EP3246479B1 - Absorber unit for absorbing sound - Google Patents

Description

The invention relates to an absorber unit for absorbing sound, particularly in closed rooms.

In the automotive industry, anechoic chambers are used to study the exterior noise of vehicles. The noise levels must be recorded in a suitable acoustic environment in order to record and assess them qualitatively and quantitatively and, if necessary, to process them in such a way that sound design is possible.

The need for anechoic rooms with cut-off frequencies f _g far below 50 Hz is increasing. Due to current developments in the automotive sector, the mouth noise on the exhaust pipe caused by the combustion engine is shifting to lower and lower frequency ranges down to around 30 Hz. Low frequencies also occur when air flows over the vehicle. Vortex shedding then occurs at the tail section, which causes a very low-frequency source noise, the so-called "thumping". This situation is examined in the automotive industry in the wind tunnel with air flow. Here, too, the noise components reach down to the 30 Hz range.

A related area is psychoacoustics, which accounts for large proportions, especially with low frequencies that are reflected in people, for example in the stomach area, so that there is a need for suitable acoustic environments in this frequency range.

Since the 1950s, anechoic rooms have been lined with structured absorbers, in particular with so-called cube or wedge absorbers. Their main feature is that above a certain frequency, known as cut-off frequency f _g , they have an absorptivity α > 99%, measured according to DIN EN ISO 10534-2 in the impedance tube. This property of an individual absorber is transferred to the room if its room boundary surfaces are lined accordingly. The quality of the acoustic free field, which results from the absorber properties, can then be determined with the help of DIN EN ISO 3745 or DIN EN ISO 26101.

A cut-off frequency of 38 Hz at an absorber depth of 1.7 m is known for structured linings. Lower limit frequencies with structured absorbers have not been achieved so far.

Apart from this limitation, experience has shown that absorber lengths t in the range of λ _g /4 or λ _g /5 would be necessary to achieve a certain cut-off frequency f _g with structured absorbers, where λ _g means the wavelength at the cut-off frequency. With a limit frequency of f _g = 30 Hz, this means an absorber depth in the range of 2.28 m < t < 2.86 m. This would not be economically justifiable due to the immense space required for the absorber and the interior space then required for the measurement. Absorption at low frequencies and where less space is required is basically to be brought about by resonators. In the case of resonance absorbers, the lining depth can be significantly reduced (t < 0.5 m), but the resonance results in a discontinuous absorption curve, which also leads to discontinuities in the anechoic room, so that the acoustic spatial field itself fluctuates and the resulting measurement error no longer spatially is to be assigned.

In addition, a resonant frequency alone is not sufficient for the applications described above, since the requirement for the degree of absorption does not only apply to the resonant frequency, but to all frequencies above the cut-off frequency.

In order to solve this problem, it is known to combine broadband absorption material with a resonator plate, which reduces the resonance quality on the one hand, but on the other hand leads to a broader band absorption range and also makes medium and higher frequencies accessible with the absorption material placed in front (see for example " Broadband compact absorbers for anechoic linings", Helmut V. Fuchs et al., CFA/DAGA'04, Strasbourg, 22-25/03/2004, pages 955 and 956 ).

Due to the resonance-like structure, however, measurements in the impedance tube can hardly be carried out here, since the clamping or boundary conditions of the plate play a decisive role in the position and amplitude of the resonance. Although reverberation room measurements according to ISO 354 are possible without further ado, such measurements lack any accuracy at very high degrees of absorption, since the underlying physical model (according to Sabine) breaks down and is no longer valid. A direct, precise physical measurement of this type of absorber is therefore not possible.

The DE 94 00 092 U1 discloses the features of the preamble of claim 1.

It is therefore an object of the invention to provide an absorber unit that has a high degree of absorption in a broad frequency spectrum that extends into a low frequency range, avoiding discontinuities in the resonance and at the same time enabling a small lining depth.

According to the invention, this object is achieved in that the absorber unit comprises a plurality of plates made of sound-absorbing material, with at least two adjacent ones Plates are spaced to form a cavity resonator for frequencies below 50 Hz with an air space therebetween.

The panels of absorptive material themselves absorb a broader spectrum of frequencies, while also serving as boundaries for air spaces, each of which has a less broad but lower-frequency absorption spectrum. Thus, the panels can combine two absorption mechanisms and absorb the desired broad frequency spectrum extending towards low frequencies and absorb discontinuities with little space requirement. Such an arrangement provides a flat absorber that has a small installation depth and at the same time good absorption properties in a wide frequency range that extends down to very low frequencies.

