US20060090958A1

US20060090958A1 - Thermoformable acoustic product

Info

Publication number: US20060090958A1
Application number: US11/210,462
Authority: US
Inventors: Michael Coates; Marek Kierzkowski; John Simmons; Bruce Gascoigne; Philip Gibbons
Original assignee: INC Corp Pty Ltd
Current assignee: Zephyros Inc
Priority date: 2004-02-25
Filing date: 2005-08-24
Publication date: 2006-05-04
Also published as: KR20070056000A; WO2005081226A1; EP1719113A1; JP2007523773A

Abstract

A thermo-formed acoustic product formed from an acoustic sheet with a relatively high flow resistance, and a layer of porous flow resistive spacer material attached to one side of the acoustic sheet and having a flow resistance substantially smaller than the acoustic sheet. The acoustic product has locally reactive acoustic behavior and an overall air flow resistance of between 2800 Rayls and 8000 Rayls. A decorative facing can be applied to the acoustic sheet.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to materials for sound absorption. More particularly it relates to thermo-formable acoustic products that have enhanced sound absorption properties and can be decoratively faced.
2. Description of the Related Art
Sound absorption provides a useful means for noise reduction in a wide variety of industrial, commercial, and domestic applications. To achieve the optimum degree of sound absorption, it is desirable to use a composite assembly of different layers, such that the maximum sound absorption is achieved in the minimal possible space, with the lowest possible mass appropriate for the application.
The sound absorption of a porous material is known to be a function of fundamental material properties, including thickness, air flow resistance, mass, stiffness, porosity, tortuosity etc, and application parameters, such as any air space behind the material, or alternatively, the acoustic and mechanical properties of any other material situated behind the porous material, such as a spacer layer, an isolation layer, or acoustic underlay.
Adding a third dimension to a sound absorbing assembly provides aesthetic and practical physical properties such as stiffness and conformance to contoured shapes, such as found in motor vehicle trim, such as, for example, for the floorpan, firewall, trunk, or parcel shelf.
In many of these applications it is desirable that the sound absorbing composite should have a decorative finish that does not detract from the sound absorption. Even more desirably, the decorative facing should have properties that actually enhance the sound absorption by becoming an integral component of the sound absorbing composite assembly. In certain applications, such as a motor vehicle floor assembly, it is desirable that the composite conforms to the shape of a surface, for example, or otherwise retains a particular shape, for example as an aesthetic feature for wall decoration.
In other applications it is desirable that the sound-absorbing composite should have sufficient strength that it can support light loads and resist mechanical damage.
In such applications it is desirable that the sound absorbing assembly, and any decorative facing, can be heat molded to the required shape in a simple and cost effective process.
The applicant is the applicant for Australian Patent Application No. 48754/00, which describes a Pinnable Acoustic Panel, comprising a decorative layer, a high flow resistive layer and a foam spacer layer. The high flow resistive layer has sufficient stiffness and density that it will retain pins used to attach papers and such to the panel. The content of this is incorporated herein by cross-reference. The applicant is also the applicant in respect of PCT/AU01/00880, which discloses a thermoformable acoustic sheet, the content of which is also incorporated herein by cross-reference.
Applications for a sound absorbing composite assembly include, but are not limited to, interior insulation for motor vehicles, and commercial decorative wall, ceiling, and floor finishes. In most instances, a decorative facing is required for aesthetic purposes or for mechanical protection.
Flow resistive thermo-formable materials have been provided, however such prior art does not address the practicality of achieving an effective sound absorbing solution. In particular, environmental, manufacturing and cost issues are a concern, whilst retaining the ability to vary the mechanical properties and maintaining or enhancing the sound absorbing properties of the product and combining this with the aesthetic quality of the product.
In some cases a decorative layer may also be included on, or attached to, the flow resistive thermo-formable material. However these applications similarly do not address the practicality of achieving an effective sound absorbing solution as discussed above.
Hence, it is an object of this invention to provide a thermo-formable acoustic product with enhanced acoustic properties, and a method of producing such a product that will overcome or at least ameliorate the disadvantages of the prior art or at least provide a useful alternative.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides a thermo-formed acoustic product formed from an acoustic sheet with a relatively high flow resistance, and a layer of porous flow resistive spacer material attached to one side of the acoustic sheet and having a flow resistance substantially smaller than the acoustic sheet, wherein the acoustic product has locally reactive acoustic behavior and an overall flow resistance of between 2800 Rayls and 8000 Rayls.
