Sound-proofing utility, especially a sound-attenuating unit

SOUND PROTECTION DEVICE, IN PARTICULAR A SOUND PROTECTION UNIT

The invention relates to a sound-proofing device which is adapted to limit the lateral appearance of airborne noise caused by motorized road traffic, at least for a certain frequency range. The invention also relates to an assembly of a soundproofing device and a diffractor arranged or to be arranged along the road, at a position between the road and the soundproofing device, and to a road provided with a soundproofing device, whether or not together with a diffractor.

Motorized road traffic can be understood to mean, for example, car traffic on a motorway, train traffic on a railroad or air traffic on a runway or runway. While driving, the vehicles that form the road traffic cause a number of different sources of (air) noise. In the case of car traffic, the most important sources are formed by the tires (rolling noise) and the engine (engine noise). At low speeds, engine noise and, from a speed of approximately 50 km / h, the rolling noise of the tires dominates. In other embodiments, not shown, the road is a railroad and the noise is caused by a train traveling over this railroad. Railway noise is mainly caused by the rolling noise of the train or, at very high speeds, by the aerodynamic noise, for example the noise from the pantograph. The different sound sources are therefore at different heights relative to the road.

To reduce the sound transmission from a road to the environment, it is known to provide one or more sound screens along the road. Behind such a sound screen there is a "shadow", which weakens the traffic noise. Particularly in the case of sound-sensitive objects such as houses and office buildings in the vicinity of such a road, sound screens are reasonably effective to at least limit the worst noise nuisance. However, the shadow of the sound behind the screen is not complete. The operation of the screen is influenced by the bending of the sound around the top of the screen. The longer the path (also referred to as the path length here) is that sound has to travel in order to arrive at the sound-sensitive object, the more effectively the screen works. The height of the soundproofing facility plays a role in this. In general, the sound-shielding effect of a high noise screen is greater than that of a low noise screen. However, a high noise screen is relatively expensive, requires special foundation and / or anchoring facilities and can sometimes not be applied from an aesthetic point of view.

More generally, sound screens are expensive facilities. Furthermore, they disfigure the environment and often occupy the residents an unobstructed view. Moreover, they have the advantage that their effectiveness is limited in the case of certain wind directions. Furthermore, sound screens are less suitable for use in situations in which sound-sensitive objects are located on both sides of the road. By reflecting sound against the sound-proofing facility on a first side of the road, this sound is after all sent to the opposite side of the road and can end up with the sound-sensitive objects situated there.

Various types of sound screens have been developed over the years. With reflective sound screens there is in particular a reflection of the sound against the screen, while with absorbent sound screens the sound is partly (also) absorbed.

Some types of sound screens provide a combination of reflection and absorption. In a known type of absorbing sound screens, a separate layer of absorption material is applied against the sound-loaded side of the screen. The screen itself can for instance be formed by a (non-absorbent, acoustically hard) concrete slab against which a slab or layer of another, acoustically soft material is applied. In a known embodiment, the absorbent material comprises a mixture of wood fiber and cement. However, such noise barriers are relatively complex and relatively expensive to manufacture and maintain. Furthermore, the known sound screens are often sensitive to external influences and the effect of the screens decreases over time, for example because the absorbent layer becomes contaminated.

It is the object of the invention to provide a sound screen in which at least one of the above-mentioned drawbacks is obviated.

It is a further object of the invention to provide a simple yet effective sound-proofing device that is robust and requires little maintenance.

It is a further object of the invention to provide a sound-proofing facility of relatively small dimensions and yet an effective sound shielding.

It is also an object of the invention to provide a sound-proofing device that is aesthetically attractive.

At least one of the above-mentioned and / or other objectives is at least partially achieved in a sound-proofing device which is adapted to limit the lateral appearance of airborne noise caused by motorized road traffic at least for a certain frequency range, the sound-proofing device comprising a plate with an acoustic hard outer surface, the plate comprising at least one sound-absorbing side, wherein the sound-absorbing side has a plurality of elongated cavity structures arranged in the plate and ending in the hard outer surface with resonance frequencies in the determined frequency range for at least partially absorbing the sound incident on the sound-absorbing side. This construction is easy to manufacture, offers good absorbent properties and requires little maintenance. Furthermore, the construction is lighter than the current concrete screens (reducing noise by omitting material leads to a lighter screen), requires relatively little material and is therefore relatively cheap and durable, requires a less heavy foundation, is cheaper to transport (from the factory to work, in the case of prefabricated sheets) and can be installed with less heavy equipment.

