WO1998002017A1

WO1998002017A1 - Inverted loudspeakers

Info

Publication number: WO1998002017A1
Application number: PCT/SE1997/001209
Authority: WO
Inventors: Mikael Carlsson
Original assignee: Harman Sweden, Filial Till Harman Audio Electronic Systems Gmbh, Tyskland
Priority date: 1996-07-08
Filing date: 1997-07-03
Publication date: 1998-01-15
Also published as: AU3638097A; SE506979C2; SE9602701D0; SE9602701L

Abstract

The invention relates to an electromagnetic converter for reproducing sound as well as to a method for assembling an electromagnetic converter. The converter comprises a so called inverted loudspeaker consisting of voice coil means (1), a magnetic circuit (5-6, 8-11) and a diaphragm (2) which are to be assembled in a basket (4). The magnetic circuit comprises a pre-magnetisable magnet (10). There can also be two pre-magnetisable magnet disks (5, 10) of opposite polarisation on either side of a magnet core in two parts (6, 11). In order to join the core parts (6, 11) with great precision, male and female guiding means (6:1, 11:1) are arranged on the core parts (6, 11).

Description

INVERTED LOUDSPEAKERS

DESCRIPTION

Technical Field

This invention relates to an electromagnetic converter for reproducing sound as well as to a method for assembling an electromagnetic converter.

Prior Art

Electroacoustic converters of different types are well-known in the prior art. Referred to here are converters, or loudspeakers, of the compact, effective type, which comprise a magnet system that is fitted to the front of the loudspeaker (a so called inverted loudspeaker) instead of the back of the loudspeaker, as is customary. In the case of such loudspeakers, a pre-magnetised magnet is used in the magnetic circuit. Another method is to use two permanent magnets of opposite polarities which are arranged facing each other. The latter magnets have surfaces of equal polarity facing each other and are thus mutually repelled. The pre-magnetised magnets are arranged on either side of a core magnet with a small air gap to a surrounding voice coil, which is directly connected to a cone- shaped diaphragm. The magnet means, voice coil, diaphragm and fastening members are arranged in a basket. See, for example US-A-4 737 992, US-A-5 371 806 and DE-A1-0 622 971.

To assemble magnet means in a loudspeaker, arrangements for fastening the magnets are usually incorporated. One disadvantage of known fastening arrangements is that these often cover such a great part of the diaphragm that the sound becomes impaired.

For the magnet means to achieve the most effective result possible, the magnets involved are aligned directly facing each other with as minimal air gap as possible between the magnetic poles in relation to the surrounding voice coil. One disadvantage of known arrangements is that such centring and assembling is difficult to achieve with substantial enough accuracy. If the air gap is not small enough, the loudspeaker's level of effectiveness is impaired.

Summary of the Invention and its Advantages

The objective of this invention is to produce a loudspeaker whose diaphragm is covered as little as possible and thereby the sound quality is increased. According to the invention, the components involved in the loudspeaker can be fastened without the diaphragm being covered unnecessarily by sound-impairing parts for fastening such as ribs or front parts. Thus, according to the invention, acoustic advantages are gained as the entire surface of the diaphragm is free, except for the part which is covered by a central cover.

Another objective of this invention is to produce a loudspeaker where the assembly of the magnet means and the voice coil means can be carried out as precisely as possible. This is achieved by having special guiding means for the assembly of the magnets. The guiding means are required because of the strong, lateral magnetic forces which exist when arranging the magnets as described above. Due to these guiding means, the loudspeaker can be easily assembled with a very small air gap between the voice coil and the magnet poles.

In addition the electromagnetic converter according to the invention is lightweight, flat and of compact depth, which is often desirable when for example, it is to be built into a car door. On top of this, it is of a simple construction and is therefore inexpensive to manufacture.

By using an effective magnetic material, such as neodymium, the converter is light which can be a great advantage in many applications. Description of an Embodiment

The invention is described below in more detail with the help of an embodiment of the invention illustrated in the drawings:

Figure 1 shows a vertical cross sectional view of an electromagnetic converter, according to the invention.

