AT520509A1 - Transducer and method for determining a diaphragm displacement - Google Patents

Abstract

Disclosed is an electrodynamic transducer (1b ... 1c) having a membrane (2), a coil (3) attached to the membrane (2) and a magnet system (4, 5, 6). The transducer (1b ... 1c) comprises movable conductive structures (9, 10) on both sides of the diaphragm (2) and immovable conductive structures (11, 12) fixedly disposed opposite to the movable conductive structures (9, 10) , Furthermore, a converter system with a converter (1b ... 1c) of the above type and an evaluation circuit (13) is presented. Finally, the invention relates to a method for determining a deflection (x) of the membrane (2) by measuring a first voltage (U1) and a second voltage (U2) between the movable conductive structures (9, 10) and the immovable conductive structures (11 , 12).

Description

BACKGROUND OF THE INVENTION

The invention relates to an electrodynamic transducer, in particular a loudspeaker, comprising a diaphragm, a coil attached to the diaphragm and a magnet system adapted to generate a magnetic field transverse to a longitudinal direction of a wound wire of the coil. Furthermore, the transducer comprises a first movable conductive structure disposed on a first side of the membrane remote from the coil, and a first immovable conductive structure fixed with respect to the magnet system opposite to the first movable conductive structure. Moreover, the invention relates to a transducer system with a transducer of the aforementioned type, wherein the transducer system comprises connection terminals, which are electrically connected to the first movable conductive structure, the first immovable conductive structure and an electronic evaluation circuit. Finally, the invention relates to a method for measuring a deflection of a diaphragm of a transducer of the type disclosed above, wherein a first voltage is measured between the first movable conductive structure and the first immovable conductive structure and wherein the deflection is calculated on the basis of the first voltage.

A converter, a speaker system and a method of the aforementioned kind are basically known from the prior art. In this context, WO 2004/080116 A2 discloses an electrodynamic loudspeaker comprising a capacitive sensor, wherein a first plate of the capacitive sensor is formed by an electrically conductive front panel of a housing of the speaker unit and wherein a second plate of the capacitive Sen sors by a conductive Layer is formed on the membrane. Movement of the diaphragm is determined using the capacitance formed by the front panel and the second panel.

A disadvantage of determining the membrane stroke by means of the prior art sensor is the inverse proportionality between the capacitance and the stroke, which leads to the necessity of a relatively complicated evaluation circuit. Further disadvantages are a low stability against electromagnetic interference, a relatively strong influence of variations of the speaker characteristics on the measurement and an increased susceptibility to measurement errors with strong deflections.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to overcome the disadvantages of the prior art and to provide an improved electrodynamic transducer, an improved transducer system, and an improved method of measuring deflection of a diaphragm. In particular, a signal proportional to the diaphragm deflection is to be provided, which is robust against interference effects.

The object of the invention is achieved by an electrodynamic acoustic transducer as defined in the opening paragraph, which additionally comprises: a second movable conductive structure arranged on a second side of the membrane facing the coil and a second immovable conductive structure which is fixed with respect to the magnet system with respect to the second movable conductive structure.

Furthermore, the object of the invention is achieved by a transducer system comprising an electrodynamic transducer as defined above and connection terminals electrically connected to the first movable conductive structure, the second movable conductive structure, the first immovable conductive structure and the second immovable conductive structure are connected to an electronic evaluation circuit.

Finally, the object of the invention is achieved by a method as defined in the introductory paragraph, wherein between a second movable conductive structure, which is arranged on a second side of the membrane facing the coil, and a second immovable conductive structure, with respect to is fixed to the magnet system opposite to the second movable conductive structure, a second voltage is measured, and the displacement is calculated based on the first voltage and the second voltage.

According to the invention, two capacitive sensing elements are used to determine the deflection of the transducer diaphragm. Advantageously, a directly proportional lifting signal is obtained. As a result, a less complex evaluation circuit is necessary for the determination of the diaphragm deflection. Furthermore, a signal is obtained that is robust against interference, robust against variations in speaker characteristics, and less susceptible to electromagnetic interference.

In particular, the first movable conductive structure and the second movable conductive structure are electrically connected to provide an advantageous series connection of two capacitances passing through the first movable conductive structure, the second movable conductive structure, the first immovable conductive structure and the second immovable conductive Structure is formed.

