal processing unit CPU which, by means of a suitable algorithm, controls the generation of the anti- sound in such a way that the strength of the noise detected by the difference sensor EM, or another suitable acoustic variable / set of variables, such as the intensity of the noise, is minimized.

As shown by solid lines in Fig. 5, the reference sensor RM and the difference sensor EM can be placed outside the attenuator construction P or, as shown by broken lines, said sensors RM', EM' can also be placed in the attenuator construction P itself, for example by applying the principles presented above in Figs. 4A to 4H.

There can be one or more reference sensors RM, RM' as well as one or more difference sensors EM, EM', depending on the application and, for example, the size of the attenuator construction P. One extreme can be considered to be a situation in which all the lamellae L of the attenuator construction P are controlled in the same way by means of one control signal D and by using, for example, only one reference sensor RM. The other extreme, in turn, is a situation in which several different control signals D are input in each single lamella L, the lamella comprising several separate speaker elements LS, and said control signals D are formed each by means of separate reference and difference sensors RM', EM'. To generate the control signals D, the signals of the sensors RM, RM', EM, EM' can, if necessary, be randomly combined as required by each control algorithm used. Figure 6 shows, in principle, the use of a feedback control system FB in controlling the generation of an anti-sound. In a control based purely on feedback, no reference sensor is used, but the control is based on the use of the difference sensor/sensors EM, EM'. In the same way as above, the difference sensors EM, EM' can be placed outside the attenuator construction P or in the attenuator construction P itself. Moreover, the number of the difference sensors EM, EM' may be freely varied, and similarly, their signals can be combined according to the need, to generate one or more control signals D controlling the lamel- lae L

Furthermore, Fig. 7 shows, in a cross-sectional view in principle, the operation of a single lamella L as a monopole source, seen from the direction of the longitudinal axis of the lamella. From the basics of the acoustics, it is generally known that when the size of the sound source, or in this case the width Wl of the lamella, is substantially smaller than λ/2 , in which λ is the wavelength of the sound generated by the sound source, the sound source (lamella L) will operate as a monopole source. It is characteristic of a monopole source that the shape of the acoustic field AN is substantially spherically or circularly symmetrical. If speaker elements are used on both surfaces S1, S2 of the lamella L, their phase must be arranged in the way shown in Fig. 7 so that the movements of the vibrating films or other sound generating surfaces on different sides S1 , S2 of the lamella have opposite directions.

Figure 8 shows, in turn, the operation of the lamella L as a dipole source. When the phases of the speaker elements or corresponding means operating on the surfaces S1 , S2 of the lamella are mutually arranged in the way shown in Fig. 7, the acoustic field AN emitted by the lamella L has the shape of the figure eight, which is typical of a dipole source.

Thus, on the basis of what has been presented above, it will be obvious for a person skilled in the art that the shape of the anti-sound field AN generated by the lamellae L can be fitted to suit each situation by adjusting the phases between the speaker elements contained in the single and/or adjacent lamellae, in other words, by using a blind- like attenuator construction P for example in the "open" or "closed" position of the lamellae L or in another position between said positions.

Embodiments of the invention

In the following, we will present some further embodiments of the invention and possibilities for applying the invention.

The attenuator construction according to the invention is suitable to be installed, for example, in front of or behind a window or, in a window with several glass panes, also in the space between the glass panes.

The attenuator construction can also be installed in various openings, channels or pipe systems, said structures transmitting noise in the space enclosed by them.

However, the attenuator construction according to the invention can also be used in an open space. When the size (typically width) of the attenuator construction is sufficient, the attenuator construction can be used to prevent the propagation of noise, for example, in halls and/or rooms by using the construction according to the invention as a partition wall. In such situations, noise cannot propagate straightforward through the attenuator construction from one side to another, and such noise which bypasses the attenuator construction through its edges, will be naturally faded because of the longer distance.

By combining attenuator constructions according to the invention, it is possible to provide a noise-protected limited space within a larger space, the "walls" and possibly "ceiling" of the space being formed by constructions according to the invention.

Instead of a planar wall, the lamellae can naturally also be made into constructions curved in different ways, such as curved walls.

In addition to mere noise attenuation, the constructions according to the invention can also be used to implement other active sound control. Using the same structure, it is possible to change the acoustics of spaces, for example by controlling the reverberation time and/or the time of propagation of indirect sounds, as well as by actively controlling the sound absorption/attenuation.

The invention is not limited only to the use in residential, business or industrial buildings or related constructions, but it can naturally also be used, for example, in ships, aircrafts, other vehicles, and also outdoors.