Figure 2 shows a magnified view of the magnet means and the voice coil means.

In Figures 1 and 2, 1 represents the voice coil means comprising a voice coil 1:1 which is secured on top of a coil bobbin 1 :2. In the embodiment, the voice coil is arranged near the front end of the tubular coil bobbin 1 :2. According to the embodiment, the voice coil 1 :1 , which can be made of, for example copper wire or the equivalent, is wound round the coil bobbin 1 :2. The voice coil means 1 are arranged in the central hole of a cone-shaped diaphragm 2. Voice coil means 1 and diaphragm 2 are then glued to each other to the rear part of the coil bobbin.

As shown in Figure 1 , the voice coil's connecting leads 1 :3 are firmly glued to the diaphragm and connected to an external connecting lead 1 :4. The coil bobbin 1:2 is made of plastic, aluminium or similar material. The diaphragm 2 is preferably made of fibre glass or of plastic, Kevlar®, paper or similar material.

A first fastening member 3 made of, for example of steel, aluminium or plastic, is fixed to the loudspeaker's basket 4 either by riveting, glueing, snapping or by another method. The fastening member 3 can also be integrated with the basket 4. According to the embodiment of the invention, the fastening member 3 can be made of a T-shaped device whose horizontal part is fixed to the underside of the basket and whose vertical part is extended inward and forward through the basket's bottom. A pre-magnetisable magnet means 5, for example a neodymium disk, is fixed to the front portion of the fastening member 3. A first core part 6 with a male means 6:1 , preferably comprising a cone-shaped centre pin, is glued to the magnet means 5. The magnet means 5 can be omitted. In the basket 4, there is a resilient centring device which is fixed to the inside of the basket 4. The centring device can be made of fabric or another resilient material.

The voice coil means 1 and the diaphragm 2 are glued together with the forward protruding fastening member 3 which supports both the pre-magnetisable magnet means 5, if this exists, and the first core part 6. The glueing takes place with the help of a so called guiding fixture between the coil bobbin 1 :2 and the first core part 6. The diaphragm is then connected to the resilient centring 7 whose purpose is to ensure that the voice coil 1 :1 is arranged axially. The connecting area between coil bobbin 1 :2, diaphragm 2 and centring device 7 is glued. The outer surface of the diaphragm 2 has a resilient arrangement which is also responsible for directing the voice coil axially.

The arrangement described so far should now be able to be used as a loudspeaker. However, in order to achieve an effective loudspeaker, a further magnet means 10, for example a neodymium disk, is included. The magnet means 10 should be able to be pre-magnetised in an opposite phase in relation to the mentioned pre-magnetised magnet means 5. The surfaces, which are turned to face each other, have in this case the same polarity and a repelling magnetic field is built up. This pre-magnetisable magnet means 10 is connected to a second core part with a female means 11:1. According to the embodiment, the rest of the magnetic circuit consists of a T-shaped device 8 where the end of the vertical portion is turned backwards and provides support for the pre- magnetisable magnet means 10 and the second core part 11. The T-shaped device^'s horisontal portion is fixed to the front edge 9:1 of a tubular cover 9. The rear edge 9:2, which forms a pole part in the magnet system, is designed to be connected to the voice coil's 1 :1 periphery when the loudspeaker is completely assembled. The second fastening member 8 and the cover 9 can also be integrated. Between the voice coil 1:1 and the cover 9, there must be a small air gap, for example of the size of one to two tenths of a millimetre. The second core part 11 , comprising a female means 11 :1 , is glued to the pre- magnetisable magnet means 10. In the embodiment, the female means is formed as a cone-shaped centre hole 11 :1. The centring and the axial directing, which are accomplished by the described components, enables a level of accuracy regarding the size of some hundredths of a millimetre. Fastening means 8, cover 9 and core parts 6 and 11 can be made of, for example, steel with a low carbon content.