In particular, the displacement x is based on the formula

calculated, wherein d1 is the distance between the first movable conductive structure and the first immovable conductive structure in the rest position of the membrane and d2, the distance between the second movable conductive

Structure and the second immovable conductive structure in the rest position of the membrane. The first voltage U1 is measured between the first movable conductive structure and the first immovable conductive structure (ie, at a first capacitance C1), and the second voltage U2 is between the second movable conductive structure and the second immovable conductive structure (ie, at a second Capacitance C2).

The voltages U1 and U2 result from the voltage divider of the complex voltage based on the series connection of the capacitors C1 and C2. This series connection is supplied by a voltage source or supply voltage, which advantageously comprises portions above a certain frequency (i.e., high frequency portions). The higher the frequency components (in particular above audio frequencies, ie> 20 kHz), the better the signal-to-noise ratio for the detected voltages U1 and U2, and thus the better the measurement of the diaphragm displacement x. The voltage source may generate a sinusoidal signal or a combination of sinusoidal signals and a noise signal.

Further details and advantages of a sound transducer of the type disclosed will become apparent from the following description and the accompanying drawings.

Advantageously, the first movable conductive structure and the first immovable conductive structure have substantially the same shape and the same size, and / or the second movable conductive structure and the second immovable conductive structure have substantially the same shape and the same size.

In this way, the determination or calculation of the membrane deflection is simplified.

In a particularly advantageous embodiment of the electrodynamic acoustic transducer, the first immovable conductive structure comprises a first inner conductive region within a first conductive ring and / or the second immobile conductive structure comprises a second inner conductive region within a second conductive ring.

In particular, the first movable conductive structure, the second movable conductive structure, the first conductive ring, and the second conductive ring are electrically connected.

By the above measures, the electric field is concentrated on the area inside the conductive rings, the electric field in this area being substantially homogeneous. Accordingly, the diaphragm displacement can be determined with high accuracy.

In the above context, it is particularly advantageous if the first inner conductive region and the second inner conductive region have substantially the same shape and the same size, and / or the first conductive ring and the second conductive ring have substantially the same shape and the same shape Have size.

In this way, the determination or calculation of the membrane deflection is simplified.

Furthermore, it is advantageous if the deflection is set by applying a control voltage to the coil to a level at which the first voltage U1 or a parameter derived therefrom and the second voltage U2 or a parameter derived therefrom essentially predetermine one Achieve relationship (in particular, are substantially the same). In this way, an influence of errors caused by stray fields is compensated. "Substantially" in this context means a deviation of ± 10% from a reference value.

Further, it is preferable that the ratio of the area of the first movable conductive structure and the first stationary conductive structure and the distance between them corresponds to the ratio of the area of the second movable conductive structure and the second stationary conductive structure and the distance therebetween. In other words, the first capacitance C1 then equals the second capacitance C2. At equal voltages U1 and U2, the diaphragm is positioned at the center of the first and second capacitances C1 and C2.

In a very particularly advantageous embodiment, a control voltage is applied to the coil in order to set the deflection to a level at which the first voltage U1 or a parameter derived therefrom and the second voltage U2 or a parameter derived therefrom essentially predetermine one Achieve relationship (in particular substantially equality) below a certain frequency, for example below 50 Hz. In the usual use, audio signals comprising a bundle of frequencies are fed into a converter, in the case of microphone speakers, for example in the range of 100 Hz to 20 kHz. Without limiting the equalization of the voltages U1 and U2 prior to processing the voltages U1 and U2 to low frequencies, e.g. by using a low pass filter (e.g., with a cutoff frequency of 50 Hz), applying the control voltage to the coil would tend to hinder the conversion of the applied audio signal.