In particular, the cavity resonator or several or all of the cavity resonators can have a natural frequency of less than 50 Hz, in particular less than 40 Hz, in particular less than 35 Hz, in particular 30 Hz.

The absorber unit preferably consists of individual absorber and air layers which are arranged in such a way that the highest possible degree of absorption is achieved with the lowest possible installation depth. This is achieved by optimizing the spacing and thicknesses of the plates and a suitable choice of absorption material, because the absorption efficiency of the resonators depends on the spacing of the plates and the absorption properties of the plates on the thickness of the plates and their flow resistance. In particular, the degree of absorption, from which the limit frequency is defined, is set to 90%. In comparison, structured absorbers have an absorptivity of 99%. Measurements with conventional flat absorbers in the higher frequency range (f > 400 Hz) show that the requirements according to DIN EN ISO 3745 can still be met if the degree of absorption is set at around 90%.

According to the invention, the absorption material comprises an anisotropic substance with fibers, the plates being designed and arranged in such a way that the fibers run at least in one of the plates along the direction of the plate sequence in the absorber unit.

The term fiber direction is used as follows: It is assumed that a majority of the fibers in a panel run in approximately the same direction, referred to as the fiber direction. In the preferred examples, this roughly corresponds to the direction of the plate sequence or a direction transverse thereto, but this does not mean that all fibers run exactly parallel or transverse to this direction or exactly parallel to one another.

After installation, the direction of the plate sequence typically corresponds to the direction in which the sound hits the absorber unit during operation.

The absorption material can, for example, comprise mineral wool or open-cell foam materials. Mineral wool is an anisotropic material consisting of layers of fibers glued together. Typically, mineral wool with fibers aligned along the direction of sound has the lowest flow resistance.

Typical length-related flow resistances (DIN EN 29053) of mineral wool are 5 to 35 kPa*s/m ² , depending on density and arrangement.

Waves are mainly absorbed when there is good impedance matching in the transition area between two media, in this case between air and absorption material. In the prior art structured absorbers, this is accomplished by the shape. In the case of the (flat) absorbers according to the invention, the impedance is preferably matched by adjusting the flow resistance of the absorption material. Materials with very low flow resistance are therefore preferred.

Many such materials have hardly any intrinsic stability, for example cotton wool or loose glass wool. The use of mineral wool reduces this problem and provides inherent stability. In particular, the panels can include mineral wool in a special installation position. In this respect, inherently stable mineral wool panels with low flow resistance can be used with a suitable arrangement. In addition, mineral wool ensures non-combustibility class A according to DIN EN 13501. Other materials that have suitable stability and suitable flow resistance are also conceivable.

The sheets of absorption material are preferably designed in such a way that they have inherent stability. This facilitates installation in the absorber unit since no special support structures have to be provided.

The panels may be arranged such that the grain direction alternates between running along the direction of panel succession and perpendicular to the direction of panel succession from panel to panel.

The absorber unit can have at least, in particular exactly three, plates. In particular, with exactly three plates, the fibers of the middle plate can run along the direction of the plate sequence and the fibers of the other two plates can run transversely to the direction of the plate sequence.

The thickness of the panels can be between 150 mm and 300 mm. The distances between the panels can be between 100 mm and 200 mm. The plates can all have the same thicknesses and spacings or at least partially different thicknesses and spacings from one another.

The absorber unit can comprise at least, in particular precisely, three panels, the thickness of a central panel being less than the thickness of the two adjacent panels and the two adjacent panels having different thicknesses.

The absorber unit can comprise a boundary surface which, with respect to the direction of the plate sequence, is arranged adjacent to one of the two outermost plates. In particular, the plate that is closest to the boundary surface can then be thicker than the middle plate and thinner than the plate that is furthest away from the boundary surface.

In particular, the plate lying closest to the boundary surface can then have a thickness of 250 mm, the middle plate can have a thickness of 200 mm and the plate lying furthest away from the boundary surface can have a thickness of 300 mm.

The absorber unit can comprise a boundary surface which is arranged adjacent to one of the two outermost plates in relation to the direction of the plate sequence. In particular, the distance between the middle plate and the plate closest to the delimiting surface can then be greater than the distance between the plate closest to the delimiting surface and the delimiting surface and smaller than the distance between the middle plate and the plate furthest from the delimiting surface lying plate.

In particular, the distance between the middle plate and the plate lying closest to the boundary surface can then be 150 mm, the distance between the plate lying closest to the boundary surface and the boundary surface 100 mm and the distance between the middle plate and the plate furthest from the boundary surface distant panel is 200 mm.

The total thickness of the absorber unit can be less than or equal to 1.5 m, preferably less than 1.4 m, in particular 1.2 m. For example, the total thickness can be between 1.1 m and 1.4 m.

