TECHNICAL BACKGROUND OF THE INVENTION

5 The present invention relates to a diffuser for an outlet of a duct or a chamber containing a flow of gas, such as air, comprising a sound damping device and an interconnection means for allowing said sound damping means to be connected to said duct or chamber, the sound damping device comprising a first element including at least one first wall of a first channel having a first channel inlet and a first channel outlet, said first element comprising a guide L0 means further defining said first channel.

Such a diffuser is known from US 3 031 944.

A diffuser for an air-conditioning apparatus is known from DE 36 42 056. The described

L5 apparatus suffers from the drawback that it only controls the direction of the flow, however without reduction of noise from the apparatus.

An acoustic energy dissipative sheet material in the form of micro-slit sheets is known from WO 97/27370.

10

Another acoustic energy dissipative sheet material in the form of micro-cracks in sheets is known from WO 99/34974.

SUMMARY OF THE INVENTION

15 An object of the invention is to provide a diffuser having improved sound damping properties substantially without affecting the flow through the outlet of the diffuser.

This object has been achieved by a diffuser of the initially defined kind, wherein

it further comprises the sound damping device further comprises a second element including at

30 least one second wall of a second channel having a second channel inlet and a second channel outlet, said first and second elements together forming a stack or roll having an inlet region and an outlet region, wherein at least a portion of at least one of said first and second elements comprises an acoustic energy dissipative sheet material, in that said second element comprises a second guide means further defining said second channel; and in that said first and second

35 guide means are arranged in relation to one another in such a way that the first channel forms a first angle in relation to the second channel, said sound damping device being adapted to receive a gas from said duct or chamber via the inlet region and to exit said gas via the outlet region of said stack of elements.

5 Hereby, acoustic energy losses are achieved directly in the channel walls between the walls of the channels inclined in relation to the general flow of the duct. Thus, the different directions of the channels will create a local pressure difference over the energy dissipative walls, such that acoustic energy will be dissipated.

L0 Furthermore, a reduced manufacture cost is achieved compared to sound dampers comprising soft sound damping material.

Suitably, said interconnection means is adapted to fit a corresponding connection means of said duct or chamber, such that said gas is allowed to enter said sound damping element.

L5

Preferably, said interconnection means is provided with a connection member for connecting said inlet region of the sound damping device to said duct or chamber. Hereby, a secure connection of the diffuser to the duct or chamber is achieved.

10 Suitably, said first and second element comprises at least one wall shaped as a disc,

respectively, said elements having a central opening, the guide means extending from said bore towards the periphery of said disc, the discs being adapted to be connected to an outlet of said duct or chamber, the guide means being adapted to receive gas from said duct or chamber via said central opening, said guide guiding the gas towards the peripheral outlet of the disc.

is

Hereby is achieved a diffuser having radial outlets.

Preferably, said interconnection means comprises a cylinder having a cross-section

corresponding to the central opening of said disc, said cylinder being provided with openings, 30 said cylinder being adapted to receive said elements in such a way said elements are allowed to receive gas entering from the interior of the cylinder via said openings.

Hereby, a gas flow is allowed from the cylinder to the sound damping device. Alternatively, said first and second element comprises at least one wall formed as a plate, said plate being shaped as a parallelogram, such as a rectangle, a square, a rhombus.

Hereby, an alternative configuration of the sound damping device is achieved.

5 By both alternatives is achieved a lower transversal dimension than e.g. walls made of soft sound absorption material. Walls made of soft sound absorption material are less suitable than walls comprising plates or discs, since soft sound absorption material requires transversal space. In other words, the transversal dimension of walls made of plates is substantially not affected by the sound absorbing sheet material.

L0

Furthermore, soft sound absorption material cannot be readily and easily cleaned.

Suitably, a connection piece is arranged to supply the first and second elements with said gas.

Suitably, said guide means comprises a guide member close to the inlet of the first channel and L5 wherein said second guide means comprises a guide member close to the inlet of the second channel, said guide means comprises a further guide member close to the outlet of the first channel and wherein said second guide means comprises a further guide member close to the inlet of the second channel. Hereby, the inlet of the first and second channels is further defined.

10 Suitably, said guide member and further guide member of said guide means together define said first channel laterally, and wherein said guide member and further guide member of said second guide means together define said second channel laterally.

Hereby, the outlet of the first and second channels is even further defined.

Preferably, the total cross-section of the first channel and the second channel corresponds 15 substantially to that of the cross-section of the channel inside which the sound damping device is adapted to be mounted, such that the sound damping device does not cause a substantial pressure drop from the inlet to the outlet of the first and second channels, respectively.

Hereby is achieved an efficient sound damping device with low flow resistance.

30

Suitably, the sound damping device further comprises a third element including at least one third wall of a third channel having an inlet and an outlet, a fourth element including at least one fourth wall of a fourth channel having an inlet and an outlet, said third and fourth elements together forming a stack or roll together with the said first and second elements, wherein at least a portion of at least one of said third and fourth elements comprises an acoustic energy dissipative sheet material, wherein

5 said third element comprises a guide means further defining said third channel;

in that said fourth element comprises a guide means further defining said second channel; said third element being arranged in relation to said second element in such a way that the third channel forms a second angle in relation to the second channel, said fourth element being arranged in relation to said third element in such a way that the third channel forms a third angle

L0 in relation to the fourth channel.

Hereby, a stack of four elements is achieved.

Preferably, the first and third channels are directed in substantially the same direction, and L5 wherein the second and fourth channels are directed in substantially the same direction.

Hereby is achieved four channels dividing the general flow in two angled flows.

Suitably, said guide means comprises a guide member close to the inlet of the third channel and wherein said guide means comprises a guide member close to the inlet of the fourth channel, and wherein said guide means comprises a further guide member close to the outlet of the third 10 channel and wherein said guide means comprises a further guide member close to the outlet of the fourth channel.

Preferably, said guide member and further guide member of said guide means together define said third channel laterally, and wherein said guide member and further guide member of said fourth guide means together define said fourth channel laterally.

is

The third angle preferably corresponds substantially to the first angle. It should however be understood that the first and third channels angled in relation to one another and the second and fourth channels angled in relation to one another, as long as the first and third channels are angled away from the second and fourth channels.

30

Preferably, at least one of said elements includes the wall of a neighbouring element. Hereby, a compact stack of elements is achieved. Alternatively, at least one of said elements includes an intermediate wall separating said element from a neighbouring element. Hereby, a stack of individual elements is achieved.

Preferably, at least every second wall is provided with protrusions and/or indentations,

5 constituting distance holding members in relation to a neighbouring wall. Hereby, it is possible to build up the stack without use of separate distance holding members. Alternatively, each wall is provided with protrusions and/or indentations, constituting distance holding members in relation to a neighbouring wall.