Preferably, the elongated cavity structures extend substantially transversely to the sound-absorbing surface and / or parallel to each other. The cavity structures further have a number of different resonance frequencies (distributed in the aforementioned frequency range) in order to be able to absorb the sound over a relatively wide frequency spectrum.

The plate is preferably monolithic and / or made of a single, acoustically hard material, such as concrete or similar material. Such monolithic plates are robust and are easy to make. The plate can be, for example, by pouring or pouring the plate material into a mold and by partially curing it either removing the material from the mold (e.g. in the case of prefab concrete) or removing the mold completely or partially (e.g. . concrete poured into the work). In both cases the said cavity structures can be formed in one go, for example by making use of moldings to be removed, whether or not after curing (such as plastic pipes and the like).

In an embodiment of the invention, the plate is a self-supporting plate which is arranged to be stably arranged on a surface. On the underside of the plate, for example, a widened portion or base can be formed with which the plate can be arranged directly on a (flat) surface. This makes a simple and quick installation of the soundproofing facility possible. In other embodiments, the plates of the soundproofing device are adapted to be attached to a support structure anchored in the substrate, for example an existing soundproofing device. For example, loose plates (e.g., blocks) can be provided that can be attached to an existing soundproofing device to give the existing screen a higher absorption value. The individual plates can have dimensions that are of the same order of magnitude as the dimensions of the existing soundproofing facility. In other embodiments, however, the loose plates are much smaller and can be attached to the existing soundproofing device at random positions in order, for example, to completely or partially cover the side of the existing soundproofing device facing the sound source with the acoustic-absorbing plates.

The elongated cavity structures can be realized in a number of different ways. A method is described above for manufacturing the soundproofing facility in which molded parts are used in a casting or pouring process to realize the hollow structures. The cavity structure can, for example, be formed by a molded part such as a plastic tube which after curing of the material of the plate is removed again. To make removal easier, such molded parts are often provided with a release mold. In other embodiments, however, the molded parts remain in the plate. The cavity structures can for example be formed by acoustically hard tubes anchored in the material of the plate, for example plastic tubes such as PVC tubes. These tubes form a lost formwork and are therefore also called formwork tubes. In other embodiments, the cavity structures are not formed by means of (casing) tubes, but the cavities are subsequently made in the cured material of the plate by drilling holes in the surface thereof.

In certain embodiments, the cavity structures are distributed substantially evenly over the sound-absorbing side of the plate. This means that the sound-proofing facility offers approximately the same degree of absorption over substantially the entire sound-loaded side. In further embodiments, the cavity structures are grouped into several groups distributed over the side of the plate, the cavity structures within each group having mutually different lengths. Each group can be essentially made up of the same cavity structures or even the same pattern of cavity structures (each with a different resonance frequency). A group comprises, for example, a predetermined pattern of adjacent cavity structures. Each cavity structure within this pattern has a different length and is therefore suitable for absorbing sound from different frequency ranges. In certain embodiments, there is a single pattern of cavity structures and this pattern is repeated over the soundproofing side. In other embodiments there are two or more different patterns of cavity structures and the different patterns are provided at different positions of the sound-proofing means.

The distribution of the cavity structures can vary at least in part over the height of an upstanding sound-absorbing side. In certain embodiments, the average cross section of the cavity structures at high positions relative to the substrate is substantially smaller than the average cross section of the cavity structures at low positions. This allows the absorption to be made dependent on the frequency content of the incident sound field. This frequency content generally varies as a function of height relative to the substrate. In this way the absorption can be further improved.

The dimensions of the cavity structures (lengths, cross-section) are preferably chosen such that the absorption is particularly high within a predetermined frequency spectrum (for example the collective spectrum associated with the predominant traffic noise sources). When the porosity (P_L.) is defined as the total cross-section of cavity structures of a certain length (L) (ie the summation of all surfaces of cavity structures (e.g. tubes) of the same length, the cross-sectional areas being taken at the respective mouth of the cavity structures) divided by the total area of ​​the respective part of the sound-proofing device (e.g. the sound-loaded side of the sound-proofing device) and expressed in percentages , it has been found that good results are achieved if this porosity (P_L.) is between 0.01% and 15%, preferably between 0.5% and 2%, even more preferably approximately 1.4%.

