WO2004016872A1 - An acoustic panel and a method of manufacturing acoustic panels - Google Patents

An acoustic panel and a method of manufacturing acoustic panels Download PDF

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Publication number
WO2004016872A1
WO2004016872A1 PCT/AU2003/001052 AU0301052W WO2004016872A1 WO 2004016872 A1 WO2004016872 A1 WO 2004016872A1 AU 0301052 W AU0301052 W AU 0301052W WO 2004016872 A1 WO2004016872 A1 WO 2004016872A1
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WO
WIPO (PCT)
Prior art keywords
cells
boundary member
acoustic panel
boundary
apertures
Prior art date
Application number
PCT/AU2003/001052
Other languages
French (fr)
Inventor
Colin Ayres
Jie Pan
Jingnan Guo
Original Assignee
Ashmere Holdings Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ashmere Holdings Pty Ltd filed Critical Ashmere Holdings Pty Ltd
Priority to AU2003254381A priority Critical patent/AU2003254381A1/en
Publication of WO2004016872A1 publication Critical patent/WO2004016872A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
    • B32B3/26—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer
    • B32B3/266—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a particular shape of the outline of the cross-section of a continuous layer; characterised by a layer with cavities or internal voids ; characterised by an apertured layer characterised by an apertured layer, the apertures going through the whole thickness of the layer, e.g. expanded metal, perforated layer, slit layer regular cells B32B3/12
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form
    • B32B3/10—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a discontinuous layer, i.e. formed of separate pieces of material
    • B32B3/12—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar shape; Layered products comprising a layer having particular features of form characterised by a discontinuous layer, i.e. formed of separate pieces of material characterised by a layer of regularly- arranged cells, e.g. a honeycomb structure
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
    • E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
    • E04B1/62—Insulation or other protection; Elements or use of specified material therefor
    • E04B1/74—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls
    • E04B1/82—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls specifically with respect to sound only
    • E04B1/84—Sound-absorbing elements
    • E04B1/86—Sound-absorbing elements slab-shaped
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C2/00—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels
    • E04C2/30—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure
    • E04C2/34—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure composed of two or more spaced sheet-like parts
    • E04C2/36—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure composed of two or more spaced sheet-like parts spaced apart by transversely-placed strip material, e.g. honeycomb panels
    • E04C2/365—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by the shape or structure composed of two or more spaced sheet-like parts spaced apart by transversely-placed strip material, e.g. honeycomb panels by honeycomb structures
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04B—GENERAL BUILDING CONSTRUCTIONS; WALLS, e.g. PARTITIONS; ROOFS; FLOORS; CEILINGS; INSULATION OR OTHER PROTECTION OF BUILDINGS
    • E04B1/00—Constructions in general; Structures which are not restricted either to walls, e.g. partitions, or floors or ceilings or roofs
    • E04B1/62—Insulation or other protection; Elements or use of specified material therefor
    • E04B1/74—Heat, sound or noise insulation, absorption, or reflection; Other building methods affording favourable thermal or acoustical conditions, e.g. accumulating of heat within walls
    • E04B2001/742—Use of special materials; Materials having special structures or shape
    • E04B2001/748—Honeycomb materials

Definitions

  • the present invention relates to an acoustic panel of the type which includes a cellular core structure sandwiched between two face sheets.
  • the present invention also relates to a method of manufacturing acoustic panels.
  • a panel which includes a honeycomb core structure defining a plurality of generally hexagonal shaped cells, and a face sheet adhesively bonded to each side of the honeycomb structure so as to sandwich the honeycomb structure between the sheets.
  • honeycomb core structure defining a plurality of generally hexagonal shaped cells
  • face sheet adhesively bonded to each side of the honeycomb structure so as to sandwich the honeycomb structure between the sheets.
  • An alternative arrangement for improving the sound absorption characteristics of a panel is to perforate one of the sheets with holes of several millimetres diameter, the ratio of the area defined by the perforations to the cross sectional area defined by the cells being greater than 10%.
  • the holes and the volume of air in the cells form Helmholtz resonators which serve to absorb some of the sound incident on the panels.