L0 Suitably, the protrusions and/or indentations are arranged such that the cross-sectional area of said channels is substantially constant. Hereby is achieved a low pressure drop over the stack of elements.

Preferably, a housing or frame is adapted to support said stack or roll of elements, said housing L5 or frame being adapted to fit a connection means of said duct or chamber. Hereby, the stack or roll of elements can be readily and easily connected to said duct or chamber.

Suitably, the total cross-sectional area of the channels of the elements is at least 70 % of the cross-sectional area of said stack, preferably at least 90% of the cross-sectional area of said 10 stack, more particular at least 95% of the cross-sectional area, most particular at least 97% of the cross-sectional area of said stack. Hereby, sound absorption is achieved without

substantially influencing the flow in the duct, i.e. the larger the total cross-sectional area of the channel, the lower the flow resistance, or in other words, the smaller the total cross-sectional area of the walls of the stack, the lower the flow resistance.

is

Suitably, said acoustic energy dissipative sheet material is made of any one of plastic, metal, hard metal and ceramics.

Hereby, it is possible to adapt the use of the plates to the environment where the sound damping device is intended to be used, e.g. at high or low temperatures or in corrosive

30 environments.

Preferably, said acoustic energy dissipative sheet material is micro-porous.

Suitably, said acoustic energy dissipative sheet material is provided with micro-perforations, such as micro-slits. It may alternatively be provided with micro-cracks or circular holes. Alternatively, said acoustic energy dissipative sheet material comprises sintered metal or sintered cemented carbide.

Preferably, the thickness of said acoustic energy dissipative sheet material is in the range

-9 -8 -7

10 m - 2 mm, more particularly 10 m - 1 mm, even more particularly 10 m - 0,9 mm.

5 Suitably, the air flow resistance of said acoustic energy dissipative sheet material is in the range 100 - 10 000 RaylsMKS, more particularly in the range 200 - 1000 RaylsMKS, even more particularly in the range 300 - 500 RaylsMKS-

Alternatively, said acoustic energy dissipative sheet material comprises a membrane damping material in the form of a non-perforated sheet, the thickness of which is in the range 10 ^"9 m - 1 L0 mm, more particularly l O^ m - 0,7 mm, even more particularly 10 ^~7 m - 0,5 mm.

Preferably, said guide means of neighbouring elements are substantially straight. Alternatively, said guide means of neighbouring elements are curved in opposite directions.

L5

DRAWING SUMMARY

In the following, the invention will be described in more detail with reference to the annexed drawings, in which

10 Figures 1 A illustrates a sound damping device of a diffuser provided with a stack of rectangular elements forming flow channels in different directions;

Figures 1 B - 1 C illustrate alternative sound damping devices of a diffuser provided with a stack of square elements forming flow channels in different directions

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Figure 2 illustrates an alternative stack of elements comprising rectangular corrugated plates in a parallel relationship;

Figures 3A and 3B are exploded views of alternative stacks of elements comprising square 30 corrugated plates arranged in a cross-wise relationship; Figure 4 illustrates an alternative stack of elements comprising square plates having annularly shaped grooves and ridges;

Figure 5 is an exploded view of an alternative stack of elements comprising square plates having spirally shaped grooves and ridges;

Figure 6 illustrates an alternative stack of elements comprising square plates with bumps and indentations;

Figure 7 illustrates a diffuser including the sound damping device of Figs. 1 B arranged in an inter-connection piece having a rectangular cross-section;

Figure 8A illustrates diffuser including a sound damping device provided with a stack of crossed rectangular plates arranged as a tubular unit; arranged inside an inter-connection piece.

Figure 8B illustrates a variant of the diffuser shown in Fig. 8A;

Figure 8C is a perspective view of the diffuser shown in Fig 8B;

Figure 9 illustrates another kind of tubular diffuser;

Figure 10 illustrates schematically a diffuser having plurality of the sound damping devices shown in Fig 7 arranged at a common inter-connection piece.

Figure 1 1 A - 11 D illustrates alternative diffusers having one a sound damping device arranged at an inter-connection piece.

Figures 12A - 12B illustrate in cross-section in part of a diffuser provided with sound damping disc shaped elements;

Figures 12C - 12D illustrate a pair of discs of the diffuser shown in Figs. 12A - 12B. Figure 13A - 13C-illustrate a micro-perforated sound energy dissipative material. DETAILED DESCRIPTION

Fig. 1A shows a sound damping device 10 for a diffuser , such as an air inlet at the end of a ventilation duct for spreading the air in a room or a chamber, while absorbing disturbing sound 5 generated e.g. by a fan. The flow enters into the sound damping device in an inlet region 1 1 a and exits in an outlet region 1 1 b.

The sound damping device 10 is in the inlet region 1 1 a provided with a first channel 12a having a first channel inlet 13a; a second flow channel 16a having a second channel inlet 14a; a third L0 flow channel 12b having an third channel inlet 15a; and a fourth flow channel 16b having a

fourth channel inlet 17a.

Furthermore, in the outlet region 1 1 b of the sound damping device, the first channel 12a has a first channel outlet 13b; the second flow channel 16a has a second channel outlet 14b;

L5 the third flow channel 12b has a third channel outlet 15b; and the fourth flow channel 16b has a fourth channel outlet 17b.

The first and third channels 12a, 12b are arranged above one another,

10 The first, second, third and fourth channels 12a, 16a, 12b, 16b are arranged above one another.

The second and fourth channels 16a, 16b are however turned perpendicularly to the first and third channels 12 a, 12b. The first and third channels 12a, 12b are parallel to one another.

Likewise, the second and fourth channels 16a, 16b are parallel to one another.

15 The first, second, third and fourth channels 12a, 16a, 12b, 16b are defined by first, second, third, fourth and fifth rectangular walls 20a, 20b, 20c, 20d, 20e in the form of rectangular plates.

At the inlet region 1 1 a, guide means 21 in the form of a first sealing means 22a, 22b is arranged at a first peripheral region 24a of every second pair of walls 20b, 20c; 20d, 20e leaving said first 30 inlet opening 14a free and hereby defining said first and third channels 12a and 12b between every other second pair of walls 20a, 20b; 20c, 20d for a guiding first flow A.

Likewise, at the inlet region, guide means 21 second sealing means 23a, 23b is arranged at a second peripheral region 24b of every second pair of walls 20a, 20b; 20c, 20d leaving the second inlet opening 18a free and hereby defining said second and fourth channels 16a and 16b between every other second pair of walls 20b, 20c; 20d, 20e for a second flow B.

As can be understood from Fig 1A, a general flow G directed towards all the first to fourth flow 5 channels, will be divided by the first and third flow channels 12a, 12b and said second and fourth flow channels 16a, 16b into said first flow A and said second flow B.

As mentioned above, the walls 20a - 20e are in the form of rectangular plates, and thus, said second peripheral region 24b is perpendicular to said first peripheral region 24a.