The overall (overall) porosity can be defined as the total cross-section of cavity structures of all different lengths (ie the summation of all surfaces of all cavity structures (e.g. tubes) in the respective part (e.g. the sound-loaded side of the sound-proofing device, the surfaces being taken in cross-section at the respective mouth of the cavity structures) divided by the total surface area of ​​the respective part of the sound-proofing device and expressed as a percentage. This overall porosity should generally be as large as possible, depending on the number of cavity structures of different lengths provided in the relevant part of the soundproofing device. Theoretically, the number of different lengths of the cavity structures cannot be more than 1 / P_L. (e.g. 1 / 0.014 = 71). In this case, the part of the sound-proofing device would be provided with cavity structures over the entire surface, which of course is not possible in practice. Construction requirements must be taken into account, such as the minimum distance between cavity structures that is necessary to maintain a solid construction.

In addition to sound-proofing features with a single sound-absorbing side, sound-proofing features with two or more sound-absorbing sides are also possible. In certain embodiments, the sound-proofing means, in the position of use, comprises, for example, a first upstanding sound-absorbing side facing the road and a second upstanding sound-absorbing side facing away from the road. In further embodiments, additionally or alternatively, the upwardly directed side of the plate is provided with a number of cavities. These cavities can be formed by the mold cavities mentioned herein so that the sound is additionally absorbed. In other embodiments, however, the cavities form a diffractor. This diffractor is arranged for deflecting upwards the noise caused by the traffic. The diffractor can comprise a number of parallel slots of different depths arranged in the sheet material, as described, for example, in WO 2015005774 A1, the contents of which are incorporated herein as a whole. Each of the slots has acoustically substantially non-absorbent walls and are free of acoustically absorbent material. Furthermore, in a state arranged along the road, the recesses, when viewed from the road, are arranged in a series of parallel resonator rows, the depth of recesses decreasing per row. Because adjacent parallel grooves have a decreasing depth from the sound-loaded side of the screen in the direction of the opposite side of the screen, it is found that a particularly good deflection of the sound can be realized.

The top of the sound-proofing device can further be oriented obliquely with respect to the sound-absorbing side (s) such that, in a roadside-arranged condition, it faces the road. In these embodiments, the sound coming from a road sound source can fall directly onto the top of the screen and thus onto the diffractor, so that a good deflection (diffraction) is the result.

As usual, the soundproofing device can be arranged parallel to the road. However, it is also possible to divide the sound-proofing device into a number of different screen parts (which each comprise one or more of the said plates) and to arrange each of these screen parts obliquely relative to the road. The screen parts are free-standing and therefore not connected to each other (although a screen part may itself consist of a number of plates coupled to each other). In embodiments of the invention, the sound-proofing device therefore comprises a number of plates arranged in a row along the road, each plate extending obliquely with respect to the longitudinal axis of the road. It is possible to arrange the screen parts (plates) in such a way that a passing vehicle can see through the gaps between the screen parts. The screen parts are then, as it were, oriented with the direction of travel of the vehicle. The angle (α) between the plates and the longitudinal axis or road axle is preferably in an angle range of 5 to 60 degrees, preferably an angle between 30 and 50 degrees, such as 45 degrees. The screen parts are preferably arranged in such a way that a sound field incident on a front or rear side of a screen part partially via that screen part to the rear or rear side. front of a neighboring screen part is reflected. Moreover, each time a sound field is incident on a side of the screen which has an absorbent design, part of the sound will be absorbed. In certain embodiments, both the front and the rear of the screen parts are acoustically absorbed, so that the sound bouncing back and forth disappears as much as possible through absorption. This sound bouncing between two adjacent screen parts can be realized, for example, if said angle (α) is in a certain angle range and said distance (b) is within a certain distance range relative to the side of the road.

Furthermore, it is possible to supplement the sound-proofing device according to one or more of the embodiments mentioned herein with an elongated diffractor arranged along the road edge (for example built up of a number of arranged diffraction plates extended into each other). The diffractor comprises at least one diffraction element to be arranged laterally beside the road, the diffraction element being provided with a pattern of cavities or recesses in its upper surface for deflecting the traffic noise in a direction that deviates from the lateral direction, the cavities or recesses having acoustically substantially non-absorbent walls and being free of acoustically absorbent material, wherein the depth of the recesses decreases with increasing distance relative to the road per row, preferably decreases monotonously. The porosity of a diffractor plate, being defined as the total mouth surface of the recesses divided by the total top surface of the diffraction plate, is at least 10%, preferably more than 50% or even more than 70% to 80%. It has been found that with these porosity values ​​and / or with the above-mentioned structural design of the diffractor, a particularly effective diffraction of the sound field incident from the vehicle occurs. As a result of this diffraction, the sound is deflected upwards in the relevant frequency range. This makes it possible to make the underside of the sound-proofing facilities lighter and / or cheaper, not to be provided with cavity structures or even to omit them altogether. In the latter case, it is possible to look underneath the noise screen and the people in the vehicle have a better view of the surroundings. According to a particular embodiment, an assembly is provided of a support structure to be anchored in the substrate and one or more of the abovementioned plates. The support structure is designed in such a way that the plates can be arranged at at least a predetermined minimum height above the substrate. The support structure can be formed by a number of uprights that can be anchored in the ground on the one hand and can support the plates on the other.

