Miniature voice coil with integrated coupling coil

1. A miniature electro-acoustic transducer comprising a voice coil attached to a diaphragm, and a magnet assembly comprising an air gap, said voice coil comprising:

a first voice coil portion at least partly positioned in the air gap of the magnet assembly, said first voice coil portion having its primary extension in a direction substantially parallel to a direction of movement of the diaphragm of the miniature transducer;

a second voice coil portion attached to the diaphragm of the miniature transducer, said second voice coil portion being positioned outside of the air gap of the magnet assembly of the miniature transducer; and

wherein the second voice coil portion, in a direction substantially perpendicular to the primary extension direction of the first voice coil portion, has a thickness being 2-5 times larger than a thickness of the first voice coil portion.

2. A miniature electro-acoustic transducer according to claim 1 , wherein the first voice coil portion defines an outer voice coil region, and wherein the second voice coil portion extends into said outer voice coil region.

3. A miniature electro-acoustic transducer according to claim 1 , wherein the first voice coil portion defines an inner voice coil region, and wherein the second voice coil portion extends into said inner voice coil region.

4. A miniature electro-acoustic transducer according to claim 1 , wherein the first voice coil portion, in a plane substantially perpendicular to the direction of movement of the diaphragm, has a substantially rectangular shape.

5. A miniature electro-acoustic transducer according to claim 1 , wherein the first voice coil portion, in a plane substantially perpendicular to the direction of movement of the diaphragm, has a substantially circular shape.

6. A miniature electro-acoustic transducer according to claim 5 , wherein an inner voice coil region of the substantially circular shape has a diameter in the range 2-4 mm, such as a diameter of approximately 3 mm.

7. A miniature electro-acoustic transducer according to claim 1 , wherein the first voice coil portion comprises a wound copper-clad aluminium wire.

8. A miniature electro-acoustic transducer according to claim 1 , wherein the second voice coil portion comprises a wound copper-clad aluminium wire.

9. A miniature electro-acoustic transducer according to claim 1 , wherein the first and second voice coil portions comprise a single copper-clad aluminium wire thereby forming an integrated voice coil.

10. A miniature electro-acoustic transducer according to claim 1 , wherein the magnet assembly comprises an inner permanent magnet and an annular permanent magnet substantially concentrically arranged on a magnetically permeable yoke, the magnet assembly further comprising an inner pole piece and an annular pole piece arranged on the inner permanent magnet and the annular permanent magnet, respectively.

11. A miniature voice coil adapted to be attached to a diaphragm of a miniature electro-acoustic transducer, said voice coil comprising:

a first voice coil portion adapted to be positioned in an air gap of a magnet assembly of the miniature transducer, said first voice coil portion having its primary extension in a direction substantially parallel to a direction of movement of the diaphragm of the miniature transducer;

a second voice coil portion adapted to be attached to the diaphragm of the miniature transducer, and adapted to be positioned outside of the air gap of the magnet assembly of the miniature transducer; and

wherein the second voice coil portion, in a direction perpendicular to the primary extension direction of the first voice coil portion, has a thickness being 2-5 times larger than a thickness of the first voice coil portion.

12. A miniature voice coil according to claim 11 , wherein the first voice coil portion defines an outer voice coil region, and wherein the second voice coil portion extends into said outer voice coil region.

13. A miniature voice coil according to claim 11 , wherein the first voice coil portion defines an inner voice coil region, and wherein the second voice coil portion extends into said inner voice coil region.

14. A miniature voice coil according to claim 11 , wherein the first voice coil portion, in a plane substantially perpendicular to the direction of movement of the diaphragm, has a substantially rectangular shape.

15. A miniature voice coil according to claim 11 , wherein the first voice coil portion, in a plane substantially perpendicular to the direction of movement of the diaphragm, has a substantially circular shape.

16. A miniature voice coil according to claim 15 , wherein an inner voice coil region of the substantially circular shape has a diameter in the range 2-4 mm, such as a diameter of approximately 3 mm.

17. A miniature voice coil according to claim 11 , wherein the first voice coil portion comprises a wound copper-clad aluminium wire.

18. A miniature voice coil according to claim 11 , wherein the second voice coil portion comprises a wound copper-clad aluminium wire.

19. A miniature voice coil according to claim 11 , wherein the first and second voice coil portions comprise a single copper-clad aluminium wire thereby forming an integrated voice coil.

20. A miniature voice coil according to claim 11 , wherein a number windings of the first voice coil portion substantially equals a number of windings of the second voice coil portion.