US2039856A - Electroacoustic device - Google Patents

Description

ay 5, 1936.. w T. TABER 290399855 ELECTROACOUSTIC DEVICE Filed May 27, 1929 Tic-1.1..

INVENTOR u ATTORNEY or vice versa, that is, telephone receivers and positioning the moving coil.

' provided with a field winding and an outer pot- Patented May 5, 1936 UNITED STATES PATENT OFFICE ELECTROAOOUSTIO DEVICE William T. Taber, Bloomfield, N. J., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application May 2'7, 1929, Serial No. 366,341 12 Claims. (01. ne -115.5)

This invention relates to electro-acoustic deshaped member ll connected at one end to one vices of the moving coil, or dynamic, type for end of the core l0, and extended inwardly at its converting electrical oscillations into sound waves other end to form an outer pole piece spaced from the pole piece formed by the other end of the core to leave an annular air gap l2. A dished diaphragm l3, conical as shown, is mounted in front of the magnet. The large end of the diaphragm is secured through a flexible portion [4 to the edge of a support or cage IS, The voice coil 20 is mounted ona tubular carrier 2| which is secured to the small or apex end of the diaphragm and extends into the annular gap I2 with the coil located between the magnet poles. The voice coil is fed through leads 22 with an audio-frequency varying current as usual.

, The carrier tube 2| and the small end of the diaphragm are centered and positioned by means of a flexible disk 25 which is fixedwithin the carrier tube and extends transversely thereof closely adjacent to the outer edge of the coil, and is secured by means of a screw 26 and spacing washer 21 to the end of the core H1, or inner pole piece. The disk 25, while permitting the necessary axial movement of the diaphragm and coil carrier, holds them against transverse movement and insures accurate positioning of the coil in the air gap, and makes it possible to havethe gap very narrow, with a minimum clearance between the coil and its carrier and the gap walls withoutdanger of contact. Most desirably, the centering disk is located within the tube close to the plane of the outer edge of the coil, thereby minimizing the effect of any slight inaccuracy of the parts; Having the centering disk secured within the coil carrying tube has the further advantage, especially when it is located well within the tube as shown, of strengthening the tube and resisting any tendency to deformation thereof.

The coil carrying tube 21 may be of any suitable material and formed in any suitable manner. I have found it most desirable, however, to make the tube of paper board and of the construction shown in Fig; 4; As here shown, the tube comprises an inner tubular member 30 extending the full length of the tube, and two spaced outer tubular members 3i and 32 spaced apart to form an external circumferential channel 33 for receiving the voice coil, the spaced outer tubes or bands 3| and 32 being of such width respectively and so spaced that the channel 33 is of desired Width and located in the desired position longitudinally of the tube. The band 32 will usually be narrow as shown, and the band 3| wider, since the tube need not extendinward substantially beyond the inner edge of the coil, and may even transmitters. The invention relates more particularly to means for mounting and transversely It is desirable that the annular air gap in the magnetic circuit of a dynamic receiver or trans mitter shall be as narrow as possible, but the narrower the gap the more necessary it becomes to have the moving, or voice, coil and its carrier, which are mounted free to move axially in the magnetic gap, accurately positioned and held against transverse movement so as to avoid contact with either the inner or outer pole pieces. The present invention aims to provide an improved coil carrier and centering means for accurately positioning the coil carrier and the diaphragm with relation to the magnetic gap and holding them against transverse movement, while permitting the required axial movement.

A coil carrier according to the invention is of tubular form and has a flexible disk fixed transversely within the tube for connection to the end of the central pole piece of the magnet. Making the tubular carrier with such a centering disk secured therein not only simplifies production, but has the important advantage of insuring accurate positioning of the carrier and voice coil in the magnetic gap regardless of slight inaccuracy, in securing the carrier tube to the diaphragm. This effects improvement in the apparatus and saving in assembly cost, since, when the centering device is secured to the diaphragm, the voice coil carrying tube must be positioned on and secured to the diaphragm with great accuracy in order that it shall be properly centered with relation to the magnetic gap.

Other features and advantages of the invention will appear from the following description of an approved embodiment of the invention. In the accompanying drawing:-

Fig. 1 shows diagrammatically a dynamic speaker embodying the invention;

Fig. 2 is a side view of the voice coil carrier with a coil thereon;

Fig. 3 is an end view of the carrier; and I Fig. 4 is an enlarged sectional view of the voice coil carrier with a coil thereon.

Referring to the drawing, and first to Fig. 1, the dynamic speaker illustrated includes the usual magnetic circuit shown as formed by a magnet of usual form having a central core l0 not extend at all beyond the inner edge of the coil. The tube should, however, extend outward suificiently to have the diaphragm spaced conveniently away from the magnet. The bands 3| and 32 are most desirably of a thickness substantially equal to the thickness of the coil, which is comparatively thin. The inner tubular member 30 is made of strong paper or light paper board as thin as possible consistent with the necessary strength. Not much strength is required in this member, especially with a layer-wound coil of very thin metallic ribbon as shown.

Such a, voice coil is more particularly described and claimed in application of Clifford E. Stevens and William T. Taber, Serial No. 366,254, filed May 27, 1929. Most desirably, the successive, insulated turns of the thin conducting strip or ribbon are cemented together and the coil as a whole cemented to the inner tubular member 30 of the carrier. The ends of the coil-forming ribbon are turned outward and secured to the carrier tube at spaced points as byeyelets 34 and may extend thence to form the flexible connections 35 to the leads 22. Obviously, coils of other suitable kinds may be used on my carriers, but layer-wound coil of thin metallic ribbon, aside from its electrical advantages, has the advantage of contributing to the strength of the coil device.