L0

According to this embodiment, a first element 40a is constituted by the walls 20a, 20b, forming the first flow channel 12a, while a second element 40b is constituted by the wall 20b of the first element 40a and the neighbouring wall 20c, the walls 20b, 20c of the second element forming said second flow channel 16a.

L5

Likewise, a third element 40c is constituted by the wall 20c of the second element 40b and the neighbouring wall 20d, forming the third flow channel 14b. In the same manner, a fourth element 40d is constituted by the wall 20d of the third element 40c and the neighbouring wall 20e, the walls of the fourth element 40d forming said fourth flow channel 16b.

10

The walls 20a - 20e are at least partly made of a sound energy dissipative sheet material. Of course, one of the walls, a plurality of the walls or even all the walls may be made of said sound energy dissipative sheet material.

15 The plates are kept at a predetermined distance by means of a frame 51 comprising distance holder members 50 at each corner of the plates, hereby creating a constant cross-section of the flow channels 12a, 12b, 16a, 16b.

Alternatively, or in combination, said distance holding members 50 may be constituted by the 30 guide means 21 , i.e. the first and second sealing members 22a-22b, 23a-23b.

An end plate may be provided on top of the first element 40a in case further stability would be needed. In order to further define the flow channels 12a, 16a, 12b, 16b, it is preferable, but not necessary, that guide means 21 is arranged in the outlet region 1 1 b in a corresponding manner, i.e. opposite to that of first and second sealing members 22a-22b, 23a-23b. In this way, a straight flow A is created in the first and third channels 12a, 12b, and a straight flow B is created in the second and fourth channels 16a, 16b, flow A being perpendicular to flow B.

After having passed the sound damping device, flows A and B exit via the outlet region 1 1 b to the surroundings, e.g. inside a chamber or a room. It should be noted that the sound damping device may comprise solely the elements 40a, 40b forming the first and second channels 12a, 12b arranged perpendicular to one another.

Figure 1 B shows another alternative, according to which the first, second, third, fourth, fifth and sixth walls 20a, 20b, 20c, 20d, 20e, 20f in the form of square plates are provided with guide means 21 in the form of elongated folds 52, also constituting integrated distance members 50. Wall 20g is an end plate 61 without folds. For better understanding of the Fig. 1 B, a distance is shown between the walls 20b, 20c; 20d, 20e; and 20f, 20g, respectively.

Every second wall 20a, 20c, 20e is turned perpendicularly to every other second sheet 20b, 20d, 20f. Thus, the elongated folds 52 of the first wall 20a bear against the perpendicularly arranged second wall 20b, hereby forming a first flow channel 12a divided into parallel channels between the folds 52. Likewise, the elongated folds 52 of the second wall 20b bear against the perpendicularly arranged third wall 20c, hereby forming a second channel 16a divided into parallel channels between the folds 52.

It should be noted that in Fig. 1 B, more or less only one of the elongated folds 52 can be seen of the second wall 20b, and in front of that particular fold 52, one of the second channels 16a is formed. This relates correspondingly to the fourth wall 20d and the sixth wall 20f. In a manner corresponding to what has been described above, the elongated folds 52 of the third wall 20c bear against the perpendicularly arranged fourth wall 20d, hereby forming a third flow channel 12b divided into parallel channels between the folds 52. Likewise, the elongated folds 52 of the fourth wall 20d bear against the perpendicularly arranged fifth wall 20e, hereby forming a fourth flow channel 16b divided into parallel channels between the folds 52. Furthermore, the elongated folds 52 of the fifth wall 20e bear against the perpendicularly arranged sixth wall 20f, hereby forming a fifth flow channel 12c divided into parallel channels between the folds 52. Likewise, the elongated folds 52 of the sixth wall 20f bear against a 5 perpendicularly arranged seventh wall 20g, hereby forming a fourth flow channel 16c divided into parallel channels between the folds 52. Of course, also the seventh wall 20g may be shaped with folds 52 in order to form a further flow channel together with a further wall etc.

Each wall 20a - 20f contacts a neighbouring wall provided with folds and turned perpendicularly L0 thereto, hereby forming first, third and fifth flow channels 12a, 12b, 12c perpendicular to second, fourth and sixth flow channels 16a, 16b, 16c.

Also in this case, the first element 40a is constituted by the first and second walls 20a, 20b, forming the first channel 12a;

L5 the second element 40b is constituted by the second wall 20b of the first element 40a and the neighbouring third wall 20c, the walls of the second element 40b forming said second channel 16a;

the third element 40c is constituted by the third wall 20c of the second element 40b and the neighbouring fourth wall 20d, forming the third channel 12b; and the fourth element 40d is 10 constituted by the fourth wall 20d of the third element 40c and the neighbouring fifth wall 20e, the walls of the fourth element 40d forming said fourth channel 16b.

Furthermore, a fifth element 40e is constituted by the fifth wall 20e of the fourth element 40d and the neighbouring sixth wall 20f, the walls of the fifth element 40e forming said fifth channel 12c. is

A sixth element 40f is constituted by the sixth wall 20f of the fifth element 40e and the neighbouring seventh wall 20g (i.e. the end plate 61 ), the walls of the sixth element forming said sixth channel 16c.

30 It should be noted that the guide means 21 in the form of the elongated extension of the folds 52 connected to a neighbouring wall avoids the need for a sealing means dividing the flow G into flows A and B (cf. Fig 1A). For the same reason, a frame is not needed, since the stack of walls is self-supporting. Furthermore, in case the folds comprise an acoustic energy dissipative material, this will add to the sound damping effect, since the sound waves will hit the acoustic energy dissipative material more often than what is the case in the embodiment shown in Fig 1A.

According to an alternative embodiment, and as shown in Fig. 1 C, the first element 40a is 5 constituted by the first wall 20a provided with guide means in the form of distance holding

means 50 in the form of folds 52 in the manner corresponding to what is described in connection with Fig. 1 B, but resting against a first intermediate wall 60a. Thus, a number of parallel first channels 12a are formed between each fold 52 and the first intermediate wall 60a.

L0 Likewise, the second element 40b is constituted by the second wall 20b provided with folds 52 resting against a second intermediate wall 60b, such that a number of parallel channels 16a are formed between each fold 52 and the second intermediate wall 60b.

Again, the third element 40c is constituted by the third wall 20c provided with folds 52 resting L5 against a third intermediate wall 60c, such that a number of parallel channels 14b are formed between each fold 52 and the third intermediate wall 60c.

Likewise, the fourth element 40d is constituted by the fourth wall 20d provided with folds 52 resting against a fourth intermediate wall 60d, such that a number of parallel channels 16b are 10 formed between each fold 52 and the fourth intermediate wall 60d.

