Laminated motor structure for electromagnetic transducer

• US 7,457,429 B2
• Filed: 12/31/2003
• Issued: 11/25/2008
• Est. Priority Date: 04/25/2003
• Status: Expired due to Fees

• Current Assignee: Steps Technology Corporation
• Original Assignee: Steps Technology Corporation
• Inventors: Stiles, Enrique M.
• Primary Examiner(s): Ensey; Brian
• Application Number:
  US10/750,468
• Publication Number:
  US 20040213430A1
• Time in Patent Office: 1,791 Days
• Field of Search: 381/396, 381/400, 381/412, 381/414, 381/419, 381/420
• US Class Current: 381/414
• CPC Class Codes: H02K 33/18 with coil systems moving upon intermittent or reversed energisation thereof by interaction with a fixed field system, e.g. permanent magnets
• CPC Class Codes: H04R 2209/021 Reduction of eddy currents in the magnetic circuit of electrodynamic loudspeaker transducer
• CPC Class Codes: H04R 9/025 Magnetic circuit
• CPC Class Codes: H04R 9/06 Loudspeakers

Abstract

An electromagnetic transducer such as an audio speaker having at least one of the soft magnetic components of its motor assembly constructed as a laminated structure of electrically insulated magnetically conductive sections. Eddy currents, which would have been induced in a monolithic component in response to an electrical signal applied to the voice coil, are prevented or significantly reduced by the electrical insulation material between the sections of the laminated component. The transducer produces less heat, is less susceptible to flux modulation, and has increased power handling and reduced distortion.

Claims

1. An audio speaker comprising:

a motor assembly having an axis and including,

a magnet,

a first magnetically conductive member magnetically coupled to the magnet, the first magnetically conductive member comprising a plurality of laminated layer sections which are magnetically coupled to but electrically insulated from each other, wherein the laminated layer sections are separated along boundaries which are substantially parallel to the axis, and

a second magnetically conductive member magnetically coupled to the magnet,

a magnetic air gap between the first and second magnetically conductive members; and

a diaphragm assembly coupled to the motor assembly and including a voice coil disposed within the magnetic air gap.

2. The audio speaker of claim 1 wherein:

each of the laminated layer sections has a substantially uniform thickness.

3. The audio speaker of claim 1 wherein:

the laminated layer sections are not all of the same thickness.

4. The audio speaker of claim 1 wherein:

each of the laminated layer sections has a substantially wedge shape.

5. The audio speaker of claim 1 wherein:

the magnet comprises an external ring magnet.

6. The audio speaker of claim 5 wherein:

the first magnetically conductive member comprises a top plate.

7. The audio speaker of claim 5 wherein:

the first magnetically conductive member comprises a pole plate.

8. The audio speaker of claim 7 wherein:

the pole plate comprises a laminated pole piece and a monolithic back plate coupled to the laminated pole piece.

9. The audio speaker of claim 7 wherein:

the second magnetically conductive member comprises a top plate which is comprised of a plurality of laminated layer sections which are magnetically coupled to but electrically insulated from each other.

10. The audio speaker of claim 1 wherein:

the magnet comprises an internal magnet.

11. The audio speaker of claim 10 wherein:

the first magnetically conductive member comprises a top plate.

12. The audio speaker of claim 11 wherein:

the first magnetically conductive member comprises a cup.

13. The audio speaker of claim 12 wherein:

the second magnetically conductive member comprises a top plate which is comprised of a plurality laminated layer sections which are magnetically coupled to but electrically insulated from each other.

14. The audio speaker of claim 1 wherein:

the magnet comprises an internal magnet; and

one of the first magnetically conductive member and the second magnetically conductive member comprises a tube yoke.

15. The audio speaker of claim 14 wherein:

the second magnetically conductive member comprises the tube yoke; and

the first magnetically conductive member comprises a pole piece.

16. The audio speaker of claim 14 wherein:

the first magnetically conductive member comprises the tube yoke.

17. The audio speaker of claim 16 wherein:

the second magnetically conductive member comprises a pole piece which is comprised of a plurality of laminated layer sections which are magnetically coupled to but electrically insulated from each other.

18. The audio speaker of claim 16 wherein the tube yoke comprises:

a plurality of substantially rectangular laminate layer sections coupled together.

19. The audio speaker of claim 18 wherein:

at least some of the substantially rectangular layer sections include holes through which a bolt may be passed from one layer section to a next layer section along an axis of the tube.

20. The audio speaker of claim 19 wherein:

the holes are formed through tabs extending from a main body of the layer section.

21. The audio speaker of claim 16 wherein:

the tube comprises a plurality of substantially V-shaped laminate layer sections coupled together; and

the top plate comprises a plurality of laminate layer sections coupled together.

22. The audio speaker of claim 21 wherein the plurality of laminate layer sections of the top plate comprises:

a plurality of one-piece top plate sections; and

a plurality of two-piece top plate sections.

