EP2441276A1

EP2441276A1 - Speaker having a center pleat

Info

Publication number: EP2441276A1
Application number: EP09760718A
Authority: EP
Inventors: Norman Gerkinsmeyer
Original assignee: Individual
Current assignee: GERKINSMEYER, NORMAN
Priority date: 2009-06-08
Filing date: 2009-11-04
Publication date: 2012-04-18
Also published as: DE102009024566A1; US9392369B2; US20120087523A1; WO2010142315A1

Abstract

The invention relates to a speaker having a sound emission direction, comprising: a cage (6); a membrane system having a membrane constructed as a sandwich and becoming thicker from the inside to the outside, an internally wound vibrating coil (16) mounted on a carrier (3) in the center and at the height of the membrane (1), wherein the membrane (1) is connected to the carrier (3), a first centering feature (2) implemented particularly sinusoidal in cross section and centering the membrane in the cage (6) in a first plane, and a second centering feature (4) implemented particularly sinusoidal in cross section and connected to the carrier (3) of the vibrating coil (16) and centering the membrane (1) in a second plane by means of the carrier (3); a symmetrically constructed stray field magnet system (7) comprising two magnets (9) having opposite pole orientation and a pole plate (8) disposed centered between the two magnets, wherein the stray field magnet system (7) centrally permeates the membrane, the vibrating coil (16) is located at the height of the pole plate (8) in the non-displaced state, and the stray field magnet system (7) is disposed centered relative to the cage (6); and a center pleat (11) forming a closed and flexible connection between the stray field magnet system (7) and the membrane system (1, 3, 16).

Description

description

Speaker with center pitch

The invention relates to a speaker with a basket, a flat membrane and a stray field magnet system, which should have the lowest possible height.

Basically, such speakers are well known. They are mainly used in consumer, pro audio, installation and in the automotive sector on land, water and air and should be assembled, integrated or installed with minimum space requirements and material usage.

However, there is the problem that such speakers on the one hand are not built flat enough, on the other hand, with respect to their sound quality, especially in the bass, are not sufficient, since these two requirements are in opposite directions.

It is therefore an object of the invention to find a construction of a flat speaker as possible while optimally sound quality, especially in the bass range.

This object is solved by the features of independent claim 1. Advantageous developments of the invention are the subject of the subordinate claims.

To properly hear, perceive or even feel a bass, you need area and stroke / amplitude. If the area becomes smaller, you need more stroke. However, this "more stroke", meaning more movement of the diaphragm, takes up space and, as previously described, there is less space in most installation situations.There is still the possibility of active equalization, meaning an electronic intervention with DSP technology, but that changes Nothing about the fact of physical laws.

The inventor has recognized that it is possible to build a speaker by the structural features of a loudspeaker according to claim 1, which on the one hand has a minimum height, on the other hand, an optimal sound result, especially in the bass area supplies. Accordingly, is used for such a speaker, a very rigid membrane with a sandwich construction, which can be made very flat thereby. To generate a maximum stroke, a symmetric stray field magnet system is used, the membrane being connected via a hollow cylindrical support to an internal voice coil. The membrane is guided to avoid unwanted wobbling movements in two planes by two centerings, with a first centering directly between the basket and membrane and a second centering between the basket and the carrier is stretched. In addition, to achieve adequate sound quality in this construction, it is absolutely necessary to use a center bead, which effectively prevents air leakage between the stray field magnet system and the voice coil, thus sealing this gap or covering residual noise therefrom.

The invention thus relates to a flat-mounted loudspeaker with a center pitch and a loudspeaker chassis with symmetrical stray field magnet.

This type of speaker is typically a relatively open non-airtight speaker system by design. What is meant is that the voice coil only surrounds the magnet, which is shaped like a more or less simple cylinder, in the center. As a result, an annular air gap is formed between the interior of the coil and the outside of the magnetic cylinder.

Through this air gap, on the one hand, when the loudspeaker is mounted in a housing and the membrane moves with the coil, the air can pass unhindered through it, producing noises that result from decompressing and compressing the air and, secondly, generating noise through the mechanics of the sound transducer itself or the loudspeaker housing can be heard unrestrained.

