Diffractor for diffracting sound

Abstract

Diffractor for diffracting sound of traffic on a travel surface with at least one diffraction plate disposed laterally beside the travel surface. The diffraction plate is provided with a pattern of recesses in the upper surface thereof for the purpose of diffracting the traffic noise in a direction which differs from the lateral direction. Each of the recesses is divided into individual resonators by intermediate walls provided in the recesses. The recesses have acoustically substantially non-absorbing walls and are free of acoustically absorbing material. The intermediate walls between adjacent resonators have at least one throughflow opening along which the rainwater can flow from the one resonator to the other.

Claims

1. A diffractor for diffracting sound of traffic on a travel surface, the diffractor comprising at least one diffraction element disposed in a lateral direction beside the travel surface, wherein the at least one diffraction element comprises a pattern of recesses in the upper surface thereof, wherein the at least one diffraction element is configured for diffracting a traffic noise in a direction which differs from the lateral direction, wherein each of the recesses is divided into individual resonators by intermediate walls provided in the recesses, wherein each of the recesses has an acoustically substantially non-absorbing wall and is free of an acoustically absorbing material, and wherein the intermediate walls between adjacent resonators comprise at least one throughflow opening configured to allow rainwater to flow from the one resonator to another, wherein the diffraction element comprises a lower plate and an upper plate placeable thereon and wherein the bottom of the recesses is formed by the upper side of the lower plate and the recesses are arranged only in the upper plate.

2. The diffractor according to claim 1, wherein the recesses take an elongate form and wherein each of the recesses is divided into a row of elongate recesses arranged successively and separated from each other via one or more intermediate walls.

3. The diffractor according to claim 1, wherein an intermediate wall comprises a throughflow opening at the position of one of the walls of the recess.

4. The diffractor according to claim 3, wherein the throughflow opening is provided between the wall of a recess to be positioned closest to the sound source and a free outer end of an associated intermediate wall.

5. The diffractor according to claim 1, wherein the throughflow opening is located between the underside of the intermediate wall and the bottom of the recess.

6. The diffractor according to claim 5, wherein the bottom is deepened over at least a part thereof.

7. The diffractor according to claim 1, wherein the bottom of a recess lies at an incline.

8. The diffractor according to claim 1, wherein the diffraction element is formed integrally and/or has a releasing form.

9. The diffractor according to claim 1, wherein the depth of the recesses decreases monotonically per row as a lateral distance relative to the travel surface increases.

10. The diffractor according to claim 1, wherein the depth of at least four of the number of successive parallel rows decreases.

11. The diffractor according to claim 1, wherein a porosity defined as an overall mouth surface area of the recesses divided by an overall upper surface area of a diffraction plate is at least 10%.

12. The diffractor according to claim 1, wherein the recesses are slot-like, the width of a resonator is about 3 cm, the width of a wall between adjacent rows of recesses is about 2 cm, a width of the throughflow openings is about 0.5 cm, and an intermediate distance between an intermediate wall of a resonator is less than 20 cm.

13. The diffractor according to claim 1, wherein the diffraction element is manufactured from concrete, plastic, metal, or a combination thereof.

14. The diffractor according to claim 1, wherein a resonance frequency of the resonators is about 500 Hz to about 1500 Hz.

15. The diffractor according to claim 1, wherein the depths of the resonators vary between 15 cm and 1 cm.

16. A travel surface assembly for traffic, the travel surface assembly comprising at least one row of diffractors according to claim 1, wherein: the travel surface assembly for traffic comprises a travel surface comprising a traffic road for motorized road traffic, a railway for train traffic, or a combination thereof, andthe at least one row of diffractors is configured to limit a lateral emission of a sound frequency from a sound source travelling over the travel surface, wherein the sound frequency is within a predetermined range.

17. The travel surface assembly for traffic according to claim 16, wherein the row of diffractors is arranged directly adjoining the travel surface.

18. The travel surface assembly for traffic according to claim 16, wherein the upper side of the diffraction element extends at least at roughly the same height as the surface of the travel surface.

19. The travel surface assembly for traffic according to claim 16, further comprising a noise-reducing screen disposed behind the at least one row of diffractors, wherein the noise-reducing screen is configured to reflect, absorb, or reflect and absorb sound diffracted by the at least one row of diffractors.