  • the frequency range for sound absorption is narrow.
  • a sound absorption layer is usually placed behind the panel.
  • the resonance frequency of the Helmholtz resonators formed by the cells is relatively high (greater than 1500 Hz)
  • such acoustic panels are relatively ineffective for a relatively low frequency range (below 1000 Hz) where noise absorption is greatly needed.
  • an acoustic panel including: a sandwich structure formed by a first boundary member, a second boundary member and a first core structure disposed between the first and second boundary members; the first and second boundary members and the first core structure defining a plurality of cells; and the first boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
  • the diameter of at least some of the apertures is substantially within the range 0.3 mm to 1mm.
  • the percentage open area is defined as the percentage of open area defined by the apertures on the first boundary member per unit area of the first boundary member.
  • the percentage open area is preferably within the range 1% to 4%.
  • the core structure is a honeycomb structure and each of the cells has a generally hexagonal cross-sectional shape.
  • the core structure defines a plurality of triangular or circular cells.
  • At least some of the cells have one associated aperture.
  • at least some of the cells have a plurality of associated apertures.
  • the first boundary member is provided with apertures of varying sizes.
  • the first boundary member is provided with apertures of varying perforation densities so as to define a varying percentage open area over the first boundary member.
  • the acoustic panel includes two or more first core structures fixed to each other so as to increase the effective volume of the cells.
  • the two or more first core structures may be in register with each other or out of register with each other.
  • the acoustic panel further includes an intermediate sheet disposed between adjacent core structures, the intermediate sheet being provided with a plurality of apertures.
  • the acoustic panel further includes a third boundary member and a second core structure disposed between the second boundary member and the third boundary member, the second boundary member, the third boundary member and the second core structure defining a plurality of cells, and the third boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
  • a method of manufacturing a perforated acoustic panel including the steps of: providing a first boundary member, a second boundary member and a first core structure; disposing the core structure between the first and second boundary members; and fixing the first core structure to the first and second boundary members; the first and second boundary members and the first core structure defining a plurality of cells; and the first boundary member being provided with apertures through which sound may pass during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
  • the diameter of at least some of the apertures is preferably substantially within the range 0.3mm to 1mm.
  • the percentage open area is within the range 1% to 4%.
  • the core structure is a honeycomb structure and each of the cells has a generally hexagonal cross-sectional shape.
  • the method further includes the step of selecting the desired percentage open area, the depth of the first core structure, the volume of each cell, and/or the flexural stiffness of the first core structure so as to construct an acoustic panel having a desired sound absorption frequency range and a desired peak sound absorption coefficient.
  • the method further includes the steps of providing two or more first core structures and fixing the first core structures together so as to increase the effective volume of the cells.
  • the two or more first core structures may be in register with each other or out of register with each other.
  • the method further includes the step of providing a perforated intermediate sheet between adjacent core structures.
  • the method further includes the steps of providing a third boundary member and a second core structure, and fixing the second core structure between the second and third boundary members, the second and third boundary members and the second core structure defining a plurality of cells, and the third boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
  • an acoustic panel including: a sandwich structure formed by a first boundary member, a second boundary member, and at least two core structures disposed between the first and second boundary members; each of the core structures defining a plurality of cells; the first boundary member being provided with a plurality of apertures; and at least one pair of an adjacent two core structures being disposed relative to each other such that the respective cells of the core structures are out of register with each other.
  • Figure 1 is a diagrammatic partially cut away plan view of an acoustic panel in accordance with an embodiment of the present invention
  • Figure 2 is a diagrammatic cross-sectional view of several adjacent cells of the panel shown in Figure 1; and Figure 3 is a graph illustrating plots of sound absorption co-efficient verses frequency for various types of acoustic panels of the type shown in Figures 1 and 2;
  • Figure 4 is a diagrammatic plan view of portions of first and second core structures of an acoustic panel in accordance with an alternative embodiment of the present invention
  • Figure 5 is a diagrammatic cross-sectional view of several adjacent cells of the panel shown in Figure 1 taken along the line N-N in the direction of the arrows. Description of a Preferred Embodiment of the Present Invention
  • an acoustic panel 10 in the form of a sandwich structure, the acoustic panel 10 including a core structure 12, in this example of generally honeycomb-like configuration, a first boundary member, in this example a first boundary sheet 14, attached to one side of the core structure 12 in any suitable way, for example using adhesive, and a second boundary member, in this example a second boundary sheet 16, fixed to an opposite side of the core structure 12 in any suitable way, for example using adhesive.