In certain designs, the soundproofing device is made of concrete. This can be unreinforced concrete, for example in the case of relatively small plates, but in other embodiments use is made of reinforced concrete. In these versions, the concrete slab is provided with an internal reinforcement, for example of steel. The reinforcement can for instance comprise a number of parallel reinforcing bars or a reinforcement mesh. In an embodiment of the invention, at least some of the cavity structures extend from the mouth into the acoustically hard outer surface of the plate over different lengths (line_n) extend into the plate, beyond the position of the reinforcement. The length (1) of these cavity structures is therefore greater than the distance (a) between the said outer surface and the reinforcement. This has the advantage that the reinforced plate can still remain relatively thin, for example only slightly thicker than the length of the longest cavity structure.

The noise generated by the traffic from the different sound sources (wheels, tires, motor, etc.) has different characteristic frequency ranges. For car or truck traffic, the absorption will have to have a high value especially at frequencies between 125 Hz and 2,000 Hz, while for train traffic the absorption must be especially between 125 Hz and 4,000 Hz maximum. The porosity, diameter and depth of the cavity structures are hereby chosen so that they in particular absorb sound in the relevant frequency range, for example between approximately 400 Hz - 2000 Hz. In a preferred embodiment of the invention, the porosity, diameter and depth of the cavity structures are chosen such that the absorption coefficient of the plate is optimized in a smaller frequency range, for example between approximately 550 Hz - 1715 Hz. Optimizing the absorption coefficient between approximately 550 Hz - 1715 Hz Hz has the advantage that, since the cavity structures resonate not only at λ-frequency (where λ is the wavelength), but also at the ³A λ frequency, the ³4 λ frequency of the largest cavity structure roughly coincides with the λ frequency of the smallest cavity structure. High values ​​for the absorption coefficient can thus also be obtained above the highest optimization frequency.

As described earlier, the outside of the sound-proofing device as well as the inside of the cavity structures is made of acoustically hard material. By this is meant material with an absorption coefficient of less than 0.15, preferably less than 0.10 and even more preferably less than 0.05 (at least in the frequency range of interest).

Further advantages, features and details of the present invention will be elucidated on the basis of the following description of some embodiments thereof. Reference is made in the description to the accompanying figures, in which:

Figure 1 is a top view of a road provided with a sound screen according to a first embodiment of the invention;

Figure 2 shows a top view of an alternative sound screen according to a second embodiment of the invention, wherein screen parts extend obliquely with respect to the road axle;

Figure 3 shows a side view of the road with the sound-proofing device according to the second embodiment;

Figure 4A shows a front view (left) and side view (right) of a (part of a) sound screen according to an embodiment of the invention;

Figure 4B shows a detail of the front view of Figure 4A;

Figure 4C shows a detail of a cross-section through the soundproofing provision of figures 4A and 4B;

Figure 4D shows a detail of a cross-section through a sound screen with double-sided absorption;

Figure 5 shows a number of possible forms of a cavity structure according to the invention;

Figure 6 shows a top view of the embodiment of Figure 2 with a number of upright screen parts in combination with a roadside diffractor;

Figure 7 is a side view of a further embodiment, in which a roadside diffractor is combined with the raised arrangement of screen parts extending obliquely with respect to the road axle;

Figure 8 shows a section through a further embodiment of a plate of a sound screen which is provided with a diffractor on the top side;

Figure 9 shows a partly cut-away perspective view of a cavity structure that has been produced with a pipe as a lost formwork element;

Figures 10A and 10B are a schematic front view of two further embodiments of the invention;

Figure 11 shows a partly cut-away perspective view of a concrete sound screen provided with a reinforcement and a number of cavity structures according to an embodiment of the invention; and

Figures 12A is a graph showing the absorption coefficient as a function of the frequency of a particular embodiment of the soundproofing device, and Figure 12B is a similar graph of another embodiment of the soundproofing device.