20. The travel surface assembly for traffic according to claim 19, comprising a support configured to support the noise-reducing screen at a distance above the ground.

21. The travel surface assembly for traffic according to claim 16, wherein the recesses are configured to produce a maximum sound reduction at a distance of about 6 m to about 10 m from the travel surface and at a height of about 3 m from the travel surface.

22. The diffractor according to claim 1, wherein the depths of all of the mutually adjacent recesses decreases.

23. The diffractor according to claim 1, wherein the recesses widen at least partially from the mouth to the bottom.

24. The diffractor according to claim 1 wherein the recesses narrow at least partially from the mouth to the bottom.

25. The diffractor according to claim 11, wherein the porosity is more than 50%.

26. The diffractor according to claim 11, wherein the porosity is more than 70%.

27. The diffractor according to claim 11, wherein the porosity is more than 80%.

28. The diffractor according to claim 12, wherein the intermediate distance between the intermediate wall of the resonator is about 10 cm.

29. The diffractor according to claim 13, wherein the diffraction element is manufactured from glass fibre-reinforced polyester, recycled polyethylene, steel-reinforced plastic, iron, steel, or a combination thereof.

30. The diffractor according to claim 14, wherein the resonance frequency of the resonators is about 700 Hz to about 1200 Hz.

31. A diffractor for diffracting sound of traffic on a travel surface, the diffractor comprising at least one diffraction element disposed in a lateral direction beside the travel surface, wherein the at least one diffraction element comprises a pattern of recesses in the upper surface thereof, wherein the at least one diffraction element is configured for diffracting a traffic noise in a direction which differs from the lateral direction, wherein each of the recesses is divided into individual resonators by intermediate walls provided in the recesses, wherein each of the recesses has an acoustically substantially non-absorbing wall and is free of an acoustically absorbing material, and wherein the intermediate walls between adjacent resonators comprise at least one throughflow opening configured to allow rainwater to flow from the one resonator to another, wherein the recesses are arranged along the travel surface in a number of successive parallel rows of resonators, wherein a depth of the recesses decreases per row in a direction away from the travel surface, and wherein the depths of ten of the mutually adjacent rows decreases.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a partially cut-away perspective view of a carriageway with a number of diffractors in the form of diffraction elements placed in a row along the travel surface;

(3) FIG. 2A is a perspective top view of a first embodiment of a diffraction plate according to the invention;

(4) FIG. 2B is an exploded perspective top view of the diffraction element of FIG. 2A in which a lower and upper plate are shown;

(5) FIG. 2C is a perspective view of the upper side of the lower plate and the underside of the upper plate of the embodiment of the invention shown in FIGS. 2A and 2B;

(6) FIG. 3A is a perspective view of a second embodiment of a diffraction plate according to the invention;

(7) FIG. 3B is a detail view of the first (front) four resonators rows of the second embodiment;

(8) FIG. 4 is a partially cut-away view of an embodiment of an assembly of a carriageway and a diffractor according to the second embodiment, wherein a noise-reducing screen is arranged adjacently of the diffractor; and

(9) FIG. 5A is a graph showing the noise reduction (in dB) for sound with a frequency of 1000 Hz resulting from the presence of a diffractor.

(10) FIG. 5B is a graph of the noise reduction (R) at 7.5 m from the sound source behind the diffractors and at different heights as a function of the frequency (f) for the situation of FIG. 5A.

DETAILED DESCRIPTION

(11) The invention relates to a diffractor for diffracting sound of traffic on a travel surface, the diffractor comprising at least one diffraction element to be disposed laterally beside the travel surface, wherein the diffraction elements are provided with a pattern of recesses in the upper surface thereof for the purpose of diffracting the traffic noise in a direction which differs from the lateral direction. The invention also relates to an assembly of a travel surface and one or more such diffractors.

(12) FIG. 1 shows a travel surface 1, more particularly a carriageway, along the shoulder 2 of which a row of diffraction elements 3 is arranged. The figure shows four diffraction elements, although it will be apparent that this number can be greater. Each of the diffraction elements 3 is recessed into the ground 4 such that, at least in the vicinity of the side of the travel surface 2, the upper surface 5 of the plate lies roughly at the same height as the carriageway.

