Electrodynamic actuator with improved magnet system

Abstract

An electrodynamic actuator (2a . . . 2l) is disclosed, which is designed to be connected to a sound emanating structure (3) and which comprises a coil arrangement (4) with at least one voice coil (5, 6) and a magnet system (7a, 7l), comprising an annular peripheral magnet system part (8a, 8l) and a center magnet system part (9a, 9l) with the coil arrangement (4) in-between. Further on, the electrodynamic actuator (2a . . . 2l) comprises a spring arrangement (15), which couples the peripheral magnet system part (8a, 8l) to the center magnet system part (9a, 9l) and allows a relative movement between the same in an excursion direction parallel to a coil axis (C). The center magnet system part (9a, 9l) comprises a center magnet (11) and at least one plate (12a . . . 13l) adjoining said center magnet (9a, 9l) in the excursion direction, wherein the at least one plate (12a . . . 13l) comprises a collar (14a . . . 14l) on its outer edge, which faces away from the center magnet (11). Additionally, an electrodynamic transducer (1) with such an electrodynamic actuator (1a . . . 1f) is disclosed.

Claims

1. An electrodynamic actuator (2a . . . 2l), designed to be connected to a sound emanating structure (3), comprising: a coil arrangement (4) with at least one voice coil (5, 6), which has an electrical conductor in the shape of loops running around a coil axis (C) in a loop section (L); a magnet system (7a, 7l), comprising an annular peripheral magnet system part (8a, 8l) and a center magnet system part (9a, 9l) with the coil arrangement (4) in-between, wherein the magnet system (7a, 7l) is designed to generate a magnetic field (B) transverse to the conductor in the loop section (L); and a spring arrangement (15) coupling the peripheral magnet system part (8a, 8l) to the center magnet system part (9a, 9l) and allowing a relative movement between the peripheral magnet system part (8a, 8l) and said center magnet system part (9a, 9l) in an excursion direction parallel to the coil axis (C), wherein the center magnet system part (9a, 9l) comprises a center magnet (11) and at least one plate (12a . . . 13l) adjoining said center magnet (9a, 9l) in the excursion direction, characterized in that the at least one plate (12a . . . 13l) comprises a collar (14a . . . 14l) on its outer edge, which faces away from the center magnet (11) in the excursion direction.

2. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein a height (h.sub.c) of the collar (14a . . . 14l), which is the extension of the collar (14a . . . 14l) in the excursion direction, is in a range of 0.05 mm to 0.2 mm, and/or a width (w.sub.c) of the collar (14a . . . 14l), which is half the difference of an outer dimension of the collar (14a . . . 14l) in a direction perpendicular to an annular course (AC) of the collar (14a . . . 14l) minus the inner dimension of the collar (14a . . . 14l) in said direction, is in a range of 0.2 mm to 0.6 mm.

3. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein a height (h.sub.c) of the collar (14a . . . 14l), which is the extension of the collar (14a . . . 14l) in the excursion direction, is in a range of 10% to 100% of the total height (h.sub.p) of the at least one plate (12a . . . 13l), which is the extension of the at least one plate (12a . . . 13l) in said excursion direction, and/or a width (w.sub.c) of the collar (14a . . . 14l), which is half the difference of an outer dimension of the collar (14a . . . 14l) in a direction perpendicular to an annular course (AC) of the collar (14a . . . 14l) minus the inner dimension of the collar (14a . . . 14l) in said direction, is in a range of 2% to 20% of the total width (w.sub.p) of the at least one plate (12a . . . 13l), which is the extension of the at least one plate (12a . . . 13l) in said direction perpendicular to the annular course (AC), and/or an area of the collar (14a . . . 14l) seen in a direction parallel to the coil axis (C) is in a range of 5% to 80% of the total area of the at least one plate (12a . . . 13l) seen in said direction.

4. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein the collar (14a . . . 14l) is continuous or broken.

5. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein the collar (14a . . . 14l) is broken and wherein arms (19) of the spring arrangement (15) are arranged in gaps (G) of the broken collar (14a . . . 14l).

6. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein the spring arrangement (15) comprises an annular outer spring area (18), which is connected to the peripheral magnet system part (8a, 8l), and spring arms (19), which protrude inwards and which are connected to the center magnet system part (9a, 9l), wherein the annular outer spring area (18) at least sectionally reaches over the collar (14a . . . 14l).

7. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein the coil arrangement (4) is connected to the peripheral magnet system part (8a, 8l) and an airgap is formed between the coil arrangement (4) and the center magnet system part (9a, 9l), or the coil arrangement (4) is connected to the center magnet system part (9a, 9l) and an airgap is formed between the coil arrangement (4) and the peripheral magnet system part (8a, 8l).

8. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein the plate (12a . . . 13l) and the peripheral magnet system part (8a, 8l) are made from soft iron.

9. The electrodynamic actuator (2a . . . 2l) as claimed in claim 1, wherein the plate (10a) adjoins the center magnet (11) above, or the plate (10b) adjoins the center magnet (11) below, or the plate (10a) adjoins the center magnet (11) above and wherein the center magnet system part (9a, 9l) comprises another plate (10b), which adjoins said center magnet (11) below in the excursion direction and which comprises a collar (14a . . . 14l) on its outer edge facing away from the center magnet (11).

10. An electrodynamic transducer (19), comprising a sound emanating structure (3) and an electrodynamic actuator (2a . . . 2l) according to claim 1, which is connected to the sound emanating structure (3).

11. The electrodynamic transducer (19) as claimed in claim 10, wherein an average sound pressure level of the electrodynamic transducer (19) measured in an orthogonal distance of 10 cm from the sound emanating surface(S) is at least 50 dB_SPL in a frequency range from 100 Hz to 15 kHz.

12. The electrodynamic transducer (19) as claimed in claim 10, wherein the sound emanating structure (3) is embodied as a membrane, as a display or as a housing part of a device, which the electrodynamic actuator (2a . . . 2l) is built into.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] These and other aspects, features, details, utilities, and advantages of the invention will become more fully apparent from the following detailed description, appended claims, and accompanying drawings, wherein the drawings illustrate features in accordance with exemplary embodiments of the invention, and wherein:

[0032] FIG. 1 shows a cross sectional view of an exemplary electrodynamic transducer;

[0033] FIG. 2 shows an oblique cross sectional view of the electrodynamic actuator used in the electrodynamic transducer of FIG. 1;

[0034] FIG. 3 shows a detailed oblique cross sectional view of the electrodynamic actuator of FIG. 2 in the area of the collars;

[0035] FIG. 4 shows an oblique view of the top plate of the electrodynamic actuator depicted in FIGS. 1 to 3;

[0036] FIG. 5 is like FIG. 3 but with an enlarged collar;

[0037] FIG. 6 shows an oblique view of the top plate of the electrodynamic actuator depicted in FIG. 5;

[0038] FIGS. 7 to 12 show oblique cross sectional views of electrodynamic actuators having plates with various shapes of collars;

[0039] FIGS. 13 to 16 show oblique views of top plates with various shapes of broken collars;

[0040] FIGS. 17 shows an oblique cross sectional view of an electrodynamic actuator having plates as depicted in FIG. 16 and

[0041] FIG. 18 shows a top view of the electrodynamic actuator of FIG. 17.

[0042] Like reference numbers refer to like or equivalent parts in the several views.

DETAILED DESCRIPTION OF EMBODIMENTS

[0043] Various embodiments are described herein to various apparatuses. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments, the scope of which is defined solely by the appended claims.

[0044] Reference throughout the specification to various embodiments, some embodiments, one embodiment, or an embodiment, or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases in various embodiments, in some embodiments, in one embodiment, or in an embodiment, or the like, in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation given that such combination is not illogical or non-functional.