  • the first boundary sheet 14 is shown partially cut away in Figure 1 for purposes of illustration.
  • the first and second sheets 14, 16 and the core structure 12 define a plurality of cells 17, each of which in this example has a generally hexagonal cross-sectional shape.
  • cells 17 each of which in this example has a generally hexagonal cross-sectional shape.
  • other cell shapes such as triangular, circular, and so on.
  • the first sheet 14 is provided with a plurality of apertures, in this example each cell 17 having one associated aperture 18, for facilitating transfer of sound into the cells 17.
  • the core structure 12 and the boundary sheets 14, 16 are formed of aluminium material.
  • any suitable material is envisaged, such as thermoplastics material or paper.
  • apertures 18 are each shown disposed centrally of a cell 17, in practice this will generally not be the case. Instead, the apertures 18 would generally be disposed at different locations relative to a respective cell 17.
  • each cell has one associated aperture, any number of apertures may be provided.
  • each aperture 18 is formed so as to have a diameter which is less than or substantially equal to one millimetre, although it will be understood that a plurality of apertures may be provided with the combined aperture area for at least some of the cells being less than or substantially equal to the area of an aperture of 1mm diameter.
  • the applicant has discovered unexpectedly that by forming apertures which have a diameter which is less than or substantially equal to 1mm, it is possible to increase the frequency range of sound absorption.
  • a preferred aperture diameter is within the range 0.3mm to 1mm and a preferred percentage open area is within the range 1% to 4%.
  • the sound absorption range and the sound absorption coefficient of the acoustic panel are also functions of the following attributes: i) the volume of each cell; ii) whether and to what degree the core structure 12 is perforated; and iii) the shear stiffness, surface mass, density and boundary conditions of the core structure 12.
  • the peak sound absorption coefficient can be shifted towards lower frequency levels.
  • a panel having a desired low frequency peak sound absorption coefficient and a relatively broad frequency range can be produced.
  • low frequency sound absorption may be further enhanced by utilising vibrations of the honeycomb core structure itself. By modifying characteristics such as stiffness of the core structure, extra sound absorption can be achieved.
  • an acoustic panel having the desired sound absorption range and peak sound absorption coefficient can be constructed.
  • At least some of the cells may be provided with two or more associated apertures, the area defined by the apertures associated with a cell being on average less than or substantially equal to the area of an aperture of 1mm diameter.
  • a further alternative embodiment involves providing the first sheet 14 with apertures of varying sizes, preferably within the diameter range 0.3mm to 1mm, and/or by providing the first sheet 14 with varying perforation densities and thereby varying percentage open areas.
  • FIG. 3 there is shown a graph 20 illustrating various plots of sound absorption coefficient versus frequency for various acoustic panels.
  • D refers to the depth of each cell 17
  • P refers to the percentage open area
  • d refers to the average diameter of the apertures.
  • a third boundary sheet and a second core structure disposed between the second and third sheets may be provided.
  • the third sheet would be provided with apertures in a similar way to the first sheet.
  • the cell volume of each cell is increased by providing multiple layers of core structures disposed in register or out of register with each other, the effect of which is to decrease the frequency for peak sound absorption.
  • an acoustic panel 40 of the type including multiple layers of core structures. Like features are indicated with like reference numerals.
  • the acoustic panel 40 includes a first boundary sheet 14 provided with a plurality of apertures 18, and a second boundary sheet 16. Disposed between the first and second boundary sheets 14, 16 are a first core structure 12 defining a plurality of first cells 17 and a second core structure 42 defining a plurality of second cells 44.
  • first and second core structures 12, 42 are disposed out of register with each other so that the cells defined by the first and second core structures 12, 42 are interconnected.