23. The audio speaker of claim 22 wherein:

the one-piece top plate sections and the two-piece top plate sections include corresponding holes through each, extending along an axis of the tube.

24. The audio speaker of claim 14 further comprising:

an external magnet magnetically coupled to the tube; and

an external top plate magnetically coupled to the external magnet.

25. The audio speaker of claim 24 wherein:

the external top plate comprises a plurality of laminated layer sections which are magnetically conductive but electrically insulated from each other.

26. The audio speaker of claim 14 further comprising:

a collar magnetically coupled to the tube and defining the magnetic air gap with the pole piece.

27. The audio speaker of claim 14 wherein the tube comprises:

shoulders adjacent the diaphragm assembly.

28. The audio speaker of claim 1 wherein the second magnetically conductive member comprises a plurality of laminated layer sections which are magnetically coupled to but electrically insulated from each other.

29. The audio speaker of claim 28 wherein:

the laminated layer sections of the first magnetically conductive member are oriented in a different direction than the laminated layer sections of the second magnetically conductive member.

30. An audio speaker comprising:

a diaphragm assembly including a voice coil, wherein the voice coil has an axis of movement; and

a motor assembly including,

a first magnetically conductive member,

a first laminated structure in which a plurality of magnetically conductive sections are mechanically coupled together and electrically insulated from each other to prevent eddy currents which would otherwise be induced by an electrical current applied to the voice coil, wherein the magnetically conductive sections are electrically insulated from each other along boundaries substantially parallel to the axis of the voice coil, and

a magnet magnetically coupled between the first magnetically conductive member and the laminated structure,

wherein the first magnetically conductive member and the laminated structure define between them a magnetic air gap within which the voice coil is disposed.

31. The audio speaker of claim 30 wherein:

the first laminated structure comprises a top plate.

32. The audio speaker of claim 30 wherein:

the first laminated structure comprises a pole yoke.

33. The audio speaker of claim 30 wherein:

the first laminated structure comprises a cup yoke.

34. The audio speaker of claim 30 wherein:

the first laminated structure comprises a tube yoke.

35. The audio speaker of claim 30 wherein:

the first magnetically conductive member comprises a second laminated structure in which a plurality of magnetically conductive sections are mechanically coupled together and electrically insulated from each other to prevent eddy currents which would otherwise be induced by the electrical current applied to the voice coil.

36. The audio speaker of claim 35 wherein:

the magnetically conductive sections of the first laminated structure have a different orientation than the magnetically conductive sections of the second laminated structure.

37. An improvement in a electromagnetic motor structure which includes a magnetically conductive yoke, a magnetically conductive top plate defining a magnetic air gap with the yoke, and a permanent magnet magnetically coupled between the yoke and the top plate, wherein the improvement comprises:

at least one of the yoke and the top plate being comprised of multiple components laminated together so as to be electrically insulated from each other, wherein the multiple components are laminated at boundaries substantially parallel to an axis of the electromagnetic motor structure;

whereby the at least one of the yoke and the top plate which is laminated has a significantly reduced susceptibility to eddy currents being induced therein by a varying magnetic flux field from a voice coil in the magnetic air gap.

38. The improvement in the electromagnetic motor structure of claim 37, wherein the improvement further comprises:

the multiple laminated components each having one of a substantially flat shape and a substantially wedge shape.

39. The improvement in the electromagnetic motor structure of claim 37, wherein the improvement further comprises:

both the yoke and the top plate being so laminated.

40. The improvement in the electromagnetic motor structure of claim 37, wherein the improvement further comprises:

the yoke comprising one of a cup, a pole plate, and a tube.

41. A method of operating an audio speaker to move a diaphragm in response to an alternating current electrical signal applied to the speaker, the method comprising:

(A) conducting magnetic flux from a magnet, thence through a first magnetically conductive member, over a magnetic air gap, thence through a second magnetically conductive member, and thence back to the magnet,

(B) conducting the electrical signal through a voice coil which is disposed within the magnetic air gap and wound around a bobbin which is coupled to the diaphragm;

(C) in response to the electrical signal being conducted through the voice coil, moving the voice coil under electromotive force in response to the presence of the magnetic flux across the magnetic air gap; and

(D) substantially preventing eddy current in at least one of the first and second magnetically conductive members, by virtue of the at least one of the first and second magnetically conductive members comprising a laminated structure of electrically insulated magnetically conductive sections, which eddy current would otherwise be induced by the electrical signal being conducted through the voice coil, wherein eddy currents induced by the voice coil are interrupted at boundaries between adjoining ones of the magnetically conductive sections, wherein the boundaries are substantially parallel to an axis of movement of the voice coil.

42. The method of claim 41 further comprising:

holding the laminated structure together with at least one bolt passed through corresponding holes which extend through the respective electrically insulated magnetically conductive sections.