In order to create perpendicularly arranged channels, the first element 40a is turned

perpendicularly to the second element 40b, while the second element 40c is turned

perpendicularly to the third element 40d etc.

is

Of course, in the embodiments of Figs. 1 B and 1 C, further or less elements may be provided in order to create further or less channels. In particular, the stack of elements may comprise solely the elements 40a, 40b forming the first and second perpendicular channels 12a, 12b.

30 Also in this case, the elongation of the folds 52 avoids the need for sealing members for dividing the flow G into A and B (cf. Fig 1 A). Unless the elements 40a - 40d are welded or glued together, a frame may be needed in order to keep the elements 40a - 40d together. On the other hand, in the embodiments of Figures 1 B and 1 C, a sealing member may of course be arranged in the inlet region 1 1 a at the edge of every second pair of walls in a manner corresponding to that of what shown in Figure 1 A, and optionally in the outlet region 1 1 b for creating flow channels 12a, 12b and 12c for flow A and flow channels 16a, 16b and 16c for 5 flow B.

In the embodiment of Figs 1 C, not only the walls 20a - 20d are at least partly made of a sound energy dissipative sheet material, but any one, a plurality or all of the first to fourth intermediate walls 60a - 60d may be partly or completely made of such material.

L0

An end plate may be provided on top of the first element 40a in order to add to the stability.

It should be noted that the elements 40a - 40d of Fig 1 A may also be constituted by a pair of walls as shown in Fig. 1 C, however without folds.

L5

Fig. 2 shows an alternative embodiment, according to which the sound damping device 10 comprises walls 20a - 20e in the form of rectangular corrugated plates with ridges 70 and valleys 72. The ridges 70 and valleys 72 of the corrugations are arranged in the same vertical plane by means of a frame 51 comprising distance holding members 50, hereby creating a 10 constant cross-section of the flow channels 12a, 12b, 16a and 16b, respectively.

In order to divide the flow G into a flow A and a flow B, the walls 20a, 20b, constituting the first element are provided with guide means 21 in the form of a first sealing member 22a at first peripheral region 24a. The walls 20b, 20c, constituting the second element 40b are provided 15 with guide means 21 in the form of a second sealing member 23a, at second peripheral region 24b. The walls 20c, 20d, constituting the third element 40c, are provided with guide means 21 in the form of a third sealing member 22b at the first peripheral region 24a. Likewise, the walls 20d, 20e, together constituting the fourth element 40d, are provided with guide means 21 in the form of a fourth sealing member 23b at the peripheral region 24b.

30

The flow A will be forced up the ridges 70 and down the valleys 72, while the flow B will be substantially straight. In the embodiment of Fig 2, at least every second of the walls 20a - 20e, but preferably each wall is at least partly made of a sound energy dissipative sheet material. However, all of the walls 20a - 20e may at least partly be made of a sound energy dissipative sheet material. Of course, the walls 20a - 20e may be completely made of a sound energy dissipative sheet 5 material.

Of course, an end plate may be provided on top of the first element 40a and under the third element 40c in order to add to the stability.

L0 Fig. 3A shows in a manner corresponding to that of Fig 1 B the sound damping device 10,

including walls 20a - 20f, however in the form of corrugated plates, having a substantially square shape after corrugation. However, according to this embodiment, the walls 20a - 20f are arranged such that the ridges 70 and valleys 72 of neighbouring sheets are substantially in a perpendicular relationship and are resting against one another, such that the ridges 70 and

L5 valleys 72 constitute distance holding members 50 in relation to the neighbouring wall 20a - 20f (for better understanding of the Fig. 3A, the walls are shown somewhat separated from one another). The walls 20a-20f thus form a stack of substantially square corrugated plates, each having an end region 24a, 24b perpendicular to one another.

10

The square corrugated walls 20a-20f may be glued or welded together at regions or points where they rest against one another. The walls 20a - 20f may also be kept as a stack by a frame, but in case they are glued or welded together, the stack is self-supporting without need for a frame. By gluing or welding the ridges 70 and valleys 72 towards one another, guide 15 means is formed for the respective channels.

The first element 40a is constituted by the first and second walls 20a, 20b. The second element 40b is constituted by the second and third walls 20b, 20c. Likewise, the third element 40c is constituted by the third and fourth walls 20c, 20d. Furthermore, the fourth element 40d is 30 constituted by the fourth and fifth walls 20d, 20e. Yet furthermore, the fifth element 40e is

constituted by the fifth and sixth walls 20e, 20f.

The first, third and fifth flow channels 12a, 12b, 12c are created by arranging a guide means 21 in the form of a sealing (not shown) at the end region 24a of and between every second wall 20b, 20c; 20d, 20e of the stack. The second and fourth flow channels 16a, 16b are created by arranging a sealing (not shown) at the perpendicular end region 24b and between every other second wall 20a, 20b; 20c, 20d; 20e, 20f of the stack. The sealing members have been omitted for better understanding of the figure.

5

Consequently, the first, third and fifth flow channels 12a, 12b, 12c are perpendicular to the second and fourth channels 16a, 16b.

Optionally, guide means 21 in the form of sealing members may be arranged in the outlet region L0 1 1 b in a corresponding manner, i.e. opposite to the sealing members at the inlet region, for creating a substantially straight flow (i.e. apart from corrugations) through the perpendicular channels of the stack.

In case an end wall is added on top of wall 20a, an additional flow channel them between would L5 be formed them between. Likewise, in case an end wall is provided underneath the sixth wall 20f, an additional sixth flow channel would be formed them between. On the other hand, it would of course be possible to add further corrugated plates and arrange them in the stack in the manner described.

10 Alternatively, as shown in Fig. 3B, underneath the end plate 61 , the first element 40a comprises the corrugated first wall 20a and a first intermediate wall 60a, in a manner corresponding to that of Fig 1 C. Distance holding members 50 towards the end plate 61 are provided in the form of the ridges 70 of the corrugated wall 20a, the ridges 70 of which being adapted to rest against the end plate 61 , such that a plurality of first channels 12a are formed between each ridge 70 and

15 the end plate 61 (for better understanding of the Fig. 3B, the walls are shown somewhat

separated from one another).

On the opposite side of the first wall 20a, the valleys 72 rest against a first intermediate wall 60a, together forming a first element 40. A plurality of additional first channels 12a' are formed 30 between each valley 72 and the first intermediate wall 60a.

The end plate 61 thus forms together with the first wall 20a the first channel 12a, while the first element 40a as such forms an additional first channel 12a', parallel the first channel 12a, both intended for the first flow A. In a corresponding manner, the second element 40b comprises the second wall 20b and the second intermediate wall 60b, a third intermediate wall 60c and the second corrugated wall 20b arranged between the second and third intermediate walls 60b, 60c. The ridges 70 of the 5 second corrugated wall 20b constitutes distance holding means 50 in relation to the second intermediate wall 60b, such that a plurality of second channels 16a are formed between the ridges 70 and the second intermediate wall 60b.