The bead used in the loudspeaker according to the invention, arranged in the middle of the loudspeaker and extending from the central magnet system (= center bead), is now intended to prevent precisely this problem and, moreover, also the acoustic short circuit which occurs due to air exchange between see front and back of the membrane takes place, prevented. For this purpose, the Mittensicke is now centric or rotationssymmtrisch mounted with the magnet, with his optional adapter or spacer or other auxiliaries and the surrounding membrane with their optional adapter or spacer or other auxiliary materials, glued or jammed.

However, it has also proven to be favorable to construct the middle part in such a way that it also has leading or centering properties, but also damping properties. Depending on the task, the choice of material is very important.

Should it also have a steaming effect _/ so a dampening rubber, rubber or plastic should be used, should it rather have centering effect is an airtight coated fabric of advantage, if it only have a sealing function, pressed foam has been found to be very positive. However, it is also conceivable to use the materials mixed or combined, for example a fabric is coated or vulcanized with rubber, rubber or plastic, etc.

Ea has also proved to be favorable by the shape of the contour of the center bead to achieve different functions or properties. Thus, it is advantageous to make the edges or ends with which the middle bead is fixed, in particular glued, more straight and / or thicker, in order to have more stability. At the same time, the radius itself should be made rather thinner, as it must be able to move in a targeted manner. It may also be advantageous to make the transition from the edges or ends to the radius even in terms of thickness or flexibility so as to allow a harmonious rolling or moving.

According to these findings described above, the inventor proposes a loudspeaker with a sound radiation direction, comprising: a basket, a membrane mystery with:

a sandwich-type membrane thickened by juainon n & ch aullan,

ADJUSTED SHEET (RULE 91) ISA / EP a voice coil mounted in the center and at the level of the diaphragm on a support and internally wound, the diaphragm being connected to the support,

a first, in particular sinusoidal, cross-section centering, which centers the membrane in the basket in a first plane,

a second, in particular sinusoidal cross-section centering, which is connected to the carrier of the voice coil and centered on the carrier, the membrane in a second plane,

- A symmetrically constructed stray field magnet system with two opposite polarity oriented magnets and a centrally disposed between the two magnets pole plate, wherein:

The stray field magnet system penetrates the membrane centrally,

- The voice coil is in the non-deflected state at the height of the pole plate

- And the stray field magnet system is arranged centrally to the basket,

- And a center bead, which forms a closed and flexible connection between the stray field magnet system and the membrane system.

In principle, it is possible to connect the voice coil, which has two electrical connections, via free wires to an amplifier, but it is more favorable if the electrical connections are connected in their course with one of the centerings, in particular arranged symmetrically and preferably with one of Centering are woven. This results in no undefined and asymmetrical forces that could affect the movement of the voice coil and thus the membrane unfavorable.

Furthermore, it is particularly advantageous if the center bead is arranged on the main emission side of the loudspeaker.

In addition, the center bead should have a maximum radius which is at most one third of the maximum radius of the membrane, so that caused by the center bead itself no interference.

It is also advantageous to design the center bead in terms of its contour and / or material thickness so that it over their Body different thickness fails. As a result, relatively more material can be used in areas which are intended to be particularly dimensionally stable and can be saved in material in areas which are to be particularly elastic. In this case, the contour or material thickness should have a smooth and / or flowing transition between different thicknesses.

It is advantageous if the center bead has a contour which is flowing from thick at the lower outer edge and adhesive surface, thinner over the radius and then thicker again to the upper inner diameter and adhesive surface.

The center bead can be made, for example, from a pressed foam or one or a mixed form of the materials listed below: rubber, plastic, airtight coated fabrics.

Furthermore, the mounting of the center bead can be made with the help of spacers. Also favorable is a one-piece version of the center bead.

Advantageously, furthermore, the stray field magnet can be formed in such a way that it has a phase or a shoulder in the area of the end face on at least one side. This can then be fixed very space-saving in terms of height Mittensicke.

The center bead itself can be arranged on the side of the membrane and connected directly to it. Alternatively, there is the somewhat less favorable, but still sufficiently effective way to connect the center bead directly to the second centering.

For producing the center bead, a spraying method or a vulcanizing method may be used.

Furthermore, the basket can be provided with openings that allow air passage, whereby an air storage is prevented. These openings in the basket can also be provided with a sound and / or air permeable fabric or fabric for protection against dust, dirt and water. At least one of the centerings can be designed as TopfZentrierung and / or have a spacer for ease of installation.

