EP1336321B1 - Electrodynamic bending moment driver - Google Patents

Description

The invention relates to a Biegemomententreiber for a sound plate having a plate speaker.

It is for example from the US 5,693,917 Plate loudspeakers are known, which operate approximately on the "piston principle", the plate of the plate speaker ideally performs no bending vibrations, but behaves as if they were completely rigid.

With less effort compared to plate speakers can be produced that allow bending vibrations of the elastic plate and also exploit Bieschwwingungsresonanzen sound as a distinctive feature. Such "multi-resonant plate speakers", sometimes called "bending wave loudspeaker" or "Distributed Mode Speaker" are, for example, from US 3,247,925 . DE-GM 199 81 34 . WO 99/52324 or EP 0 924 959 known.

Multiresonance plate loudspeakers are usually excited by electrodynamic drivers, which - as in the WO 97/09842 or the DE 198 25 866 set out to attack at certain preferred positions. The edge and the center of the plate are considered to be hardly suitable for an excitation position. To distinguish from the subject invention, these drivers are referred to as "single force driver".

For example, if the front and back of the disk are for image projection or transparency, a driver placed in the visible area of the disk would be extremely annoying. In these applications, it is therefore necessary that the drive engages in the edge region.

From the WO 00/13464 is a so-called "torque driver" known in which bending vibrations are excited by bending moments. In contrast to the punctually attacking "single power drivers", the "torque drivers" can be placed anywhere on the disk, so also in the edge area.

However, the known torque drivers presuppose that the plate is weakened by recesses at the drive location, that bulky lever mechanics forces convert into forces or that combined large-area conventional "single force driver" combined pairs are placed close to each other. A circumferential support frame, which should cover the drive system in plates provided for display purposes, would either protrude too far into the plate surface or protrude too high out of the plane of the plate.

The object of the invention is therefore to provide a Biegemomententreiber for sound panels having plate speakers, in particular multi-resonant panel speakers, in which these disadvantages do not occur.

The object is achieved by a bending moment driver according to claim 1 and a bending moment driver according to claim 9. Embodiments and further developments of the inventive concept are the subject of dependent claims.

Advantage of the invention is that the strength of the plate is impaired in any way and only a narrow, flat frame cover for the Bieengomententreiber is required.

This is achieved in a first alternative by an electrodynamic bending moment driver with a voice coil, which is wrapped around the sounding plate along the boundary surface such that the voice coil axis is parallel to the plate normal and with a permanent magnet system, the is arranged at a small distance from the boundary surface of the sound plate and generates a voice coil penetrating magnetic field, which has different strength and / or directions depending on the location along the circumference of the voice coil such that by a current flowing in the voice coil signal current in the regions near the poles Voice coil an opposing force pair parallel to the plate normal arises that impresses a bending moment on the sound plate via a the distance associated magnetic poles of the permanent magnet system corresponding lever arm.

The bending moment driver according to the invention engages on the edge of the sound plate in such a way that the bending moments act only in the boundary surface (cut surface) and / or a narrow edge zone. The excitation mechanism does without notches, cuts, recesses, etc., so that the strength of the sound panel is not affected. Furthermore, the geometry of the edge can be optimized in such a way that the bending moment drivers according to the invention no longer interfere with the surfaces of the sound plate intended for optical use.

Preferably, therefore, the permanent magnet system is designed and arranged so that it covers the intended for optical use radiating surfaces of the sound panel geometrically in any part of the radiating surface.

In this case, the bending moment driver is preferably designed such that the bending moments generated by it only act on the boundary surfaces and / or on the edge region of the emitting surfaces of the sound plate. In such a drive system, the magnetic field at each pole exit surface is directed substantially perpendicular to the plate edge and normal to the plate normal.

Furthermore, a permanent magnet system may be provided that at least one pair of poles of opposite polarity which each act on the voice coil with substantially the same amount of magnetic field strength.

Preferably, a pair of poles may each have a permanent magnet and two magnetically conductive Polkernschenkel. Alternatively, a pair of poles may each comprise two separate like individual permanent magnets whose respective field vectors are oppositely directed with respect to the voice coil. In addition, the two permanent magnets can be connected to one another with a soft-magnetic yoke.

Finally, in both alternatives, a soft magnetic yoke with a tuned to the distance of the individual permanent magnet length on the side facing away from the permanent magnet side of the voice coil be embedded in the sound plate, so that the magnetic flux located outside of the voice coil permanent magnet system via the yoke located within the voice coil is closed. The permanent magnets may preferably be of the rare earth type.

