Micro converter, audio device and hearing aid

1. An electro-acoustic micro-converter for generating sound from an electronic input signal, in particular for a device worn in an ear of a user, comprising a device housing with a sound output in which a membrane assembly is suspended with freedom of movement, the membrane assembly comprising an acoustic membrane and a coil element connected thereto, wherein the coil element is provided with connecting means for receiving the electronic input signal and extends in a coil gap, and wherein the device housing comprises magnet means which maintain a magnetic field in the coil gap, the magnet means comprising a permanently magnetic magnet body, wherein the magnet body is located within an at least substantially rectangular first contour around which the coil gap with the coil element therein extends while at least substantially following the contour, the device housing comprises adjacently of the coil gap at least one magnetically conductive wall part extending along an at least substantially rectangular second contour which surrounds the first contour, and the membrane extends over the whole magnet body at least substantially parallel to a main plane formed by the first contour, and on a side remote from the magnet body is in open communication with a hollow sound chamber which is bounded by magnetically non-conductive chamber walls and of which a chamber wall oriented substantially transversely of the membrane is provided with the sound output.

2. The micro-converter as claimed in claim 1 , wherein the at least one wall part parallel to the main plane comprises an overall magnetically conductive surface area of at least about 5 square millimeters.

3. The micro-converter as claimed in claim 1 , wherein the second contour defines a contour of the device housing and the membrane is tensioned over at least substantially a whole surface thereof.

4. The micro-converter as claimed in claim 3 , wherein the at least one wall part has a wall thickness of at least about 170 micron.

5. The micro-converter as claimed in claim 1 , wherein the at least one wall part comprises a ferro-metal.

6. The micro-converter as claimed in claim 1 , wherein the magnet means comprise within the first contour a first magnetically inducible pole body which is in contact with the magnet body, and the first pole body is surrounded in a spatially separated relation by at least one further magnetically inducible pole body while enclosing the coil gap.

7. The micro-converter as claimed in claim 1 , wherein the at least one further pole body extends from the at least one wall part.

8. The micro-converter as claimed in claim 6 , wherein the at least one further pole body extends parallel to the main surface over an area of at least about 5 square millimeters inside the coil gap.

9. The micro-converter as claimed in claim 6 , wherein the pole bodies comprise a ferro-metal.

10. The micro-converter as claimed in claim 1 , wherein the magnet body comprises a highly energetic ferromagnetic alloy.

11. The micro-converter as claimed in claim 1 , wherein the coil body comprises flat windings wound from wire of at least one metal from a group comprising copper, aluminium, silver and gold.

12. The micro-converter as claimed in claim 1 , wherein the coil body comprises flat windings with an overall length of at least about 3 meters, and the magnet means maintain a magnetic field with a magnetic flux density B through the coil element in the order of 0.8 Tesla.

13. The micro-converter as claimed in claim 1 , wherein the device housing is flat with a length of at least about 4.5 millimeters which is bounded by opposite at least substantially rectangular front walls with a diagonal dimension of less than 4.5 millimeters, more particularly the device housing is at least substantially block-shaped with a length in the order of about 5 millimeters and a width of about 3.5 millimeters, wherein the wall part has a height in the order of about 1.8 millimeters.

14. The micro-converter as claimed in claim 1 , wherein the sound chamber is enclosed by walls of a magnetically inert material, in particular a material from a group of stainless steel, copper, brass and plastics.

15. The micro-converter as claimed in claim 1 , wherein the housing comprises on a side remote from the sound chamber a further hollow chamber which is closed to the outside and which is in open communication with the membrane via at least one sound channel.

16. An audio device comprising a device which is worn in the ear and which is adapted and intended to be worn at least substantially wholly concealed in an auditory canal of a user, wherein the device worn in the ear comprises a micro-converter as claimed in claim 1 .

17. A hearing aid comprising an audio device as claimed in claim 16 .

18. The micro-converter as claimed in claim 1 , wherein the at least one wall part comprises a ferro-metal, and is manufactured from a material from a group comprising iron, nickel, nickel-iron, silicon-iron and cobalt-iron.

19. The micro-converter as claimed in claim 6 , characterized in that wherein the pole bodies comprise a ferro-metal selected from the group consisting of iron, nickel, and iron/nickel in at least substantially equal quantities.

20. The micro-converter as claimed in claim 1 , wherein the magnet body comprises aluminum-nickel-cobalt, samarium-cobalt or neodymium-iron-boron.