In order to homogenize the field line course and improve the field strength above and below the stray field magnet system, a slice of magnetic material can additionally be arranged in each case. For this purpose it may also be advantageous if a thin copper ring or a copper cup is arranged around the outer edge of the pole plate. Likewise, the basket may be made of a non-magnetic material.

Furthermore, it is possible to facilitate the installation of the speaker by the individual parts of the stray field magnet system, so the magnets and the pole plate are provided with a central bore through which a non-magnetizable screw can be performed for ease of assembly, which is removed after assembly.

Furthermore, the production can be carried out by a part of the speaker in an object to be integrated, for example, a door trim of a car, and mounted during assembly, the other missing parts to be mounted.

With regard to the configuration of the sandwich-like membrane, it is advantageous if it becomes thicker from the outer edge to the middle, preferably in a continuously straight or in a continuously curved shape.

In principle, it is advantageous to make the membrane as flat as possible in order to save height. Advantageously, the membrane should be rotationally symmetrical in this case and, based on its surface directed toward the main emission direction, have a cone opening angle of 80 ° to 95 ° between the axis of rotation and the conical surface. If the membrane is not rotationally symmetrical, the described opening angle should likewise not be exceeded.

Alternatively, in the case of a rotationally symmetrical shaped membrane, with respect to its two-sided surfaces, in each case a cone opening angle of 90 ° to 95 ° between rotational axis and conical surface are provided. Again, if the membrane is not rotationally symmetric, the described opening angle should likewise not be exceeded.

For a compact construction as possible, the membrane may have an inner hollow cylindrical edge which is connected to the carrier of the voice coil, wherein the membrane with respect to its inner hollow cylindrical edge in the stroke direction of the voice coil can be arranged symmetrically to the voice coil or with respect to its inner hollow cylindrical edge in the stroke direction of Voice coil one-sided offset to the voice coil, but can be arranged in the voice coil.

Furthermore, advantageously, the hollow cylindrical carrier of the voice coil have a greater height than the inner hollow cylindrical edge of the membrane, wherein advantageously the support of the voice coil on one side substantially further protrudes from the inner edge and is connected there to the second centering.

In addition to the above-described optimized embodiment of the stray field magnet system and its arrangement with respect to the basket and the membrane further contributes to the shape and design of the membrane not inconsiderable to the invention flat construction of the speaker. In particular, the membrane should be designed to achieve a very stable structure as a sandwich, which is particularly advantageous if the membrane is flat with respect to its center plane or with respect to the sections of its center line shown here between their outer surfaces, that has a cone angle of 90 °. Based on a thinning towards the edge membrane, the cone angle is then even more than 90 °, optionally up to 95 °. In principle, however, it is also possible to easily arch the membrane in its main sound radiation direction. With respect to a cone cone angle can be realized up to 80 °. However, as soon as the outer edges of the membrane protrude beyond the curvature of the center bead at its maximum deflection, this undesirably increases the height of the loudspeaker. In the following the invention with reference to the preferred embodiments with reference to the figures will be described in more detail, with only the features necessary for understanding the invention features are shown.

They show in detail:

1 inventive speaker with an internally wound voice coil with voice coil bobbin, a bead, a Flachsandwichmembran, a basket, a flat centering, an annular air gap with air passage and a symmetric stray field magnet with its pole plate, the Mittensicke is indicated only by dashed lines;

Fig. 2 detail I of Fig. 1 with an internally wound

Voice coil with voice coil bobbin, with a bead, with a Flachsandwichmembran, a basket, flat centering and a symmetrical stray field magnet system consisting of two magnets mounted opposite polarity with a pole plate in between, a spacer for mounting and the annular air gap marked by its arrows the air passage direction;

FIG. 3 shows speakers from FIG. 1 without center bead in a 3D view in order to better illustrate the annular air gap with air passage; FIG.

