SOUND ABSORPTION STRUCTURE

• US 3,734,234 A
• Filed: 11/08/1971
• Issued: 05/22/1973
• Est. Priority Date: 11/08/1971
• Status: Expired due to Term

• Current Assignee: Leslie S. Wirt
• Original Assignee: Leslie S. Wirt
• Inventors: Wirt, Leslie S.
• Primary Examiner(s): Wilkinson, Richard B.
• Assistant Examiner(s): Gonzales, John F.
• Application Number:
  US05/196,616
• Time in Patent Office: 561 Days
• Field of Search: 181/33G,33GA,33C,33E,33H,33HA,33HB 343/18A 333/98R,83R
• US Class Current: 181/286
• CPC Class Codes: E04B 1/86 slab-shaped
• CPC Class Codes: E04B 2001/748 Honeycomb materials
• CPC Class Codes: E04B 2001/8428 containing specially shaped acoustical bodies, e.g. funnels, egg-crates, fanfolds
• CPC Class Codes: E04B 2001/8433 with holes in their face
• CPC Class Codes: F02K 1/827 Sound absorbing structures or liners
• CPC Class Codes: F16L 55/033 Noise absorbers F16L55/027 takes precedence
• CPC Class Codes: G10K 11/172 using resonance effects
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft
• CPC Class Codes: Y10T 428/24149 Honeycomb-like
• CPC Class Codes: Y10T 428/24273 including aperture

Abstract

A sound absorbing structure, generally comprising a honeycomblike cellular layer, an impermeable backing closing one end of the cells, a permeable facing covering the other end of the cells, and oblique porous or permeable partitions having a specified flow resistance in each cell, for providing controlled acoustic absorption over a wide range of frequencies and having a minimum ability to wick and retain liquids. The operation of the structure is relatively independent of the materials from which it is made, and may for example be fabricated entirely from metal. It is particularly suitable for sound attenuation in jet engines and other adverse environmental conditions requiring sound absorptive panels, baffles, duct liners, and duct splitters.

Claims

1. A sound absorbing structure comprising:

means defining an acoustical wave guide having an open sound receiving end for constraining the propagation of sound as essentially planar waves along a path defined by the boundaries of the wave guide; and

, a permeable member located within said wave guide and having at least a portion thereof inclined with respect to said path.

2. A sound absorbing structure as defined in claim 1 including impermeable means closing one end of said wave guide.

3. A sound absorbing structure as defined in claim 2 including an air permeable, relatively sound-transparent sheet closing the other end of said wave guide.

4. A sound absorbing structure as defined in claim 1 wherein said waveguide has a transverse dimension which is less than one-half wavelength of the sound to be absorbed.

5. A sound absorbing structure as defined in claim 2 wherein said permeable member has a predetermined leakage path around at least a part of its perimeter.

6. A sound absorbing structure as defined in claim 2 wherein said permeable member extends substantially the length of said wave guide.

7. A sound absorbing structure as defined in claim 1 wherein said wave guide defining means is tubular.

8. A sound absorbing structure as defined in claim 1 wherein said permeable member comprises a sheet of felted metal fibers.

9. A sound absorber which is linear over a wide range of sound pressure levels, comprising:

a parallel array of acoustical wave guides each having an open sound-receiving end, and each having a transverse dimension which is less than one-half wavelength of the sound to be absorbed; and

, a plurality of permeable flow resistive partitions, each of which is obliquely disposed within a corresponding wave guide of said array.

10. A sound absorber comprising:

a plurality of corrugated wall-defining means coplanarly arranged to provide a plurality of side-by-side compartments;

an impermeable sheet disposed perpendicularly to said wall-defining means for closing like ends of said compartments; and

, a plurality of partitions each of which is obliquely disposed within a corresponding one of said compartments.

11. A sound absorber as defined in claim 10 wherein said wall-defining means are permeable and said partitions are impermeable.

12. A sound absorber as defined in claim 10 wherein said wall-defining means are impermeable and said partitions are permeable.

13. A sound absorber as defined in claim 10 including:

a relatively sound-transparent sheet covering the ends of said compartments opposite said impermeable sheet.

14. A sound absorber comprising:

an impermeable backing sheet;

a plurality of impermeable, elongate, parallel, spaced-apart partitions extending perpendicularly from said backing sheet; and

, a plurality of ribbon members having a width equal to the spacing between said partitions and each of which is disposed between a corresponding pair of said partitions, said ribbon members having a repetitive saw-tooth folded shape wherein the base of said folds abuts said backing sheet and the apex of said folds is substantially coplanar with the edges of said partitions which extend away from said backing sheet, and at least a portion of said ribbon members being permeable.

15. A sound absorber as defined in claim 14 wherein each of said ribbon members has an impermeable portion extending perpendicularly from said backing sheet, and a permeable portion slanting from said perpendicular portion.

16. A sound absorber as defined in claim 14 including:

a relatively sound-transparent sheet abutting said edges of said partitions extending away from said backing sheet.

17. A sound absorber as defined in claim 16 wherein said relatively sound-transparent sheet and said backing sheet comprise at least arc sections of coaxial cylinders.

18. A sound absorber comprising:

an impermeable backing sheet;

a first series of permeable spaced-apart elongate members having their lower edges secured to said backing sheet and extending obliquely therefrom in a first direction; and

, a second series of permeable elongate members interposed between corresponding pairs of said first series of members and having their lower edges abutting the corresponding adjacent lower edges of said first series of members and extending obliquely from said backing sheet in a second direction so as to permit the upper edges of adjacent pairs of said first and secured series of members to intersect.

19. A sound absorber as defined in claim 18 wherein said backing sheet comprises at least a section of a cylinder and said first and second series of members are curved in the direction of their major dimension.

