Sound absorbing device

Claim 2

Apparatus for damping a sound field propagating in a fluid propagation medium within a main channel (1) having a closed cross-sectional periphery, comprising at least one first lattice work (2) arranged in said main channel (1) for extending between a first longitudinal section and a second longitudinal section of the free main channel cross-section, said lattice work being comprised of first and second thin partition wall means crossing each other and subdividing the free channel cross-section in the manner of a guide blade into a plurality of partial channels (3) for juxtaposed and superposed branching between said first and second longitudinal sections, said partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimensions of said partial channels, said length being at least a quarter of the wavelength of the sound oscillation having the lowest fundamental frequency of said sound field, wherein at least predetermined ones of adjacent partial channels (3) have different lengths for producing different sound oscillation states therein to be out of phase in said predetermined ones of adjacent partial channels, whereby in said predetermined ones of adjacent partial channels local sound pressure differences are produced and distributed over their length, said partition wall means (2) between said predetermined ones of adjacent partial channels (3) of different lengths being permeable for the propagation medium, at least over a partial length for causing at least partly local sound pressure difference compensation of said local sound pressure differences by a flow of the propagation medium from the one of the predetermined ones of said adjacent partial channels (3) into the adjacent one thereof, said wall means comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium.

Claim 3

The sound damping apparatus as claimed in claim 1, wherein at least one (5) of the two faces (5,6) of said lattice work (2) at which the partial channels open into said first and second sections, respectively, is obliquely inclined with respect to the channel direction.

Claim 4

The sound damping apparatus as claimed in claim 1, wherein said main channel includes a bent elbow portion and said lattice work (2) is arranged in said elbow portion (7) of said main channel (1).

Claim 5

The sound damping apparatus as claimed in claim 1, wherein said first and second partition wall means comprise a plurality of first and second straight plate means, said first plate means running horizontally and parallel with said channel direction and said second plate means being arranged in a plane lying parallel with said channel direction and crossing said horizontal plate means at right angles thereto, whereby a plurality of said partial channels are formed having generally a rectangular cross-section.

Claim 6

A lattice work for damping a sound field propagation in a fluid propagation medium within a main channel, said lattice work comprising thin partition wall means crossing each other for subdividing the free main channel cross section in the manner of a guide blade, when placed into said main channel, for branching it between a first and a second longitudinal section of the main channel into a plurality of partial channels (3), said partial channels having a longitudinal dimension which is larger than the corresponding cross-sectional dimension of said partial channels, said lattice work being shaped to have said partial channels open at both end thereof, said longitudinal direction of said partial channels running in the direction of the main channel when the lattice work is placed into said main channel, wherein at least some of adjacent partial channels (3) have different lengths for the sound oscillation state therein, whereby in said adjacent partial channels local sound pressure differences are produced and distributed over their length, at least part of the partition wall means being permeable for the propagation medium for the local sound pressure transfer from one partial channel (3) into an adjacent one, to at least locally and partly compensate said local sound pressure differences, said partition wall means having a thickness of 3.5 mm.

Claim 7

A lattice work for damping a sound field propagation in a fluid propagation medium within a main channel, said lattice work comprising thin partition wall means crossing each other for subdividing the free main channel cross section in the manner of a guide blade, when placed into said main channel, for branching it between a first and a second longitudinal section of the main channel into a plurality of partial channels (3), said partial channels having a longitudinal dimension which is larger than the corresponding cross-sectional dimension of said partial channels, said lattice work being shaped to have said partial channels open at both end thereof, said longitudinal direction of said partial channels running in the direction of the main channel when the lattice work is placed into said main channel, wherein at least some of adjacent partial channels (3) have different lengths for the sound oscillation state therein, whereby in said adjacent partial channels local sound pressure differences are produced and distributed over their length, at least part of the partition wall means being permeable for the propagation medium for the local sound pressure transfer from one partial channel (3) into an adjacent one, to at least locally and partly compensate said local sound pressure differences, said partition wall means having a thickness of 3.5 mm.