Preferably the acoustic sheet has a favorable aesthetic appearance. In one embodiment, the acoustic sheet is a decorative layer, such as a carpet, textile or other permeable film facing. In another embodiment, the acoustic sheet is formed by a decorative layer and at least one additional flow resistive layer.
Preferably, the porous flow resistive spacer material is a fibrous web. Even more preferably, the fibrous web spacer material has a vertically-lapped construction so that the fibers are oriented in a plane normal to that of the acoustic sheet.
It is also preferable that the fibers of the fibrous web spacer material are at least partially thermally bonded together.
It is also preferable that the fibrous web spacer material is thermally molded. The molding can be to a final shape or an intermediate shape for further molding or processing.
Preferably, in one aspect the fibrous web spacer material is formed from high melt and low melt fibers. Preferably, the low melt fibers are a bi-component fiber. In another preferred aspect the low melt fibers are a mono-component fiber.
Preferably, in another aspect the acoustic sheet includes a flow resistive layer formed from high melt and low melt fibers. Preferably, the flow resistive layer is compressed to give the desired air flow resistance. Even more preferably, the low melt fibers are selected to have a temperature resistance that is applicable to the intended use.
Preferably, the thermo-formed acoustic product has a total air flow resistance of between 3000 Rayls to 5000 Rayls. More preferably, the thermo-formed acoustic product has a total air flow resistance of between 3200 Rayls to 4500 Rayls.
Preferably, the fibrous web spacer material has an air flow resistance of between 100 Rayls to 800 Rayls. Even more preferably, the fibrous web spacer material has an air flow resistance of between 200 Rayls to 400 Rayls.
Preferably, the fibrous web spacer material has a density of 150-2000 g/m². The density of the fibrous web spacer material is determined by the specific acoustic and physical properties desired of the overall system. Preferably, the acoustic sheet has a density of 150-2000 g/m². The density is selected on the basis of the acoustic and physical properties desired of the overall system.
Preferably, the thermo-formed acoustic product can be used for a multiplicity of purposes, including, but not exclusive to insulation for machinery and equipment, motor vehicle insulation, domestic appliance insulation, dishwashers and commercial wall and ceiling panels.
Preferably, the acoustic product has a sag resistance to temperatures at or about 150° C. For example in automotive engine bay applications the part should exhibit minimal sag at operating temperatures.
In another aspect, the present invention is a method of forming a thermo-formed acoustic product formed from an acoustic sheet with a relatively high flow resistance, and a layer of porous flow resistive spacer material attached to one side of the acoustic sheet and having a flow resistance substantially smaller than the acoustic sheet, including the steps of heating the porous flow resistive layer and acoustic sheet, and molding the acoustic sheet and porous flow resistive layer wherein the acoustic product has locally reactive acoustic behavior and an overall air flow resistance of between 2800 Rayls and 8000 Rayls and the porous flow resistive spacer material attached to one side of the acoustic sheet.
In one embodiment porous flow resistive spacer material is attached to one side of the acoustic sheet during molding. In another embodiment the porous flow resistive spacer material is attached to one side of the acoustic sheet prior to molding. Preferably the porous flow resistive spacer material is laminated to the acoustic sheet prior to being molded.
In one embodiment the acoustic sheet and porous flow resistive layer are supplied to the molding process in roll form. Alternatively, the acoustic sheet and porous flow resistive layer are supplied to the molding process in sheet form.
In one embodiment, the acoustic product is molded in a cold molding tool. In this embodiment it is preferable that a thermo-formed acoustic product is formed by a flow resistive spacer material having crystalline fibers.
In another embodiment, the acoustic product is molded in a hot molding tool. In this embodiment it is preferable that a thermo-formed acoustic product is formed by a flow resistive spacer material having amorphous fibers.
Preferably the heating the acoustic product is achieved with infrared radiation, hot air, or a combination of hot air and infra red radiation.
In another aspect the acoustic product is formed from predominantly one polymer type. Preferably, the acoustic product is formed predominantly from polyester fibers or polypropylene fibers.
In another aspect the acoustic properties of the acoustic product are assisted by the three-dimensional geometry of the molded product.