  • the first and second core structures 12, 14 may be fixed together using adhesive and may additionally include an intermediate sheet which is perforated.
  • the intermediate sheet may take the form of a perforated adhesive layer or may be formed of fibrous material.
  • this alternative arrangement enables all the air volume defined by the first and second cells 17, 44 to be utilised in order to provide sound absorption at low frequencies and thereby effective use of the first and second cells 17, 42 even if some of the apertures are blocked.
  • the intermediate sheet may be configured with any suitable pattern and has the effect of allowing relative motion of the intermediate sheet so as to maintain the low frequency structure strength and improve noise transmission loss at high frequency.
  • any suitable method may be used.
  • the boundary sheets may be fixed to the core structure using adhesive and the apertures may be formed by drilling perforation holes after fixing the first sheet 14 to the core structure 12.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Architecture (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Multimedia (AREA)
  • Electromagnetism (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
  • Building Environments (AREA)

Abstract

An acoustic panel (10) is disclosed which includes a sandwich structure formed by a first boundary member (14), a second boundary member (16) and a first core structure (12) disposed between the first and second boundary member (14, 16). The first and second boundary members (14, 16) and the first core structure (12) define a plurality of cells (17), and the first boundary member (14) is provided with apertures (18) through which sound may pass into the cells (17) during use. At least some of the cells (17) each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.

Description

ANACOUSTICPANELANDAMETHOD OF MANUFACTURINGACOUSTICPANELS
Field of the Invention
The present invention relates to an acoustic panel of the type which includes a cellular core structure sandwiched between two face sheets. The present invention also relates to a method of manufacturing acoustic panels.
Background of the Invention
It is known to provide a panel which includes a honeycomb core structure defining a plurality of generally hexagonal shaped cells, and a face sheet adhesively bonded to each side of the honeycomb structure so as to sandwich the honeycomb structure between the sheets. Such panels are in common use as internal walls, ceilings, and partitions in aircraft, ships and trains due to their low weight and high stiffness.
However, such panels provide very little absorption to incident sound. In order to improve the sound absorption characteristics of the panels, additional sound absorptive materials such as polymer foams have been used to cover the panels. If the sound to be absorbed is of relatively low frequency, the sound absorptive materials need to be relatively thick. This increases the weight and cost of the panels and can also constitute a fire hazard.
An alternative arrangement for improving the sound absorption characteristics of a panel is to perforate one of the sheets with holes of several millimetres diameter, the ratio of the area defined by the perforations to the cross sectional area defined by the cells being greater than 10%. The holes and the volume of air in the cells form Helmholtz resonators which serve to absorb some of the sound incident on the panels.
However, since the acoustic resistance of such holes is very small, the frequency range for sound absorption is narrow. To improve the frequency range, a sound absorption layer is usually placed behind the panel. In addition, since the resonance frequency of the Helmholtz resonators formed by the cells is relatively high (greater than 1500 Hz), such acoustic panels are relatively ineffective for a relatively low frequency range (below 1000 Hz) where noise absorption is greatly needed.
Summary of the Invention
In accordance with a first aspect of the present invention, there is provided an acoustic panel including: a sandwich structure formed by a first boundary member, a second boundary member and a first core structure disposed between the first and second boundary members; the first and second boundary members and the first core structure defining a plurality of cells; and the first boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
Preferably, the diameter of at least some of the apertures is substantially within the range 0.3 mm to 1mm.
In this specification, the percentage open area is defined as the percentage of open area defined by the apertures on the first boundary member per unit area of the first boundary member. The percentage open area is preferably within the range 1% to 4%.
In one embodiment, the core structure is a honeycomb structure and each of the cells has a generally hexagonal cross-sectional shape.
In an alternative embodiment, the core structure defines a plurality of triangular or circular cells.
Preferably, at least some of the cells have one associated aperture. In an alternative arrangement, at least some of the cells have a plurality of associated apertures.
In one arrangement, the first boundary member is provided with apertures of varying sizes. In addition, or alternatively, the first boundary member is provided with apertures of varying perforation densities so as to define a varying percentage open area over the first boundary member.