A second alternative of a bending moment driver according to the invention comprises an electromagnet system comprising a pole core, a permanent coil through which a signal current flows around the pole core, and a torque-receiving, permanent magnet embedded in the plate and fixedly connected to the sound plate, the pole core acting like a pliers Edge of the sound plate comprises such that the normal of the Polaustrittsflächen are parallel to the plate normal and there is a substantially homogeneous magnetic field between the Polaustrittsflächen. The field vector of the embedded permanent magnet in the plane of the sound plate, ie perpendicular to the plate normal lie.

The sunken permanent magnet can be plate or rod-shaped and completely embedded in the plate be. The recessed permanent magnet is preferably dimensioned so that it does not protrude from the plate at any point. With a slender design of the recessed permanent magnet (ie, the extent normal to the plate edge is of the order of the plate thickness), a narrow edge zone is achieved, thus achieving optimum utilization of the radiating surface of the sound panel for optical purposes.

Furthermore, it can be provided that the extent of the sunken permanent magnet in the central direction, that is perpendicular to the edge of the sound plate in the order of the plate thickness. Furthermore, the direction of the magnetic field lying in the plane of the sound plate in the yoke can be aligned parallel or perpendicular to the edge of the sound plate.

In addition, in all the panel loudspeakers according to the invention a holding frame can be provided, on which the sound plate is mounted in the region of the bending moment transmission by means of flexible retaining pads. However, it is also possible to provide a plurality of, for example three bending moment converters, whose imaginary connecting lines span a triangle and which support the sound plate.

Figur 1

das der vorliegenden Erfindung zugrundeliegende Funk- tionsprinzip,

Figur 2

eine erste bevorzugte Ausführungsform eines Biegemo- mententreibers in einer Anwendung bei einem Platten- lautsprechers,

Figur 3

eine zweite bevorzugte Ausführungsform eines Biege- momententreibers in einer Anwendung bei einem Plat- tenlautsprechers.

The invention will be explained in more detail with reference to the embodiments illustrated in the figures of the drawing. It shows:

FIG. 1

the principle underlying the present invention,

FIG. 2

A first preferred embodiment of a bending momentum driver in an application in a plate loudspeaker,

FIG. 3

a second preferred embodiment of a bending momentum driver in an application in a plate loudspeaker.

To illustrate the underlying principle of the invention is according to FIG. 1 a sound plate 1 of a Multiresonanzplattenlautsprechers 6 is provided, which is bounded rectangular in the embodiment and has a length L, a width W and a thickness H. The sound plate 1 is excited in the edge region with one or more moments M1, M2. In the exemplary embodiment, such moments M1, M2 are generated by a respective force pair f ⁺ ₁ , f ^- ₁ or f ⁺ ₂ , f ^- ₂ with a distance d ₁ , d ₂ effective as a lever. The moments M1, M2 engage either in a boundary surface 2 corresponding to the cut surfaces of the sound plate 1 (see Figure la) or in a narrow edge region 3 with a width e, which is in the order of the plate thickness H (see. FIG. 1b ).

In FIG. 2 an embodiment is shown in which the excitation of the boundary surface 2 in accordance with the in FIG. 1a The principle of action is shown.

FIG. 2a shows first the (eg rectangular bordered) sound plate 1. You can see one of the two radiating surfaces 4 and two of the cut surfaces. 2

FIG. 2b shows the liberated voice coil 5 of an electrodynamic excitation system.

In Figure 2c Now, the voice coil 5 and the sound board 1 are shown in conjunction with each other, wherein the plate edge 2 of the sound plate 1 is used as a bobbin. The voice coil 5 is firmly connected to the plate edge. The length of the voice coil bobbin is determined by the height of the plate edge, that is determined by the thickness H of the sound plate 1.

Figure 2d shows a complete (except frame / mount) multi-resonant plate speaker with the integrated, inventive electrodynamic drive system. In this case, the plate edge of the sound plate 1 connected to the voice coil 5 is equipped with pairs of permanent magnets 7. The permanent magnets 7 are arranged on the boundary surface 2 such that their field vectors are perpendicular to the coil axis of the voice coil 5. In this way, the forces f ⁺ ₁ , f ^- ₁ and f ⁺ ₂ , f ^- ₂ , as in FIG. 1 shown, impress bending moments in the plate edge. In this way, an electrodynamic, linear transducer is used according to a novel, "tangential-variable" principle in which the voice coil 5 passing permanent magnetic field depending on the location along the circumference of the voice coil 5 has a different strength and direction.

