GB2427378A

GB2427378A - Moulding speaker cone constructions

Info

Publication number: GB2427378A
Application number: GB0512363A
Authority: GB
Inventors: Steve Parry; John Holland; John Whittaker
Original assignee: Metflex Precision Mouldings Ltd
Current assignee: Metflex Precision Mouldings Ltd
Priority date: 2005-06-17
Filing date: 2005-06-17
Publication date: 2006-12-27
Also published as: GB0512363D0

Abstract

A speaker cone construction is made by (a) placing a disc of cone material 30 in a conical cavity 26 of a mould 20, which includes a central boss 24 to define a central aperture for the cone, and (b) introducing a rubber or equivalent material into the cavity 26 for moulding of an integral rim or surround. The mould is divided into parts 21, 25. Surface 28 of mould part 25 is roughened or textured to promote preffered adhesion of the moulded body to that surface. The cavity 26 is filled with rubber material in a pressure moulding step which forms an integral cone moulding encapsulating the conical disc 30. The moulding material may be introduced first, followed by opening of the mould so that the moulded material adheres to part 25. Disc 30 is then placed on part 21 and the mould is closed. Alternatively, disc 30 may be placed first, followed by closing the mould and introducing thermosetting rubber. The cone may have a rib or maybe corrugated.

Description

SPEAKER CONE CONSTRUCTIONS This invention relates to cone constructions for loud speakers for use in sound systems such as hi-fi systems or public address systems or the like. The cone comprises a shaped diaphragm having an electromagnetic transducer usually mounted centrally of the cone which produces audio-frequency vibrations which are resonated and amplified by the cone. The transducer may be covered by a central domed cap which protects against dust drawn into the speaker. The cone is typically made from a mesh or perforated sheet of metal or synthetic material, such as a polyaramid or polyamide plastic, fabricated as a disc with a central aperture and then shaped into a straight or curved cross-section cone, by pressing for example (a typical curved cross-section cone may be 'flared' like the bell of a trumpet, that is a hyperbolic or parabolic curve). The outer edge of the cone is joined to a surrounding frame and a speaker body by a flexible surround comprising an annular strip of rubber or equivalent material. This has the function of preventing air from being drawn into the speaker body around the back of the cone, and also minimises reverberation of resonant frequencies being passed from the cone to the speaker body. The surround is usually attached to the outer edge of the cone using adhesive. In an alternative, the surround is injection moulded onto the periphery of the cone, using a thermoplastic elastomer. To give desired properties of airtightness of the cone, it is also sometimes necessary in a separate step, to either coat the cone (especially in the case of a metallic cone), or to calendar the material, by applying heat and pressure, if of a suitable thermoplastic material, to close pores in the material. Otherwise, doping or closing of pores is often done by brush using a phenolic resin. Ideally, the cone should oscillate as a perfect piston in the axial direction of the speaker, without ripples or torsion. In practice ripples often form, with regions of the cone vibrating in static or progressive waves formed in the unsupported area of the cone. An object of the invention is to provide a speaker cone construction, and a method of making such a speaker cone construction which can be made in and carried out as a single step process, and provide a speaker cone with improved acoustic properties. This may be inclusive of a speaker cone, dust plug and thermosetting rubber surround. According to the invention, a method of making a speaker cone construction comprises providing a two-part mould, one part thereof having a textured surface to promote adhesion thereto, introducing a rubber or equivalent material into the mould, compressing the material in the mould, opening the mould so that the rubber adheres to the textured surface, placing a disc of cone forming material in the mould on the non-textured surface, and closing the mould to bed the disc into the rubber material. The cone forming material may be a known cone material such as a mesh or perforated sheet or metal, or a woven fabric or non-woven sheet of synthetic material such as polyamide or polyaramid yarns fibres or sheet material. The mould may be shaped to give a conical configuration to the cone material, which may be introduced as a flat disc of the cone material or be pre-formed, preferably having a central aperture for a central body to project through. The mould is also preferably configured to provide an annular zone around the edge of the cone, which will be filled only with the rubber or equivalent material and provide an integrally moulded part forming a surround for the cone, to join the same to the speaker body. The material used may comprise a thermosetting rubber compound. Thermosetting rubber has advantages over thermoplastics as better physical properties can be achieved without need for the addition of an incompressible medium such as plastics. The rubber material is preferably vulcanised directly to the material of the cone, and not bonded by adhesive etc. The moulding process preferably comprises a compression moulding process, although injection moulding may be used instead. The moulding step may be used to produce one or more ribs or other raised rubber structures on the cone material. These may be arranged for example as radial ribs or ridges, or one or more concentric ribs or ridges equi-spaced or otherwise arranged from the axis of the cone. Such ribs may be effective in preventing formation of localised oscillations in the cone. In a further possible method, the cone may be formed with concentric or radial corrugations or pleats. These provide a mechanical reinforcement, and an alternative means for preventing parasitic oscillations. The rubber preferably strikes through pores or perforations in the cone material and covers or encapsulates at least one face thereof completely, and may cover both faces of the cone material. From another aspect, the invention provides a speaker cone construction wherein the cone material is integrated with a rubber material by moulding to provide a cone having a rubber annular surround which is integral with the cone. The cone construction is preferably made by a method or preferred method according to the invention. A preferred cone construction may comprise a core of cone material such as a mesh or perforated sheet of metal, or woven or non woven material or sheet of for example polyamide or polyaramid yarns or fibres or sheet, covered on one or both faces with the rubber material, which is preferably a thermosetting rubber. This may strike through pores or interstitial holes in the mesh or weave etc of the cone material, and is integral with the annular surround or cover one or both sides of a metal cone. Advantageously, the cone may be formed with a rubber bead on one surface extending concentrically of the axis of the cone and radially equidistant from said axis. Alternatively