In one arrangement, the acoustic panel includes two or more first core structures fixed to each other so as to increase the effective volume of the cells. The two or more first core structures may be in register with each other or out of register with each other.
In one arrangement, the acoustic panel further includes an intermediate sheet disposed between adjacent core structures, the intermediate sheet being provided with a plurality of apertures.
In one embodiment, the acoustic panel further includes a third boundary member and a second core structure disposed between the second boundary member and the third boundary member, the second boundary member, the third boundary member and the second core structure defining a plurality of cells, and the third boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
In accordance with a second aspect of the present invention, there is provided a method of manufacturing a perforated acoustic panel, said method including the steps of: providing a first boundary member, a second boundary member and a first core structure; disposing the core structure between the first and second boundary members; and fixing the first core structure to the first and second boundary members; the first and second boundary members and the first core structure defining a plurality of cells; and the first boundary member being provided with apertures through which sound may pass during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
The diameter of at least some of the apertures is preferably substantially within the range 0.3mm to 1mm.
Preferably, the percentage open area is within the range 1% to 4%.
In a preferred embodiment, the core structure is a honeycomb structure and each of the cells has a generally hexagonal cross-sectional shape.
Preferably, the method further includes the step of selecting the desired percentage open area, the depth of the first core structure, the volume of each cell, and/or the flexural stiffness of the first core structure so as to construct an acoustic panel having a desired sound absorption frequency range and a desired peak sound absorption coefficient.
In one arrangement, the method further includes the steps of providing two or more first core structures and fixing the first core structures together so as to increase the effective volume of the cells. The two or more first core structures may be in register with each other or out of register with each other.
In one arrangement, the method further includes the step of providing a perforated intermediate sheet between adjacent core structures.
In one embodiment, the method further includes the steps of providing a third boundary member and a second core structure, and fixing the second core structure between the second and third boundary members, the second and third boundary members and the second core structure defining a plurality of cells, and the third boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter. '
In accordance with a third aspect of the present invention, there is provided an acoustic panel including: a sandwich structure formed by a first boundary member, a second boundary member, and at least two core structures disposed between the first and second boundary members; each of the core structures defining a plurality of cells; the first boundary member being provided with a plurality of apertures; and at least one pair of an adjacent two core structures being disposed relative to each other such that the respective cells of the core structures are out of register with each other.
Brief Description of the Drawings
The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which;
Figure 1 is a diagrammatic partially cut away plan view of an acoustic panel in accordance with an embodiment of the present invention;
Figure 2 is a diagrammatic cross-sectional view of several adjacent cells of the panel shown in Figure 1; and Figure 3 is a graph illustrating plots of sound absorption co-efficient verses frequency for various types of acoustic panels of the type shown in Figures 1 and 2;
Figure 4 is a diagrammatic plan view of portions of first and second core structures of an acoustic panel in accordance with an alternative embodiment of the present invention; and Figure 5 is a diagrammatic cross-sectional view of several adjacent cells of the panel shown in Figure 1 taken along the line N-N in the direction of the arrows. Description of a Preferred Embodiment of the Present Invention
Referring to Figures 1 and 2 of the drawings, there is shown an acoustic panel 10 in the form of a sandwich structure, the acoustic panel 10 including a core structure 12, in this example of generally honeycomb-like configuration, a first boundary member, in this example a first boundary sheet 14, attached to one side of the core structure 12 in any suitable way, for example using adhesive, and a second boundary member, in this example a second boundary sheet 16, fixed to an opposite side of the core structure 12 in any suitable way, for example using adhesive.
The first boundary sheet 14 is shown partially cut away in Figure 1 for purposes of illustration.
The first and second sheets 14, 16 and the core structure 12 define a plurality of cells 17, each of which in this example has a generally hexagonal cross-sectional shape. However, it will be understood that other cell shapes are possible, such as triangular, circular, and so on.
The first sheet 14 is provided with a plurality of apertures, in this example each cell 17 having one associated aperture 18, for facilitating transfer of sound into the cells 17.
In this example, the core structure 12 and the boundary sheets 14, 16 are formed of aluminium material. However, it will be understood that any suitable material is envisaged, such as thermoplastics material or paper.