Likewise, the valleys 72 of the second corrugated wall 20b constitute distance holding means 50 L0 in relation to the third intermediate wall 60c, such that a plurality of additional second channels 16a' are formed between the ridges 70 and the second intermediate wall 60b, the second channels 16a and the additional second channels 16a' being in a parallel relationship and constituting channels for the second flow B.

L5 The second corrugated wall 20b of the second element 40b is arranged perpendicularly to the first corrugated wall 20a of the first element 40a.

The third element 40c comprises the third intermediate wall 60c, a fourth intermediate wall 60d and a third corrugated wall 20c, arranged between the third and fourth intermediate walls 60c,

10 60d. The ridges 70 of the third corrugated wall 20c constitutes distance holding means 50 in relation to the third intermediate wall 60c, such that a plurality of third channels 12b are formed between the ridges 70 and the third intermediate wall 60c. Likewise, the valleys 72 of the third corrugated wall 20c constitutes distance holding members 50 in relation to the fourth intermediate wall 60d, such that a plurality of additional third channels 12b' are formed between

15 the valleys 72 and the fourth intermediate wall 60d. The third channels 12b and the additional third channels 12b' are in a substantial parallel relationship and constitute channels for the first flow A.

The third corrugated wall 20c of the third element 40c is arranged perpendicularly to the second 30 corrugated wall 20b of the second element 40b.

The fourth element 40d comprises the fourth intermediate wall 60d, a fifth intermediate wall 60e and a fourth corrugated wall 20d, arranged between the fourth and fifth intermediate walls 60d, 60e. The ridges 70 of the fourth corrugated wall 20d constitutes distance holding means 50 in relation to the fourth intermediate wall 60d, such that a plurality of fourth channels 16b are formed between the ridges 70 and the fourth intermediate wall 60d. Likewise, the valleys 72 of the fourth corrugated wall 20d constitutes distance holding means 50 in relation to the fifth intermediate wall 60e, such that a plurality of additional fourth channels 16b' are formed 5 between the valleys 72 and the fifth intermediate wall 60e. The fourth channels 16b and the additional fourth channels 16b' are in a parallel relationship and constitute channels for the second flow B.

The fourth corrugated wall 20d of the fourth element 40d is arranged perpendicularly to the third L0 corrugated wall 20c of the third element 40c.

The fifth element 40e comprises the fifth intermediate wall 60e, a sixth intermediate wall 60f and a fifth corrugated wall 20e, arranged between the fourth and fifth intermediate walls 60e, 60f. The fifth intermediate wall 60e and the fifth corrugated wall 20e together form a fifth channel L5 12c, and the sixth intermediate wall 60f and the fifth corrugated wall 20e together form an

additional fifth channel 12c' in a manner corresponding to that of the first and the third elements 40a, 40c. Thus, the fifth channel 12c and the additional fifth channel 12c' are parallel to one another.

10 Furthermore, the fifth corrugated wall 20e of the fifth element 40e is arranged perpendicularly to the fourth corrugated wall 20d of the fourth element 40d.

The fifth channel 12c and the additional fifth channels 16c' are in a parallel relationship and constitute channels for the second flow A.

is

Consequently, the flow channels and additional flow channels 12a, 12a', 12b, 12b', 12c, 12c' of the first, third and fifth elements 40a, 40c, 40e are parallel to one another and perpendicular to the flow channels and additional flow channels 16a, 16a', 16b, 16b' of the second and fourth elements 40b, 40d in order to divide the flow G in a first flow A and a second flow B,

30 substantially perpendicular to one another through the sound damping device 10.

By this configuration, the cross-section of all channels 12a, 12b, 16a and 16b will be substantially constant and have substantially the same cross-sectional dimensions. Also in this case, the elongation of the ridges 70 and the valleys 72 avoids the need for a distance holding members in the form of sealing members for dividing the flow G into first flow A and second flow B. Thus, as shown in Fig. 3A, the flow G will be divided into flows A and B without need for a distance holding member in the form of a frame in the corner of the plates.

5

It would of course be possible to add guide means 21 in the form of sealing members between every second element of the stack in a manner corresponding to what is described in connection with Fig 3A.

L0

Again, the walls 20a - 20f and the intermediate walls 60a - 60f may be kept together as a stack by a frame 51 . Hereby, mounting as a single unit at the outlet into a chamber or a room of a ventilation duct is facilitated.

L5 Fig. 4 shows a stack of substantially square walls 20a, 20b, 20c, 20d, 20e, 20f, 20g, 20h, 20i, 20j, 20k, 20I in the form of plates provided with annularly shaped ridges 70 and valleys 72. A portion of the stack has been cut off for improving understanding of the figure.

Guide means 21 in the form of sealing members 22a - 22e are provided in the peripheral region 10 24a and between every second wall at the inlet region 1 1 a and the outlet region 1 1 b of the

sound damping element. Furthermore, sealing members 23a - 23f are provided in the perpendicular peripheral region24b and between every other second wall at the inlet and outlet regions 1 1 a, 1 1 b.

15 Hereby, distance holding means 50 is provided for keeping the stack of walls 20a - 201 at a desired distance from one another, in order to divide the general flow G into a first flow A in flow channels 12a - 12f and a second flow B in flow channels 16a - 16e.

Preferably, but not necessarily, the size of the sealing members 22a - 22e and 23a - 23f are 30 chosen such that a constant cross-section of the flow channels 12a - 12f and 16a - 16e is

achieved. Even though the size of the sealing members 22a - 22e may be the same as the size of the sealing members 23a - 23f, it is contemplated that the size of the sealing members 22a - 22f may be different from the size of the sealing members 23a - 23f.

5 Fig. 5 shows in an exploded view a stack of walls 20a - 20e in the form of plates provided with a spirally shaped ridge 70 and a spirally shaped valley 72. By turning the sheets at an angle, preferably perpendicularly or 180° to one another, the ridge 70 and the valley 72 of neighbouring sheets will constitute distance holding means 50. The stack of walls may be glued or welded together at contact areas between the ridges 70 and the valleys, or just rest towards one

L0 another.

It would of course be possible to arrange the corrugated plates in a stack of walls at a distance from one another by means of a suitable distance holding means (cf. Fig. 4), instead of gluing of welding them together.

L5

Disregarding whether the walls of the stack are glued together, guide means are provided for keeping the walls at a distance from one another and for separating the flow G in flows A and B in a manner corresponding to that described in connection with Fig. 4. Thus, guide means in the form of sealing members (omitted form the figure for facilitating understanding thereof) are 10 provided in the peripheral region and between every second wall at the inlet region 1 1 a and the outlet region 1 1 b of the sound damping element. Furthermore, guide means sealing members are provided in the perpendicular peripheral region and between every other second wall at the inlet and outlet regions 1 1a, 1 1 b.