Fig. 4 loudspeaker according to the invention with one-piece basket design in a 3D view, on which a center bead is mounted on the simplified illustrated cylindrical symmetrical stray field magnet and the membrane to cover the annular air gap with air passage or seal;

Fig. 5 speaker with one-piece basket construction in

Section view, on which the center bead is mounted on the simplified cylindrical symmetrical stray field magnet and the membrane and thus covers the annular air gap with air passage or seals;

6 loudspeaker with one-piece basket construction in its sectional view, on which the center bead is mounted on the simplified cylindrical symmetrical stray field magnet, wherein the stray field magnet net system has a broad phase to which the center thickness is attached;

Fig. 7 speaker with multi-part basket design in

Sectional view with respect to the 6 inverted structure, wherein the center bead is mounted on the opposite of the main emission direction lower side of the cylindrical symmetrically constructed stray field magnet;

Fig. 8 Center line in section in 3D view with different thickness contour and material thickness.

FIG. 1 shows a loudspeaker whose frequency response extends into the bass range, with an internally wound voice coil on a cylindrical voice coil carrier 3, with a first centering or bead 2, a flat to planar diaphragm 1, a basket 6, a flat one The stray field magnet system 7 consists of a centrally arranged pole plate 8 and above and below it fixed magnet 9. According to the invention, the air gap 5 is schematically represented by a second centering 4 and an annular air gap 5 between the voice coil and the voice coil carrier indicated Mittensicke 11 covered and closed, which is mounted between the stray field magnet system 7 and the membrane system, consisting of membrane 1, voice coil 3 and 4 centering. Here the center bead is attached to the upper magnet 9 and to the membrane 1 itself. Through a circle a detail I is circumscribed with the stray field magnet system 7.

FIG. 2 shows the detail I from FIG. 1, with the voice coil 16 wound inside the voice coil former 3 and, with the first centering 2, with the flat sandwich membrane 1, the basket 6, the second centering 4 and the symmetrically configured stray field magnet system 7, consisting of two opposite polarity mounted magnets 9 with a pole plate arranged therebetween 8. At the bottom of the magnet system, a spacer 10 is arranged, which also facilitates the assembly. In particular, in this detailed representation of the annular air gap 5 between voice coil or voice coil and stray field magnet system can be seen by the 1 air in the air passage 15 can flow during a lifting movement of the membrane and - if no countermeasures - can cause noise. To avoid such noise, the loudspeaker according to the invention has a center bead 11, here shown only schematically, which seals and covers this air gap 5.

Furthermore, it can be seen in FIG. 2 that with the second centering 4, on the underside thereof, the line feeders 14 are connected symmetrically, so that no unilateral mechanical influences are exerted by these electrical connections 14.

Furthermore, FIG. 2 also shows the cone opening angle α between the axis of symmetry and the front surface of the membrane 1.

FIG. 3 shows the loudspeaker from FIG. 1 in a 3D view, but for a better view of the air gap on the magnet system without center bead.

FIG. 4 shows the loudspeaker with a one-piece basket construction from FIG. 1 in a 3D view, in which case the center bead 11 according to the invention is mounted on the stray field magnet system shown in simplified form and on the membrane 1. As a result, the annular air gap is covered or sealed with its air passage. Thus, resulting noise or their propagation through the center bead 11 are avoided.

5 shows an exemplary loudspeaker according to the invention, here with a one-piece basket construction, in a sectional view, on which the center bead 11 is mounted on the simplified cylindrical and symmetrical stray field magnet system 7 and the membrane 1 and which thus covers or covers the annular air gap with air passage 5 seals. The stray field magnetic system 7 corresponds here and in all other figures in its construction to the illustrations of Figures 1 and 2. The membrane 1 is designed here as a simple flat sandwich membrane, but also in an improved variant of the outside itself in cross-section tapered membrane of Figure 1 correspond.

FIG. 6 shows the loudspeaker with a one-piece basket construction in a sectional view, on which the center bead 11 is mounted on the cylindrically symmetrical stray field magnet system 7 shown in simplified form. To save height, here the upper magnet of the stray field magnet system 7 is provided with a phase 13, is attached to the center bead 11 to save space, so that it does not protrude beyond the height of the magnet system. As an alternative to the oblique phase shown here, a shoulder can also be incorporated into the magnet on which the center bead is fastened.

FIG. 7 shows the loudspeaker according to the invention with a multi-part basket construction in a sectional view. In contrast to FIGS. 1 to 6, in which a main sound radiation direction directed away from the basket was present, here the main emission direction points in the direction of the basket, so that a reverse construction is present. Therefore, in this example, the center bead 11 is placed from below on the cylindrical symmetrical stray field magnet system 7 shown in simplified form and mounted on the second centering 4.