FIG. 2e shows a section through the sound plate 1 starting from a marking line AB Figure 2d , In the exemplary embodiment, a permanent magnet 7 cut in FIG. 2d has the south pole 8 facing outwards and the north pole 9 pointing inwards. As usual with conventional electrodynamic drives, a vibrating gap 11 of the width h is present, so that the permanent magnets 7 do not touch the voice coil 5.

The edge of the sound plate 1 offers space for several magnet pairs. As a result, different lever lengths d (d ₁ , d ₂ ) can be realized on the same panel loudspeaker, with which different bending wavelengths can preferably be addressed. The magnet pairs are preferably fixed in a peripheral holding frame (not shown).

FIG. 2f shows the situation FIG. 2e in the section CD with view normal to the plate surface 4. You can see the two separate permanent magnets 7, a piece of wire of the voice coil 5 and a section of the sound plate. 1

Although in Figure 2d the effective magnetic poles are each realized by a separate permanent magnet, there is also the possibility of pairwise combination to magnetic systems whose yoke at the south pole and north pole has a distance (for example, d ₁ , d ₂ ).

Such an alternative is in Figure 2g shown. A single permanent magnet 7 provides with the help of a plate edge bent toward soft magnetic pole core 17 in the resonant gap of the coil 5, the same magnetic field conditions, as they are characterized by the two magnets Fig. 2f would have been produced.

FIG. 2h shows as a further alternative, a development of the embodiment Fig. 2g , The magnetic field of the open ends of the pole core 17 is closed by a soft magnetic yoke 18 which is embedded in the plate edge and firmly anchored there.

A significant advantage is that the drive system after FIG. 2 in the embodiments shown above, no proportion of the plate surface occupied and that the associated magnet system does not protrude above the plate height (thickness H). In addition, the sound panel 1 is not weakened by cuts or other measures, but rather reinforced by the additional voice coil 5 on the contrary.

Even with the "tangential-variable" variant of the electrodynamic drive system according to the invention of a multi-resonance plate loudspeaker, the permanent magnet induction vector B is perpendicular to the coil current vector I at each magnetic pole. The Lorenz vector applies locally to the force F on a combined conductor length L _S effective in the pole region. equation $$\mathrm{F}\mathrm{=}{\mathrm{L}}_{\mathrm{S}}\left(\mathrm{IXB}\right)$$

The force vector stands parallel to the voice coil axis. Since the induction vector B and the conductor length L _S are constant in time, the relationship between the force F and the coil current vector I and thus the signal current is linear.

Another, on the in FIG. 1b The principle-based embodiment shown in FIG FIG. 3 shown. This electromagnetic, peripheral torque driver consists of a combination of permanent magnet and electromagnet. The permanent magnet is a light, preferably rod-shaped, permanent magnet 12, 12 '(eg, rare earth magnet such as neodymium), which is embedded in the edge region of the sound plate 1. The electromagnet consisting of a pole core 14 and a fixed magnetic coil 13 through which the signal flows generates a torque in the permanent magnet 12, 12 '. This permanent magnet 12, 12 'then transmits the torque as a bending moment on the edge of the sound plate 1. With pads 25, the sound plate 1 can be held in the correct position between the pincer-shaped legs of the pole core 14. An air gap between sound plate 1 and pole core 14 can be filled with the pad 25.

The alternating field 16 of the electromagnet in the air gap can initially be regarded as homogeneous. Depending on the shape and size of the permanent magnet 12 located in this alternating field 16, which generates a constant field 15, the following approach can explain the generation of the torque:

In the magnetically weakly conductive interior of the permanent magnet 12, a vectorial addition of the induction Bp of the permanent magnet 12 and the induction B _{S of} the signal current I takes place. Thus, the entire induction B is the same $$\mathrm{B}\mathrm{=}{\mathrm{B}}_{\mathrm{P}}+{\mathrm{B}}_{\mathrm{S}}$$

wobei mit α der Zwischenwinkel bezeichnet wird. Für die Feldenergie W im Inneren des Permanentmagneten 12 ergibt sich somit $$\mathrm{W}\mathrm{=}\mathrm{V}{\mathrm{B}}^{\mathrm{2}}/\mu ,$$

wobei mit V das Volumen des Permanentmagneten 12 und mit µ die Permeabilität bezeichnet wird. Die Feldenergie ist winkelabhängig aufgrund der Winkelabhängigkeit der Gesamtinduktion B. Die Feldenergie des äußeren Feldes (B_S) bleibt bei Änderungen des Zwischenwinkels α näherungsweise konstant. Somit ergibt sich das Drehmoment M zu $$\mathrm{M}\mathrm{=}\mathrm{dW}\mathrm{/}\mathrm{d\alpha }\mathrm{=}-2\left(\mathrm{V}\mathrm{/}\mathrm{\mu }\right){\mathrm{B}}_{\mathrm{P}}{\mathrm{B}}_{\mathrm{S}}\sin \left(\mathrm{\alpha }\right)\mathrm{.}$$