the cone may be formed with radial or concentric pleats or corrugations. A preferred method of making a speaker cone construction according to the invention, a moulding apparatus for use therein, and a speaker cone according to the invention made thereby will now be described, by way of example and with reference to the accompanying drawings, wherein:- Figure 1 is a diagram showing a prior art speaker cone in cross section; Figure 2 is an enlarged detail of Figure 1, showing how the cone is connected to an annular rubber surround in the prior art; Figure 3 is a diagrammatic cross-section of a mould used in the method of the invention; Figure 4 is an enlarged detail of Figure 3 showing the differing surface structures of the opposed faces of the mould; Figure 5 is an enlarged cross-section similar to Figure 2, showing one embodiment of cone in accordance with the invention;Figure 6 is a view similar to Figure 5 showing a second embodiment of cone in accordance with the invention; Figure 7 is a diagram similar to Figure 1 showing a cone according to the invention in accordance with one embodiment thereof; and Figure 8 is a diagram similar to Figure 7 showing a cone according to a further embodiment of the invention. Referring first to Figure 1, a prior art speaker cone arrangement comprises a conical member 10 which comprises a disc of a mesh woven or perforated material such as metal or plastics mesh, woven cloth or foraminous sheet material, with a central aperture, and which has been formed into a cone in a press. The edges of the conical member 10 are connected to the body of the speaker by an annular rubber surround 11, which is adhered around the rim of the conical member by adhesive 12 (see detail view of Figure 2). The central aperture of the cone accommodates an electromagnetic transducer 13, which is covered by a protective dome 14. The transducer produces sound vibrations which are communicated to the cone 10 which amplifies the acoustic signal. Ideally the cone 10 vibrates in unison like a piston axially of the cone, but in practice resonances and harmonics disturb this, leading to break up and unwanted effects such as loud harmonic tones. In an attempt to remedy these shortcomings of known cones, the invention provides an improved cone construction, by a method using a mould such as is illustrated in Figure 3. Figure 3 is a diagrammatic cross-section of a mould 20 for producing a cone arrangement according to the invention. The mould 20 comprises a base part 21 having a conical formation, 22 surrounded by a shallow moat 23. The conical formation 22 has a central boss 24. The conical formation defines the conical contour of the cone arrangement produced, and the moat 23 defines an annular surround for the cone. The central boss 24 serves to define the customary central aperture of the cone. The mould 20 also comprises an upper part 25 of a corresponding hollow conical shape. This defines a moulding chamber 26 in the form of a hollow cone with a peripheral flange together with the base part 21. Parts 27, shown in this case at the top (hub) of the mould are provided for introduction of rubber material. The inner surface 28 of the upper part 25 is 'textured' as shown in the enlargement of Figure 4, whilst the opposing surface 29 of the chamber 26, formed by base part 21, is smooth. The form of the 'texturing' may comprise grooves, stipples, or simply be achieved by roughening of the surface. The surface 29 of part 21 however is as smooth as can be attained by machining. The textured surface 28 has the effect of providing a key with rubber moulding material introduced into the mould after the same has set, whilst the smooth surface 29 ensures a clean release. This has the effect that when the mould is opened, the partially cured or vulcanised moulded body will adhere to the rough surface 28 of the upper part 25 and be carried by it, leaving the lower part 21 free. After full curing, the moulded body no longer adheres and can be cleanly removed from the mould. In a first moulding procedure described by way of example, thermosetting rubber elastomer is introduced into the mould, and then on setting, the mould is opened and the moulded body is covered by the upper part 25 leaving the lower part free. A disc of cone-material 30 is then placed on the conical formation 22 of the lower part, and the mould is closed again, with the moulded rubber body still on the upper part 25. The mould is pressed fully closed, the effect of this is to achieve impregnation and encapsulation of the cone of material 30 with the thermosetting rubber, providing a composite integral moulded article comprising a conical part reinforced by the cone material 30 and an integral annular surround. In an alternative moulding procedure, the disc of cone material 30 is first placed in the mould, which is closed, then thermosetting rubber is introduced to the mould, and allowed to set. This has the effect of coating the disc 30 on both sides, but may not necessarily achieve full impregnation. The resulting composite article is then removed from the mould. More usually, coating of both sides can be achieved with fabric by complete strike through of the rubber under injection pressure. Figure 5 is a detailed sectional view of a first embodiment of cone produced by the method described, wherein a formamlinous cone material 30 e.g. a plastics mesh of say polyaramid fibres, is coated on one side with a layer 31 of thermosetting rubber elastomer, which strikes through the interstices of the mesh, thereby impregnating the mesh. Figure 6 shows a similar view of a second embodiment of cone produced by a method according to the invention. Wherein the mesh material 30 is coated on both sides by a layer 32 of the thermosetting rubber elastomer which has struck through the interstices of the mesh thereby fully encapsulating and impregnating the mesh 30. Figure 7 and 8 illustrate in diagrammatic views similar to Figure 1, two possible cone arrangements in accordance with the invention. The cones here are rubber-cone components made by the method according to the invention. In Figure 7, the cone 40 surrounds a central part comprising the cover 14 and transducer 13, and is in accordance with the invention an integrated structure of rubber elastomer and a reinforcement material as described above, formed with an integral annular surround 41. The cone 40 is modified by the provision at about half its radius of a rib or bead 42 which is moulded onto the rear surface of the cone 40 as part of the process described in connection with Figure 5, the mould 20 being configured by means of a channel in the upper part 25 to produce such a rib. This rib 42 has the important effect of damping any harmonic or parasitic vibration might disrupt the proper vibrations of the cone due to localised oscillations. A further embodiment is shown in Figure 8, wherein the cone 45 is shown to be formed with a multiplicity of concentric corrugations or pleats 46. This may be achieved by appropriate shaping of the mould parts, and has advantages in damping unwanted harmonics and the like. The scope of the invention is not limited to the details of the embodiments described above, and variations may be made thereto within the scope of the invention.