The present invention, as detailed above, provides the advantages of a multi-purpose clean, energy efficient, low cost, recyclable material as a thermo-formable acoustic sheet with enhanced and consistent acoustical properties while providing a favorable aesthetic appearance in preferred embodiments. A further advantage is that the present invention provides an insulation that provides a lower resonance than current systems, has superior resilience and predictable mechanical properties.
A further advantage of the above process is that the product is formed in a fast cycle time, to provide cost-effective solutions for use as an insulation in original equipment, such as motor vehicles and dishwashers, wall and ceiling linings and other industrial commercial and domestic purposes.
It is a further advantage of this invention to produce an enhanced thermo-formable acoustic product with less energy than conventional systems, providing an improved environmental outcome.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, with reference to the accompanying drawings.
FIG. 1. Schematic illustration of one embodiment of the thermo-formed acoustic product according to the present invention.
FIG. 2. Schematic illustration of another embodiment of the thermo-formed acoustic product according to the present invention.
FIG. 3. Schematic illustration of another embodiment of the thermo-formed acoustic product according to the present invention.
FIG. 4. Schematic illustration of an embodiment of the thermo-formed acoustic product according to the present invention.
FIG. 5. Schematic illustration of an embodiment of the thermo-formed acoustic product according to the present invention.
FIG. 6. A plot of transmission loss versus frequency for the composite formed in Example 1.
FIG. 7. A plot of sound absorption coefficient versus frequency for the composite formed in Example 1.
FIG. 8. A plot of sound absorption coefficient versus frequency for different average fiber size with a fiber blend of 600 gsm.
FIG. 9. A plot of sound absorption coefficient versus frequency for two samples having a 23 mm thick spacer layer and a 13 mm thick spacer layer.
FIG. 10. A plot of transmission loss versus frequency for two samples having a 23 mm thick spacer layer and a 13 mm thick spacer layer.
FIG. 11. A plot of stiffness and loss factor versus density for samples with 2.5 denier average fiber size.
FIG. 12. A plot of stiffness and loss factor versus density for samples with 3.7 denier average fiber size.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with reference to preferred embodiments. It should be understood that the below described a limited number of embodiments of the invention and modifications can be made without departing from the scope of the invention.
In certain circumstances, the actual sound absorption achieved in a practical example of application can be less than that inferred from laboratory testing. This has been shown to result from the effect of sound transmission behind and parallel to the sheet. In acoustic terms, this material is installed in a non-locally reactive situation.
Those familiar with the concepts of flow resistive screens as sound absorption media, will appreciate that the acoustic performance achieved in real life will be superior in the event that the installation allows the thermo-formable acoustic sheet to behave in a locally reactive manner.
Referring to FIG. 1, in one embodiment of the present invention a thermo-formable acoustic product 1 is shown which is formed from an acoustic sheet 2, and a layer of porous flow resistive spacer material 4. The product is typically applied to a surface 5, usually conforming to that shape. The acoustic sheet 2 has a favorable aesthetic appearance by virtue that the acoustic sheet is a decorative layer, such as a carpet. Alternatively the acoustic sheet 2 can be a flow resistive layer only where a favorable aesthetic appearance is not required.
Referring to FIG. 2, in another embodiment of the present invention a thermo-formable acoustic product 6 is shown which is formed from a decorative layer 9, a compressed flow resistive acoustic layer 7, and a layer of porous flow resistive spacer material 10. The product is typically applied to a surface 11, usually conforming to that shape.
The decorative layer may be an automotive carpet, or a commercial textile. In one embodiment, the decorative layer is a decorative fabric which has been previously coated with an adhesive resin so as to bind the fibers and to control the air permeability. Such a coating may be applied in any of the well-known means of coating textiles. The coating is preferably a thermoplastic adhesive powder, web or film, extruded thermoplastic resin or a liquid coating. The coating process must be finely controlled so as to ensure a consistent and even coating of the decorative fabric and a pre-determined air flow resistance, and hence the performance of the decorative layer as an element of the acoustic product.
The flow resistive compressed acoustic sheet 7 is formed by a similar processes as described in PCT/AU01/00880, and has an air flow resistance in the range of 2800-7000 mks Rayls, more preferably in the range 3000-5000 mks Rayls and even more preferably in the range of 3200-4500 mks Rayls.