Claim 8

Apparatus for damping a sound field in a fluid propagation medium within a main channel having a closed cross-sectional periphery, comprising at least two lattice works spaced from each other by a longitudinal section of the free main channel cross-section, each of said lattice works being comprised of first and second partition wall means crossing each other and subdividing the free main channel cross-section into a plurality of juxtaposed and superposed partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimension of said partial channels, wherein at least predetermined ones of adjacent partial channels have different characteristic dimensions for producing different sound oscillation states therein, whereby in said predetermined ones of adjacent partial channels local sound pressure differences are produced and distributed over their length, said partition wall means between said predetermined ones of adjacent partial channels of different characteristic dimensions being permeable for the propagation medium, at least over a partial length to cause at least partly local sound pressure difference compensation of said local sound pressure differences by a flow of the propagation medium from one of the predetermined ones of said adjacent partial channels into the adjacent one thereof, said wall means comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium, said longitudinal section having a longitudinal dimension corresponding approximately to a quarter or half of the wave length of a sound oscillation in the lower range of the frequency spectrum of said field.

Claim 9

Apparatus for damping a sound field in a fluid propagation medium within a main channel having a closed cross-sectional periphery, comprising at least two lattice works spaced from each other by a longitudinal section of the free main channel cross-section, each of said lattice works being comprised of first and second partition wall means crossing each other and subdividing the free main channel cross-section into a plurality of juxtaposed and superposed partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimension of said partial channels, wherein at least predetermined ones of adjacent partial channels have different characteristic dimensions for producing different sound oscillation states therein, whereby in said predetermined ones of adjacent partial channels local sound pressure differences are produced and distributed over their length, said partition wall means between said predetermined ones of adjacent partial channels of different characteristic dimensions being permeable for the propagation medium, at least over a partial length to cause at least partly local sound pressure difference compensation of said local sound pressure differences by a flow of the propagation medium from one of the predetermined ones of said adjacent partial channels into the adjacent one thereof, said wall means comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium, said longitudinal section having a longitudinal dimension corresponding approximately to a quarter or half of the wave length of a sound oscillation in the lower range of the frequency spectrum of said field.

Claim 10

The sound damping apparatus as claimed in claim 6, wherein said main channel includes a bent elbow portion and one of said lattice works is arranged in said elbow portion, the other of said lattice works being spaced from said elbow portion.

Claim 11

Apparatus for damping a sound field propagating in a fluid propagation medium within a main channel having a closed cross-sectional periphery, comprising at least two lattice works spaced from each other by a longitudinal section of the free main channel cross-section, each of said lattice works being comprised of first and second partition wall means crossing each other and subdividing the free main channel cross-section into a plurality of juxtaposed and superposed partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimensions of said partial channels, wherein at least predetermined ones of adjacent partial channels have different lengths for producing different sound oscillation states therein, whereby in said predetermined ones of adjacent partial channels of different lengths local sound pressure differences are produced and distributed over their length, said partition wall means between said predetermined ones of adjacent partial channels of different lengths being permeable for the propagation medium, at least over a partial length to cause at least partly local sound pressure difference compensating of said local sound pressure differences by a flow of the propagation medium from one of the predetermined ones of said adjacent partial channels into the adjacent one thereof, said wall means comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium said longitudinal section having a longitudinal dimension corresponding approximately to a quarter or half of the wave length of a sound oscillation in the lower range of the frequency spectrum of said sound field.

Claim 12

Apparatus for damping a sound field propagating in a fluid propagation medium within a main channel having a closed cross-sectional periphery, comprising at least two lattice works spaced from each other by a longitudinal section of the free main channel cross-section, each of said lattice works being comprised of first and second partition wall means crossing each other and subdividing the free main channel cross-section into a plurality of juxtaposed and superposed partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimensions of said partial channels, wherein at least predetermined ones of adjacent partial channels have different lengths for producing different sound oscillation states therein, whereby in said predetermined ones of adjacent partial channels of different lengths local sound pressure differences are produced and distributed over their length, said partition wall means between said predetermined ones of adjacent partial channels of different lengths being permeable for the propagation medium, at least over a partial length to cause at least partly local sound pressure difference compensating of said local sound pressure differences by a flow of the propagation medium from one of the predetermined ones of said adjacent partial channels into the adjacent one thereof, said wall means comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium said longitudinal section having a longitudinal dimension corresponding approximately to a quarter or half of the wave length of a sound oscillation in the lower range of the frequency spectrum of said sound field.

