GB2373957A

GB2373957A - Panel-form loudspeaker diaphragm structures

Info

Publication number: GB2373957A
Application number: GB0107731A
Authority: GB
Inventors: Charles Bream
Original assignee: New Transducers Ltd
Current assignee: NVF Tech Ltd
Priority date: 2001-03-28
Filing date: 2001-03-28
Publication date: 2002-10-02
Also published as: GB0107731D0

Abstract

A method of forming a panel-form structure 1 for use as a bending wave loudspeaker diaphragm, comprising arranging a plurality of elongate tubular members 2 side by side and generally in a planar array, and bonding the tubular members 2 to form the structure for example; by heating or the use of adhesive. A covering layer may be provided on either face of the straw panel.

Description

TITLE : PANEL-FORM STRUCTURES DESCRIPTION The invention relates to panel-form structures, e. g. for forming bending wave acoustic radiators.

It is known to form such bending wave acoustic radiators as composite panels having a core sandwiched between face skins, and it is also known to form such structures in other ways, e. g. by extrusion.

From one aspect, the invention is a method of forming a panel-form structure comprising arranging a plurality of elongate tubular members side by side and generally in a planar array, and uniting the tubular members to form the structure. The tubular members may be thermoplastic and the uniting of the members one with the other may be by thermoplastic fusion. Alternatively or additionally, the tubular members may be bonded together using an adhesive.

More than one layer of the tubular members may be united, and the axial orientation of the members in the different layers may be the same or different.

The method may involve providing a facing layer, e. g. of sheet material on one or both face surfaces of the structure and fixing the facing layer (s) to the structure.

This may be achieved at the same time as when uniting the

tubular members or may be done afterwards.

From another aspect the invention is a panel form structure comprising a plurality of elongate Lubular members arranged side by side and in mutual contact and united along their lengths.

From yet another aspect, the invention is a panel-form bending wave acoustic radiator comprising a structure of tubular members as defined above. as defiiied abc-ve.

Thus by means of this invention, a bending wave loudspeaker may be manufactured from a'raft'of hollow tubu-tar members or"straws" that have been bonded or fused together (see Figure 1). This construction leads to the formation of a lightweight non-porous structure, which may be used as a DML panel.

The straws may be fabricated from a range of

materials includina I C", f ME't a materials including, but not limited to, plastics, metals, composites & papers and may be manufactured by extrusion, tube rolling or similar techniques. In the case of thermoplastics the tubular members may be fused together by passing a hot fluid (such as air) through the assembled straws. Provided, the fluid is at the correct temperature and adequate pressure is applied, the thermoplastic straws will soften and the areas in contact will thermofuse together to form the raft on cooling.

As shown in Figure 2 the raft can be used on its own, or in combination with one or two facings. The functions of the facings are to enhance the surface appearance and/or increase the stiffness of the structure. The facings may, or may not, be made from the same material as the straw-raft and may be bonded/fused in the same operation.

The mechanical and acoustic properties of the strawraft can be optimised by controlling the following parameters: . Straw'diameter' . Straw wall thickness Straw material

. Cross sectional shape of straw (see Figure 3) . Variations in the straw wall thickness (see Figure 4) * Raft construction (see Figure 5) Figure 3 shows a range of straw profiles which could be used. During the forming process the areas in contact bond/fuse to form the web sections in the final structure.

Since the shape of the straw profile determines the orientation of these webs, the profile shape can be used to control the bending stiffness in x direction. Figure 4 details how variations in the wall thickness in the individual straw sections effects the (facing thickness/ web thickness) ratio in the final profile. Both of these techniques can be used to control the mechanical

performance and hence, optimise the acoustic performance of the panel.

Figure 5 shows alternative constructions of the raft.

These include, but are not limited to, multilayer, curved (non-flat) and cross ply constluctions. In these cases the number of layers, degree of curvature and number & orientation of cross-plies can all be used to optimise the acoustic properties of the panel.