At least one of the plates can be covered by a perforated plate on one or both main sides of the plate or in the form of a perforated plate cassette. especially the The plate lying closest to the sound source during operation can advantageously be designed in the form of a perforated plate cassette. At least one of the plates can be designed in the form of a link pack. In particular, the panels that do not face the sound directly during operation can be integrated into a splitter package.

The use of perforated sheet cassettes and/or baffle packs is advantageous because the structure of the panels themselves and the absorber unit is simple and inexpensive.

The absorber unit can be designed in such a way that the air spaces can be used to install cables or pipes. This enables an advantageous structure in the corresponding applications where a large number of cables have to be laid for the power supply and/or for data exchange, for example from sensors or the like.

Fig. 1

eine schematische, nicht maßstabsgetreue Schrägansicht einer ersten Ausführungsform der erfindungsgemäßen Absorbereinheit,

Fig. 2

eine schematische, nicht maßstabsgetreue Schnittansicht der ersten Ausführungsform und

Fig. 3

eine schematische, nicht maßstabsgetreue Schrägansicht einer zweiten Ausführungsform der erfindungsgemäßen Absorbereinheit.

Further features and advantages are explained below with reference to the exemplary figures. It shows:

1

a schematic oblique view, not true to scale, of a first embodiment of the absorber unit according to the invention,

2

a schematic, not to scale sectional view of the first embodiment and

3

a schematic oblique view, not true to scale, of a second embodiment of the absorber unit according to the invention.

In figure 1 a first preferred embodiment of the absorber unit 1 is shown, which comprises three plates 2, 3, 4 made of absorption material, which are also referred to as absorber packages alone or installed in perforated metal cassettes or baffles. The direction of the plate sequence is marked here with the arrow 5. Arrow 6 indicates the approximate direction in which the sound will hit the absorber unit during operation. It should be noted that the absorber unit can also have a different number of absorber packages.

An air space 8 is arranged in each case between two adjacent absorber packages. Preferably, the absorption material of all absorber packs is mineral wool, the fibers of which run in the middle absorber pack 3 along the direction of the plate sequence of the absorber packs (ie in operation the direction of sound) and in the other two absorber packs transversely to it. Alternatively, an open-cell foam can also be used for the two outer absorber packs. However, the orientation of the fibers can also be chosen differently or other materials can be used as long as there are suitable flow resistances.

The three absorber packs can, for example, have a thickness of d=300 mm, e=200 mm and f=250 mm and a distance of a=200 mm or b=150 mm. However, values for the thickness and distances can also deviate from these values, which mainly depends on the materials used and the desired absorption properties.

The absorber unit can be delimited by an element 7, for example a wall or a boundary surface, which is part of the absorber unit. For example, as in the figure 1 shown, the absorber unit in operation, for example at a distance of c = 100 mm, on a wall (or the ceiling) of a room, which preferably has a high flow resistance.

During operation, the first absorber package 2 faces directly the sound source. For example, if the absorber unit is attached to the ceiling or wall of a room, the first absorber pack faces directly the interior of the room. The first absorber package is preferably in the form of a plate installed in a perforated sheet metal cassette (not shown here). This can optionally also be color coated. The two rear absorber packs 3, 4 are each preferably in the form of a link pack (not shown here) in which the respective plate is integrated. According to the measurement specification, they can be arranged behind the absorber package on the inside of the room.

A backdrop package includes a backdrop frame into which the panel is fitted. Thus, the plate can be inserted into the link frame and held by projections on the inner walls or on the edges of the link frame on the inner walls. In particular, these projections can run along several, in particular all, sides of the connecting link frame. Thus the panels are supported along their edges and can be slid into the frame guided by the projections. For example, the panels can be inserted from above. The backdrop frame is slightly wider than the inserted plate. It would also be possible to provide a groove in the frame in which the plate is inserted. For additional support and to prevent the panels from bulging, a strip, for example a perforated strip, can be drawn from one side of the link to the other behind a panel.

In each baffle frame, typically exactly one plate is used along the direction of the sound. It is possible for several panels to be placed one on top of the other, for example if the panels are made in a smaller size than the frame. For example, a panel could be 1200 x 600mm, while the height of the backdrop frames could be around 3 meters, allowing multiple panels to be stacked on top of each other have to be used. In a backdrop frame, the panel or panels can be formed from exactly one type of mineral wool or have a layered structure of layers of different types of mineral wool.