15 The result is also in this case a substantially straight flow path, for creating a substantially

straight flow (apart from what is caused by the spiral ridges and valleys) through the mutually perpendicular channels of the stack,

It would also be possible to provide the walls with two or more parallel spirals of ridges and 30 valleys. It would furthermore be possible to turn every second wall upside down instead of

turning them 90° or 180°. Fig. 6 shows a stack of walls 20a - 20e in the form of square plates provided with protrusions in the form of positive bumps 70' surrounded by similarly shaped indentations in the form of negative bumps 72' in the opposite direction.

5 First sealing members 22a, 22b are arranged between every second wall at regions 24a on one side, while second sealing means are provided between every other second wall at

perpendicular region 24b for dividing a flow G in a first flow A in channels 12a - 12c and a second flow B in flow channels 16a, 16b, 16c.

L0 Combined guide means 21 and distance holding means 50, in the form of sealing members 22a- 22c and 23a - 23b are shaped in such a way that positive bumps 70' of neighbouring walls are placed above one another and negative bumps 72' are placed above one another in order to achieve flow channels 12a - 12c preferably of the same cross-section, and flow channels 16, 16b of the same cross-section. In addition, or alternatively, a frame may be used for achieving a

L5 desired cross-section of the mutually perpendicular flow channels and/or for facilitating mounting at the end of a duct or chamber, such as a ventilation duct.

Fig. 7 shows the sound damping device 10 of the kind shown and explained in connection with Fig. 1 B, arranged at the end of an inter-connection piece 103 having rectangular cross-section.

10 The inter-connection piece 103 is intended to be connected to a not shown connection piece of a duct or chamber containing a pressurized gas, such as air in a ventilation duct. The sound damping device is provided with square walls (see 20a - 20f in Fig 1 B) and an end plate 61 in such a way that the flow cannels 12a, 12b, 12c and the flow channels 16a, 16b, 16c divide the general flow G into first flow A and second flow B. In order to achieve this, the corner of the

15 stack of plates, or in other words, the diagonal of the stack of plates is directed towards the flow direction G.

After the sound damping device, in the direction of flow of the interconnection piece 103, the flows A and B exit in the surrounding atmosphere, or into a room or chamber. An additional end 30 plate may be provided in the bottom of the stack, i.e. below channel 16c. As already explained in connection with Fig 1 B, the guide means 21 in the form of elongated folds 52 not only constitute distance holding means 50, but also sealing members; if needed, the folds are welded or glued towards the neighbouring wall. It should be noted, the diffusor 101 may instead be provided with the sound damping device of the kind shown and explained in connection with Fig 1 C, i.e. comprising intermediate walls.

It is contemplated that in case a square shape of the walls of the sound damping device is 5 chosen, the sound damping device of any one of the embodiments shown and discussed in connection with Figs. 2, 3A, 3B, 4, 5 and 6 may be used inside the diffusor 101 .

The cross-section of the duct may of course be square rather than rectangular.

L0 Fig. 8A shows a circular cylindrical diffusor 101 comprising an interconnection piece103

provided with a sound damping device 10 comprising a frame 51 in the form of a circular cylindrical housing 90 and rectangular elements 40 or walls 20 as shown in etc. arranged at an angle relative to one another in the range 10° - 150°, more particular 30° - 140°, even more particular 40° - 100°, most particular 60° - 94°.

L5

The circular cylindrical housing 90 has open ends 91 a, 91 b parallel to one another and across an axis through its elongation. Thus, the edges of elements 40 or walls 20 extend through the open ends 91 a, 91 b of the cylinder. Of course, the width of the walls becomes narrower in a direction across the walls due to the cylindrical shape of the housing 90.

10

The diffusor can be connected directly to a circular opening or a circular cylindrical connection piece of a not shown duct of chamber. Preferably, the circular cylindrical connection piece is adapted to receive the inter-connection piece 103 in such a way that a tight fir is accomplished.

15 As shown in Figs 8B and 8C, the edges the rectangular elements 40 or walls 20 may be cut in order to conform to the open ends 91 a, 91 b of the circular cylindrical housing 90. Thus, the walls 20 etc. will after cutting be in the form of a non-perpendicularly angled parallelogram, i.e. in case the sides are of equal length, each wall would have the shape of a rhombus.

30 The sound damping device 10 is thus formed as a circular cylindrical unit 92, provided with elements 40a - 40k including walls 20a - 20x and furthermore guide means 21 in the form of sealing members 22a - 22g; 23a - 23f. The first sealing members 22a, 22b etc. and the second sealing members 23a, 23b etc. allow the flow G to be divided in a cross-wise manner inside the cylinder. Due to the circular cross- section of unit 92, the width of the rhombus 20e is broader than the width of the rhombus 20a and 20.

5

It would of course be possible to arrange a sound damping device provided with rectangular elements or walls inside a duct having a rectangular (see Fig. 7) or square cross-section.

According to the embodiment of Fig 9, a first wall 20a (partly broken away) in the form of a L0 corrugated plate is formed to a cylindrical shape and is placed between a guide means 21 in the form of a circular cylindrical housing 90 (partly broken away), and a first intermediate wall 60a (partly broken away) formed to a circular cylindrical shape, however of a smaller diameter than that of the housing 90. Thus, the axial extension of the circular cylindrical housing 90, the first wall 20a, the intermediate wall 60a, the second wall 20b is preferably substantially the same as L5 that of the intermediate wall 60b, respectively.

The diameters of the housing 90 and the first intermediate wall 60a are chosen such that the ridges 70 if considered needed are allowed to be connected e.g. by gluing to the interior of the housing 90, while the valleys 72 if considered needed are allowed to be connected to exterior of 10 the first intermediate wall 60a. Hereby is created a first element 40a having a first flow channel 12a parallel to an additional first flow channel 12a'.

Furthermore, a second wall 20b in the form of a corrugated plate is formed to a cylindrical shape and is placed inside said first circular cylindrical intermediate wall 60a.

is

The diameter of the wall 20b is chosen such that its ridges 70 if considered needed are allowed to be connected to the interior of the first cylindrical intermediate wall 60a, e.g. by gluing. A second circular cylindrical wall 60b having a smaller diameter than that of the first cylindrical intermediate wall 60a, is placed inside said second wall 20b. The diameter of the second 30 cylindrical intermediate wall 60b is chosen such that the valleys 72 of the second corrugated cylindrical sheet 20b are allowed to be connected to the exterior of the second cylindrical intermediate wall 60b, e.g. by gluing or welding if considered needed. Hereby, a second element 40b is created having a second flow channel 16a parallel to an additional second flow channel 16a'.