The amount of the resulting vector of the total induction B is therefore in scalar notation: $$\mathrm{B}\mathrm{=}\mathrm{+}\sqrt{{{\mathrm{B}}^{\mathrm{2}}}_{\mathrm{P}}\mathrm{+}{{\mathrm{B}}^{\mathrm{2}}}_{\mathrm{S}}\mathrm{+}\mathrm{2}{\mathrm{B}}_{\mathrm{P}}{\mathrm{B}}_{\mathrm{S}}\cos \left(\mathrm{\alpha }\right)}\mathrm{.}$$

where α denotes the intermediate angle. For the field energy W inside the permanent magnet 12 thus results $$\mathrm{W}\mathrm{=}\mathrm{<figure-callout\; id="2"\; label="V\; B"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">V\; </figure-callout>}{\mathrm{B}}^{}{\mathrm{}}^{\mathrm{2}}/\mu .$$

where V is the volume of the permanent magnet 12 and μ is the permeability. The field energy is angle-dependent due to the angular dependence of the total induction B. The field energy of the external field (B _S ) remains approximately constant with changes in the intermediate angle α. Thus, the torque M is added $$\mathrm{M}\mathrm{=}\mathrm{dW}\mathrm{/}\mathrm{d.alpha}\mathrm{=}-2\left(\mathrm{V}\mathrm{/}\mathrm{\mu }\right){\mathrm{B}}_{\mathrm{P}}{\mathrm{B}}_{\mathrm{S}}\sin \left(\mathrm{\alpha }\right)\mathrm{,}$$

The torque M is maximum, if - as in FIG. 3 shown - the vector of induction B _{S is} perpendicular to the vector of induction Bp.

Thus, in the context of simplifying assumptions, the torque M is proportional to the induction B _{S of} the signal current and thus proportional to the signal current I itself. This is superimposed by an (imputed) saturation magnetization of the permanent magnet 12, 12 'achieved linear effect of the attraction on a ferromagnetic, not saturated yoke, ie a force that is proportional to the square of the signal current I. Depending on the saturation state of the permanent magnet 12, 12 'outweighs the linear or quadratic force component, which is to be understood as an indication, the permanent magnet 12, 12' as possible to make entirely of hard magnetic material. That is, a material with high saturation magnetization and high coercive field.

In the embodiment according to FIG. 3a while the torque vector is parallel to the plate edge, so that the bending moment also supports the low-frequency first modal form of the bending vibration.

The longitudinal axis of the permanent magnet 12 'can also be aligned parallel to the edge, as indicated in FIG. 3b. Then, the torque vector will point to the center of the tone plate 1, where the bending moment will tend to curve the edge of the plate. This tendency is preferably responsive to the higher frequency flexural vibration modes. In this embodiment, the pole core 14 does not need to be projected far enough into the emitting surface of the sound plate 1 as, for example, in the embodiment according to FIG FIG. 3a the case is.

By tapering the cross section in particular perpendicular to the sound plate 1 of the two legs of the pole core 14 and by largely omitting the elastic pad (spring elements 25) and by extreme flattening of the magnetic coil 13 and the pincer-like legs of the pole core 14 may as in Figure 3c shown a remarkably flat design of the electromagnetic drive system with an edge parallel-oriented electromagnet as in FIG. 3b be achieved shown.

In this case, the bending moment drivers shown are preferably placed in an edge region extending from an edge of the sound plate 1 in the direction of the center of the sound plate 1, wherein the edge region in the direction of the center of the plate is approximately equal to the thickness of the sound plate 1.