The measurement of the diaphragm displacement or the adjustment of a rest position of the diaphragm can be made on the basis of the voltages U1 and U2 or on the basis of parameters derived therefrom. Advantageously, the parameters derived from the voltages U1 and U2 are the absolute values of the voltages U1 and U2, the square values of the voltages U1 and U2, or the root mean square values of the voltages U1 and U2. Accordingly, a control voltage can be applied to the voice coil and changed until an absolute value of the first voltage U1 and an absolute value of the second voltage U2 or a square value of the first voltage U1 and a square value of the second voltage U2 or a root mean square value of the first voltage U1 and a quadratic mean value of the second voltage U2 substantially reach a predetermined relationship. In this way, the deviation compensation method is based on a relation of the energy in the capacitors 01, C2, or based on a relation of a parameter derived from the energy in the capacitors C1, C2. Especially when the predetermined relationship is a predetermined ratio, both arithmetic operations performed on the numerator and denominator do not change the relationship.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features, details, aspects of the invention, and advantages of the invention will become more apparent from the following detailed description, the appended claims, and the accompanying drawings, which illustrate features according to exemplary embodiments of the invention. Show it:

Figure 1 is a cross-sectional view of a transducer according to the prior art;

Figure 2 is a cross-sectional view of a first embodiment of the invention having conductive structures forming two capacitances above and below the membrane;

Figure 3 is a circuit diagram of the converter shown in Figure 2;

Figure 4 is a cross-sectional view of a second embodiment of the invention having conductive structures concentrating the electric field on the center region of the transducer;

Figure 5 is a circuit diagram of the converter shown in Fig. 4 and

FIG. 6 shows the transducer from FIG. 2 with a tumbling diaphragm.

In the various views, like reference numerals refer to like or equivalent parts.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following, various embodiments for various devices will be described. Numerous specific details are set forth in order 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. However, one skilled in the art will appreciate that the embodiments may be practiced without such specific details. In other instances, well-known processes, components and elements have not been described in detail so as not to distract from the embodiments described in the specification. It will be understood by those skilled in the art that the embodiments described and illustrated herein are non-limiting examples, and thus it is to be understood that the particular 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 claims that follow. Wherever in the specification reference is made to "various embodiments", "some embodiments", "(exactly) an embodiment" or "(any) embodiment" or the like, this means that a particular feature, structure or a particular property described in connection with the embodiment are included in at least one embodiment. Thus, the words "in various embodiments", "in some embodiments," "in (exactly) one embodiment," or "in (any embodiment," or the like) to be read variously throughout the specification are not necessarily all referring to the same embodiment Thus, in one or more embodiments, the particular features, structures, or properties may be combined in any suitable manner, and the particular features, structures, or properties illustrated or described in connection with one embodiment may be wholly or partially confined with the features, structures, or characteristics of any or several others

Embodiments are combined, if such a combination is not illogical or pointless.

It should be noted that the singular forms "a / e /" and "the" used in this specification and subsequent claims include the possibility of multiple reference objects unless the content clearly dictates otherwise.

The terms "first," "second," and the like in the specification and claims, if any, are used to distinguish between similar elements, and are not necessarily descriptive of a particular one sequential or chronological order. It should be understood that the terms so used may be interchangeable under appropriate circumstances insofar as the embodiments of the invention described herein can be practiced, for example, in sequences other than those illustrated herein or otherwise described. Furthermore, the terms are intended to "include," "have," and their variations cover a non-exclusive inclusion such that a process, method, subject, or device that includes a list of elements is not necessarily limited to these elements but may include other elements that are not expressly listed or are intrinsic to the process, method, subject, or device. All directions (eg "plus", "minus", "top", "bottom", "up", "down", "left", "right", "left", " to the right "," front "or" front / rear "," rear "or" rear "," top "," bottom "," above "," below "," above " "," Below "," vertically "," horizontally "," clockwise "and" counterclockwise ") are used for identification purposes only, to facilitate the reader's understanding of the present disclosure, and do not impose any limitations, particularly with regard to Position, orientation or use of the particular aspect of the disclosure. It should be understood that the terms used herein are interchangeable under appropriate circumstances insofar as the embodiments of the invention described herein can be practiced, for example, in other orientations than those illustrated or otherwise described herein.

As used herein, the terms "configured for" and "configured for" and similar terms indicate that the apparatus, apparatus or system in question is designed and / or constructed (eg, by appropriate hardware, software and / or components), to fulfill one or more specific task-related purposes and not that the device, device or system in question is capable of performing the task-related purpose only.

