GB2125652A

GB2125652A - Loudspeaker voice coil

Info

Publication number: GB2125652A
Application number: GB08230355A
Authority: GB
Inventors: Richard Irving Bean
Original assignee: Harman International Industries Inc
Current assignee: Harman International Industries Inc
Priority date: 1982-06-01
Filing date: 1982-10-25
Publication date: 1984-03-07
Also published as: BE895043A; NL8204198A; DE3239843A1; JPS58215199A; FR2527883A1

Abstract

A loudspeaker voice coil assembly of high performance and improved power handling capability while being relatively cheaper to produce is wound of square or rectangular cross-section wire (20) on its side (22) rather than on its edge (24), as is conventionally done. The coil preferably has an even number of layers. The wire may be enamelled. An adhesive or a thermosetting plastics coating may be provided on the wire. <IMAGE>

Description

SPECIFICATION Loudspeaker voice coil This invention relates to the type of windings useful in acoustic transducers commonly referred to as voice coils. In such devices, a cone or diaphragm is driven by electrical signals in the audio frequency range in such a manner that the diaphragm moves the air to reproduce sound. The diaphragm is driven by a voice coil assembly attached to the diaphragm wherein the voice coil is positioned within an air gap formed in a permanent magnet assembly. When the voice coil is excited by the audio frequency currents, the coil moves in atranslational manner to impart the desired motion to the diaphragm.

In past methods of constructing voice coils, it was typical to construct a coil, considering that it was preferred to be lightweight, by winding round wire on a bobbin. It was found however that using round wire resulted in a relatively inefficient transducer in that the round wire left considerable interstices between adjacent coil turns and between successive turns of the wire. Given a certain volume of magnetic air gap, the sensitivity of moving coil transducers depends upon the number of turns of wire which can be placed in the space provided.

An additional factor relates to the power handling capability of transducer voice coils. It has long been known that such transducers could be made to handle greater power by providing more metal in the coil which would act to dissipate the heat generated in the voice coil. An early solution was to utilize wire having a rectangular cross section, typically having the side-to-edge ratio in the range of four to one to seven to one. The wire would then be wound on edge thereby achieving a large number of turns in the coil and likewise resulting in a very dense coil with very few interstices so that greater power could be handled and more sensitivity achieved.

The edge-wound voice coil has been used conventionally particularly in high fidelity loudspeakers for many years. Typical of the prior art is United States Patent Specification No. 3,935,402, which shows a high power dissipation voice coil utilizing the edgewound principle and disclosing improvements in the power handling capability thereof. It is believed that the edge-wound coil was first disclosed in a Bell System Technical Journal dated January, 1928, in an article entitled "A High-Efficiency Receiver for a Horn-Type Loudspeaker of Large Power Capacity" by E.C. Wente and A.L. Thuras.

As may be anticipated, several problems are encountered in forming an edge-wound voice coil.

As discussed in the specification of United States Patent No. 1,956,826, it is difficult to obtain an even cylindrical contour for the coil. The wire is small and it is difficult to keep the flat sides in strict parallel relationship, and automatic coil winding devices are not usable. Additionally, although higher coil density is obtainable, it is difficult to wind the coil tightly without distorting the contour, as the wire has a tendency to lean over. Further, it will be apparent that as only one layer of turns of wire is utilized, the resulting coil has the leads at opposite ends of the coil such that a lead dressing problem must be dealt with thereby adding to the manufacturing costs.

What has been discovered is that a voice coil having comparable performance to the expensively made edge-wound coils including higher power handling capabilities can be manufactured easily and less expensively by choosing rectangularly formed wire of various side-to-edge aspect ratios wherein the side or greater dimension of the wire is laid against the bobbin rather than the edge. There are several advantages of this discovery. With the greater dimension of the wire laid against the surface of the bobbin, the coil can be wound tighter than the edge-wound version, providing greater density and therefore increasing the power handling capability. Other performance characteristics are duplicative of the edge-wound versions.

The additional advantages of the present invention are a lower manufacturing cost due to several factors: first of all, the coil can be wound on automatic coil winding machines; and secondly, by using multiple layers of an even number, the leads or ends of the coil both come off the same side thereby eliminating the need to dress the ends or leads and therefore eliminating that manufacturing step. Thirdly, this flat-wound coil is wound directly on the coil former, whereas edge-wound coils are wound in long sticks on a mandrel, then separated, cut and a paper form inserted. Thus, the flat-wound coil eliminates several manufacturing steps.

A further advantage of this invention is that it is possible to provide the coil wire with a coating of adhesive material or the like as it is wound on the bobbin so that following the winding process, the adhesive is set causing all the wire to adhere in a finished and secure form.

The invention will become further apparent by referring to the following detailed description given by way of example with reference to the accompany- ing drawings, in which: Figure 1 is a partial isometric view of a prior art edge-wound voice coil; and Figures 2 and 3 show alternative forms, partly in cross section, of the voice coil configuration of the present invention.