It will be understood that although in this example the apertures 18 are each shown disposed centrally of a cell 17, in practice this will generally not be the case. Instead, the apertures 18 would generally be disposed at different locations relative to a respective cell 17.
It will also be understood that although in this example each cell has one associated aperture, any number of apertures may be provided. In this example, each aperture 18 is formed so as to have a diameter which is less than or substantially equal to one millimetre, although it will be understood that a plurality of apertures may be provided with the combined aperture area for at least some of the cells being less than or substantially equal to the area of an aperture of 1mm diameter.
The applicant has discovered unexpectedly that by forming apertures which have a diameter which is less than or substantially equal to 1mm, it is possible to increase the frequency range of sound absorption. The applicant has also discovered that a preferred aperture diameter is within the range 0.3mm to 1mm and a preferred percentage open area is within the range 1% to 4%.
The sound absorption range and the sound absorption coefficient of the acoustic panel are also functions of the following attributes: i) the volume of each cell; ii) whether and to what degree the core structure 12 is perforated; and iii) the shear stiffness, surface mass, density and boundary conditions of the core structure 12.
In particular, by increasing the volume of each cell, for example by increasing the depth of each cell, the peak sound absorption coefficient can be shifted towards lower frequency levels. In this way, by providing apertures of diameter less than 1mm and appropriately selecting the cell depth, a panel having a desired low frequency peak sound absorption coefficient and a relatively broad frequency range can be produced.
In addition to high sound absorption as a result of the microperforations, low frequency sound absorption may be further enhanced by utilising vibrations of the honeycomb core structure itself. By modifying characteristics such as stiffness of the core structure, extra sound absorption can be achieved.
By selecting an appropriate average aperture diameter less than or equal to 1mm and adjusting the above attributes, an acoustic panel having the desired sound absorption range and peak sound absorption coefficient can be constructed.
As an alternative, instead of providing each cell with one associated aperture, at least some of the cells may be provided with two or more associated apertures, the area defined by the apertures associated with a cell being on average less than or substantially equal to the area of an aperture of 1mm diameter.
A further alternative embodiment involves providing the first sheet 14 with apertures of varying sizes, preferably within the diameter range 0.3mm to 1mm, and/or by providing the first sheet 14 with varying perforation densities and thereby varying percentage open areas.
Referring to Figure 3, there is shown a graph 20 illustrating various plots of sound absorption coefficient versus frequency for various acoustic panels. In relation to the graph 20, it will be understood that "D" refers to the depth of each cell 17, "P" refers to the percentage open area, and "d" refers to the average diameter of the apertures.
A first plot 22 corresponds to sound absorption coefficients of an acoustic panel in accordance with the present invention with D = 48mm, P = 1.82% and d equals 0.8mm. A second plot 24 corresponds to an acoustic panel in accordance with the present invention with D = 19mm, P = 1.86% and d = 1mm. A third plot 26 corresponds to an acoustic panel in accordance with the present invention with D = 19mm, P = 1.4% and d = 0.8mm. A fourth plot 28 corresponds to an acoustic panel in accordance with the present invention with D = 8.5mm, P = 1.4% and d = 0.6mm. For reference purposes, a fifth plot 30 is also shown, the fifth plot 30 corresponding to a non-perforated honeycomb-type panel with D = 19mm, P = 0% and d = 0mm.
As can be seen in Figure 3, by varying the attributes D, P and d, the frequency corresponding to the peak sound absorption coefficient and the range of absorbed frequencies can be modified.
As an alternative embodiment, a third boundary sheet and a second core structure disposed between the second and third sheets may be provided. With this embodiment, the third sheet would be provided with apertures in a similar way to the first sheet.
In a further alternative embodiment, the cell volume of each cell is increased by providing multiple layers of core structures disposed in register or out of register with each other, the effect of which is to decrease the frequency for peak sound absorption.
Referring to Figures 4 and 5 of the drawings, there is shown an alternative embodiment of an acoustic panel 40 of the type including multiple layers of core structures. Like features are indicated with like reference numerals.