In PCT/AU01/00880, the preferred flow resistance range is limited by the practical application of the product, however the preferred range of flow resistance for the enhanced thermoformable acoustic sheet has been selected to provide the optimum acoustic properties for the intended applications. The increased flow resistance is achieved by increasing the compaction density and further reducing the volume of the interstatial spaces within the acoustic sheet. This is achieved through controlling the process parameters of time, temperature and pressure, applied to the fibrous web during manufacture of the acoustic sheet. In addition, it has also been found that further optimisation of the fiber blend, and web density, makes it possible to achieve a flow resistance in the preferred range.
For practical purposes, the product must have a temperature resistance appropriate for the intended application. For certain automotive applications, the sheet must have a low sag modulus at temperatures up to about 150° C.
The product can be formed into a three dimensional shape, so providing an air space and structural rigidity. Such a shape can also form partially enclosed cells, such as a honeycomb, or egg-carton type structure, that will provide local reactivity and increase the acoustical performance of the thermo-formed acoustic product.
The sheet 7 is produced from a fibrous web of 150-2000 g/m². It is clear that for cost minimisation, the lowest practical web weight is desired. The web is compressed by between 15 and 25 times. The thickness of the web has an influence on the air flow resistance, however the inventors have demonstrated through modelling and practice, that the desired acoustic properties can be achieved through a combination of different fiber selections and ratios, thicknesses and processing conditions.
The flow resistive material 10 is produced in planar form and may be presented as a roll or as a sheet. In one form of the invention, the flow resistance of the material can be achieved or enhanced through the application of an adhesive resin. The resin may be applied in a powder, fiber or film form, preferably in a dry lamination or coating process.
The resin can be selected from a range of thermoplastic, or thermoset, polymers. Preferred thermoplastic resins include, but are not limited to, polyester and polyproylene.
From a cost perspective, the selection of resin and fiber will often be determined by the lowest possible cost to achieve the appropriate level of acoustic and physical performance.
In a preferred embodiment, the thermo-formable acoustic product is produced from one individual polymer system so that it can be readily recycled, in particular polyester or polypropylene.
The web of fibrous material used to produce the flow resistive acoustic sheet 7 is preferably produced from a vertically-lapped web of high loft thermally bonded material as produced by the vertical-lapping process, known as the STRUTO process under Patent WO 99/61963, although other processes for producing a vertically, or rotary, lapped web would also be suitable. Suitable low and high melt materials can be used as the respective fibers, which can of mono- or bi-component form. Alternative web forming systems, such as cross-lapping, air laid, and needle punching can also be used, however these have been found to result in a web with less consistent acoustic properties. The web is consolidated by heating and compressing, as described in PCT/AU01/00880.
As an extension of prior art revealed in PCT/AU01/00880, the consolidation of the fibrous web can be conducted as an in-line process immediately following production of the fibrous web. The fibrous web is preferably formed as previously described by the vertical lapping process, but other web forming processes, such as cross-lapping, and/or needle punching and/or thermal bonding can also be used. A more consistent acoustic performance is obtained through the vertical lapping process.
A flow resistive screen does not behave in a locally reactive manner unless the air space behind the screen provides some acoustic impedance. To induce locally reactive behavior in the thermo-formed acoustic product, it is necessary to insert a flow resistive material into the air space, or alternatively to break up the air space into a cellular or honeycomb structure as previously described.
As a preferred embodiment, a vertically lapped fibrous web is used as a flow resistive spacer material to fill the void created by the air space, however other forms of porous materials can also serve this purpose, for example polyurethane foam, needle punched fibrous webs or a cross lapped thermally bonded fibrous webs. The mechanical and acoustical properties of the spacer material are critical to ensuring the optimum acoustic performance of the composite.
The fibrous web spacer material can be attached to the thermo-formable acoustic sheet by lamination or by mechanical means, for example riveting, coupling or plastic welding. In one embodiment, an adhesive 3, 8 may also be used between the acoustic sheet and the fibrous web spacer material.
Where a powder adhesive has been used to control the flow resistance of the sheet 7, this adhesive can be heat reacted to act as an adhesive for the fibrous web spacer material. This can be achieved through contact heating, hot air impingement, or indirect heating, such as infrared, or other similar means.
Where the adhesive system that controls the flow resistance of the sheet is in the fibrous form, it may be advantageous to use an additional hot melt adhesive in powder, web, film or similar form. The use of such an adhesive layer can also be used to control the final flow resistance of the sheet and fibrous web spacer material composite.