Connection indications (e.g., "attached," "coupled," "connected," and the like) are to be construed broadly and may include intermediate elements present between a connection of elements, as well as relative movement between elements. Thus, connection information does not necessarily imply that two elements are directly connected and fixed with respect to each other. It is intended that all matter contained in the above description or in the accompanying drawings shall be interpreted as illustrative and not restrictive. Details or structures may be changed without departing from the spirit of the invention as defined in the appended claims. All numerical expressions used in the specification and claims, which express measurements, etc., are in any case to be understood as modified by the term "about" or "substantially", which means in particular a deviation of ± 10% from a reference value.

Fig. 1 shows a prior art transducer 1a comprising a diaphragm 2, a coil 3 attached to the diaphragm 2 and a magnet system comprising in this example a magnet 4, a cup plate 5 and an upper plate 6 , The magnet system 4, 5, 6 generates a magnetic field B across a longitudinal direction of a wound wire of the coil 3 as shown in FIG. The membrane 2 comprises a bending section 2a and a middle section 2b, which in this example is stiffened by a plate. Furthermore, the converter 1a comprises a

Housing 7 with an outlet 8. The deflection of the diaphragm 2 is designated in the example shown in Fig. 1 with "x". The electrodynamic sound transducer 1a can be designed as a loudspeaker. As is well known, a current flowing through the coil 3 causes movement of the diaphragm 2 and thus sound passing through the outlet 8.

FIG. 2 shows a first example of a transducer 1b, the construction of which is comparable to the transducer 1a shown in FIG. In contrast to the latter, however, the transducer 1b comprises a first movable conductive structure 9, which is arranged on a first (upper) side of the membrane 2 facing away from the coil 3, and a second movable conductive structure 10, which faces on one of the coil 3 second (lower) side of the membrane 2 is arranged. Furthermore, the transducer 1b comprises a first immovable conductive structure 11 fixed with respect to the magnet system 4, 5, 6 fixed against the first movable conductive structure 9, and a second immovable conductive structure 12 with respect to the magnet system 4, 5, 6 is fixedly disposed opposite to the second movable conductive structure 10.

The first movable conductive structure 9 and the second movable conductive structure 10 are electrically connected in this example. Furthermore, a first connection terminal T1 is electrically connected to the first movable conductive pattern 9 and the second movable conductive pattern 10. A second connection terminal T2 is electrically connected to the first immovable conductive structure 11, and a third connection terminal T3 is electrically connected to the second immovable conductive structure 12. Further, in Fig. 3, the connection terminals T1 ... T3 are connected to an optional electronic evaluation circuit 13, thereby providing a converter system.

FIG. 3 shows a simplified representation of the transducer 1b shown in FIG. Concretely, FIG. 3 shows a voltage source generating the supply voltage U, which is connected to a first capacitance C1 formed by the first movable conductive structure 9 and the first immovable conductive structure 11 and a second capacitance C2 passing through the second conductive

Structure 10 and the second immovable conductive structure 12 is formed. The first capacitance C1 and the second capacitance C2 can be calculated as follows:

where A1 is the area of the first movable conductive structure 9 and the first stationary conductive structure 11, d1 is the distance between the first movable conductive structure 9 and the first immovable conductive structure 11 at rest of the diaphragm 2, A2 is the area of the second movable one conductive structure 10 and the second immovable conductive structure 12, d2 is the distance between the second movable conductive structure 10 and the second immovable conductive structure 12 in the resting state of the membrane 2 and εο is the permittivity in the empty space.

A first capacitor voltage U1 can be measured between the second terminal T2 and the first terminal T1, and a second capacitor voltage U2 can be measured between the first terminal T1 and the third terminal T3. The voltages U1 and U2 can be calculated as follows:

where Z1 is the complex resistance of the first capacitance C1 and Z2 is the complex resistance of the second capacitance C2. The current I through the capacitors C1 and C2 can be calculated as follows:

Advantageously, the first movable conductive structure 9 and the first immovable conductive structure 11 have substantially the same shape and the same size, and the second movable conductive structure 10 and the second immovable conductive structure 12 have substantially the same shape and the same size as shown in Fig. 2. Under this condition, the voltages U1 and U2 can be calculated as follows:

