GB2327903A

GB2327903A - A speaker cone and a method of manufacture thereof

Info

Publication number: GB2327903A
Application number: GB9825783A
Authority: GB
Inventors: John Cameron
Original assignee: Kurt Mueller
Current assignee: Kurt Mueller
Priority date: 1997-10-14
Filing date: 1997-10-14
Publication date: 1999-02-10
Anticipated expiration: 2017-10-14
Also published as: GB2327902B; GB9825782D0; GB2327902A; GB2328177A; GB2328177B; GB9825783D0; GB9721644D0; GB2327903B; GB9621644D0

Abstract

A speaker cone comprises a cone piston 43 whose annular edge is connected by an annular intermediate elastomeric flexible joint 42, 44 to an annular surround 41, in which the surround 41 and the cone piston 43 are substantially more rigid than their joint and are of different material or materials from the elastomeric joint material. The surround is usually of hard plastics and the cone of hard thermoplastics.

Description

SPEAKER CONE This invention relates to a method of manufacture of a speaker cone having a cone piston and an annular elastomeric surround, suitable for use in a loud speaker.

The invention also relates to a speaker cone having an elastomeric surround.

Loud speaker cones are described for example in US-A-3961378, typically using a cone of paper flexibly mounted at its periphery for axial movement, and with a voice coil at the centre operating in an annular magnetic air gap. Research and development of speaker cones over the years has aimed at improving the fidelity of sound reproduction, reducing the complexity and cost of manufacture, and reducing the mass, this latter aim being particularly important for automotive use. Broadly speaking the more rigid the cone piston, which is the paper or plastics diaphragm, the less total harmonic distortion; and the greater the excursion, i.e. the range of axial movement, then the louder the sound produced by the speaker. More sound can be produced for less effort when lighter weight speaker cones are used, and this enables lighter weight magnets to be used, leading overall to lighter loud speakers. A variety of plastics moulding techniques have been used, one example being described in US-A-3961378, and another, involving split iine moulding, being disclosed in GB-A-2228391 and more recently in EP-A-552040. These publications illustrate a particular difficulty in the moulding of speaker cones, namely the poor flow characteristics of molten elastomers when moulding components of thin cross-section, particularly the flexible surround for the speaker cone piston. The split line moulding technique disclosed in EP-A-552040 necessarily involves the production of solidified spume formed as an outer annular ring.

This sprue has to be tom off whilst the elastomeric material is still hot from the injection step, and the material is either wasted or is recycled; there is a limit to the amount of recycling possible, since the quality of the material is of paramount importance to the performance of the loud speaker.

A further consideration in the manufacture of speaker cones is the ease of packaging and transportation. Speaker cones which are floppy or are vulnerable to damage by folding or from extemally applied pressure are costly to package.

The invention provides a speaker cone comprising a cone piston whose annular edge is connected by an annular intermediate elastomeric flexible joint to an annular surround, in which the surround and the cone piston are substantially more rigid than their joint and are of different material or materials from the elastomeric joint material.

This invention also provides a method of manufacture of such a speaker cone, comprising positioning the cone piston and the annular surround in a mould cavity defining the intended shape of the intermediate elastomeric flexible joint therebetween, injecting elastomeric material directly into the mould cavity by means of a hot manifold and hot tip system with the hot tip or tips ending within the portion of the cavity corresponding to the said joint, allowing the elastomeric material to flow throughout the said portion of the cavity and thereby to overiap an annular edge of the cone piston and an annular edge of the annular surround for bonding thereto, and allowing the elastomeric material to solidify and to bond to the speaker cone and to the annular surround.

With the benefit of the invention, it is possible to produce a speaker cone whose outer annular surround is sufficiently rigid that the cone, as a component part, can be handled much more easily than if it were still floppy. This facilitates packaging and transport.

This invention is capable of producing speaker cones of a variety of shapes including those of circular and oval cross-section. In this specification, the term "annular" is intended to have a broad meaning, not restricted to circular or oval shapes.

Preferred features of the invention are described in the dependent claims, and will be illustrated in the following examples.

In order that the invention may be better understood, a preferred embodiment of the moulding method, and two examples of speaker cones, will now be described, by way of example only, with reference to the accompanying schematic drawings, in which Figure 1 is an elevation of a two-part mould for a speaker cone; Figures 2 and 3 are cross-sections taken respectively along the lines A to A and B to B of Figure 1, through the two-part mould in the closed configuration, and further including a cone piston held in the mould cavity; and Figures 4 and 5 are respectively a perspective view and a side elevation of a circular speaker cone manufactured using a mould different from that shown in Figures 1 to 3.

The two-part injection mould shown in Figures 1 to 3 is of generally conventional construction, and is mounted for automatic reciprocation along the mould axis to and from the closed position illustrated. Apparatus, not shown, is provided for inserting a cone piston 10 into the open mould cavity before an injection process, and for releasing the completed speaker cone following the injection process. The main novel feature of interest is the shape of the mould cavity which defines the annular surround for the cone piston; and the hot tip injection points 22A to 22D shown in Figure 1.

In this example, the cone piston 10 is a paper diaphragm with a central aperture.