Claims

1. A method of making a speaker cone construction, comprising providing a two-part mould one part of the mould having a textured surface to promote adhesion thereto; introducing a rubber or equivalent material into the mould; compressing the material in the mould; opening the mould so that the rubber adheres to the textured surface; placing a disc of cone-forming material in the mould on the non-textured surface, and closing the mould to bed the disc into the rubber material.

2. A method according to claim 2 wherein the cone-forming material is any one of a mesh of metal, a perforated sheet of material, a woven fabric, or a non-woven web of synthetic material such as polyamide or polyaramid yarns, fibres, or sheet material.

3. A method according to claims 1 or 2 wherein the mould is shaped to give a conical configuration to the cone material.

4. A method according to claim 3, wherein the cone material is introduced to the mould as a flat disc thereof.

5. A method according to claim 3 wherein the cone material is pre-formed into a conical shape.

6. A method according to claims 3, 4 or 5 wherein the disc of cone-forming material has a central aperture.

7. A method according to any preceding claim wherein the mould is configured to provide an annular zone around the edge of the cone which will be filled only with the rubber or equivalent material, without any cone-forming material to provide an integrally moulded part forming a surround for the cone, to join the same to a speaker body.

8. A method according to any preceding claim wherein the rubber material is a thermosetting rubber compound.

9. A method according to claim 8 wherein the thermosetting rubber compound is vulcanised directly to the cone-forming material.

10. A method according to any preceding claims wherein one or more ribs or other raised rubber structures are formed by the moulding step on the cone.

11. A method according to claim 10 wherein said raised rubber structures comprise radial ribs or ridges.

12. A method according to claim 10, wherein said raised rubber structures comprise one or more concentric ribs or ridges about the axis of the cone.

13. A method according to any one of claims 1 to 9 wherein the cone is formed with a plurality of concentric or radial corrugations or pleats.

14. A method according to any preceding claim comprising a compression moulding step, whereby the rubber strikes through pores or perforations in the cone material and covers or encapsulates at least one face thereof completely.

15. A speaker cone construction wherein the cone material is integrated with a rubber material by moulding to provide a cone having a rubber annular surround which is integral with the cone.

16. A speaker cone construction according to claim 15 comprising a core of cone material covered on one or both faces with the rubber material.

17. A speaker cone construction according to claim 15 or 16, made by a method according to any one of claims 1 to 14.