The acoustic panel 40, as with the acoustic panel 10 shown in Figures 1 and 2, includes a first boundary sheet 14 provided with a plurality of apertures 18, and a second boundary sheet 16. Disposed between the first and second boundary sheets 14, 16 are a first core structure 12 defining a plurality of first cells 17 and a second core structure 42 defining a plurality of second cells 44.
As can be seen in Figures 4 and 5, in this embodiment the first and second core structures 12, 42 are disposed out of register with each other so that the cells defined by the first and second core structures 12, 42 are interconnected.
The first and second core structures 12, 14 may be fixed together using adhesive and may additionally include an intermediate sheet which is perforated. The intermediate sheet may take the form of a perforated adhesive layer or may be formed of fibrous material.
It will be understood that this alternative arrangement enables all the air volume defined by the first and second cells 17, 44 to be utilised in order to provide sound absorption at low frequencies and thereby effective use of the first and second cells 17, 42 even if some of the apertures are blocked.
It will also be understood that this arrangement creates an air pump effect between neighboring cells so as to encourage extra air damping in the panel.
Furthermore, it will be understood that the intermediate sheet may be configured with any suitable pattern and has the effect of allowing relative motion of the intermediate sheet so as to maintain the low frequency structure strength and improve noise transmission loss at high frequency.
In order to construct an acoustic panel in accordance with the present invention, any suitable method may be used. For example the boundary sheets may be fixed to the core structure using adhesive and the apertures may be formed by drilling perforation holes after fixing the first sheet 14 to the core structure 12.
Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

CLAIMS:
1. An acoustic panel including: a sandwich structure formed by a first boundary member, a second boundary member and a first core structure disposed between the first and second boundary members; the first and second boundary members and the first core structure defining a plurality of cells; and the first boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
2. An acoustic panel as claimed in claim 1 , wherein the diameter of at least some of the apertures is substantially within the range 0.3 mm to 1mm.
3. An acoustic panel as claimed in claim 1 or claim 2, wherein the percentage open area defined by the apertures is within the range 1% to 3%.
4. An acoustic panel as claimed in any one of claims 1 to 3, wherein the core structure is a honeycomb structure and each of the cells has a generally hexagonal cross- sectional shape.
5. An acoustic panel as claimed in any one of claims 1 to 3, wherein the core structure defines a plurality of triangular or circular cells.
6. An acoustic panel as claimed in any one of the preceding claims, wherein at least some of the cells have one associated aperture.
7. An acoustic panel as claimed in any one of the preceding claims, wherein at least some of the cells have a plurality of associated apertures.
8. An acoustic panel as claimed in any one of the preceding claims, wherein the first boundary member is provided with apertures of varying sizes.
9. An acoustic panel as claimed in any one of the preceding claims, wherein the first boundary member is provided with apertures of varying perforation densities so as to define a varying percentage open area over the first boundary member.
10. An acoustic panel as claimed in any one of the preceding claims, wherein the acoustic panel includes two or more first core structures fixed to each other so as to increase the effective volume of the cells.
11. An acoustic panel as claimed in claim 10, wherein the two or more first core structures are out of register with each other.
12. An acoustic panel as claimed in claim 10 or claim 11, further including an intermediate sheet disposed between adjacent core structures, the intermediate sheet being provided with a plurality of apertures.
13. An acoustic panel as claimed in any one of the preceding claims, further including a third boundary member and a second core structure disposed between the second boundary member and the third boundary member, the second boundary member, the third boundary member and the second core structure defining a plurality of cells, and the third boundary member being provided with apertures through which sound may pass into the cell during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
14. A method of manufacturing a perforated acoustic panel, said method including the steps of: providing a first boundary member, a second boundary member and a first core structure; disposing the core structure between the first and second boundary members; and fixing the first core structure to the first and second boundary members; the first and second boundary members and the first core structure defining a plurality of cells; and the first boundary member being provided with apertures through which sound may pass during use, wherein at least some of the cells each have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
15. A method as claimed in claim 14, wherein the diameter of at least some of the apertures is preferably substantially within the range 0.3mm to 1mm.