An annular elastomeric surround is injected over the peripheral edge of the cone piston using the hot tip injection process. As shown most clearly in Figure 2 and Figure 3, the annular surround consists of two flat ring portions joined by a thin, flexible semitoroidal portion 14. The inner flat ring portion of flange 12 overlaps the periphery of the cone piston 10, and is defined between an inner edge 11 and an outer edge 13. The inner ring 12 is formed integrally with the semitoroidal joint portion 14 and has a similar thickness to it. A relatively thick flat outer ring portion or flange 16 is formed integrally with the outer edge 15 of the semitoroidal joint 14. During moulding, the mould faces define a shut-off region 17 which defines the outer edge of the outer flat ring portion 16, preventing the molten elastomeric material from flowing radially beyond this edge.

The molten elastomeric material is injected through four spaced hot tip injection points 22A to 22D shown in Figure 1. (In other embodiments of the invention, two or three hot tips could be used.) One such injection point is shown as 22 in Figure 3. As shown in Figure 3, the hot tip injection point 22 communicates with a hot manifold 24 within block 23 of the right hand mould part 20. The mould is designed so that the elastomeric material spreads evenly around the portion of the mould cavity which defines the intended future shape of the elastomeric surround 11 to 16. Thus the mould faces of the mould parts 20 and 21 are machined precisely to give the thickness required, allowing for the thickness of the cone piston 10.

During injection moulding, the elastomeric material spreads throughout the mould cavity within the shut-off area 17, and the thin inner flat ring portion 12 bonds with a fusion-bond joint to the face of the cone piston 10, in the example where the cone piston is made of paper. Whether the cone piston is of paper or of thermoplastics or other plastics materials, the bond is formed during the solidification of the elastomeric material and is assisted by the pressure between the faces of the mould parts 20, 21: it is formed as a lap joint.

With this injection method, no sprue is formed anywhere except in the form of the circular ends of the hot tips 22. These take the form of small cylindrical projections on the surface of the elastomeric surround, and have no deleterious effect on the loud speaker.

Due to the hot tip method of feeding the elastomer molten material to the mould cavity, no runner system is required, so no degating is required, and no waste material is generated requiring re-grinding; also, there is no need for any post-moulding operation, such as the removal of sprue.

A suitably adapted mould, corresponding to that of Figures 1 to 3, can be used to make a three part speaker cone as shown in Figures 4 and 5. In this example, the cone is of circular section, but oval or other sections would of course be possible. In this example, a thin, relatively flexible elastomeric joint 44 is formed by injection moulding between preformed relatively rigid inner and outer mouldings 43 and 41.

Preferably, the preformed rigid mouldings are of a hard material, usually thermoplastics such as polypropylene. They need not be formed of the same material, but this is advantageous in reducing the cost of manufacture. The flexible joint 42 has the same general shape as that joint 12 to 16 shown in Figures 1 to 3, in that it has a substantially semitoroidal thin joint portion 42 formed integrally with an inner flat ring portion 44 which forms a lap joint with the cone piston 43 whose aperture 46 is at the centre. The outer periphery of the flexible elastomeric joint 42 is also bonded as a lap joint to the outer, relatively rigid surround or flange 41.

Whilst a variety of injection moulding techniques could be used, including split line moulding, the hot tip injection moulding process described with reference to Figures 1 to 3 is preferred.

We have found that a satisfactory lap joint can be formed in such a process, between the elastomeric flexible material and the relatively hard thermoplastics material of the cone piston 43 and the outer surround 41. It is easier to optimise the strength of this bond when the same material is chosen for the outer surround 41 as for the cone piston 43.

Using this invention, it is possible to produce a component, such as that illustrated in Figures 4 and 5, which has a precisely guaranteed build height, in the axial direction, from the outer flange 41 to the base of the cone neck 45. With the rigidity of the outer flange 41, handling and packaging is made easier.

Claims

1. A speaker cone comprising a cone piston whose annular edge is connected by an annular intermediate elastomeric flexible joint to an annular surround, in which the surround and the cone piston are substantially more rigid than their joint and are of different material or materials from the elastomeric joint material.

2. A speaker cone according to claim 1, in which the cone piston and the surround are of the same material.

3. A speaker cone according to claim 1 or 2, in which the surround is of a hard plastics material.

4. A speaker cone according to any of claims 1 to 3, in which the cone piston is of a hard plastics material.

5. A speaker cone according to claim 2 or 4, in which the cone piston is of a hard thermoplastics material.

6. A method of manufacture of a speaker cone according to any of claims 1 to 5, comprising positioning the cone piston and the annular surround in a mould cavity defining the intended shape of the intermediate elastomeric flexible joint therebetween, injecting elastomeric material directly into the mould cavity by means of a hot manifold and hot tip system with the hot tip or tips ending within the portion of the cavity corresponding to the said joint, allowing the elastomeric material to flow throughout the said portion of the cavity and thereby to overlap an annular edge of the cone piston and an annular edge of the annular surround for bonding thereto, and allowing the elastomeric material to solidify and to bond to the speaker cone and to the annular surround.