It should be noted that all speakers shown here have an upward main sound radiation.

Finally, FIG. 8 shows a center bead 11 in section with a 3D view. In this illustration, the different thickness contour or material thickness 12 of the material is particularly clearly visible.

It has been found to be particularly favorable to construct the center bead 11 so that it also has leading or centering but also damping properties. Depending on the task, the choice of material is important here. Should it also have a dampening effect, a dampening rubber, rubber or plastic should be used; if it has a centering effect, an air-tight coated fabric is an advantage if it is only a sealing function pressed foam has turned out to be very positive.

But it is also possible to use the materials mixed or combined. For example, a fabric coated with rubber, rubber or plastic or vulcanized.

It has also proved to be favorable to achieve different functions or properties by shaping the contour of the center bead. Thus, it is advantageous to make the edges or ends with which the bead is glued / mounted or fixed, rather straight and or thicker to achieve more stability, while the radius itself should be made rather thinner, as this targeted must be able to move. It may also be beneficial to make the transition from the edges or ends to the radius even in the thickness or flexibility fluid to allow a harmonious rolling or moving.

Overall, therefore, the invention proposes a very compact and in particular flat-mounted loudspeaker, which is particularly suitable for installation in consoles with little depth, without sacrificing excellent sound quality, especially in the bass range.

It is understood that the above-mentioned features of the invention can be used not only in the combination given above, but also in other combinations, without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

1 membrane

2 beads

3 voice coil bobbins

4 centering

5 air gap

6 basket

7 stray field magnet system

8 pole plate Magnets Spacer for mounting Center bead Material thickness Phase Electrical connecting cable to the voice coil Wrong air flow Voice coil Conical opening angle

Claims

claims

1 . Loudspeaker with a sound radiation direction with:

1 . 1, a basket {6), 1 .2. a membrane system. with: aüJBävf Ih no

1.2.1. a sandwich-type membrane (1) which thickens from one to the other and becomes thicker,

1.2.2. a voice coil (16) mounted on a support (3) in the center and at the level of the diaphragm (1) and internally wound, the diaphragm (1) being connected to the support (3),

1.2.3. a first, in cross-section in particular sinusoidal formed centering (2), which centered the membrane (1) in the basket (6) in a first plane _r 1.2.4. a second, in cross-section in particular sinusoidal formed centering (4) which is connected to the carrier (3) of the voice coil (16) and on the carrier (3) centering the membrane in a second plane, 1.3. a symmetrically constructed stray field magnet system

(7) having two magnetically polarized magnets (9) and a pole plate (8) arranged centrally between the two magnets, wherein:

1.3.1. the scattering oil magnet (7) penetrates the membrane (1) centrally,

1.3.2. the voice coil (16) is in the non-deflected state at the level of Polplattö (8)

1,3,3 "and the stray field magnetizer (7) centric to the basket

(6), 1.4. and a center bead (11) which forms a closed and flexible connection between the stray field magnetizer (7) and the diaphragm system (1, 3, IS).

2. Loudspeaker according to the preceding claim 1, characterized in that the voice coil has two electrical connections, which is connected on its course with one of the centerings (2, 4).

3. Loudspeaker according to the preceding claim 2, characterized in that dasa the two e- lektrischen connections (14) of the voice coil (16) with one of the centerings (2, 4) are woven.

4. Loudspeaker according to one of the preceding claims 1 to 3, characterized in that the center bead (11) is arranged on the main emission side of the loudspeaker.

5. Loudspeaker according to one of the preceding claims 1 to 4, characterized in that the center bead (11) has a maximum radius which is at most one third of the maximum radius of the membrane.

6. Loudspeaker according to one of the preceding claims 1 to 5, characterized in that the center bead (11) has a contour and / or thickness, which is different in thickness.

7. loudspeaker according to the preceding claim 6, characterized in that the contour or material thickness has a soft and / or flowing thickness transition.

8. Loudspeaker according to one of the preceding claims 1 to 7, characterized in that the center bead (11) is made of a pressed foam.

9. Loudspeaker according to one of the preceding claims 1 to 8, characterized in that the mounting of the center bead (11) by means of spacers (10) is made.

10. Loudspeaker according to one of the preceding claims 1 to 9, characterized in that the center bead (11) is made in one piece.