The second corrugated cylindrical wall 20b is arranged such that the corrugations thereof are 5 substantially at an angle to the corrugations of the first corrugated cylindrical wall 20a. Thus the first flow channel 12a and its parallel additional first flow channel 12a', both for the first flow A are arranged at said angle to the second flow channel 16a and its parallel additional second flow channel 16a', both for the second flow B.

L0 The angle may be perpendicular, even though it may be in the range 10° - 150°, more particular 30° - 140°, even more particular 40° - 100°, most particular 60° - 94°.

In Fig 9 only two elements 40a, 40b have been shown, while further elements 40c, 40d etc. towards the centre of the cylinder have been omitted for better understanding of the figure.

L5

Alternatively, the first and second cylindrical intermediate walls 60a, 60b shown in Fig. 9 may be excluded. Instead, the first and second corrugated walls 20a, 20b may be directly connected to one another by connecting the valleys 72 of the first corrugated wall 20a perpendicularly to the ridges 70 of the second corrugated sheet wall 20b (cf. Fig. 3A).

10

Figure 10 shows schematically a diffusor 101 having a cylindrical body 118 with four radial or transversal outlets 1 16 and one axial outlet 1 17. To each outlets 1 16, 1 17, a sound damping device 10 according to any one of the previously described variants having square elements is connected via connection pieces 104. As shown schematically, the general flow G inside the 15 cylindrical body is divided into five general flows, in turn divided into flows A and B inside the sound damping devices 10. At the outlet region 1 1 b, the flow is diffused or distributed to the surroundings and is at the same time sound attenuated.

The shown cylindrical body 1 18, being part of the diffusor device 1 10, constitutes an

30 interconnection piece 103 adapted to be connected to a not shown connecting portion of a gas outlet of a duct or a chamber, the connecting portion having a slightly smaller or larger lateral dimension compared to the cylindrical body, such that a tight fit inside or outside the cylindrical body 1 18 is allowed. It should however be noted that the sound damping devices 10 may instead be connected directly to a chamber or duct via the connection pieces 104. In such a case the connection pieces 104 will constitute inter-connection pieces.

5 Figs 1 1 A - 1 1 B show an alternative configuration, according to which an inter-connection piece 103 is provided with sound absorbing elements 10, having walls provided with sound attenuating means. Each element 40a, 40b, 40c comprises a number of bent guide means 21 , having an inlet region 1 1 a and an outlet region 1 1 b. The guide means 21 are bent in opposite directions in every second layer, i.e. every second element has guide members bent in the same direction,

L0 whereas every other second layer has guide members bent in the opposite direction.

By this configuration, a diffusing effect is achieved in combination with a sound attenuating effect while the flow G inside the inter-connection piece is divided into flows A and B in the sound absorbing device 10.

L5 It should be noted that the sound absorbing device 10 may instead be connected directly to the outlet of a duct or a chamber.

Fig 1 1 C and 1 1 D shows an alternative configuration for creating a larger diffusing effect.

According to this alternative, the elements 40a, 40b, 40c, 40d continue along both sides of the 10 cylindrical body 1 18 of inter-connection piece 103 via the end of the cylindrical body (cf. Fig 10).

In Figs. 10 and 1 1A - 1 1 D, it should be understood the cross-section of the cylindrical body 1 18 may be circular, oval, or polygonal, such as triangular, rectangular, square, pentagonal etc. Figs. 12A - 12B show a diffusor 105 comprising a sound damping device 10 adapted to be 15 connected to a duct or a chamber. The diffusor 105 has a hollow cylinder 1 10 provided with radially arranged walls 20a, 20b in the form of discs 1 12a, 1 12b of equal diameter and an end plate 61 in the form of a disc of substantially the same diameter as the discs 1 12a, 1 12b. The hollow cylinder is also provided with an axial inlet 1 14 for a gas flow G and radial outlets 1 16 in the mantle 1 18 of the cylinder 1 10.

30

Every second disc 1 12a is provided on one side with guide means 21 in the form a plurality of fins 120a bent to an arc shape in a clockwise direction, while every other second disc 1 12b is provided on one side with guide means 21 in the form a plurality of fins 120b bent to an arc shape in a counter-clockwise direction, see also Figs 12C and 12D. It is contemplated that the guide means in the form of fins may instead be straight but still directed in opposite directions.

The opposite side of the discs 1 12a, 1 12b is flat, respectively.

5

The fin 120a of the disc 1 12a is connected to the flat side of the disc 120b. Likewise, the fin 120b of the disc 1 12b is connected to the flat side of the disc 120a.

Thus, in a manner corresponding to that of Fig 1 B, the first element 60a is constituted by the end L0 plate 61 and the wall 20a (i.e. the first disc 1 12a), the second element 60b is constituted by the wall 20a (i.e. the first disc 1 12a) and the wall 20b (i.e. the first disc 1 12b) etc.

A stack of discs 1 12a, 1 12b is arranged on the cylinder 1 18 in such a way that every second disc is provided with an arc-shaped, clockwise directed fin, while every second disc is provided L5 with an arc-shaped, counter-clockwise directed fin. On top of the uppermost disc 120a, the end plate 61 is provided.

Hereby, a plurality of first and second flow channels 12a, 16a are created between the neighbouring discs 1 12a, 1 12b and the fins 120a or 120b. The radial inner end of the first and 10 second flow channels is connected to the radial outlets 1 16 in the mantle 1 18 of the cylinder 1 10, respectively, while the radial outer end of the first and second flow channels 12a, 16a are open to the surroundings.

Hereby, the first flow channels 12a for flow A is angled in relation to the second flow channel 25 16a for flow B.

As can best be seen in 12B, the number of discs may be more than two. Of course, the numbers of discs is not limited to what is shown in fig. 10, and may extend towards close to the inlet. This relates correspondingly to the radial outlets 1 16.

30

It should however be noted that it would be possible to provide each disc 1 12b, 1 12c etc with an intermediate wall in the form of a disc (cf. the intermediate walls 60a - 60d of Fig. 1 C). Each such combination of a disc and intermediate wall in the form constituting the second element, third element etc. The number of walls of the different embodiments of the sound damping device described above are interchangeably applicable to the other embodiments, respectively. Likewise, the number of elements of the different embodiments of the sound damping device described above are 5 interchangeably applicable to the other embodiments, respectively. It should be noted that the number of walls may be as few as a single one, forming an intermediate wall of two elements.

In all above described embodiments, one of, a plurality of or all of the walls 20a, 20b etc. are at least partly provided with a sound energy dissipative sheet material. Of course, it may be L0 completely constituted by a sound energy dissipative sheet material.

The absorption degree of such a sound attenuation element 16 depends i.a. on the perforation degree. It is not difficult to calculate mathematically the perforation degree of a sheet or plate provided with circular holes. However, the perforation degree of a sheet or plate provided with micro-slits or micro-cracks is much more difficult to calculate. It is therefore preferable to L5 measure the airflow resistance in accordance with the accepted method described in ASTM C 522 - 73 for achieving a comparable size of the perforation degree, utilising the unit Rayls _M Ks It should in this context be noted that 1 Rayls _M Ks = 1 N-s/m ³ = 1 Pa s/m = 1 kg/s m ² .