20. A sound absorber comprising:

a parallel array of acoustical wave guides each having an open sound-receiving end;

a plurality of partitions each of which is obliquely disposed within a corresponding wave guide of said array; and

, means providing a predetermined acoustic leakage around at least a part of the perimeter of said partitions.

21. A sound absorber as defined in claim 20 including:

a common impermeable backing member closing like ends of said array of wave guides opposite said open sound-receiving ends.

22. A sound absorber as defined in claim 21 including:

a common, relatively sound-transparent, member extending over the sound-receiving ends of said array of wave guides.

23. A sound absorber as defined in claim 20 wherein said partitions comprise two triangularly-disposed sections.

24. A sound absorber comprising:

a tubular acoustical wave guide, the transverse dimensions of which is a fraction of the wavelength of the sound to be absorbed, having a closed end and an open sound-receiving end;

a first permeable partition segment extending obliquely at a first angle from said closed end; and

a second permeable partition segment contiguous with said first segment and extending therefrom at a second angle with respect to said closed end.

25. A sound absorber as defined in claim 24 wherein said wave guide has a hexagonal cross section.

26. A sound absorber as defined in claim 24 wherein the juncture between said segments extends across the transverse axis of said wave guide.

27. A sound absorber as defined in claim 24 wherein said first and second segments comprise felted metal fibers.

28. A sound absorber as defined in claim 24 wherein the perimeters of said first and second segments abut and are secured to the interior walls of said wave guide.

29. A sound absorbing structure, comprising:

a substantially impermeable backing member;

wall means secured to said backing member and extending upwardly therefrom for forming a walled compartment of uniform height which is open at one end and which is closed at the other end by said backing member; and

, an air-permeable partition disposed within said compartment so as to divide the volume thereof into two subcompartments, said partition being everywhere angularly disposed with respect to the plane of the open end of said compartment.

30. A sound absorbing structure, comprising:

a substantially impermeable support sheet;

a relatively sound-transparent facing sheet spaced apart from said support sheet by a predetermined distance;

wall means interposed between said facing sheet and said support sheet, and secured thereto, for defining a plurality of cellular compartments; and

, permeable partition means obliquely disposed with respect to said facing sheet and support sheet for dividing each of said compartments into two subcompartments.

31. A sound absorbing structure as defined in claim 30 wherein said partition means comprises:

a plurality of permeable conical members one each of which is disposed within each of said compartments, the base areas of said cones being substantially co-extensive with the base area of said compartments.

32. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide; and

a flow resistive sheet located within said wave guide and having at least a portion thereof inclined with respect to said path, said sheet having a finite flow resistance greater than 80 cgs Rayls as measured at a pressure differential corresponding to the sound pressure in said wave guide.

33. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide;

means closing one end of said wave guide; and

, a permeable member located within said wave guide and having at least a portion thereof inclined with respect to said path, said permeable member having a flow resistance approximately equal to 2 Rho C . sec theta where Rho equals the density of the fluid medium through which sound is propagated in said wave guide, c equals the speed of sound, and theta equals the angle between said inclined member and said end closing means.

34. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide; and

, a permeable member located within said wave guide and having at least a portion thereof inclined with respect to said path, the permeability of said permeable member being such as to have an effective flow resistance equal to A Rho c sec theta where Rho is the density of the fluid medium through which sound is propagated in said wave guide, c is the velocity of sound in said medium, theta is the angle of inclination between said permeable member and a plane perPendicular to the wave guide apex, and A Congruent 2.

35. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide; and

, a permeable member located with said wave guide and having at least a portion thereof inclined with respect to said path, the permeability of said permeable member being such as to have a flow resistance equal to A Rho c sec theta where Rho is the density of the medium through which sound is propagated in said wave guide, c is the velocity of sound in said medium, theta is the angle of inclination between said permeable member and a plane perpendicular to the wave guide axis, and A has a value in the range from 1 to 10.

36. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide;

means closing one end of said wave guide; and

a conically-shaped permeable member located within said wave guide, the apex of which is adjacent said one end closing means.

37. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide;

means closing one end of said wave guide; and

, a pyramidal-shaped permeable member located with said wave guide, the apex of which is adjacent said one end closing means.

38. A sound absorbing structure comprising:

means defining an acoustical wave guide having an hexagonal cross section for constraining the propagation of sound wave along a path defined by the boundaries of the wave guide; and

, a permeable member located within said wave guide and having at least a portion thereof inclined with respect to said path.

39. A sound absorber as defined in claim 38 including:

a relatively sound-transparent sheet covering the face of said array opposite said impermeable sheet.

40. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide;

means closing one end of said wave guide; and

, a conically-shaped permeable member located within said wave guide, the base of which abuts said one end closing means.

41. A sound absorbing structure comprising:

means defining an acoustical wave guide for constraining the propagation of sound waves along a path defined by the boundaries of the wave guide;

means closing one end of said wave guide; and

, a pyramidal-shaped permeable member located within said wave guide, the base of which abuts said one end closing means.

42. A sound absorber which is linear over a wide range of sound pressure levels, comprising:

a parallel array of acoustical wave guides each having a transverse dimension which is less than one-half wavelength of the sound to be absorbed;

an impermeable sheet closing like ends of the wave guides comprising said array; and

, a plurality of permeable flow resistive partitions, each of which is obliquely disposed within a corresponding wave guide of said array.

43. A sound absorber comprising:

a parallel array of acoustical wave guides;

a plurality of partitions each comprising a contiguous section of an integral, folded, ribbon obliquely disposed within a corresponding wave guide of said array; and

, means providing a predetermined acoustic leakage around at least a part of the perimeter of said partitions.