Referring to Figure 1,there is shown flat rectangularwire 10 wound with its narrow edge 12 on a bobbin 14 until enough turns have been accumulated, as desired, to form an accumulated winding forming the voice coil. As is conventionally known, the voice coil will be situated within an air gap and it is conventional to leave a very small amount of clearance between the bobbin on one side and the edge of the voice coil on the other as it is known that the smailer the space between the pole pieces of the magnet and the cylindrical surfaces of the voice coil, the greater will be the temperature dissipation abilities of the unit.Some air gap must be left however to provide for translational movement of the voice coil and therefore a given volume is provided to work with in the air gap and, as mentioned previously, it is desired to fill that volume with as many turns of winding and as much metallic material as possible.

Figures 2 and 3 demonstrate alternative forms of wire coils embodying the invention. It is to be noted that the volume of air space occupied by the windings is the same, or can readily be madethe same in both Figures 2 and 3 as in Figure 1. Turning first to Figure 3, the bobbin 14 has now been provided with a plurality of turns of wire 20 having a different aspect ratio, that is an edge-to-side ratio which can be varied substantially for various reasons to be explained more fully hereinafter but in which the side 22 is laid along the bobbin 14. By choosing the ratio of the sides 22 to the edges 24, a desired number of turns of wire can be accomplished to fill the volume of the air gap to provide the desired sensitivity for the transducer. The wire of rectangular cross section is covered with enamel for insulation purposes.By winding the wire 20 on the bobbin 14 with a coil winding machine, a helical coil is formed and, as will be apparent, multiple layer coils can be tightly wound. By providing an even number of layers in the coils, an additional problem mentioned previously can be solved in that the finished coil will have the ends or leads coming from the same side of the coil thereby eliminating the need for providing a means for dressing the leads back around and out of the coil form for a connection to the input terminals. Although highly efficient and less expensive coils can be manufactured utilizing an odd number of layers, it is an additional advantage of this invention that the even number of layers will contribute to a further reduction of manufacturing costs and this is an advantage over the prior edge-wound coils.

Figure 2 demonstrates what may be considered the lower limit of the invention in that the wire 30 has a square cross-section. This configuration still permits automatic winding on coil machines and still permits the turns to be wound tightly on the bobbin l4withoutdistortingthewindings orthe resultant coil cylinder. It will be apparent that various aspect ratios of edge-to-side dimension can be chosen from square to rectangular depending in part on the number of turns desired yet still substantially filling the volume of the associated magnet air gap leaving a minimum of interstices between the windings.

An additional, preferred, feature of the invention is the provision of and use of an adhesive or thermosetting plastics material tightly to bond the windings together in a finished coil cylinder. This may be accomplished in several ways; one is to provide the rectangular or square wire upon which enamel has previously been provided as is conventional with voice coil wires, with an additional coating of thermosetting adhesive before it is wound onto the bobbin. An alternative would be to wind a first layer of winding on the bobbin and then to apply to that first layer a thin coating of thermosetting material, then to wind onto that the second layer of winding.

One would proceed with additional layers if additional layers are to be made. When the winding is completed, an electrical current is briefly applied to the ends of the coil causing it to heat up and set the adhesive. Instead of a thermosetting adhesive, one can employ an adhesive reactive to solvents such as acetone or methyl ethyl ketone.

Claims

1. A loudspeaker voice coil comprising a winding of wire intimately bonded together, the wire having a a rectangular cross section in which the aspect ratio between the side and the edge is 1:1 or greater, the side of the wire being aligned in the same direction as the central axis of the coil.

2. A loudspeaker voice coil comprising a winding of wire of two or more layers, the wire having a rectangular cross section wherein the ratio of the side to the edge is not less than one to one, and wherein the edge is aligned with the axis of the coil.

3. A loudspeaker voice coil comprising a winding of wire of an even number of layers, the wire having a rectangular cross section wherein the ratio of the side to the edge is not less than 1 the side of the wire being aligned with the axis of the coil.

4. The loudspeaker voice coil of claim 3 wherein the wire is bonded intimately together by adhesive.

5. A loudspeaker voice coil made by first forming a length of wire having a rectangular cross section wherein the side is equal to or greater than the edge, coating said wire with insulating means, winding said wire on a cylindrical coil form with the side thereof adjacent said coil form to form a first layer, and winding additional turns of said wire in the same fashion over said first layer to form a second layer.

6. A loudspeaker voice coil formed as set forth in i claim 5, further including the steps of coating said wire with adhesive then, afterforming said layers, causing said adhesive to set.

7. A loudspeaker voice coil formed as set forth in claim 5 or 6, wherein the adhesive is a thermosetting compound, the adhesive having been set by causing electrical current to flow in said wire.

8. A loudspeaker voice coil formed as set forth in claim 6, wherein said adhesive has been caused to set by immersion of said coil in a solvent.

9. A loudspeaker voice coil constructed and arranged substantially as herein described with reference to and as illustrated in Figure 2 or Figure 3 of the accompanying drawing.