[0045] It must be noted that, as used in this specification and the appended claims, the singular forms a, an and the include plural referents unless the content clearly dictates otherwise.

[0046] The terms first, second, and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms include, have, and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0047] All directional references (e.g., plus, minus, upper, lower, upward, downward, left, right, leftward, rightward, front, rear, top, bottom, over, under, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of the any aspect of the disclosure. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

[0048] As used herein, the phrased configured to, configured for, and similar phrases indicate that the subject device, apparatus, or system is designed and/or constructed (e.g., through appropriate hardware, software, and/or components) to fulfill one or more specific object purposes, not that the subject device, apparatus, or system is merely capable of performing the object purpose.

[0049] Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims. Nevertheless, the term connected within the disclosure in particular can mean direct connection (without intermediate parts), and the term couple within the disclosure in particular can mean direct or indirect connection (with or without intermediate parts).

[0050] All numbers expressing measurements and so forth used in the specification and claims are to be understood as being modified in all instances by the term about or substantially, which particularly means a deviation of 10% from a reference value.

[0051] FIG. 1 shows a cross sectional view of an exemplary electrodynamic transducer 1, which comprises an electrodynamic actuator 2a being connected to a sound emanating structure 3. In addition, FIG. 2 shows an oblique cross sectional view of the electrodynamic actuator 2a used in the electrodynamic transducer 1 of FIG. 1, FIG. 3 shows a detailed oblique cross sectional view of the electrodynamic actuator 2a of FIG. 2 in the area of the collars 14a, 14a, and FIG. 4 shows an oblique view of the top plate 12a of the electrodynamic actuator 2a depicted in FIGS. 1 to 3.

[0052] The electrodynamic actuator 2a comprises a coil arrangement 4 with two voice coils 5, 6 and a magnet system 7a with an annular peripheral magnet system part 8a and a center magnet system part 9a with the coil arrangement 4 in-between. The two voice coils 5, 6 each have an electrical conductor in the shape of loops running around a coil axis C in a loop section L, and the magnet system 7a is designed to generate a magnetic field B transverse to the conductor in the loop section L.

[0053] In detail, the peripheral magnet system part 8a comprises or is formed of an annular ring body 10. Moreover, the center magnet system part 9a comprises a center magnet 11 and a first plate or top plate 12a (referenced simply as first plate 12a hereinafter), which adjoins the center magnet 11 above in the excursion direction, and a second plate or bottom plate 13a (referenced simply as second plate 13a hereinafter), which adjoins said center magnet 11 below in the excursion direction. The first and the second plate 12a, 13a each comprises a collar 14a, 14a on its outer edge (a raised edge area respectively), which faces away from the center magnet 11 in the excursion direction. Accordingly, the first plate 12a comprises a collar 14a on its outer edge facing upwards, and the second plate 13a comprises a collar 14a on its outer edge facing downwards. Generally, the plates 12a, 13a and the peripheral magnet system part 8a can be made from soft iron.

[0054] Further on, the electrodynamic actuator 2a comprises a spring arrangement 15, which couples the peripheral magnet system part 8a to the center magnet system part 9a and which allows a relative movement between the peripheral magnet system part 8a and said center magnet system part 9a in an excursion direction parallel to the coil axis C. Concretely, the spring arrangement 15 comprises a first spring or top spring 16 (referenced simply as first spring 16 hereinafter) arranged above the magnet system 7a and a second spring or bottom spring 17 (referenced simply as second spring 17 hereinafter) arranged below the magnet system 7a.

[0055] In this example, the springs 16, 17 each comprise an annular outer spring area 18, which is connected to the peripheral magnet system part 8a, and spring arms 19, which protrude inwards and which are connected to the center magnet system part 9a. The particular shape of the springs 16, 17 depicted in FIGS. 1 to 3 is just exemplary and other shapes of springs are applicable as well. It should also be noted that the spring arms 19 are not necessarily interconnected but a couple of individual spring arms 19 can form the first spring 16 and the second spring 17.