The backdrop frame can be perforated or made of smooth sheet metal. When the sets of backdrops are set up, they can be placed on the ground and stacked on top of each other if necessary. This is particularly advantageous for room heights greater than 3 meters, because the backdrop frames should not be chosen arbitrarily large to ensure stability. To prevent tipping and to set the distances safely, the scenes can be connected, for example screwed, to brackets that are attached to the walls.

The air layers between the individual packages can optionally be used for installations of all kinds (cables, pipes, etc.), which is not shown here.

figure 2 shows a section of the embodiment described above. Here the fiber directions are indicated by hatching.

figure 3 FIG. 12 shows an oblique view of an absorber unit which is designed essentially as in the first embodiment, but which has a boundary surface 7. FIG. No wall shown here, as the absorber unit can in principle also be used free-standing.

The boundary surface can be arranged, for example, at a distance of c=100 mm from the third absorber package 4 and preferably has a high flow impedance. A cavity resonator is thus also produced between the boundary surface and the third absorber package. Again, the distance can be chosen differently.

It should be understood that features mentioned in the embodiments described above are not limited to these specific combinations and can also be in any other combination as long as they fall within the scope of the invention, which is defined solely by the appended claims.

Claims (14)

1. An absorbing unit (1) for absorbing sound, in particular in closed rooms, comprising a plurality of plates (2, 3, 4) made of sound-absorbent material, wherein at least two adjacent plates (2, 3, 4) are spaced from each other for creating an air space (8) therebetween thus forming a cavity resonator for frequencies below 50 Hz,

   characterized in that the absorbent material comprises an anisotropic fabric including fibers,

   wherein the plates are configured and arranged such that the fibers in at least one of the plates (2, 3, 4) run along the direction of the plate sequence (5) in the absorbing unit (1).
2. The absorbing unit according to claim 1, wherein the cavity resonator has a natural frequency of less han 50 Hz,
   in particular less than 40 Hz, more particularly of less than 35 Hz and in particular of 30 Hz.
3. The absorbing unit according to any one of the preceding claims, wherein the absorbent material comprises mineral wool or open-cell foams.
4. The absorbing unit according to any one of the preceding claims, wherein the plates (2, 3, 4) made of absorbent material are configured two exhibit inherent stability.
5. The absorbing unit according to any one of the preceding claims, wherein the absorbent material comprises fibers and the plates (2, 3, 4) are arranged such that the direction of the fibers between plates alternates between the direction of the plate sequence (5) and perpendicular to the direction of the plate sequence (5).
6. The absorbing unit according to any one of the preceding claims, wherein the absorbent material comprises fibers comprising at least three plates (2, 3, 4), wherein the fibers of the middle one of the three plates (3) extend along the direction of the plate sequence (5) and the fibers of the other two plates (2, 4) extends transverse to the direction of the plate sequence (5).
7. The absorbing unit according to any one of the preceding claims, wherein the thickness of the plates (2, 3, 4) is between 150 mm and 300 mm and/or wherein the distances between the plates (2, 3, 4) are between 100 mm and 200 mm.
8. The absorbing unit according to any one of the preceding claims, wherein the plates (2, 3, 4) have equal or at least partially different thicknesses and distances.
9. The absorbing unit unit according to any one of the preceding claims, comprising at least three of said plates (2, 3, 4), wherein the thickness of the middle plate (3) of said three plates is smaller than the thickness of the two adjacent plates (2, 4) and the two adjacent plates (2, 4) differ in thickness.
10. The absorbing unit according to claim 10, wherein the absorbing unit (1) comprises a boundary surface (7) disposed adjacent one of the two outer panels (4), and wherein the plate (4) closest to the boundary surface (7) is thicker than the middle panel (3) and thinner than the panel (2) furthest from the boundary surface (7).
11. The absorbing unit according to any one of the preceding claims, comprising three plates or the three of said plates (2, 3, 4), wherein said absorbing unit (1) comprises the or a boundary surface (7) arranged adjacent to one of the two outermost plates (2, 4), wherein the distance between the middle plate (3) of the three plates and the plate (4) closest to the boundary surface (7) is greater than the distance between the plate (4) closest to the boundary surface (7) and the boundary surface (7) and smaller than the distance between the middle plate (3) and the plate (2) furthest from the boundary surface (7).
12. The absorbing unit according to any one of the preceding claims, wherein the total thickness of the absorber unit (1) is less than or equal to 1.5 m, preferably less than 1.4 m, in particular 1.2 m.
13. The absorbing unit according to any one of the preceding claims, wherein at least one of the plates (2, 3, 4) is covered by a perforated plate on one or both main sides of the plate or is configured in the form of a cassette made of perforated plate.
14. The absorbing unit according to any one of the preceding claims, wherein at least one of the plates (2, 3, 4) is integrated into a baffle package.

Images