(13) The diffraction element has a pattern of slot-like recesses (including deepened portions, cavities, channels, trenches, grooves and the like) 6 which extend in longitudinal direction and optionally in mutually parallel zones, these slot-like recesses being bounded by two standing walls, which walls are optionally connected to each other locally by means of transverse partitions or intermediate walls. Recesses 6 are arranged at different distances (a.sub.1, a.sub.2) relative to the roadside 2 of travel surface 1 (in a lateral direction 45 away from the travel surface, i.e. perpendicularly of the longitudinal axis of the travel surface).

(14) The upper side of diffraction element 3 can be arranged at a slight incline relative to the travel surface so that the height increases as said distance (a) increases. In other embodiments the upper side of the diffraction element is however wholly coplanar with travel surface 1.

(15) FIGS. 2A-2C show a determined embodiment of such a diffraction element in more detail. The diffraction element according to this embodiment is plate-like. In the shown embodiment diffraction element 12 comprises an upper plate 10 and a separate lower plate 11. Upper plate 10 is a plate with a substantially flat upper side 24. A large number of recesses 6 is arranged in the plate. Each of the recesses 6 forms a row 13, wherein the rows of recesses run substantially parallel to each other. Each recess 6 is divided into different compartments using standing intermediate walls 15. Each compartment forms a resonator 16.

(16) In the shown embodiment the number of rows 13 equals sixteen. In other embodiments the number of rows can of course be smaller or greater.

(17) The individual resonators in a determined row 13 preferably all have the same depth. The depths of resonators 16 generally differs however in different rows 13. In the shown embodiment the depth of successive rows (as seen from the travel surface in lateral direction 45) for instance sometimes decreases and sometimes increases. In other embodiments the shown embodiment can be modified so that the depth of each successive row decreases.

(18) Each of the resonators 16 is constructed from a number of standing walls (usually vertical, although inclining walls are also possible), more particularly a front wall 26, rear wall 27 and two intermediate walls 15. Each of the walls is manufactured from acoustically hard (i.e. substantially non-absorbing) material and resonators 16 are further empty. This means that no absorbing material or other type of material is present in the resonators.

(19) FIGS. 2A-2C also show a lower plate 11. This lower plate 11 is preferably flat on the underside and provided on the upper side with a number of grooves 29. Grooves 29 extend parallel to each other and are dimensioned and arranged such that each groove can be placed directly below an associated row of recesses. Provided on the two longitudinal sides of each groove are upright edges 30 on which the underside 25 of upper plate 10 can rest.

(20) Each of the intermediate walls 15 is embodied on the underside thereof such that a gap is present between the underside thereof and associated groove 29. The groove forms the bottom of the recess. The intermediate space between the underside of the intermediate wall and the bottom functions as throughflow opening 20 for water which has found its way into the resonators.

(21) Because a throughflow opening 20 is present between each of the intermediate walls 15 and the bottom of the associated grooves 29, the water can flow from the one resonator to the other. In order to initiate the flow of water grooves 29 are placed at an incline, which means that they slope to some extent. Under the influence of gravitational force a flow of water is hereby set into motion through the successive throughflow openings in direction 31 (FIG. 2B). In the shown embodiment the incline is such that the throughflow of the water through the throughflow opening takes place in a single direction 31 at a time. In other embodiments it is however also possible to have a part of the water flow in one direction and another part of the water in the other direction, for instance alternately per row.

(22) Said throughflow opening 20 can be realized in that the bottom of groove 29 is deepened to some extent relative to the upper side of edges 30. In other embodiments the bottom is however flat, and the edges are omitted. The throughflow opening is formed in this embodiment by shortening the intermediate walls 15 on the underside. An opening is hereby created between the underside of the intermediate walls and the bottom. In yet another embodiment the throughflow opening is created by shortening the intermediate wall to some extent as well as giving the bottom a deepened form.

(23) Because the throughflow openings provide for drainage of the rainwater, the action of the resonators will not deteriorate, or at least less so, when water gets into them. Because the drainage via the throughflow openings further takes place via the side surfaces of the resonators and since openings 20 are located in or under intermediate walls 15, the throughflow openings have no or hardly any effect on the acoustic properties of the resonators. This is caused by the fact that, since the sound waves are largely incident perpendicularly of the rows, no difference in sound pressure occurs in longitudinal direction of the resonators. No wave propagation therefore occurs in longitudinal direction, and sound does not therefore leak from one resonator to the other. The operation of the resonators hereby remains substantially intact, despite the presence of the throughflow openings.