In the manufacture of these panels, the straws may be either continuous 01 discontinuous. In Lhe continuous case, the raft profile will be uniform in the y direction, e I I iL--r L, c-) rit iriuous c- i : d i s c : o r i L i r I Li C) Li 3. 1) li-, C, (DiL resulting in d panel with anisotropic mechanical properties. In the discontinuous case me raf"could be assembled from hollow spheres, cubes, or slmilar * 9 -, c-mh 1 e c-I f 1-1c) i i ow spheres, 02-'s : i ni -i-FA Istructures. This type of assembly enables panels with more isotropic properties to be produced.

Finally, the level of acoustic damping in the structure can be controlled by : e The selection of straw material used a The amount and type of adhesive used * Using a combination of different straw materials Example of Invention To demonstrate the invention a single layer strawraft has been produced by bonding 3mm diameter circular sectioned hollow polypropylene straws together using a single layer of 25gsm hot melt film adhesive (Sarna-Xiro

P71) interleaved between the straws. The structure was bonded at 90 C under nominal pressure to give an areal density of 530gsm. For an acoustical evaluation, a 3mm thick 200gsm extruded corrugated plastic sheet has been used as a control.

Figure 6 shows that the straw-raft produces a comparable acoustic performance to the corrugated plastic control. The 2dB reduction in sensitivity of the strawraft reflects its higher areal density. Figure 7 demonstrates how the low frequency output can be enhanced by terminating the raft edges in a rigid frame using compliant foam.

Claims

1 A ; 4 tÇ I-f, r, S. i') L 0 JLt. L) C. l t > e 1 ;) 5~ ;-, S 1 (iez ii I L-1 F ; 7 11 I,-L"I I-L L 7 arr ngir. cj a nluralLy of elongaLe Lubul. ar n' : : nh & r Fd'by cC11"1"anCn r : Cj niT : :, L \1 1 ('lUIFJd (" L LlL) L ;' ;'d. :. IIIE : :' : : ìhp1"C= : ; : ; 1 eif , X T, t ì \. l f > cs r) r, !-r n t :.' S] r1 f-f > ) ; e !. (illt5'l t lbL cumUll'c : lll : :.. j, : U" :'Ò : 1CJl : KJ"P ! ; L= ; :" C) 7- e. iongdLe LubL : : :' : l1 s L-e X, -ic,-IC rlc I-a C, iayer sd bv siac'nd Qcuraiv ir ulana arrav and L.. iiiLin ! hf : : Lubaar memne'.-", n d ;''' :''n y'ne draphrag :"..

Lnan oiiL'layer o"ne dub'a. a' :'-members is uni co.. t 8 [t. l ~ e t l e T w S, t 1l t e l l 5"-f (''1 6. A'.'n & . iiod accoro. incj' : o claim 5, wherein Lh & d' ; frerenL layers ae armreo so ha Llic axial orrenc. atron of"he members mi rd-. o' ailie ; :'era' layers'. s dirferenr..

7. A meLhod acoordinq to any preceding claim, comprising providing a facing layer ol cheer mat'enaj on one or Doch face surfaces or r. he srruomre and fixing the racing layer (s) o the structure.

8. A method accordrng to claim 7, wherein the fixing of the layer (s) to the st > -ucture S. A rneshoc dccorctlng to cla~m 1, wElerein the fixiIlg of tne or each facing rayer is done at the same time as when uniting the tubular members.

9. A panel-form structure comprising a plurality of

elongate tubular members arranged side by side and in mutual contact and united along their lengths. 10. A panel-form structure being a loudspeaker diaphragm comprising a plurality of elongate tubular members arranged side by side and in mutual contact and united along their lengths.

11. A panel-form structure according to claim 9 or claim 10, wherein the tubular members are fabricated from one or more of a range of materials including plastics, metals, composites and papers.

12. A panel-form structure according to any one of claims 9 to 11, wherein the tubular members are formed by extrusion.

13. A panel-form structure according to any of claims 9 to 12, wherein a facing layer of sheet material is bonded to each surface of the structure.

14. A panel-form structure according to claim 13, wherein the facing layers are made from the same material as tubular members.

15. A panel-form structure as substantially hereinbefore described with reference to, and as illustrated in Figures 1 to 5.

16. A bending wave panel-form loudspeaker diaphragm substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.