One kind of a sound energy dissipative sheet material 140 is shown in Figs. 13A - 13C, being in the form of a micro-perforated sheet of plastic or metal, such as stainless steel or aluminium 10 provided with micro-slits 150. The air flow resistance of the micro-perforated sound absorbing element may be 400 Rayls _M Ks, even though it may be in the range 100 - 10 000 Rayls _M Ks, more particular in the range 200 - 1000 Rayls _M Ks, even more particular 300 - 500 Rayls _M Ks-

The micro-slits 150 are of the sound absorbing element are preferably made by cutting the sheet 140 by means of a knife roll having a wavy shape against another edge, hereby resulting in a 15 first slit edge 150a and a second slit edge 150b partly pressed out of the material plane.

Subsequently, the first and second slit edges 150a, 150b are pressed back by a subsequent rolling operation. Hereby, micro-slits 150 of a predetermined length 154 and predetermined width 156 are created. The width 156 is preferably in the range 10 ^~10 -10 ^"3 m. The length 22 of the micro-slits 18 may be as small as 10 ^~9 m, but may instead extend in substantially the whole 30 lateral extension of the wall 20a, 20b etc. comprising, constituted by a single sheet 140. It should be noted, that cutting may instead be performed by use of laser or a water jet cutter.

The micro-perforations may alternatively be performed as micro-cracks or as through holes of any shape, such as circular, triangular or polygonal. They may on the other hand be constituted by compressed metal fibres or a sintered material or be made of a non-woven or woven 5 material.

Hereby, an acoustic impedance is created by transmission losses between neighbouring channels.

A gas flow, e.g. by air in a duct or chamber, will create noise. The noise may in addition be L0 created by use of a fan connected to the duct or chamber e.g. in a ventilation system or water flowing in a water cooling system of a ventilation system. The noise may alternatively be created by use a compressor or a combustion engine even if not connected to the duct. This may be the case in the sitting compartment of a vehicle, such as a bus or a car.

The thickness of the sheet is in the range 10 ^"9 m - 2 mm, more particular 10 ^"8 m - 1 mm, even L5 more particular 10 ^"7 m - 0,9 mm.

It should also be noted that instead of micro-slits 150 the micro-perforated sound absorbing element may be provided with substantially circular through-holes, having a diameter of 10 ^"9 -10 ^"3 m.

It should also be noted that the length 154 and width 156 of the micro-slits 150 is chosen in 10 combination with the number of slits (or any other kind of the above described micro- perforations), in such a way that sheet 140 has perforation degree with the above described range of air flow resistance.

It should be noted that the sound absorbing device of all embodiments may be provided with a frame 51 or a housing.

is

Disregarding the use of the sound damping device according to the invention, it is important to reduce the flow resistance, such that the gas flow is substantially not affected.

Consequently, in order to reduce transmission losses, the reduction of the cross-section is to be 30 kept low. By choosing the thickness and/or number of the walls, it is possible to achieve a total cross- sectional area of the flow channels of the elements of at least 70 % of the cross-sectional area of said stack in order to. Hereby, a low flow resistance is achieved. On the other hand, by 5 choosing a predetermined shape of the walls, it is possible to achieve a total cross-sectional area of the flow channels of at least 90% of the cross-sectional area of said stack. Depending of the number of walls chosen, it is however possible to achieve total cross-sectional area of the flow channels of at least 95%, or even more than 97%.

L0 Example

A ventilation duct has a cross-section of 15 cm * 15 cm. A diffuser 101 in accordance with the invention is provided with a sound damping device 10 and inter-connection means 103 having a rectangular cross-section, in the manner shown in Fig 7.

L5 A stack of plates 20a - 20e, the plates having each a thickness of 1 mm, hereby forming six flow channels (cf. Fig 1 B).

The cross-section of the duct is, 15 * 15 cm = 225 cm ² , and the thickness of the five plates together is 5 mm. Thus, the cross-sectional area of the five plates together is 15 cm * 0,5 cm = 10 7,5 cm ² .

Consequently, the relation between the cross-sectional area of the inter-connection means 103 and the total cross-sectional area of the flow channels of the stack is (225 - 7,5) / 225 = 0,97, i.e. 97 %.

IS

First and third channels 12a, 12b are arranged perpendicularly to second and fourth channels 16a, 16b and in relation to the general flow G of the duct such that the first flow A as well as the second flow B is 45° in relation to the general flow G.

30 By the angled channels 12a, 12b, 16a, 16b in relation to the general flow direction G, sound energy losses are achieved directly in the channels, since the inlet of first, second, third and fourth all channels are all inclined in relation to the general flow of the interconnection means. Furthermore, since the plates are made of a micro-perforated material, sound energy losses will occur due to pressure differences between the channels 12a, 12b, 16a, 16b through the micro- perforations.

5 OPERATION

An air flow inside a duct, such as a ventilation duct exiting into the atmosphere or room via an air inlet, may cause noise from the fan creating the flow of air. By the diffuser 101 in accordance with the invention, the air is spread in different directions while simultaneously damping said LO noise.

The corresponding relates to a pressurized chamber provided with a gas under pressure, provided with a security valve and a diffuser. In such a case, the created noise is generated in the valve.

L5

Reference signs used

A first flow

B second flow

G general flow

10 sound damping device

1 1 a inlet region

1 1 b outlet region

12a first flow channel

12a' additional first flow channel

12b third flow channel

12b' additional third flow channel

12c fifth flow channel

12c' additional fifth flow channel

13a first channel inlet

13b first channel outlet

14a second channel inlet

14b second channel outlet 15a third channel inlet

15b third channel outlet

16a second flow channel

16a' additional second flow channel

5 16b fourth flow channel

16b' additional fourth flow channel

16c sixth flow channel

17a fourth channel inlet

17b fifth channel outlet

L0 20a - 20g wall

21 guide means

22a, 22b first and third sealing means

23a, 23b second and fourth sealing means

24a, 24b peripheral region

L5 40a first element

40b second element

40c third element

40d fourth element

40e fifth element

10 50 distance holding member

51 frame

52 fold

60a - 60d intermediate wall

61 end plate

25 70 ridge

70' positive bump

72 valleys

72' negative bump

90 circular cylindrical housing

30 91 a, 91 b open end

92 circular cylindrical unit duct

diffuser central bore

interconnection means connection piece

cylindera, 1 12b, 1 12c first disc, second disc, third disc axial inlet radial outlet

axial outlet cylindera, 120b fin

sheet

micro-slitsa first slit edge

b second slit edge

length

width