Figure 1 shows a top view of an example of a road (in particular a traffic road 1) over which motorized vehicles (e.g. passenger cars 2) drive. While driving, the vehicle supplies a few sources of (air) noise. The most important noise sources are formed by the tires (rolling noise) and the engine (engine noise). At low speeds the engine noise dominates and at higher speeds the rolling noise of the tires starts to play a bigger role. In other embodiments, not shown, the road is a railroad and the noise is caused by a train traveling over this railroad. Railway noise is mainly caused by the rolling noise from the wheels of the train or, at very high speeds, by the aerodynamic noise, for example the noise from the pantograph. The different sound sources are therefore at different heights relative to the road.

Fangs the road 1, for example parallel to the imaginary longitudinal axis 20 of the road (also referred to herein as the road axis), and at some distance (b) from the side thereof is an elongated, upright sound-proofing device, in particular a sound-shielding unit such as a sound screen 6. The soundproofing facility extends over a large length and is essentially uninterrupted. The height of the raised sound screen can vary: with higher sound loads, a higher sound screen is generally applied than with low noise loads.

In the embodiment shown, the sound-proofing device 6 comprises a number of concrete plates 7,7 ', 7' placed in line with each other and connecting to each other. These plates are attached either directly to the substrate (o) or indirectly via a foundation and / or support structure. The concrete slabs are absorbent on the sound-loaded side, i.e. on the side facing the road. The sound incident on the sound-proofing device is therefore partly reflected and partly absorbed.

The sound-loaded side 3 of the screen 6, despite the fact that the screen is made of acoustically hard material (in this case concrete), has absorbing properties due to the presence of a large number of cavity structures. These cavity structures themselves are in principle not adapted to absorb the sound, but together with the remaining, reflective surface of the screen, form the sound-absorbing surface. The surface of the cavity structures and the remaining surface therefore cooperate in absorbing the incident sound field. The cavity structures have walls of acoustically hard material (since they are formed into an acoustically hard material) and are furthermore free of material that is acoustically absorbent material. The remaining surface, ie the surface of the sound-proofing facility between the cavities, is also acoustically hard (and therefore non-absorbent). The cavity structures in short form resonators with which, in combination with the remaining non-absorbent surface that is not contained in the cavities, sound around and around the associated resonance frequencies can be partially absorbed.

Figures 4A-4C show an example of such a plate of a sound screen according to an embodiment of the invention. The figures show that a large number of cavity structures 10 are provided in the surface of the soundproofing device. The cavity structures have a substantially elongated shape (Figure 4C) with a substantially circular shape and constant cross-section over the length (Figures 4B and 4C). The same cavity structures together form a number of resonators for providing a desired absorption spectrum, the absorption being explained by a mass balance just before the sound-absorbing surface, the resonances of the medium contained in the cavity structures and the viscous and thermal properties of the medium. The absorption caused by a certain cavity structure depends inter alia on the length (1) of the tube that forms the cavity structure. In order to be able to absorb the incident sound field over a relatively wide absorption spectrum, tubes of different lengths are used, each tube of a certain length being suitable for absorbing a relatively narrow frequency range.

In a particular embodiment, the absorbent side of the soundproofing device is divided into a large number of characteristic areas 5 (shown in dotted line in Figure 4B). The regions 5 can each have the same surface, but varying surfaces are also possible. For example, the porosity should decrease for obliquely incident sound waves. Because with higher noise barriers the angle of the incident sound waves is higher at higher positions (and therefore more obliquely incident), a lower porosity can be chosen at higher positions. A collection of cavity structures is provided in each area, each of which has a different length. In the embodiment shown in Figure 4B, 16 cavity structures are provided in each area, but in other embodiments this number may be larger or smaller. Each of the cavity structures is therefore suitable for absorption in its own corresponding frequency range. The cavity structures within a certain area 5 thus together ensure a relatively broadband absorption. The pattern of cavity structures in the area 5 can be repeated in the other areas from which the sound-absorbing surface of the sound-proofing device is constructed and thus realize a broadband absorption distributed uniformly over the sound-loaded side of the sound-proofing device.

For example, if the number of tubes is 16, the radius of the (cylindrical) tubes is 5.5 mm and the lengths (1; with i = 1 -16) of the respective tubes are 47, 50, 53, 56, 60, 64, 68, 73, 78, 85, 91, 99, 108, 119, 131 and 145 mm, the characteristic area becomes, for example, a square area of ​​approximately 85x85 mm². This square characteristic area can be repeated over the entire surface of the soundproofing facility or a part thereof. With this choice of lengths and radii of the tubes, the distance between the underlying tubes is approximately 1 cm. This means that when the soundproofing device is made of, for example, concrete, the walls between the different pipes are sufficiently thick to allow a structurally robust construction. Figure 12A shows a graph with the absorption coefficient of this embodiment as a function of the frequency. The graph clearly shows the short quarter-wavelength resonance peaks and the three-quarter wavelength resonance peaks caused by each of the cavity structures of this embodiment. As follows from the graph, a relatively high absorption coefficient has been realized over a relatively broad spectrum.