[0056] For example, the electrodynamic actuator 2a can be connected to the sound emanating structure 3 by means of a glue layer or adhesive sheet (not shown in FIG. 1). For this reason, the electrodynamic actuator 2a advantageously can comprise a flat mounting surface, for example on the first spring 16, which is intended to be connected to the sound emanating structure 3. In particular, the sound emanating structure 3 has a sound emanating surface S and a backside opposite to the sound emanating surface S, wherein the electrodynamic actuator 2a is connected to said backside.

[0057] The sound emanating structure 3 can be a passive structure, for example a part of a housing of a device, which the electromagnetic actuator 2a is built into. However, the sound emanating structure 3 can also have a special function itself. For example, if the sound emanating structure 3 is embodied as a display, the electrodynamic actuator 2a together with the display forms an output device (for both audio and video data). Further on, the sound emanating structure 3 can also be a membrane. In this case, the electrodynamic actuator 2a together with the membrane forms a speaker.

[0058] In general, a speaker or an electrodynamic transducer 1 (or output device) of the kind disclosed hereinbefore preferably produces an average sound pressure level of at least 50 dB_SPL in a frequency range from 100 Hz to 15 kHz measured in an orthogonal distance of 10 cm from the sound emanating surface S. In particular, the above average sound pressure level is measured at 1 W electrical power and more particularly at the nominal impedance.

[0059] It should also be noted at this point that a display forming the sound emanating structure 3 in FIG. 1 may be connected elastically to a housing of the device, which the display is part of. In such a case, the display may be seen as a rigid membrane part of a membrane, wherein the display like a rigid membrane part mainly moves in the piston mode. Accordingly, borders between an electrodynamic transducer 1 and a speaker can blur into one another particularly in such a case.

[0060] A force applied to the sound emanating structure 3 to generate sound may be generated by the inertia of the part of the electrodynamic actuator 2a, which is moved in relation to the sound emanating structure 3 (which is the center magnet system part 9a in FIG. 1), or because the part of the electrodynamic actuator 2a, which is moved in relation to the sound emanating structure 3, is fixed to another part (e.g. to a housing of a device, which the electrodynamic actuator 2a is built into).

[0061] A connection between the sound emanating structure 3 and the electrodynamic actuator 2a is not necessarily done on the spring arrangement 15 (here on the first spring 16) but can also be done on the annular ring body 10 or an intermediate part. Moreover, the sound emanating structure 3 can also be connected to the center magnet system part 9a what in turn causes the peripheral magnet system part 8a being moved in relation to the sound emanating structure 3. In other words, roles of the center magnet system part 9a and the peripheral magnet system part 8a change in this case.

[0062] The term annular in the context of the annular peripheral magnet system part 8a does not only mean closed rings but also annular arrangements of individual segments forming a ring as a whole. For example, the annular peripheral magnet system part 8a may comprise individual segments forming a ring as a whole. The segments may touch each other, but they can also be spaced from one another. In particular, the annular peripheral magnet system part 8a may comprise straight segments, wherein the corner region is left out.

[0063] FIGS. 1 to 4 show an embodiment of an electrodynamic actuator 2a with comparably small collars 14a, 14a. However, this is no binding feature and the collars 14b, 14b may also be bigger as this is shown in FIGS. 5 and 6, wherein FIG. 5 shows a detailed oblique cross sectional view of another embodiment of an electrodynamic actuator 2b in the area of the collars 14b, 14b, and FIG. 6 shows an oblique view of the top plate 12b of the electrodynamic actuator 2b depicted in FIG. 5.