In addition to noise suppression based on the active generation of an anti-sound, the attenuator construction can also be implemented as being passively noise attenuating. The size and orientation of the lamellae and the passively sound attenuating materials used in them can be selected in a way known as such by a person skilled in the art (basic principle of the so-called lamella attenuator) so that the con- struction consisting of the lamellae will passively well suppress frequencies which are, for example, higher than 500 Hz. At frequencies lower than this, in turn, sound is suppressed actively by generating an anti-sound, wherein it is possible to make such a hybrid active-passive attenuator with a construction which is optimal for each purpose. The active suppression of higher sounds with an anti-sound becomes more difficult as the frequency is increased, due to e.g. the higher computing capacity and more complex control algorithms required of the signal processing unit CPU of the control system.

Claims

Claims:

1. A construction (P) for active sound attenuation and/or processing by means of an anti-sound (AN) with a opposite phase, to be installed on the sound propagation path, characterized in that the construction (P) consists of planar and preferably elongated lamellae (L) next to each other, which lamellae (L), being substantially parallel to each other in the longitudinal direction (HE), form a Venetian blind type construction, and of which lamellae (L) at least some comprise one or more elements (LS) to generate an anti-sound.

2. The construction (P) according to claim 1 , characterized in that the single element (LS) to produce an anti-sound is a flat speaker element or the like (LS) arranged on the surface (S1, S2) parallel to the plane of the lamella (L).

3. The construction (P) according to claim 2, characterized in that speaker elements (LS) are placed on both sides of the lamella (L), i.e., on both surfaces (S1 , S2) opposite to each other parallel to the plane of the lamella.

4. The construction (P) according to any of the preceding claims, characterized in that the generation of the anti-sound (AN) produced by the lamellae (L) is arranged to be controlled by using a feedforward (FF) or feedback (FB) control system.

5. The construction (P) according to any of the preceding claims, characterized in that the attenuator construction (P) itself comprises one or more sound detecting sensors (M, RM', EM'), by means of which sensor/sensors the anti-sound produced by the lamellae (L) can be controlled in a feedforward (FF) or feedback (FB) controlled manner.

6. The construction (P) according to any of the preceding claims, characterized in that the sound producing speaker elements (LS) and/or the sound detecting sensors (M, RM', EM') are made of an electromechanical film (EMFi).

7. The construction (P) according to claim 6, characterized in that the sound producing speaker element (LS) and the sound detecting sensor or sensors (M, RM', EM') are integrated in the same component made of an electromechanical film.

8. The construction (P) according to any of the preceding claims, characterized in that at least some of the lamellae (L) comprise one or more passively sound attenuating elements (SA).

9. The construction (P) according to any of the preceding claims, characterized in that the design and/or disposition of the lamellae (L) is arranged to be passively sound attenuating.

10. The construction (P) according to any of the preceding claims, characterized in that the width (Wl) of a single lamella (L) in relation to the wavelength of the anti-sound to be generated by the lamella, and the phase of the speaker elements (LS) arranged on opposite surfaces (S1 , S2) of the single lamella (L), are selected so that the lamella (L) operates substantially as a monopole source.

11. The construction (P) according to any of the preceding claims, characterized in that the width (Wl) of a single lamella (L) in relation to the wavelength of the anti-sound to be generated by the lamella, and the phase of the speaker elements (LS) arranged on opposite surfaces (S1 , S2) of the single lamella (L), are selected so that the lamella (L) operates substantially as a dipole source.

12. The construction (P) according to any of the preceding claims, characterized in that the construction (P) is arranged to be used in connection with a window or a corresponding opening.

13. The construction (P) according to any of the preceding claims, characterized in that the construction (P) is arranged to be used in connection with a ventilation duct or the like.

14. The construction (P) according to any of the preceding claims, characterized in that one or more constructions (P) are arranged in relation to each other so that they constitute a limited space protected from noise in connection with a larger space.

15. The construction (P) according to any of the preceding claims, characterized in that the Venetian blind construction formed by the lamellae (L) is arranged to be opened and closed as a Venetian blind, by rotating the lamellae (L) in relation to their longitudinal axis (HE).

16. The construction (P) according to any of the preceding claims, characterized in that the Venetian blind construction formed by the lamellae (L) is arranged to be moved aside as a Venetian blind, by bundling the lamellae (L) together.

17. The construction (P) according to any of the preceding claims, characterized in that the construction (P) is further arranged to actively produce an effective sound, to influence the acoustics of the installation space.