11. Loudspeaker according to one of the preceding claims 1 to 10, characterized in that the stray field magnet (7) on at least one side of a phase (13) or a shoulder on the front page at which the center bead (11) is attached.

12. Loudspeaker according to one of the preceding claims 1 to 11, characterized in that the Mittensicke (11) consists of one or a mixed form of the materials of the list below: rubber, plastic, airtight coated fabrics,

13. Loudspeaker according to one of the preceding claims 1 to 12, characterized in that the center bead (11) is connected directly to the membrane (1).

14. Loudspeaker according to one of the preceding claims 1 to 12, characterized in that the center bead (11) is directly connected to the second centering (4).

15. Loudspeaker according to one of the preceding claims 1 to 14, characterized in that the center bead (11) has a contour (12) flowing from thick at the lower outer edge and adhesive surface, thinner over the radius and then thicker to the upper inner diameter and Adhesive surface is.

16. Loudspeaker according to one of the preceding claims 1 to 15, characterized in that the center bead (11) is made by injection molding.

17. Loudspeaker according to one of the preceding claims 1 to 15, characterized in that the center bead (11) is produced in the vulcanization process.

18. Loudspeaker according to one of the preceding claims 1 to 17, characterized in that a thin copper ring or copper cup around the outer edge of the pole plate (8) is fixed around.

19. Loudspeaker according to one of the preceding claims 1 to 18, characterized in that the basket (6) is provided with openings.

20. Loudspeaker according to the preceding claim 19, characterized in that openings in the basket (6) are provided with a sound and / or air-permeable fabric or fabric.

21. Loudspeaker according to one of the preceding claims 1 to 20, characterized in that at least one of the centerings (2, 4) is a TopfZentrierung.

22. Loudspeaker according to one of the preceding claims 1 to 21, characterized in that at least one of the centerings (2, 4) has a spacer.

23. Loudspeaker according to one of the preceding claims 1 to 22, characterized in that in order to homogenize the field line course and improve the field strength above and below the stray field magnet system (7) each additionally a disc of magnetic material is arranged.

24. Loudspeaker according to one of the preceding claims 1 to 23, characterized in that the basket (6) consists of a non-magnetic material.

25. Loudspeaker according to one of the preceding claims 1 to 24, characterized in that the individual parts of the stray field magnet system (magnets and pole plate) have a central bore for ease of assembly by means of a non-magnetizable screw.

26. Loudspeaker according to one of the preceding claims 1 to 25, characterized in that the production takes place by a part of the loudspeaker takes place in the object to be integrated and when assembling the other missing parts are mounted to it.

27. Loudspeaker according to one of the preceding claims 1 to 26, characterized in that the membrane (1) from the outer edge to the middle is thicker, preferably continuously straight or in a continuously curved shape.

28. Loudspeaker according to one of the preceding claims 1 to 27, characterized in that the membrane (1) is rotationally symmetrical and has a cone opening angle of 80 ° to 95 ° between the axis of rotation and conical surface with respect to their directed to Hauptabstrahlrichtung surface.

29. Loudspeaker according to one of the preceding claims 1 to 27, characterized in that the membrane (1) is rotationally symmetrical and based on their two-sided surfaces each having a cone angle (α) of 90 ° to 95 ° between the axis of rotation and conical surface.

30. Loudspeaker according to one of the preceding claims 1 to 29, characterized in that the membrane (1) has an inner hollow cylindrical edge which is connected to the carrier of the voice coil.

31. Loudspeaker according to the preceding Patent Claim 30, characterized in that the membrane (1) with respect to its inner hollow cylindrical edge in the stroke direction of the voice coil (16) is arranged symmetrically to the voice coil (16).

32. Loudspeaker according to the preceding claim 30, characterized in that the membrane (1) with respect to its inner hollow cylindrical edge in the stroke direction of the voice coil (16) on one side offset from the voice coil (16), but in the region of the voice coil (16) is arranged.

33. Loudspeaker according to one of the preceding claims 30 to 32, characterized in that the hollow cylindrical carrier (3) of the voice coil (16) has a greater height than the inner hollow cylindrical edge of the membrane (1).

34. Loudspeaker according to the preceding claim

33, characterized in that the hollow cylindrical carrier (3) of the voice coil (16) on one side substantially further protrudes from the inner edge of the there and is connected to the second centering.