[0064] In detail, a favorable height he of the collar 14a . . . 14b, which is the extension of the collar 14a . . . 14b in the excursion direction, is in a range of 0.05 mm to 0.2 mm and/or a width w.sub.c of the collar 14a . . . 14b, which is half the difference of an outer dimension of the collar 14a . . . 14b in a direction perpendicular to an annular course AC of the collar 14a . . . 14b minus the inner dimension of the collar 14a . . . 14b in said direction, is in a range of 0.2 mm to 0.6 mm.

[0065] Alternatively or in addition it is of advantage if a height h.sub.c of the collar 14a . . . 14b is in a range of 10% to 100% of the total height h.sub.p of the at least one plate 12a . . . 13b, which is the extension of the at least one plate 12a . . . 13b in said excursion direction, and/or the width w.sub.c of the collar 14a . . . 14b is in a range of 2% to 20% of the total width w.sub.p of the at least one plate 12a . . . 13b, which is the extension of the at least one plate 12a . . . 13b in said direction perpendicular to the annular course AC and/or an area of the collar 14a . . . 14b seen in a direction parallel to the coil axis C is in a range of 5% to 80% (in particular in a range of 5% to 50% and more particularly in a range of 5% to 20%) of the total area of the at least one plate 12a . . . 13b seen in said direction.

[0066] By use of the collars 14a, 14a, at least the following parameters of the electrodynamic actuator 2a can be influenced without influencing the mass and the oscillation behavior of the center magnet system part 9a much: flux density, magnetic resistance, magnetic spring, maximum operating excursion, maximum excessive excursion.

[0067] For example, the height he of the collar 14a . . . 14b directly influences the flux density, the magnetic resistance and the reluctance. However, as can be envisaged from FIGS. 1 to 6, the height he also has an influence on the maximum operating excursion (which is caused by a current flowing through the voice coils 5, 6) because out of the magnetic field B the voice coils 5, 6 do not move. Finally, the height he influences the maximum excessive excursion (which is caused by an external acceleration), i.e. the excursion until a movement of the moving part of the electrodynamic actuators 2a, 2b (which is the center magnet system part 9a, 9b in the above examples) is blocked. In detail, the center magnet system part 9a, 9b hits the spring arrangement 15 upon excessive excursion in the above examples. However, a movement of the moving part of the electrodynamic actuator 2a, 2b may also be blocked by other parts in other embodiments, for example by dedicated stoppers.

[0068] FIGS. 7 to 12 now show various oblique cross sectional views of electrodynamic actuators 2c . . . 2h having plates 12c . . . 13h with various shapes of collars 14c . . . 14h. In detail, FIG. 7 shows an electrodynamic actuator 2c with plates 12c, 13c with collars 14c, 14c having a cross section in the shape of a half circle, FIG. 8 shows an electrodynamic actuator 2d with plates 12d, 13d with collars 14d, 14d with a triangular cross section, FIG. 9 shows an electrodynamic actuator 2e with plates 12c, 13c with collars 14c, 14c with inner roundings, FIG. 10 shows an electrodynamic actuator 2f with plates 12f, 13f with collars 14f, 14f with a square cross section and with inner grooves, FIG. 11 shows an electrodynamic actuator 2g with plates 12g, 13g with collars 14g, 14g with a chamfered square cross section and with inner grooves, and FIG. 12 shows an electrodynamic actuator 2h with plates 12h, 13h with collars 14h, 14h with a rounded square cross section and with inner grooves. Generally, the shape of the cross section of the collars 14c . . . 14h influence the magnetic flux. For example, the grooves concentrate the magnetic flux and roundings smoothen the magnetic flux. By the proposed measures, the design of the collars 14c . . . 14h can easily be adapted to the demands when designing an electrodynamic actuator 2g . . . 2h.

[0069] In the examples of FIGS. 1 to 6, the collars 14a . . . 14b are continuous. That is why the disclosed advantages are obtained on the whole plates 12a . . . 13b. However, this is no necessary condition. In this context, FIGS. 13 to 16 show further examples of first plates 12i . . . 12l with broken collars 14i . . . 14l, that means with gaps G within the collars 14i . . . 14l. In this way, the disclosed advantages are obtained only at sections of the plates 12i . . . 12l, however, with the advantage of a reduced weight of the same and other advantages as the case may be.