LIST OF REFERENCE NUMBERS

1

sound board

2

Boundary surface

3

border zone

4

radiating

5

voice coil

6

Multi soundboard speaker

7

permanent magnet

8th

South Pole

9

North Pole

11

vibration gap

12, 12 '

permanent magnet

13

solenoid

14

pole core

15

Magnetic DC field vector

16

Magnetic alternating field vector

17

yoke

18

embedded yoke

25

pad

d ₁ , d ₂

yoke length

Claims (15)

1. An electrodynamic bending moment driver for a membrane loudspeaker (6) including a sounding plate (1), characterised by a moving coil (5), which is wound around the sounding plate (1) along the boundary surface so that the moving coil axis is parallel to the plate normal and a permanent magnet system (7) which is arranged at a small distance from the boundary surface (2) of the sounding plate (1) and produces a magnetic field, which passes through the magnetic coil (5) and has a different intensity and/or direction in dependence on the location along the periphery of the moving coil (5) such that as a result of a signal current flowing in the moving coil (5) in the regions of the moving coil (5) close to the poles, one or more opposing pairs of forces with vectors extending normal to the plane of the plate are produced, whereby in each case one force is directed towards the interior of the plate and one is directed out of the sounding plate (1) so that in each case a bending moment is applied to the sounding plate (1) over a lever arm corresponding to the spacing of associated magnetic poles of the permanent magnet system (7).
2. A bending moment driver as claimed in claim 1, characterised in that the permanent magnet system (7) is so constructed and arranged that it acts contactlessly on the edge of the plate from outside the sounding plate (1) so as to surround it in a non pincer-like manner.
3. A bending moment driver as claimed in claim 1 or 2, characterised in that it is so constructed and arrangeable that the bending moments produced by it act on the boundary surface (2) and/or on the edge region of the radiation surfaces (4) of the sounding plate (1).
4. A bending moment driver as claimed in one of the preceding claims, characterised in that the permanent magnet system (7) has at least one pair of poles of opposite polarity, both of which act on the moving coil (5) with substantially the same magnitude of magnetic field strength.
5. A bending moment driver as claimed in claim 4, characterised in that a pair of poles has a respective permanent magnet (7) and two magnetically conductive pole core limbs (17).
6. A bending moment driver as claimed in claim 4, characterised in that a pair of poles has two respective separate, similar, individual permanent magnets (7), the field vectors of which are oppositely poled with respect to the moving coil (5).
7. A bending moment driver as claimed in claim 6, characterised in that the two permanent magnets (7) are connected together with a soft magnetic yoke (17).
8. A bending moment driver as claimed in claim 6 or 7, characterised in that a soft magnetic yoke (18) with a length matched to the spacing of the individual permanent magnets (7) is embedded into the sounding plate (1) on the side of the moving coil (5) remote from the permanent magnets (7) so that the magnetic flux of the permanent magnet system (7) located outside the moving coil (5) is closed by means of the yoke (18) situated within the moving coil (5)
9. A bending moment driver for a membrane loudspeaker including a sounding plate, characterised by an electromagnet system (13,14), which includes a pole core (14), a fixed coil (13) through which a signal current flows and which is wound around the pole core (14) and a separate permanent magnet (12,12'), which is embedded in the sounding plate (1) and is firmly connected to the sounding plate (1), wherein the pole core surrounds the edge of the sounding plate (1) in the manner of pincers such that the normals of the pole outlet surfaces extend parallel to the plate normal and a substantially homogeneous magnetic field occurs between the pole outlet surfaces.
10. A bending moment driver as claimed in claim 9, characterised in that the field direction in the permanent magnet (12,12') is situated in the plane of the sounding plate (1) and thus perpendicularly to the plate normal.
11. A bending moment driver as claimed in claim 9 or claim 10, characterised in that the permanent magnet (12,12') is of plate-shaped or rod-shaped construction and is completely embedded in the sounding plate (1).
12. A bending moment driver as claimed in claim 9, 10 or 11, characterised in that the dimension of the permanent magnet (12,12') normal to the edge of the sounding plate (1) is of the order of the thickness of the plate.
13. A bending moment driver as claimed in one of claims 9-12, characterised in that the direction of the magnetic field (15), lying in the plane of the sounding plate (1), in the permanent magnet (12,12') is aligned parallel to the edge of the sounding plate (1).
14. A bending moment driver as claimed in one of claims 9-12, characterised in that the direction of the magnetic field vector (15), lying in the plane of the sounding plate (1), in the permanent magnet (12,12') is aligned perpendicularly to the edge of the sounding plate (1).
15. A bending moment driver as claimed in one of the preceding claims, characterised in that the bending moment driver is positionable in an edge region extending from one edge of the sounding plate (1) in the direction of the centre of the sounding plate (1) and the edge region in the direction of the plate centre is approximately equal to the thickness of the sounding plate (1).

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