Claim 13

The sound damping apparatus as claimed in claim 6, wherein said different characteristic dimensions of adjacent partial channels includes the length thereof whereby said adjacent partial channels have different lengths.

Claim 14

The sound damping apparatus as claimed in claim 8, wherein one of the facing faces of said first and second adjacent lattice works is obliquely inclined with respect to the main channel direction, the other face being perpendicular to the main channel direction.

Claim 15

Apparatus for damping a sound field propagating in a fluid propagation medium within a main channel having a closed circular cross-section periphery, comprising at least one first lattice work arranged in said main channel for extending between a first longitudinal section and a second longitudinal section of the free main channel cross-section, said lattice work being comprised of a plurality of partition walls extending radially with respect to the main channel cross-section, and a plurality of wallsheets running concentrically or in a spiral with respect to the main channel axis and crossing said radial partition walls, thereby subdividing the free main channel cross-section in the manner of a guide blade into a plurality of partial channels for branching between said first and second longitudinal sections, said partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimensions of said partial channels and which is at least a quarter of the wave length of the sound oscillation having the lowest fundamental frequency of said sound field, wherein at least predetermined ones of adjacent partial channels have different characteristic dimensions for producing different sound oscillation states therein to be out of phase in said predetermined ones of adjacent partial channels, thereby producing in said predetermined ones of adjacent partial channels local sound pressure differences distributed over their lengths, said partition walls between said predetermined ones of adjacent partial channels of different characteristic dimensions being permeable for the propagation medium, at least over a partial length, to cause at least partly local sound pressure difference compensation of said local sound pressure differences by a flow of the propagation medium from one of the predetermined ones of adjacent partial channels into the adjacent one thereof, said partition walls comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium.

Claim 16

Apparatus for damping a sound field propagating in a fluid propagation medium within a main channel having a closed circular cross-section periphery, comprising at least one first lattice work arranged in said main channel for extending between a first longitudinal section and a second longitudinal section of the free main channel cross-section, said lattice work being comprised of a plurality of partition walls extending radially with respect to the main channel cross-section, and a plurality of wallsheets running concentrically or in a spiral with respect to the main channel axis and crossing said radial partition walls, thereby subdividing the free main channel cross-section in the manner of a guide blade into a plurality of partial channels for branching between said first and second longitudinal sections, said partial channels running in the direction of the main channel and being open at both longitudinal ends and having a length which is larger than the cross-sectional width dimensions of said partial channels and which is at least a quarter of the wave length of the sound oscillation having the lowest fundamental frequency of said sound field, wherein at least predetermined ones of adjacent partial channels have different characteristic dimensions for producing different sound oscillation states therein to be out of phase in said predetermined ones of adjacent partial channels, thereby producing in said predetermined ones of adjacent partial channels local sound pressure differences distributed over their lengths, said partition walls between said predetermined ones of adjacent partial channels of different characteristic dimensions being permeable for the propagation medium, at least over a partial length, to cause at least partly local sound pressure difference compensation of said local sound pressure differences by a flow of the propagation medium from one of the predetermined ones of adjacent partial channels into the adjacent one thereof, said partition walls comprising a damping material, such as felt or sintered material, for frictionally damping said flow of the propagation medium.

Claim 17

The sound damping apparatus as claimed in claim 11, wherein said different characteristic dimensions of adjacent partial channels includes said the length thereof whereby said adjacent partial channels have different lengths.

Claim 18

The sound damping apparatus as claimed in claim 12, wherein at least one of the two faces of said lattice work at which the partial channels open into said first and second sections, respectively, is obliquely inclined with respect to the channel direction.

Claim 19

The sound damping apparatus as claimed in claim 11, wherein said main channel includes a bent elbow portion and said lattice work is arranged in said elbow portion of said main channel.