For example, if the number of tubes is 25, the radius of the (cylindrical) tubes is 7 mm and the lengths (i1 with i = 1 -25) of the respective tubes are 45, 47, 49 , 51, 53, 55, 58, 60, 63, 66, 69, 72, 76, 79, 83, 88, 92, 97, 103, 109, 115, 122, 129, 137 and 144 mm, the characteristic area becomes for example a square area of ​​approximately 120x120 mm² (porosity about 27%). This square characteristic area can be repeated over the entire surface of the soundproofing facility or a part thereof. Also with this choice of lengths and radii of the tubes, the distance between the underlying tubes is again about 1 cm, so that a firm noise barrier is obtained. Figure 12B shows a graph with the absorption coefficient of this embodiment as a function of the frequency. The graph clearly shows the short quarter-wavelength resonance peaks and the three-quarter wavelength resonant sermons caused by each of the cavity structures of this embodiment. As follows from the graph, a relatively high absorption coefficient over a broad frequency spectrum has also been realized in this embodiment.

In a particular embodiment, the absorption coefficient of the sound-proofing device as a function of the frequency, i.e. the addition of individual absorptions of the cavity structures of the sound-proofing device, is optimized in a frequency range between approximately 550 Hz and 1715 Hz. Optimizing the absorption within this frequency range has the advantage that, since the tubes resonate not only at a% λ but also at³4 λ, the ³4 λ length frequency of the largest tube approximately coincides with the * 4 wavelength frequency of the smallest tube. The tubes therefore participate twice in absorbing the incoming sound. This means that relatively high absorption values ​​can be obtained, such as that beyond the highest optimization frequency (i.e. above 1715 Hz).

The soundproofing device can be provided on one upstanding side with the said cavity structures, as is shown for example in figure 4C. In other embodiments, one of which is shown in Figure 4D, the soundproofing feature may also be provided with cavity structures on two or more sides. Otherwise, this embodiment can be the same as that of figures 4A and 4B, for example in that it is provided with a widened foot. In certain embodiments, the screen is of two-sided design, that is to say, on the two opposite sides, which are opposite each other, are provided with the cavity structures, so that sound absorption occurs on both sides. In a preferred embodiment, the lengths of the cavity structures on both sides of the sound-proofing device are adapted to each other. Relatively long cavity structures in a first side of the screen can be positioned opposite relatively short cavity structures in a second, opposite side of the screen and vice versa. This is possible because the distribution of lengths on both sides is in principle the same. In this way a particularly light construction can be realized which absorbs on both upright sides. This construction further requires only a simple foundation because the wind load decreases.

In figure 4A it is shown that the sound-proofing device is provided with a widened foot 20 on the underside. In both cases, the base and the rest of the sound-proofing facility form a monolithic whole. In these embodiments, the plate is of self-supporting design so that it can remain stable and without further technical support means on the substrate (O). This makes a quick and easy placement of the soundproofing facility possible, which has a positive effect on the total costs for realizing the soundproofing facility. It is furthermore possible, for example, to make sound-absorbing partition walls (preferably provided with double-sided absorption by cavity structures on both sound-laden sides, as shown in Figure 4D) between two lanes that are lighter and require less material than the existing solid concrete partition walls and moreover still absorb some of the noise.

In other embodiments (not shown in the figures), the plates are attached to a separate support structure. The support structure can for instance consist of a number of support posts arranged in the substrate at regular mutual distances. The rear of the plates are fitted against these support posts and coupled to them so that a stable whole is created. In still further embodiments, the sound-proofing means consists of plates of limited dimensions that can be fitted against an already existing sound-proofing screen.

In this way, an existing sound screen, for example of the reflective type only, is a sound screen of the absorbent type.