The deflection x is thus

If the distance d1 + d2 between the first immovable conductive structure 11 and the second immovable conductive structure 12 is known and the deflection x is set to zero (static rest position), d1 and d2 can be determined using the ratio

be calculated. If U1 is equal to U2, there is the situation of a symmetric air gap in which even errors caused by stray fields are compensated. Non-symmetric values of U1 and U2 can be corrected by applying a voltage to coil 3 to shift the actual position to the desired symmetrical zero position. In particular, the values of U1 and U2 are low-pass filtered before being compared. The cutoff frequency of the low-pass filter is, for example, 50 Hz. Accordingly, a control voltage is applied to the coil 2 such that the first voltage U1 substantially

is equal to the second voltage U2 below a frequency of 50 Hz or the first voltage U1 and the second voltage U2 reach a predetermined relationship below a frequency of 50 Hz.

The measurement of the diaphragm displacement or the adjustment of a rest position of the diaphragm 2 can be made on the basis of the voltages U1 and U2 or on the basis of parameters derived therefrom. Advantageously, the parameters derived from the voltages U1 and U2 are the absolute values of the voltages U1 and U2, the square values of the voltages U1 and U2, or the root mean square values of the voltages U1 and U2. Accordingly, a control voltage can be applied to the coil 3 and changed until an absolute value of the first voltage U1 and an absolute value of the second voltage U2 or a square value of the first voltage U1 and a square value of the second voltage U2 or a root mean square value of the first voltage U1 and a root mean square value of the second voltage U2 substantially reaches a predetermined relationship. In this way, the deviation compensation method is based on a relation of the energy in the capacitors C1, C2, or based on a relation of a parameter derived from the energy in the capacitors C1, C2. Especially when the predetermined relationship is a predetermined ratio, both arithmetic operations performed on the numerator and denominator do not change the relationship.

Generally, it is advantageous if the supply voltage U comprises portions above a certain frequency (i.e., high frequency portions). The higher the frequency components (in particular above audio frequencies, ie in particular> 20 kHz), the better the signal-to-noise ratio for the detected voltages U1 and U2, and thus the better the measurement of the diaphragm displacement x. The voltage source may generate a sinusoidal signal or a combination of sinusoidal signals and a noise signal.

The formulas given above are valid for the case of a homogeneous electric field present between the conductive structures 9. In order to keep the field lines concentrated between the conductive structures 9 ... 12, conductive ring structures may be added to the array. 4 therefore shows an embodiment of an electrodynamic acoustic transducer 1c, wherein the first immovable conductive structure 11 comprises a first inner conductive region 11a within a first conductive ring 11b and the second immobile conductive structure 12 comprises a second inner conductive region 12a within a second conductive ring 12b includes. In this embodiment, the first movable conductive pattern 9, the second movable conductive pattern 10, the first conductive ring 11b, and the second conductive ring 12b are electrically connected. Advantageously, also the first inner conductive region 11a and the second inner conductive region 12a have substantially the same shape and the same size, and also the first conductive ring 11b and the second conductive ring 12b have substantially the same shape and the same size , as shown in Fig. 4.

FIG. 5 shows a simplified representation of the converter 1c shown in FIG. In addition to the capacitors C1 and C2 known from FIG. 3, the electrical circuit comprises a first stray capacitance C1p formed by the first inner conductive region 11a and the first conductive ring 11b and a second stray capacitance C2p passing through the second inner conductive Region 12a and the second conductive ring 12b is formed. The voltages U1 and U2 can be calculated as follows:

This extra capacity alters the above simple ratio to a more complex nonlinear relationship between U1 and U2. On the other hand, the homogeneity of the fields is significantly improved and the stray field capa

Activity is a more or less constant factor that can be considered in an extended formula. The stray field could actually be somewhat weaker, but since it is more or less constant and independent of the deflection x of the membrane 2, it is advantageously taken into account by the above formulas.

In addition to the presented measuring methods for determining the displacement x (piston mode), wobbling of the diaphragm 2 can be detected by using the conductive structures 9 ... 12 of the transducer 1b, 1c. Fig. 6 shows a state of the known from Fig. 2 transducer 1b, in which the membrane 2 wobbles without a piston-like movement. Although the diaphragm 2 is in its rest state with respect to the displacement x (the displacement is zero in FIG. 6), a distance between the first movable conductive structure 9 and the second fixed conductive structure 11 and between the second movable conductive structure 10 changes and the second immovable conductive structure 12. The distance between the second movable conductive structure 10 and the second immovable conductive structure 12 is designated by "y" in FIG.