(24) The above described first embodiment of a diffraction element is plate-like and is therefore also referred to as a diffraction plate. In other embodiments the diffraction elements are embodied as paving stones or bricks (for instance moulded clinkers), wherein one brick or more bricks together form the above described resonators.

(25) FIGS. 3A and 3B and the left-hand part of FIG. 4 show a second embodiment of a diffraction element 33 according to the invention. In this embodiment the element has an integral construction. The element particularly takes a wholly releasing form, which makes it easily possible to produce the plate in a mould. Diffraction element 33 is provided on the side 34 facing toward travel surface 1 with a number of upright recesses 35. The edges 36 adjacently of these recesses are preferably arranged against the side of carriageway 1. Recesses 35 enable downward drainage of rainwater and dirt which lands on the lying edge 37 of plate 33. Dirt from the travel surface can hereby be prevented from finding its way into the resonators located therebehind.

(26) A number of elongate recesses 39 are once again arranged in upper side 38 of diffraction plate 33. Each of the recesses forms a row 40, wherein the recesses are arranged substantially parallel to each other and have a distance increasing in each case relative to the travel surface (as seen from the travel surface 1 in a direction 45 away from the travel surface, perpendicularly of the longitudinal axis of travel surface 1). Each recess 39 of a row 40 is divided into individual resonators by means of intermediate walls 50.

(27) Referring to FIG. 3B, the depth d.sub.1 of first row 46 is greater than the depth d.sub.2 of second row 47. The depth d.sub.2 of second row 47 is in turn likewise greater than the depth d.sub.3 of third row 48, and so on. Although this need not necessarily be the case in all embodiments, in the shown embodiment the depth of the resonators decreases monotonically in each case in successive resonator rows 40.

(28) As stated above, each recess 39 is divided into individual resonators by means of intermediate walls 50. In contrast to the intermediate walls in the first embodiment, which mutually connect standing walls 26, 27 and form as it were partitions between the two walls, intermediate walls 50 are formed such that a standing, gap-like throughflow opening 55 is present between at least one of the standing walls 51, 52. In the shown embodiment throughflow opening 55 is provided on the travel surface side dof resonator 49, i.e. on the side of wall 52 located closest to travel surface 1. Throughflow opening 55 is formed by having the free outer end 57 of each intermediate wall 50 end some distance (characteristically about 5 mm) from the opposite wall 52 of resonator 49. This throughflow opening 55 extends over substantially the whole height of the resonator and also to the bottom thereof. This makes it possible for water which may have got into the resonators to flow quickly from the one resonator via throughflow opening 55 to an adjacent resonator. By now providing all resonators with such openings it is possible to transport the rainwater from one resonator to another resonator and further in the direction of a further water drain.

(29) In a preferred embodiment the bottoms 59 of recesses 39 take a form inclining to some extent relative to the travel surface so that the water flows in one determined direction under the influence of gravitational force, preferably in the direction of the further water drain (not shown).

(30) It is also the case in this embodiment that, due to the location of the throughflow opening, i.e. on the side of the resonators and therefore not in one of the walls or in the bottom, the relevant acoustic properties of the resonators are not affected, or hardly so, while water can still be drained so as to keep the resonators free of water.

(31) As already set forth, the depth of the recesses in the diffraction element preferably decreases from row to row (as the distance relative to the travel surface increases). The cross-section of the second embodiment of the diffraction element shown in FIG. 4 for instance shows that there are sixteen rows of resonators, wherein the first row of resonators is the deepest (typically 8 cm deep or, in the case of car traffic, 15 cm deep) and the subsequent rows of recesses become increasingly less deep. It has been found that, when this sequence of depths is applied, a surprisingly high noise reduction can be realized in the relevant frequency range. It has further been found that the at least three, preferably four, but most preferably at least ten successively placed rows of recesses have a depth decreasing in each case in order to realize a high sound attenuation. Even if the depth increases again after a series of rows of decreasing depth, the results remain reasonably good. Embodiments in which three successive recesses therefore have an increasing depth produce good results, and certainly when these three recesses are located relatively close to the source (for instance in the first 6 rows), also already provide good results. It is however recommended that all rows have a monotonically decreasing depth.