The centering member or disk 25 may be of any suitable form and material giving the necessary flexibility to permit the desired freedom of axial movement of the tube while preventing transverse movement thereof. It need not be a sheet or plate but may be of any suitable construction to resist movement of the tube in at least three directions in a transverse plane. Most desirably, it is made from a piece of strong but sulflciently flexible material, such as paper or fibre board or very thin metal or Bakelized fabric partly cut away between peripheral and central portions to make it more flexible, as, for example, as shown in Fig. 3. The central portion of the disk has an opening 31 to receive a fastening screw, and the peripheral portion serves as an interior strengthening flange for the tube. The disk should be fixed securely, and, most desirably, permanently in the tube. I have found it best to cup or otherwise shape a piece of the sheet material so that it shall have a flange 36 extending at right angles from the disk proper of a size to fit within the tube, and most desirably of a width to extend to the edge of the tube when the disk is positioned within the tube. The flange is cemented or otherwise suitably secured to the tube wall.

What is claimed is:

1. An electro-acoustic device, comprising a magnetic circuit having a central pole piece and an annular air gap about the end of the pole piece, an acoustic diaphragm, a tubular voice coil carrier attached to the diaphragm and extending therefrom into the magnetic gap, a flexible disk serving as a centering member extended transversely within the tubular carrier intermediate its ends and provided with a peripheral flange for attachment thereto, means for securing said disk to the end of the central pole piece, and a voice coil wound around said tubular carrier.

2. An electro-acoustic device, comprising a magnetic circuit having a central pole piece and an annular air gap about the end of the pole piece, a dished direct-acting diaphragm, a voice coil, and a tubular voice coil carrier attached to the apex of the diaphragm and extending therefrom into the magnetic gap, a. flexible disk serving as a centering member extended transversely within the tubular carrier intermediate its ends and provided with a peripheral flange for attachment thereto, means for securing said disk to the end of the central pole piece, and a voice coil Wound around said tubular carrier.

3. An electro-acoustic device, comprising a magnetic circuit having a central pole piece and an annular air gap about the end of the pole piece, a dished direct-acting diaphragm, a voice coil, and a tubular voice coil carrier secured to the small end of the diaphragm and extending therefrom into the air gap, the carrier tube having a circumferential groove in which the coil is located, a flexible disk serving as a centering member extended transversely within the tubular carrier intermediate its ends and provided with a peripheral flange for attachment thereto, means for securing said disk to the end of the central pole piece, and a voice coil wound around said tubular carrier.

4. The combination with a direct-acting conical diaphragm for an electro-acoustic device, of a tubular voice coil carrier secured to the small end of the diaphragm, a flexible disk serving as a centering member extending transversely within the tubular carrier intermediate its ends and provided with a peripheral flange for attachment thereto, and a voice coil wound around said tubular carrier.

5. A voice coil carrier for an electro-acoustic device, consisting of a hollow cylinder of non-conducting and non-magnetic material having an external circumferential groove for receiving the coil, a flexible disk serving as a centering member extending transversely within the tubular carrier intermediate its ends and provided with a periph eral flange for attachment thereto, and a voice coil wound around said tubular carrier.

6. A tubular voice coil carrier, having a flexible centering disk extending across the interior thereof and spaced from either end thereof, said disk provided with a flange which constitutes the attaching means to the coil carrier.

'7. A tubular voice coil carrier, having an external circumferential voice coil groove, and having a flexible centering disk extending across the interior thereof spaced from either end thereof and close to a transverse plane extending through the groove, said disk provided with a flange which constitutes the attaching means to the coil carrier.

8. A voice coil device for an electro-acoustic device, comprising a hollow cylinder of non-conducting and non-magnetic material, and a voice coil mounted in an externally reduced portion of the cylinder and having its outer surface substantially flush with the outer surface of the cylinder, the cylinder having a flexible disk extending across the interior thereof to serve as a centering member, said disk provided with a flange which constitutes the attaching means to the coil carrier.

9. In telephonic apparatus of the character described, the combination with a conical diaphragm of large diameter, of a field pole plate and a pole spaced therefrom to form an air gap, a voice coil disposed for axial vibration in said air gap, a form for said coil having an elongated neck projecting beyond said pole plate, means for securing said diaphragm to the end of said neck remote from said coil, and a lead from said coil anchored to said neck between said coil and the adjacent end of said diaphragm, said lead extending flexibly from said anchorage to the external circuit. said anchorage disposed at such point on said neck that at maximum axial vibration of said coil the flexible portion of said lead is prevented from contacting with said pole plate.

10. A movable member for an acoustical device comprising a diaphragm, an annular support of insulating material connected to said diaphragm, a coil of wire wound on said annular support, a lead-out for each end of the wire of the coil comprising a flexible conductor connected thereto, and means for attaching each flexible conductor at its connected end to said support alone.

11. The method of manufacturing a driving coil for attachment to a diaphragm of an acoustical device which comprises forming an annular support from insulating material, winding a coil of wire on said support, electrically connecting to each end of the wire of said coil a conductor of flexible material, and fastening one end of each conductor to the support at a point adjacent its connection to said wire, said fastening being independent of said diaphragm.

12. In telephonic apparatus, the combination with a diaphragm, of a voice coil for actuating said diaphragm, an annular form on which said voice coil is disposed and which extends at substantially the diameter of said coil to said diaphragm, a lead for connecting said voice coil to an external circuit taking off directly from said coil form and independently of said diaphragm, and means defining the point of take off comprising means for anchoring the lead to the coil form at a point between said coil and said diaphragm.

WILLIAM T. TABER.

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