Since the capacitance C2 is inversely proportional to the distance y, the gain on the left side in Fig. 6 exceeds the loss on the right side. For this reason, a modulation of the capacitance C2 caused by a wobble amplitude of ~ 10% of d2 in a conventionally sized converter 1b causes a current modulation of about 1.34% at doubled frequency, which can be clearly separated from in-phase current modulation caused by the piston mode , The same applies in principle to the first capacitance C1, which is likewise modulated by wobbling.

The presented method for calculating the position x of the diaphragm 2 can be used to compensate for nonlinearities of the transducer 1b, 1c. For example, the nonlinear graph of the driving force factor BL results in a non-linear conversion of the electrical signals fed into the coil 3 into a movement of the diaphragm 2. If the position x of the diaphragm 2 is known, this non-linearity can be compensated by varying the electrical signals.

In general, the converter 1b, 1c or the membrane 2 in plan view have any shape, in particular a rectangular, circular or egg shape.

It should be noted that the invention is not limited to the aforementioned embodiments and exemplary implementations. Developments, modifications and combinations are also within the scope of the claims and will be apparent to those skilled in the art from the foregoing disclosure. Accordingly, the methods and structures described and illustrated herein are meant to be illustrative and exemplary rather than limiting the scope of the present invention. The scope of the present invention is defined by the appended claims, including equivalents already known and not foreseeable at the time of filing this application. While various embodiments of this invention have been set forth to some extent, many modifications to the disclosed embodiments are conceivable for those skilled in the art without departing from the spirit or scope of this disclosure.

REFERENCE LIST 1a ... 1c transducer 2 membrane 2a bending section 2b stiffened central section 3 coil 4 magnet 5 pot plate 6 top plate 7 housing 8 outlet 9 first movable conductive structure 10 second movable conductive structure 11 first immovable conductive structure 11a first inner conductive region 11 b first conductive ring 12 second immobile conductive structure 12a second inner conductive region 12b first conductive ring 13 evaluation circuit C1 first capacitance C1p first stray capacitance C2 second capacitance C2p second stray capacitance d1 distance between first movable and immovable conductive

Structure at rest of the transducer d2 distance between second movable and immovable conductive

Structure at rest of the converter I Current T1 ... T3 Connection connections U Supply voltage for the voltage divider of the complex voltage U1 First voltage U2 Second voltage x Displacement y Distance between the second movable and immovable conductive

Structure in the tumbling state of the transducer

Claims (16)