(32) FIG. 5A shows the results of the simulation of a sound field diffracted by a diffractor according to an embodiment of the invention. The source is located 3 cm (h=0.03 m) above the ground, at a=0.3 m. The diffractor consists of slots of about 3 cm wide at a mutual spacing of 2 cm. The width of the throughflow openings (drainage gaps) is 5 mm and the intermediate distance between the intermediate walls amounts to about 10 cm. The first resonator lies at a distance of 75 cm from the source and depths are respectively 79, 65, 54, 47, 43, 42, 40, 36, 28, 17, 4, 1, 1, 1, 1, 1 mm (plate dimensions about 80?80 cm). The noise reduction is shown at a frequency of 1000 Hz. The noise reduction at about 7.5 m from the source thus varies between about 4 and 7 decibel. Similar reductions are feasible at other frequencies related to traffic noise (for instance between 500 Hz and 1200 Hz).

(33) FIG. 5B shows a graph in which the reduction as a result of the diffractor is shown as a function of the frequency and at different heights, at 7.5 m from the source. At low frequency the reduction is thus highest at 3 m.

(34) FIG. 4 shows a further embodiment of the invention. In the situation of FIG. 4 a number of the diffraction plates 33 shown in FIGS. 3A-B are placed along travel surface 1. The diffraction plate is provided in the above described manner with a number of resonators. Arrows 60, 61, 62 indicate that sound waves coming from travel surface 1 are first incident in shearing manner (direction 60) on the diffraction plate and are diffracted upward (direction 61, 62) by the resonators. The sound forms as it were a diffraction lobe in which the sound is carried away obliquely upward. This means that an area (designated schematically with 63) is created under the diffraction lobe in which there is some measure of sound attenuation in the desired predetermined frequency range. In order to prevent the sound finding its way above said area 63 from also causing nuisance, in this embodiment a noise-reducing screen 65 is arranged at a greater distance from the travel surface, although preferably in the vicinity thereof. Noise-reducing screen 65 is arranged on a support 66. This support can take a relatively light form and is preferably embodied such that the traffic participants on travel surface 1 can see therethrough. Noise-reducing screen 65 is provided in known manner some distance above the ground. This noise-reducing screen can reflect the sound incident thereon. The surface of noise-reducing screen 65 facing toward travel surface 1 preferably takes an absorbing form. The surface can be provided for this purpose with an absorbent material layer 70. It is further possible to also arrange further diffractors 69 on the upper side 68 of noise-reducing screen 65 for further diffraction of sound waves shearing therealong.

(35) Noise-reducing screen 65 has the advantage compared to a traditional noise-reducing screen that it can take an open form on the underside (i.e. at the position of support 66) so that the traffic participant has a view of his or her surroundings and/or the wind has less influence on the construction. The construction of support and noise-reducing screen can hereby take a lighter form, and a heavy foundation construction can be dispensed with.

(36) In other embodiments of the invention (not shown) the resonators are formed more deeply than in the embodiment of FIGS. 3 and 4. When the diffraction element is applied along a quiet road surface, for instance a sound-absorbing road surface, the peak of the traffic noise lies at a lower level, characteristically around 700 Hz. It has been found that somewhat deeper recesses can preferably better be applied in such situations. It has further been found that the diffraction effect is more robust with the deeper resonators. The effect becomes noticeable at lower frequencies, while the effect is still maintained sufficiently at higher frequencies.

(37) According to a particularly advantageous embodiment, recesses with respective depths of 142, 131, 121, 114, 109, 107, 107, 107, 105, 102, 97, 90, 82, 75, 72 mm (?3 mm) are applied in a sequence as seen from the travel surface. The intermediate distance between the intermediate walls amounts to about 16 cm. The width of the recesses amounts to for instance 35 mm (?5 mm).

(38) In determined embodiments the walls of the recesses take an inclining form. The width of a recess is more particularly greater on the upper side than the width at the bottom of the recess. This ensures that the recesses have a releasing form, which simplifies the manufacture of the diffraction elements. Such diffraction elements are further easy to keep clean.

(39) The present invention is not limited to the above described embodiments. The rights sought are defined by the following claims, within the scope of which numerous modifications can be envisaged.