The fibers selected for fibrous web spacer material influence the final acoustic properties significantly. Accordingly the fibrous web spacer material is preferably formed from fibers within the range of 0.5 to 6 denier, preferably 0.5 to 3 denier, and more preferably from 0.5 to 1 denier. These fiber sizes are nominated on the basis of staple fiber, however the melt blown process can produce fibers in even smaller deniers, producing higher flow resistance and an even more beneficial result.
Of course, it is understood that the denier of a fiber relates to the mass per 9000 m of fiber. A polymer with a low specific gravity will have more fibers per unit of mass, and volume for a given mass. Accordingly, a low density polymer, such as polypropylene will have more fibers, at the same denier, than the equivalent mass of say polyester fiber. In this event a fibrous web spacer material produced from a low density polymer, such as polypropylene is a preferred form of this invention.
The thermo-formed acoustic product is formed by heating the acoustic sheet and porous layer, and molding them to a desired three dimensional shape. After molding, the acoustic sheet is attached to the porous layer to form an integral acoustic product. The three dimensional shape could be an intermediate shape or a final shape. The heating of the acoustic sheet and porous layer can be conducted before or during molding.
Where the porous layer is laminated to the acoustic sheet, it is possible to also thermoform the spacer material in the same process. In this event the spacer material can be selected from a fibrous web comprising fibers with an appropriately selected melting range. Alternatively, the porous layer may consist of fibers with a substantially higher melting range than the thermo-formable acoustic sheet, and may remain unaffected by the molding process. Attachment of the porous layer may be achieved by lamination as described, or by mechanical means, such as staples or other form of mechanical fastener.
The spacer material may optionally be placed into the molding tool prior to the placement of the heated acoustic sheet into the molding tool. The heat retained in the sheet is often sufficient to cause adhesion to the pieces placed into the mold, however an adhesive layer may be required for more secure adhesion. As a further variation on this flexible process, sheets or pieces of porous layer may be separately adhered to the thermoformed sheet, after the molding process. Once again these pieces may be adhesively or mechanically secured. In some cases the pieces may be installed independently onto the panel to which the thermoformed acoustic sheet is attached.
For applications requiring low sag at elevated temperature, for example those found in engine bays of motor vehicles, of the thermo-formed acoustic product, the selection of the fibers used to form the fibrous web spacer material is important. When the acoustic product is formed in a cold, or cool mold, crystalline fibers have been found to increase the sag resistance compared to amorphous fibers. When the acoustic product is formed in a hot mold, amorphous fibers have been found to increase the sag resistance compared to crystalline fibers.
The fibrous web spacer material of the preferred embodiment has previously been described as a vertically lapped, thermally bonded non-woven produced by the STRUTO, or other, process. When this fibrous web spacer material is thermoformed with, or without, the thermo-formable acoustic sheet, the vertical fibers adopt a v-orientation by flexing at the centre-line of the web. Alternatively the fibers may adopt a z-orientation, by flexing at the outer layers of the web. In both instances, this results in a change in the mechanical properties of the web, making it behave more effectively as a spring, improving resilience and resulting in a lower cut-off frequency.
As shown in FIG. 3, in another embodiment of the present invention a thermo-formable acoustic product 12 is shown which is formed from a decorative layer 13, a compressed flow restive acoustic layer 15, a layer of porous flow resistive spacer material 17, and a second flow resistive acoustic sheet 19 may also be used to further mechanically stabilise the product, or assist in the attachment to another surface 20. The surface may also have holes 21. As with the previous embodiments, an adhesive layer 14, 15 and 18 may also be provided to assist attachment.
Referring to FIG. 4, in another embodiment of the present invention a thermo-formable acoustic product 28 is shown which is formed from a decorative layer 22, a compressed flow resistive acoustic layer 24, and a layer of porous flow resistive spacer material 26 and adhesive layers 23 and 24 between those layers. The product is applied to a surface 27, conforming to that shape.
Referring to FIG. 5, in another embodiment of the present invention a thermo-formable acoustic product 35 is shown which is formed from a decorative layer 29, a compressed flow resistive acoustic layer 30, and a layer of porous flow resistive spacer material 31 and adhesive layers 32 and 33 between those layers. The product is thermo-formed to conform the shape of the surface 34.
The following examples are provided exemplary examples of preferred embodiments of the present invention.

