GB2251204A

GB2251204A - Loudspeakers

Info

Publication number: GB2251204A
Application number: GB9126261A
Authority: GB
Inventors: Patrick Arthur Leach; David Ian Leach; Terence Rob Collinson-Marshall
Original assignee: TGI PLC
Current assignee: TGI PLC
Priority date: 1990-12-20
Filing date: 1991-12-11
Publication date: 1992-07-01
Also published as: GB9126261D0

Abstract

A method of making a loudspeaker cone and flexible surround assembly comprising arranging an injection moulded plastics cone (1) in the mould cavity of an injection moulding apparatus and injection moulding an elastomeric material onto the periphery of the cone under heat and pressure to form a surround or suspension (2) which is chemically bonded to the material of the cone. The invention is also a loudspeaker cone and surround assembly wherein the surround is an injection moulding formed directly on to the cone. <IMAGE>

Description

TITLE: LOUDSPEAKERS DESCRIPTION The invention relates to loudspeakers and more particularly to drive units for loudspeakers.

It is known to make the cones of loudspeakers from materials such as paper, plastics and metal sheet, although increasingly the chosen material is a plastics material such as polypropylene since this material has good characteristics for this particular use.

Conventional polymer cones are vacuum-moulded from sheet by a process using heat to soften the plastics.

Drawn down over a shaped mould, the material is thinnest at the apex or peak of the cone, with the highest tension at this position. This is the converse of what is desired, namely a stronger, thicker section at the cone neck for good termination to the driving coil, and a thinner, low mass region at the marginal edge. Preferably the cone section should be gently tapered to provide a well-ordered break-up behaviour, while the join to the flexible surround should be imperceptible to minimise standing wave reflections at the boundary between the surround and cone.

The most basic loudspeaker cone is formed about its periphery with a corrugation which forms a suspension or surround by which the cone is able to move under the influence of its drive means which is usually a moving coil motor. More advanced speaker cones are provided with a peripheral suspension in the form of a corrugated member of flexible rubber or other elastomeric material and which is sometimes known as a roll surround. Such elastomeric suspensions are normally compression moulded from thermosetting elastomeric materials and are secured to the material of the cone with the aid of an adhesive. This requires skilled hand assembly to ensure concentricity and a reliable bond and is thus slow and expensive. This form of assembly is however usually justified by the improved acoustic performance which results from the provision of a compliant suspension for the cone.

It is an object of the invention to provide a loudspeaker cone and suspension or surround assembly which can be made without the need for hand assembly so that variations in manufacture and thus in performance, which have previously been commonplace, can be avoided or at least mitigated.

In the following description the term cone will be used to describe any kind of air moving device whether flat or conical or of other shape and whether or not it is driven by a moving coil or other mechanism.

According to the invention there is provided a loudspeaker cone and surround assembly wherein the surround is an injection moulding formed directly onto the cone.

From another aspect the invention is a loudspeaker cone and surround assembly wherein the cone is an injection moulding formed directly onto the surround. In this way the cross-sectional thickness of the cone can be tailored as desired, e.g from relatively thick near the centre to relatively thin near its margin.

Preferably the cone is of a plastics material and the surround is of an elastomer. Preferably both cone and surround are injection moulded. Advantageously, the cone comprises a polypropylene polymer and the surround comprises a styrene-ethylene butylene-styrene polymer.

This combination of materials results in the materials of the cone and the surround becoming chemically bonded together during the injection moulding step. This chemical bonding largely obviates the problem of de-lamination which frequently occurs with hand assembled loudspeaker cone and surround assemblies when using adhesives.

In assembling a loudspeaker drive unit it is conventional to attach the cone and surround assembly to a chassis member with the aid of an adhesive applied to the outer marginal edge of the surround. Since the chassis is usually of metal, it is necessary to employ special adhesives such as cyanoacrylates to bond the elastomeric surround to the metal chassis. Such adhesives can be harmful and are prohibited in some countries. As an alternative an annular paper ring or gasket can be fixed to the margin of the surround using non-harmful adhesives and again non-harmful adhesives can be used to fix the paper ring or gasket to the drive unit chassis. This procedure involves extra work.

In accordance with the present invention and to obviate the extra production step while avoiding the need for harmful adhesives, a paper or the like gasket may be directly moulded onto the surround when the surround is made. Thus the paper gasket can be placed in the mould before the elastomer is injected to form the surround.

The junction between the material of the cone and the material of the surround preferably comprises an overlapping portion to lend strength to the joint. If desired the material of the surround can overlap both sides of the outer peripheral margin of the cone. Where the external appearance of the loudspeaker is important, it may be desirable that the overlap is invisible, in which case it can be situated only on the rear surface of the cone.

Preferably the junction between the cone and the surround is situated close to the edge of the active portion of the surround, that is to say the portion designed to move in use, so that the material of the surround does not form part of the air driving activity of the cone since this might adversely influence the acoustic characteristics of the cone.

From a further aspect the invention is a method of making a loudspeaker cone and flexible surround assembly comprising arranging a cone in the mould cavity of an injection moulding apparatus and injection moulding a surround material onto the periphery of the cone under heat and pressure to form a surround or suspension which is chemically bonded to the material of the cone.

Preferably the cone comprises polypropylene and is injection moulded and preferably the surround comprises an elastomeric material.

From yet another aspect the invention is a method of making a loudspeaker cone and flexible surround assembly comprising arranging a surround in a mould cavity of an injection moulding apparatus and injection moulding a cone material onto the surround under heat and pressure to form a cone which is chemically bonded to the material of the surround.

Preferably the cone comprises polypropylene and preferably the surround comprises an elastomeric material and is injection moulded.