An electrodynamic transducer (1b ... 1c) comprising a diaphragm (2), a coil (3) attached to the diaphragm (2) and a magnet system (4, 5, 6) adapted to apply a magnetic field ( B) transverse to a longitudinal direction of a wound wire of the coil (3), characterized by a first movable conductive structure (9) arranged on a first side of the membrane (2) facing away from the coil (3), a second one movable conductive structure (10) disposed on a second side of the diaphragm (2) facing the coil (3), a first immovable conductive structure (11) fixed with respect to the magnet system (4, 5, 6) the first movable conductive structure (9), and a second immovable conductive structure (12) fixed with respect to the magnet system (4, 5, 6) opposite to the second movable conductive structure (10). 2. Electrodynamic acoustic transducer (1b ... 1c) according to claim 1, characterized in that the first movable conductive structure (9) and the second movable conductive structure (10) are electrically connected. 3. Electrodynamic acoustic transducer (1b ... 1c) according to claim 1 or 2, characterized in that the first movable conductive structure (9) and the first immovable conductive structure (11) have substantially the same shape and the same size and / / or the second movable conductive structure (10) and the second stationary conductive structure (12) have substantially the same shape and the same size. 4. Electrodynamic acoustic transducer (1b ... 1c) according to one of claims 1 to 3, characterized in that the first immovable conductive structure (11) comprises a first inner conductive region (11a) within a first conductive ring (11b) and / or the second immovable conductive structure (12) comprises a second inner conductive region (12a) within a second conductive ring (12b). 5. Electrodynamic acoustic transducer (1b ... 1c) according to claim 4, characterized in that the first inner conductive region (11a) and the second inner conductive region (12a) have substantially the same shape and the same size and / or the first conductive ring (11 b) and the second conductive ring (12 b) have substantially the same shape and the same size. 6. Electrodynamic acoustic transducer (1b ... 1c) according to claim 4 or 5, characterized in that the first movable conductive structure (9), the second movable conductive structure (10), the first conductive ring (11b) and the second conductive Ring (12b) are electrically connected. 7. transducer system, characterized by an electrodynamic acoustic transducer (1b ... 1c) according to one of claims 1 to 6, comprising connection terminals (T1 ... T3) electrically connected to the first movable conductive structure (9), the second movable conductive Structure (10), the first immovable conductive structure (11) and the second immovable conductive structure (12) and to an electronic evaluation circuit (13) are connected. 8. Method for measuring a deflection (x) of a membrane (2) of an electrodynamic sound transducer (1b ... 1c), which additionally has a coil (3) attached to the membrane (2) and a magnet system (4, 5, 6) which is adapted to generate a magnetic field (B) transverse to a longitudinal direction of a wound wire of the coil (3), between a first movable conductive structure (9) facing away from the coil (3) first side the membrane (2) is arranged, and a first immovable conductive structure (11), which with respect to the magnet system (4, 5, 6) is arranged fixedly opposite the first movable conductive structure (9), a first voltage (U1) and between a second movable conductive structure (10) disposed on a second side of the diaphragm (2) facing the coil (3) and a second immovable conductive structure (12) fixed relative to the magnet system (4 , 5, 6) fixed g is arranged above the second movable conductive structure (10), a second voltage (U2) is measured, and the deflection (x) is based on the first voltage (U1) and the second voltage (U2) or on the basis of one of the first voltage (U2). U1) and a parameter derived from the second voltage (U2). 9. The method according to claim 8, characterized in that the deflection (x) based on the formula wherein (d1) is the distance between the first movable conductive structure (9) and the first immovable conductive structure (11) in the rest position of the diaphragm (2), and (d2) the distance between the second movable conductive structure (10 ) and the second immovable conductive structure (12) in the rest position of the membrane (2). 10. The method according to claim 8 or 9, characterized in that the deflection (x) by applying a control voltage to the coil (3) to a Ni is set at which the first voltage (U1) or a parameter derived therefrom and the second voltage (U2) or a parameter derived therefrom substantially reach a predetermined relationship. 11. The method according to claim 10, characterized in that the deflection (x) by applying a control voltage to the coil (3) is set to a level at which the first voltage (U1) or a parameter derived therefrom and the second voltage (U2) or a parameter derived therefrom substantially reach a predetermined relationship below a certain frequency. 12. The method according to claim 11, characterized in that the first voltage (U1) or a parameter derived therefrom and the second voltage (U2) or a parameter derived therefrom are filtered by a low-pass filter. 13. The method according to any one of claims 10 to 12, characterized in that from the voltages (U1) and (U2) derived parameters to absolute values of the voltages (U1) and (U2) and to the coil (3) a Control voltage is applied and changed until an absolute value of the first voltage (U1) and an absolute value of the second voltage (U2) substantially reach a predetermined relationship, or at derived from the voltages (U1) and (U2) parameters Square values of the voltages (U1) and (U2), and to the coil (3) a control voltage is applied and changed until a square value of the first voltage (U1) and a square value of the second voltage (U2) have substantially a predetermined relationship or the parameters derived from the voltages (U1) and (U2) are quadratic averages of the voltages (U1) and (U2) and a control voltage is applied to the coil (3) and as long as we change d until a root mean square value of the first voltage (U1) and a root mean square value of the second voltage (U2) substantially reach a predetermined relationship. 14. The method according to any one of claims 8 to 13, characterized in that between the first immovable conductive structure (11) and the second immovable conductive structure (12) a supply voltage (U) is applied, wherein the first movable conductive structure (9) and the second movable conductive structure (10) are electrically connected, and wherein the supply voltage (U) comprises portions above a certain frequency. 15. The method according to claim 14, characterized in that the supply voltage (U) comprises only portions above a certain frequency. 16. The method according to claim 14 or 15, characterized in that it is a noise signal at the supply voltage (U).