EXAMPLE 1

A compressed flow resistive sheet comprising both high melt and low melt bicomponent polyester fibers was formed in accordance with PCT/AU01/00880. The sheet comprised 70% 4 denier low melt bicomponent fibers, and 30% 6-denier high melt polyester staple fibers. The total mass of the flow resistive sheet was 1000 g/m².
A vertically-lapped spacer web made from 30% 2-denier bicomponent polyester fibers, 20% 12-denier and 50% 6-denier polyester staple fibers was laminated to the flow resistive sheet with heat reactivated hot melt powder applied at a rate of 30 g/m². The total mass of the spacer layer was 800 g/m².
The resultant product had a total flow resistance of 3200 Rayls and was 23 mm thick.
The composite was tested in an alpha cabin, using Toyota test specification TSL 0600G—Test method for acoustic materials, for sound absorption and transmission loss and the results were compared with a target specification based on the prior art, with the same total mass. The product of the current invention demonstrated improved low frequency sound absorption as shown in FIG. 7 and a higher transmission loss as shown in FIG. 6.

EXAMPLE 2

Three samples of spacer layers similar to the spacer layer formed in Example 1 were formed using 2.5, 3.7 and 6 denier average fiber size except that the spacer layer had a total mass of 600 gsm. A plot of the sound absorption coefficient versus frequency of the three samples is shown in FIG. 8.

EXAMPLE 3

A similar product was formed to the product formed in Example 1 except that the spacer layer was 13 mm thick and had a total mass of 400 gsm. FIGS. 9 and 10 show the effect of the thickness of the spacer layer on the sound absorption coefficient and the transmission loss at frequencies between 200 Hz and 6300 Hz.

EXAMPLE 4

A similar product was formed to the product formed in Example 2 except four samples having densities of 400, 600, 800 and 1000 grams per square meter were formed using a blend of fibers having a 2.5 denier average fiber size. The dynamic properties of stiffness and loss factor were measured for each sample and a plot of stiffness and loss factor versus density appears as FIG. 11.

EXAMPLE 5

A similar product was formed to the product formed in Example 2 except four samples having densities of 400, 600, 800 and 1000 grams per square meter were formed using a blend of fibers having a 3.7 denier average fiber size. The dynamic properties of stiffness and loss factor were measured for each sample and a plot of stiffness and loss factor versus density appears as FIG. 12.
The foregoing describes only certain embodiments of the invention and modifications can be made without departing from the scope of the invention.

Claims

1. A thermo-formed acoustic product formed from an acoustic sheet with a relatively high flow resistance, and a layer of porous flow resistive spacer material attached to one side of the acoustic sheet and having a flow resistance substantially smaller than the acoustic sheet, wherein the acoustic product has locally reactive acoustic behavior and an overall air flow resistance of between 2800 Rayls and 8000 Rayls.

2. A thermo-formed acoustic product according to claim 1 wherein the acoustic sheet has a favorable aesthetic appearance.

3. A thermo-formed acoustic product according to claim 2 wherein the acoustic sheet is a decorative layer, such as a carpet, textile or a fabric facing.

4. A thermo-formed acoustic product according to claim 3 wherein the decorative layer is selected from the group consisting of a carpet, a textile and a permeable film facing.

5. A thermo-formed acoustic product according to claim 2 wherein the acoustic sheet includes a decorative layer and at least one additional flow resistive layer.

6. A thermo-formed acoustic product according to claim 1 wherein the porous locally reactive flow resistive spacer material is a fibrous web.

7. A thermo-formed acoustic product according to claim 6 wherein the fibrous web spacer material has a vertically-lapped construction so that the fibers are oriented in a plane normal to that of the acoustic sheet.