[0070] In a very advantageous embodiment, arms 19 of the spring arrangement 15 are arranged in the gaps G of the broken collar collars 14i . . . 14l. In this context, FIGS. 17 and 18 show an example of an electrodynamic actuator 21 which uses the plates 12l, 13l as depicted in FIG. 16. By use of the proposed measures, the spring arms 19 can be prevented from being damaged by the center magnet system part 9l in case it reaches its maximum excessive excursion caused by excessive external acceleration. Instead, the annular outer spring area 18 at least sectionally reaches over the collar 14l, 14l and the center magnet system part 9l hits the comparably rigid annular outer spring area 18 when it reaches its maximum excessive excursion. However, in another design, the center magnet system part 9a, 9l may hit another part of the electrodynamic actuator 2a . . . 2l, for instance, dedicated stoppers.

[0071] In the aforementioned examples, the coil arrangement 4 is connected to the peripheral magnet system part 8a, 8l and an airgap is formed between the coil arrangement 4 and the center magnet system part 9a, 9l. However, this is no necessary condition, and the coil arrangement 4 may also be connected to the center magnet system part 8a, 8l wherein an airgap is formed between the coil arrangement 4 and the peripheral magnet system part 8a, 8l. In this case, the roles of the center magnet system part 9a, 9l and the peripheral magnet system part 8a, 8l change in view of their relative movement.

[0072] Finally, it is noted that although in the aforementioned examples, the electrodynamic actuator 2a . . . 2l comprises a first and a second plate 13a . . . 13l, in other embodiments the electrodynamic actuator 2a . . . 2l may also comprise just a first plate 10a adjoining the center magnet 11 above or below. This advantageous if the disclosed advantages are just needed on one of the top plate 12a . . . 12l and the bottom plate 13a . . . 13l or if the coil arrangement 4 comprises just one voice coil 5 or 6.

[0073] One should also note that the cross section of a collar 14a . . . 14l is independent of whether it is continuous or broken. In particular, this means that the examples shown in FIGS. 1 to 12 may be used in any combination with the examples shown in FIGS. 13 to 16.

[0074] Generally, it should also be noted that the disclosed collar 14a . . . 14l is not bound to a particular shape of the electrodynamic actuator 2a . . . 2l, but various other shapes are possible as well. For example, the electrodynamic actuator 2a . . . 2l instead of having a square footprint may also have a general polygonal shape or may be circular or oval. Polygonal shapes do also include polygons with rounded corners. Moreover, the disclosed collar 14a . . . 14l is not bound to a particular shape of the springs 16, 17 and the voice coils 5, 6. Instead, springs 16, 17 with different shape and number and voice coils 5, 6 with different shape and number may be used in the context of the disclosed collar 14a . . . 14l as well.

[0075] Finally it is noted that the scope of the present invention is defined by the appended claims, including known equivalents and unforeseeable equivalents at the time of filing of this application. Although numerous embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure.

LIST OF REFERENCES

1 electrodynamic transducer
2a . . . 2l electrodynamic actuator
3 sound emanating structure
4 coil arrangement
5 first (upper) voice coil
6 second (lower) voice coil
7a, 7l magnet system
8a, 8l peripheral magnet system part
9a, 9l center magnet system part
10 outer ring
11 center magnet
12a . . . 12l first (top) plate
13a . . . 13l second (bottom) plate
14a . . . 14l collar
15 spring arrangement
16 first (upper) spring
17 second (lower) spring
18 outer spring area
19 spring arm
h.sub.c height of collar
h.sub.p total height of plate
w.sub.c width of collar
w.sub.p total width of plate
AC annular course of collar
B magnetic field
C coil axis
G gap in collar
L loop section
S sound emanating surface