A CAP FOR AN ELECTRO-ACOUSTIC TRANSDUCER

Abstract

The invention relates to a cap (1) for an electro-acoustic transducer (2), which cap (1) comprises a first portion (3) having a form matching in shape and dimensions at least a top part of a magnetic center pole piece (4) of the transducer (2) and an opening (5) for receiving said magnetic center pole piece (4), wherein the first portion (3) includes at least one recess (6) with reduced material thickness on a lateral face (7) of the first portion (3). Also, the invention relates to: (i) a method (100) of manufacturing a capped center pole piece for an electro-acoustic transducer (2); (ii) a capped center pole piece for an electro-acoustic transducer (2); and (iii) an electro-acoustic transducer (2) comprising the cap (1) or the capped center pole piece.

Claims

1. A capes for an electro-acoustic transducer, which cap comprises a first portion having a form matching in shape and dimensions at least a top part of a magnetic center pole piece of the transducer and an opening for receiving said magnetic center pole piece, wherein the first portion includes at least one recesses with reduced material thickness on a lateral face of the first portion.

2. The cap according to claim 1, wherein the recess is positioned on the lateral face of the first portion so as to face a voice coil and a top plate, wherein the recess has a length in a direction parallel to a longitudinal axis of the first portion substantially equal to a length of the voice coil or a thickness of the top plate.

3. The cap according to claim 1, wherein the first portion includes two recesses positioned symmetrically with respect to the longitudinal axis of the first portion.

4. The cap according to claim 1, wherein a number of recesses is substantially equally spaced along the lateral face of the first portion.

5. The cap according to claim 1, wherein the cap comprises a second portion having a form matching in shape and dimensions the top plate of the transducer and an opening for receiving said top plate, wherein the second portion includes at least one aperture and/or at least one recess with reduced material thickness on a lateral face of the second portion, which aperture or recess is positioned on the lateral face of the second portion so as to face the recesses on the lateral face of the first portion.

6. The cap according to claim 5, wherein the cap comprises a third portion extending from the opening of the first portion to the opening of the second portion.

7. The cap according to claim 6, wherein the third portion, has a drop-like form.

8. A method of manufacturing a capped center pole piece for an electro-acoustic transducer, wherein the method comprises: providing a cap according to claim 1; placing the cap into a casting die adapted to receive the cap; filling the cap with a powder comprising a magnetic material; and pressing the powder from the opening of the first portion, so that the powder fills the aperture and/or the recess of the cap.

9. A capped center pole piece for an electro-acoustic transducer, wherein the capped center pole piece comprises a center pole piece and a cap according to claim 1, wherein a magnetic material fills the aperture and/or the recess of the cap.

10. An electro-acoustic transducer, wherein the transducer comprises a center pole piece and a cap according to claim 1.

11. An electro-acoustic transducer wherein the transducer comprises a center pole piece and a capped center pole piece according to claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1: Cross-section view of a loudspeaker comprising a cap according to the invention.

[0042] FIG. 2A: Cap according to the prior art.

[0043] FIGS. 2B-C: Variants of a cap according to the invention.

[0044] FIG. 3A: Electric current flow for a cap according to the prior art.

[0045] FIGS. 3B-C: Electric current flow for variants of a cap according to the invention.

[0046] FIG. 4: L.sub.E curves comparison

[0047] FIG. 5: Cap having a height smaller than the length of the voice coil.

[0048] FIG. 6: Cap with a drop-like third portion.

[0049] FIG. 7: Flow chart of a method of manufacturing a capped center pole piece.