One method of making the loudspeaker cone and flexible surround assembly comprises injection moulding a polypropylene cone in a first cavity in an injection moulding machine and thereafter altering the shape of the cavity to define a peripheral surround cavity into which the peripheral edge of the cone extends and injection moulding an elastomer into the surround cavity whereby it chemically bonds to the edge of the cone. Alternatively the cone can be moulded first in one mould cavity and then transferred to another mould cavity in which the surround is injection moulded onto the cone.

The polypropylene used for the cone may be a homopolymer or co-polymer and may comprise a proportion of a filler such as mica. The plastic material will have a high melt flow index to allow the material to be moulded in a cavity having a thin section.

The elastomer of the suspension is preferably a styrene-ethylene butylene-styrene polymer such as that sold by Evode Plastics Limited under their registered trademark Evoprene G. Preferably the elastomer has a shore A hardness below 40.

A preferred injection moulding apparatus will have two injection units and barrels one of which injects the material of the cone into the mould cavity and the other of which injects the material of the suspension into the mould cavity.

The cone could be moulded from other plastics such as ABS, polystyrene, PVC, nylon or polyethylene or any other rigid polymer. The surround is preferably of styreneethylene butylene-styrene but could be of flexible PVC or of a thermoplastic rubber alloy compound.

The invention is diagrammatically illustrated by way of example in the accompanying drawings in which: Figure 1 is a perspective view of a loudspeaker cone and surround assembly made in accordance with the present invention; Figure 2 is a scrap cross section of part of the loudspeaker cone and suspension assembly of Figure 1, and taken on the line II - II of Figure 1, and Figure 3 is a scrap cross-sectional view corresponding to Figure 2 of a modified arrangement.

In the drawings there is shown a loudspeaker drive cone and surround assembly of generally conventional appearance and comprising a frusto-conical drive cone 1 which, in use, is attached at its inner margin 11 in any convenient manner to a loudspeaker drive motor, e.g. a moving coil, not shown, the outer margin 3 of the cone 1 being attached to a compliant surround or suspension 2 which in turn is secured in any convenient fashion to a loudspeaker drive unit chassis (not shown). In the present case the peripheral margin 3 of the loudspeaker drive cone 1 has been injection moulded from polypropylene and the flexible elastomeric surround or suspension 2, which is of generally conventional configuration, has been injection moulded thereon.The surround is annular in shape and comprises an outer flange 5 by which it is attached to the loudspeaker drive unit chassis (not shown), a part circular roll or bellows 6 which is the active part of the cone suspension and an inner flange 7, which is moulded onto the rear face 9 of the cone 1 so as to overlap the outer margin 3 of the cone to some extent. The overlapping join is thus invisible in use. The outer edge 8 of the cone 1 is preferably positioned closely adjacent to the roll or bellows 6 of the surround 2 so that the surround does not adversely affect the acoustic properties of the cone.

The material of the surround 2 is a styrene-ethylene butylene-styrene which bonds chemically under the heat and pressure of the injection moulding process to the polypropylene cone to form an integral unit therewith, thereby obviating the need to glue the cone and surround together as has been necessary heretofore. In this way the alignment between the cone and surround can be controlled more predictably than is the case with hand assembly, and the connection between the cone and surround can be achieved consistently.

In the arrangement of Figure 3, a paper gasket 10 is arranged in the mould prior to the injection moulding of the surround 2, whereby the gasket 10 is bonded to the flange 5. In this way the cone and surround unit can be secured to the chassis (not shown) of a drive unit using conventional, that is, non-harmful, adhesives.

The invention thus provides a novel drive cone and surround assembly which can be manufactured more efficiently than was previously the case.

Claims

1. A loudspeaker cone and surround assembly wherein the surround is an injection moulding formed directly onto the cone.

2. A loudspeaker cone and surround assembly where the cone is an injection moulding formed directly onto the surround.

3. A loudspeaker cone and surround assembly according to claim 1 or claim 2, wherein the cone comprises a plastics material and the surround comprises an elastomeric material, and wherein the cone and the surround are injection mouldings.

4. A loudspeaker cone and surround assembly according to claim 3, wherein the cone comprises a polypropylene polymer and the surround comprises a styrene-ethylene butylenestyrene polymer.

5. A loudspeaker cone and surround assembly according to any preceding claim, wherein a paper gasket is moulded onto a peripheral margin of the surround.

6. A loudspeaker cone and surround assembly substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

7. A loudspeaker drive unit incorporating a cone and surround assembly as claimed in any preceding claim.

8. A method of making a loudspeaker cone and flexible surround assembly comprising arranging a cone in the mould cavity of an injection moulding apparatus and injection moulding a surround material onto the periphery of the cone under heat and pressure to form a surround which is chemically bonded to the material of the cone.

9. A method according to claim 8, comprising forming the cone by injection moulding.

10. A method of making a loudspeaker cone and flexible surround assembly comprising arranging an elastomeric surround in a mould cavity of an injection moulding apparatus and injection moulding a cone material onto the surround under heat and pressure to form a cone which is chemically bonded to the material of the surround.

11. A method according to claim 10, comprising forming the surround by injection moulding.

12. A method according to any one of claims 8 to 11, wherein the cone comprises a plastics material and the surround comprises an elastomeric material.

13. A method according to any one of claims 8 to 12, wherein the cone comprises polypropylene polymer.

14. A method according to any one of claims 8 to 13, wherein the surround comprises a styrene-ethylene butylenestyrene polymer.

15. A method according to any one of claims 8 to 14, comprising arranging a paper gasket in a portion of the mould cavity in which the surround is to be formed, whereby on injection moulding the surround, the paper gasket is bonded thereto.

16. A method of making a loudspeaker cone and flexible surround assembly substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

17. A loudspeaker incorporating a loudspeaker cone and flexible surround assembly constructed substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.