16. A method as claimed in claim 14 or claim 15, wherein the percentage open area is within the range 1% to 3%.
17. A method as claimed in any one of claims 14 to 16, wherein the core structure is a honeycomb structure and each of the cells has a generally hexagonal cross-sectional shape.
18. A method as claimed in any one of claims 14 to 17, further including the step of selecting the desired percentage open area, the depth of the first core structure, and/or the volume of each cell so as to construct an acoustic panel having a desired sound absorption frequency range and a desired peak sound absorption coefficient.
19. A method as claimed in any one of claims 14 to 18, further including the steps of providing two or more first core structures and fixing the first core structures together so as to increase the effective volume of the cells.
20. A method as claimed in claim 19, wherein the two or more first core structures are out of register with each other.
21. A method as claimed in claim 19 or claim 20, further including the step of providing a perforated intermediate sheet between adjacent core structures.
22. A method as claimed in any one of claims 14 to 21, further including the steps of providing a third boundary member and a second core structure, and fixing the second core structure between the second and third boundary members, the second and third boundary members and the second core structure defining a plurality of cells, and the third boundary member being provided with apertures through which sound may pass into the cells during use, wherein at least some of the cells have an associated aperture area which is less than or substantially equal to the area of a substantially circular aperture of 1mm diameter.
23. An acoustic panel including: a sandwich structure formed by a first boundary member, a second boundary member, and at least two core structures disposed between the first and second boundary members; each of the core structures defining a plurality of cells; the first boundary member being provided with a plurality of apertures; and at least one pair of an adjacent two core structures being disposed relative to each other such that the respective cells of the core structures are out of register with each other.
PCT/AU2003/001052 2002-08-19 2003-08-19 An acoustic panel and a method of manufacturing acoustic panels WO2004016872A1 (en)

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AU2002950852A AU2002950852A0 (en) 2002-08-19 2002-08-19 An acoustic panel and a method of manufacturing acoustic panels

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EP2008805A1 (en) * 2007-06-27 2008-12-31 Nimbus Group GmbH Sound-absorbing room dividing element
WO2012008883A1 (en) * 2010-07-16 2012-01-19 Общество С Ограниченной Ответственностью "Интер-Ремонт" Honeycomb material
DE102017205515A1 (en) * 2017-03-31 2018-10-04 BTU Cottbus-Senftenberg Helmholtz resonator liner
US10971128B2 (en) 2015-04-10 2021-04-06 Mra Systems, Llc Acoustic liner and methods of constructing an acoustic liner

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DE2458260A1 (en) * 1974-12-10 1976-06-16 Karlheinz Schulz Compound panel for sound insulation in buildings - has offset honeycomb or corrugated layers of different thickness
CA1094605A (en) * 1978-04-21 1981-01-27 Seiichi Sahara Panel member and process for manufacturing same
DE3411924A1 (en) * 1984-03-30 1985-10-10 G + H Montage Gmbh, 6700 Ludwigshafen Vibration-resistant heat-insulating lining made of tile elements and a tile element for this purpose
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EP0341652B1 (en) * 1988-05-10 1994-08-10 Manville Corporation Corrugated paperboard automative liner
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WO1994003327A1 (en) * 1992-08-03 1994-02-17 Supracor Systems, Inc. Perforated honeycomb
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* Cited by examiner, † Cited by third party
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EP2008805A1 (en) * 2007-06-27 2008-12-31 Nimbus Group GmbH Sound-absorbing room dividing element
WO2012008883A1 (en) * 2010-07-16 2012-01-19 Общество С Ограниченной Ответственностью "Интер-Ремонт" Honeycomb material
US10971128B2 (en) 2015-04-10 2021-04-06 Mra Systems, Llc Acoustic liner and methods of constructing an acoustic liner
DE102017205515A1 (en) * 2017-03-31 2018-10-04 BTU Cottbus-Senftenberg Helmholtz resonator liner
DE102017205515B4 (en) 2017-03-31 2021-09-02 BTU Cottbus-Senftenberg Helmholtz resonator liner

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AU2008100620A4 (en) 2008-08-07
AU2003254381A1 (en) 2004-03-03
AU2010233057A1 (en) 2010-11-04
AU2002950852A0 (en) 2002-09-12

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