Figure 9 shows a further embodiment of the invention, in which the cavity structure is formed by a plastic tube 21 that remains in the material of the plate 7 as lost formwork. In the case of a sound screen consisting of concrete plates, which concrete plates are manufactured by pouring liquid concrete into a mold, it is possible to provide the mold with a large number of such plastic pipes 21. The plastic pipes are of suitable length (corresponding to the length of the desired cavity structures) and are arranged in suitable positions, so that after filling the mold with liquid concrete and hardening it in one go, a plate with the desired absorbing properties can be made. realized. The plastic tubes can be removed from the plate after the manufacturing process, but preferably they remain in the material. If the plastic pipes are sufficiently acoustically hard, the cavities formed can also function as sound-absorbing cavity structures for pipes that are left behind. In embodiments where it is desirable to remove the tubes, they preferably have a release form, for example the shape of a truncated cone 23 (Figure 5), such that the tubes can still be pulled out of the material of the screen afterwards.

The cavity structures may have a cross-section that is constant over the length, but in other embodiments, the cross-section increases as the distance from the mouth to the end of the cavity structure increases. These shapes are releasing and are therefore often used if the tubes have to be pulled out of the sheet material again at the end of manufacture. The cavity structures may further have various cross-sectional shapes, including a substantially circular 24, oval 25, rectangular 26.28 or triangular 27 cross-section, as shown in Figure 5.

Figure 10A shows a view of a sound screen in which the average cross section of the cavity structures 28 at relatively high positions relative to the substrate (o) is smaller than the average cross section of the cavity structures 29 at the low positions. For higher positions, the angle of incidence is generally greater. This means that the porosity must be smaller. A smaller porosity can be realized by smaller diameter cavities but then with the same distance between the cavities, the same diameter but then greater distance between the cavities become larger, and / or several tubes of a greater number of lengths. For simplicity's sake, preference is often given to a constant distance between cavities and cavities of smaller diameter, as shown in Figure 10. In this way an even further improved general sound absorption can be obtained. Figure 10B shows a similar sound screen as in Figure 10A. In this embodiment, the rows of cavity structures are alternately shifted with respect to each other (about half the distance between adjacent cavity structures). This makes it possible to achieve more cavity structures and therefore a higher porosity with the same structural requirements.

Figure 2 shows an embodiment in which the plates of the sound-proofing device are not placed substantially parallel along the road (such as the situations in Figure 1), but obliquely with respect to the longitudinal axis of the road. In the embodiment shown, a number of plates 7, 7 ', 7 "are arranged at some mutual distance (M) relative to each other. In other embodiments, groups of two or more sound-absorbing plates placed one behind the other are arranged obliquely with respect to the longitudinal axis 20. The plates 7 -7 ”are placed behind each other in such a way that a row of sound-absorbing plates is created. The angle (α) between the longitudinal axis 20 of the road and the respective plates can vary, for example between 30 and 50 degrees. In the embodiment shown, the angle is equal to approximately 45 degrees.

Figure 2 also shows how noise from the car 2, for example engine and / or tire noise, in the direction P! is sent to the rear of a plate 7 'of the sound-proofing device. The sound is reflected on the sound-absorbing rear side 9 of the plate 7 'and is directed in the direction P₂ from a further absorbent plate 7 ". The incident sound field is at least partially absorbed by the absorbent side 8 of this plate 7 '. The rest of the sound is reflected and disappears in further direction P₃. The absorption quality of the second absorbent plate 7 "and the loss due to the reflection against the first plate 7" ultimately determines how much noise there is in direction P₃disappears. An advantage of this embodiment is that the driver of the passing sound source can look through the sound-proofing facility and keep sight of his surroundings. By providing the screen on both upright sides with the cavity structures defined herein, the total absorption of the soundproofing device can be increased with respect to embodiments in which only one upright side of the soundproofing device of said cavity structures is provided. A further advantage of tilting the plates of the sound-proofing device is therefore that use can be made of both the front and the rear of the plates, which can increase the sound absorption and thus the sound-shielding effect of the entire sound screen.

As already stated above, in a further, non-shown embodiment, the opposite (rear) side 9 of each of the plates 7-7 "is not provided with an absorbent side (due to the presence of cavity structures). In this embodiment too, the sound can be absorbed by the plates, but this only happens on a single side of the relevant plate.

Figure 6 shows yet another embodiment of the invention.