8. A thermo-formed acoustic product according to claim 7 wherein the fibers of the fibrous web spacer material are at least partially thermally bonded together.

9. A thermo-formed acoustic product according to claim 8 wherein the fibrous web spacer material is formed from high melt and low melt fibers.

10. A thermo-formed acoustic product according to claim 9 wherein the low melt fibers are a bi-component fiber.

11. A thermo-formed acoustic product according to claim 9 wherein the low melt fibers are a mono-component fiber.

12. A thermo-formed acoustic product according to claim 1 wherein the acoustic sheet includes a flow resistive layer formed from high melt and low melt fibers.

13. A thermo-formed acoustic product according to claim 12 wherein the flow resistive layer is compressed to give the desired air flow resistance.

14. A thermo-formed acoustic product according to claim 12 wherein the low melt fibers are selected to have a temperature resistance that is applicable to the intended use.

15. A thermo-formed acoustic product according to claim 1 wherein the thermo-formed acoustic product has an overall air flow resistance of between 3000 Rayls to 5000 Rayls.

16. A thermo-formed acoustic product according to claim 15 wherein the thermo-formed acoustic product has an overall air flow resistance of between 3200 Rayls to 4500 Rayls.

17. A thermo-formed acoustic product according to claim 1 wherein the porous spacer material has an air flow resistance of between 100 Rayls to 800 Rayls.

18. A thermo-formed acoustic product according to claim 17 wherein the porous spacer material has an air flow resistance of between 200 Rayls to 400 Rayls.

19. A thermo-formed acoustic product according to claim 1 wherein the porous spacer material has a density of 150-2000 g/m².

20. A thermo-formed acoustic product according to claim 1 wherein the acoustic sheet has a density of 150-2000 g/m².

21. A thermo-formed acoustic product according to claim 1 wherein the acoustic product has a sag resistance to temperatures at or about 150° C.

22. A method of forming a thermo-formed acoustic product formed from an acoustic sheet with a relatively high flow resistance, and a layer of porous flow resistive spacer material attached to one side of the acoustic sheet and having a flow resistance substantially smaller than the acoustic sheet, including the steps of heating the porous flow resistive layer and acoustic sheet, and molding the acoustic sheet and porous flow resistive layer wherein the acoustic product has locally reactive acoustic behavior and an overall air flow resistance of between 2800 Rayls and 8000 Rayls and the porous flow resistive spacer material is attached to one side of the acoustic sheet.

23. A method of forming a thermo-formed acoustic product according to claim 22 wherein the porous flow resistive spacer material attached to one side of the acoustic sheet during molding.

24. A method of forming a thermo-formed acoustic product according to claim 22 wherein the porous flow resistive spacer material attached to one side of the acoustic sheet prior to molding.

25. A method of forming a thermo-formed acoustic product according to claim 24 wherein the porous flow resistive spacer material is laminated to the acoustic sheet prior to being molded.

26. A method of forming a thermo-formed acoustic product according to claim 22 wherein the acoustic sheet and porous flow resistive layer are supplied to the molding process in roll form.

27. A method of forming a thermo-formed acoustic product according to claim 22 wherein the acoustic sheet and porous flow resistive layer are supplied to the molding process in sheet form.

28. A method of forming a thermo-formed acoustic product according to claim 22 wherein the acoustic product is molded in a cold molding tool.

29. A thermo-formed acoustic product formed by the method of claim 28 wherein fibers used to form the flow resistive spacer material are crystalline fibers.

30. A method of forming a thermo-formed acoustic product according to claim 22 wherein the acoustic product is molded in a hot molding tool.

31. A thermo-formed acoustic product formed by the method of claim 30 wherein fibers used to form the flow resistive spacer material are amorphous fibers.

32. A method of forming a thermo-formed acoustic product formed according to claim 22 wherein heating the acoustic product is achieved with infra red radiation, hot air, or a combination of hot air and infra red radiation.

33. A thermo-formed acoustic product according to claim 1 wherein the acoustic product is formed from predominantly one polymer type.

34. A thermo-formed acoustic product according to claim 33 wherein the acoustic product is formed predominantly from polyester fibers or polypropylene fibers.