NOTATIONS

[0050] L: Length of an aperture or a recess

[0051] L.sub.vc: Length of the voice coil

[0052] T: Thickness of the top plate

[0053] Z: Longitudinal axis of the first portion

[0054] 1: Cap

[0055] 2: Electro-acoustic transducer

[0056] 3: First portion

[0057] 4: Magnetic center pole piece

[0058] 5: Opening of the first portion

[0059] 6: Aperture or recess

[0060] 7: Lateral face of the first portion

[0061] 8: Magnetic top plate

[0062] 9: Voice coil

[0063] 10: Air-gap

[0064] 11: Second portion

[0065] 12: Third portion

[0066] 15: Ventilation hole

PREFERRED EMBODIMENTS OF THE INVENTION

[0067] FIG. 1 shows a loudspeaker 2 comprising: a cylindrical center pole piece 4, a top plate 8 having a thickness T, an air-gap 10, a voice coil 9 having a length L.sub.vc and adapted to move along a direction parallel to the longitudinal axis Z, and a cylindrical cap 1 having an opening 5 for receiving the center pole piece 4 and a ventilation hole 15. The cap 1 has two recesses 6 on its lateral face 7 that are positioned symmetrically with respect to the longitudinal axis Z and face the voice coil 9. In particular, the cap 1 is constituted only by the first portion 3.

[0068] FIG. 2A shows a cylindrical cap 1 according to the prior art. It is noticeable that the cap 1 has a ventilation hole 15 on its top face, but no aperture or recess on its lateral face 7.

[0069] FIG. 2B shows a cylindrical cap 1 according to an embodiment of the invention. It is noticeable that the cap 1 has a ventilation hole 15 on its top face and a slit 6 on its lateral face 7. The slit 6 extends for length L along a direction parallel to the longitudinal axis Z of the cap 1. In particular, the cap 1 is constituted only by the first portion 3.

[0070] FIG. 2C shows a cylindrical cap 1 according to another embodiment of the invention. It is noticeable that the cap 1 has a ventilation hole 15 on its top face and a slit 6 that departs from the ventilation hole 15, crosses the top face of the cap 1, reaches the circumference at the top face of the cap 1, continues down on the later face 7 of the cap 1 along a direction parallel to the longitudinal axis Z and ends at the circumference at the bottom face of the cap 1.

[0071] Note that by adjusting, for example, the length L of the slit 6 (from the slit 6 in FIG. 2B to the slit 6 of FIG. 2C) the resulting effect can be regulated.

[0072] FIGS. 3A-C show a simplified model of the flow of the electric current on the caps 1 in FIGS. 2A-C. It is noticeable that the slit 6 in FIG. 3B branches out the electric current flowing on the cap 1.

[0073] FIG. 4 shows the behaviour of L.sub.E with respect to the voice coil 9 displacement in the same direction (In) or in an opposite direction (Out) with respect to the longitudinal axis Z. It is noticeable that: (i) the case with no cap 1 results in the highest positioned L.sub.E curve in the diagram; the case with a cap 1 as in FIG. 2A results in a low positioned L.sub.E curve, which is though dependent on the voice coil 9 displacement; (iii) the case with a cap 1 having two slits 6 as in FIG. 2B that are positioned symmetrically with respect to the longitudinal axis Z results in a low positioned L.sub.E curve, which is practically independent from the voice coil 9 displacement; and (iv) the case with a cap 1 as in FIG. 2B results in an L.sub.E curve that is shifted lower down with respect to the case with no cap 1.

[0074] FIG. 5 shows T-formed center pole piece 4 of a loudspeaker. In this exemplary embodiment, contrarily to the embodiment of FIG. 1, the cap 1 has a height shorter than the length 1, of the voice coil 9. In particular, the magnet system is based on a center-placed magnet.

[0075] FIG. 6 shows a T-formed center pole piece 4 of a loudspeaker. In this exemplary embodiment, the cap 1 is composed of a first portion 3, a second portion 11 and a third portion 12 having a drop-like form. The second portion 11 has a recess 6 that faces a recess 6 on the first portion 3.

[0076] FIG. 7 shows a method 100 of manufacturing a capped center pole piece for an electro-acoustic transducer 2. The method 100 comprises: providing 101 a cap 1 as described above; placing 102 the cap 1 into a casting die adapted to receive the cap 1; filling 103 the cap 1 with a powder comprising a magnetic material; and pressing 104 the powder from the opening 5 of the first portion 3, so that the powder fills the aperture and/or the recess 6 of the cap 1.