This embodiment is based on the embodiment shown in Figure 2, that is to say the embodiment in which the sound-proofing device consists of a number of parts arranged obliquely with respect to the longitudinal axis of the road. However, it is also possible to apply the embodiment of Fig. 5 to the embodiment shown in Fig. 1, that is to say the embodiment in which the sound-proofing device consists of a long row of parts placed one behind the other. Figure 5 shows that in the verge 3 between the soundproofing facility and the road an elongated strip 35 of diffractor plates 36, 36 'placed one behind the other is arranged on the substrate (O). The diffractor plates 36 are arranged in the substrate such that the top of the diffractor plates 36, 36 'are approximately at the same height as the top of the substrate. The diffractor plates 36 consist of a number of parallel slots of different depth arranged side by side. The slots form resonators with resonance frequencies in the range of the frequencies of the sound to be deflected, in particular frequencies around approximately 1 kHz. The slots are designed as a cavity, the walls of which are substantially non-absorbent and are furthermore free of any acoustic-absorbing material. The plates ensure that the sound coming from the sound source (for example the car 2) is bent in the direction that deviates from the lateral direction. In other words, the sound propagating along the top of the diffractor plate is deflected upwards. Incidentally, it is not the case that only a row of diffractor plates can be arranged next to the sound-proofing facility. In further embodiments, in addition to the row of diffractor plates 36,36 '(optional) additional diffractor plates (shown in dotted lines in Figure 6) are used to deflect the sound propagating through the openings between the sound screen parts.

How the sound can bend upwards is shown in the embodiment of figure 7. This embodiment largely corresponds to that of figure 6, with the difference that the plates 37 are placed at a distance (h) above the substrate (o) , for example by mounting it on a separate support structure (legs). The sound from the car is sent to the resonators in the diffractor (direction P₄). Depending on the wavelength of the sound, this is deflected upwards by an associated slit-shaped resonator 37 (direction P₅). The sound thus reaches the lower strip of the plate 37 and is absorbed there by the mold cavities. In an area from the subsurface up to the minimum height H no or very little noise is incident. The sound-proofing device on the underside therefore does not have to be provided with a sound-absorbing layer or, as in the embodiment shown in Figure 6, the sound-proofing device can be omitted entirely on the underside. This makes the overall construction of the soundproofing device lighter and traffic on the road through the underside of the soundproofing device has a view of its surroundings. For further details of the diffractor and diffractor plates mentioned herein, reference is made to the international patent application WO 2015005774 A1 of the applicant, the contents of which are incorporated herein in their entirety.

Figure 8 shows a further embodiment of the invention, in which on the upper side of the plate 17, which is provided with absorbent cavity structures at least on the front side 18 (but in some embodiments also has such cavity structures on the rear side) also on the upper surface Has 30 special features. The upper surface of the sound-proofing device extends obliquely with respect to the upstanding side 8 and thus with respect to the substrate in use. The angle of inclination (β), as shown in Figure 8, is herein chosen such that the sound transported from the sound source on the way to the top of the screen can be bent by a number of diffractors 31 provided in the upper surface 30. The diffractors may, for example, be composed of a number of elongated and parallel resonator slots 32. With a small distance between the road and the sound-proofing facility, the angle β will generally have to be greater than with a large distance. For further details of such diffractors, reference is made to the above-mentioned patent publication WO 2015005774 A1.

The diffractors 31 on the upper side of the sound-proofing means consist of slots 32 extending in the longitudinal direction of the sound-proofing means. at least there is no acoustically absorbent material provided therein. From the viewing side (side 8) of the soundproofing device in the direction of the rear side, the depth (length) of the diffuser slots 32 decreases in each case. Furthermore, the mouth of each of the diffractor slots 32 is each time located at a greater height than the mouth of the previous diffractor slot. The depths of the reactor slots preferably decrease monotonously, but, in other embodiments, some variation in depth may occur. As a result of the presence of the diffractor 31, the sound transported along the top of the soundproofing device is deflected upwards so that the sound-shielding effect of the soundproofing device is further increased.

Figure 11 shows a further embodiment of the invention, wherein the soundproofing device is made of reinforced concrete. This sound screen thus comprises a reinforcement 44 known per se, which reinforcement consists of, for example, a metal grille. The reinforcement is, for example, arranged in the center of the plate, but in other embodiments it can also be arranged closer to the front or the rear. In this embodiment, the cavity structures 45 are arranged such that at least a part of the cavity structures can extend beyond the position of the reinforcement 44 (as indicated by the dotted lines 46). Therefore, at the location of the reinforcement, either no cavity structures are situated or only a group of cavity structures with a relatively small length. This makes it possible on the one hand to reinforce the location but on the other to use virtually the total thickness of the plate to provide cavity structures therein. Incidentally, this does not only apply to embodiments in which the cavity structures extend only on one side (visible side) of the sound-proofing facility, but also in the aforementioned embodiments in which the cavity structures are provided on both sides (and the screen is therefore absorbent on both sides) .

The present invention is not limited to the embodiments thereof described herein. The scope of protection is defined by the appended claims, within the scope of which numerous modifications are conceivable.