The core parts 6 and 11 are now joined by means of glueing and then orientated axially with the help of pin 6: 1 and guiding hole 11 : 1. An air gap of some tenths of a millimetre must exist between the voice coil and respective magnet poles.

If the core parts 6 and 11 do not have their pin 6:1 and their guiding hole 11:1 , it would be difficult to achieve a small enough air gap 12 (1/10 mm) and thus effectively assemble an inverted loudspeaker of good quality. This is because there is a very strong lateral magnetic force and it is consequently very difficult to centre the magnets.

It is apparent for those skilled-in-the-art that the above described embodiment of the invention is only one example and that the components included can have another design and be made of other material within the scope of the invention. For example, the fastening member does not have to be T-shaped and the magnets, voice coil and fastening member can have other cross-sections, just as the basket, diaphragm, male and female means and so on. Likewise, the respective fastenings can be done by other means than glueing.

Claims

1. A method, in an electromagnetic converter for reproducing sound, for assembling and centring voice coil means (1), magnet means (5-6, 8-11) and a diaphragm (2) in a basket (4), characterised in that a first construction is assembled, which comprises:

- said basket (4) in which is arranged a resilient centring device (7) and a first fastening member (3) with a pre-magnetised magnet means (5) where appropriate, as well as with a first core part (6) with male means (6:1) - said diaphragm (2) with a coil bobbin (1:2) arranged in its centre hole, which bobbin supports a voice coil (1:1), the first construction being prepared by arranging the coil bobbin (1 :2) on the first fastening member (3); a second construction is assembled, which comprises: - a magnetic circuit consisting of a cover (9) with a second fastening member (8) inside this, on which a pre-magnetisable magnet means (10) with a second core part (11) with female means (11 :1) is arranged; after which both of the constructions are put together by joining both of the core parts (6,11) and directing them axially with help of the male and female means (6:1, 11 :1).

2. Electromagnetic converter for reproducing sound comprising: a first construction consisting of:

- a basket (4) in which is arranged a resilient centring device (7) and a first fastening member (3) and a first core part (6), as well as

- a diaphragm (2) supporting in its centre hole a coil bobbin (1 :2) with a voice coil (1:1), the coil bobbin (1 :2) being arranged on the said first fastening member (3); and a second construction consisting of. - a magnetic circuit comprising a cover (9), within which is arranged a second fastening member (8) on which a pre-magnetisable magnet means (10) is arranged as well as a second core part (11), characterised in that the core parts (6, 11) include male and female means (6:1 , 11 :1) by means of which the core parts being directed axially when they are joined together.

3. Electromagnetic converter according to claim 2, characterised by the male and female means being composed of a pin (6:1) and a guiding hole (11 :1), respectively.

4. Electromagnetic converter according to any of the claims 2-3, characterised by furthermore a pre-magnetised magnet means (5) being arranged between the first fastening member (3) and the first core part (6).

5. Electromagnetic converter according to claim 4, characterised by the pre- magnetised magnet means (5, 10) being comprised of neodymium disks or suchlike.

6. Electromagnetic converter according to any of the claims 2-5, characterised by the first fastening member (3) comprising a T-shaped device fixed in the basket whose horizontal portion is attached under the basket and whose vertical portion is extended up through the basket (4) and on the end supports the first core part (6).

7. Electromagnetic converter according to any of the claims 2-6, characterised by the second fastening member (8) comprising a T-shaped device whose horizontal portion is attached to one peripheral edge (9:1) of the cover (9) and whose vertical portion is extended in the basket (4) and on the end supports the second core part (11).

8. Electromagnetic converter according to any of the claims 2-7, characterised by the cover's other peripheral edge (9:2) being arranged in connection with the voice coil (1:1) with an air gap in-between. o

9. Electromagnetic converter according to any of the claims 2-8, characterised by the second fastening member (8) being integrated with the cover (9).

10. Electromagnetic converter according to any of the claims 2-7, characterised by the diaphragm (2) and the centring device (7) being attached to the coil bobbin (1) in the same area.