WO2022123512A2

WO2022123512A2 - Capacitor armature for stators of electrostatic loudspeaker and corresponding high voltage amplifier

Info

Publication number: WO2022123512A2
Application number: PCT/IB2021/061562
Authority: WO
Inventors: Diego Barone; Giandomenico Gonella
Original assignee: Debago S.R.L.
Priority date: 2020-12-10
Filing date: 2021-12-10
Publication date: 2022-06-16
Also published as: WO2022123512A3

Abstract

A capacitor armature comprises electric power conduction means having an electrical conductor provided with an insulating sheath and integral with the supporting structure and adapted to be connected to high voltage power supply means for the generation of an electric field. The electrical conductor is co-molded on the supporting structure to be integral therewith without the possibility of displacements. A high-voltage amplifier comprises voltage generation means adapted to be applied to at least one load and having a modified SRPP-type driving circuit with an input branch provided with a first solid-state active component and a first resistor for the passage of a first current, an output branch placed in series with the input branch and provided with a second active solid-state component and a second resistor for the passage of a second current, a third branch placed in parallel to the portion of the first circuit comprising the first resistor and configured to introduce a non-linearity capable of producing an increase in the first current and allowing the output section of the output branch to deliver all the current required by the load.

Description

CAPACITOR ARMATURE FOR STATORS OF ELECTROSTATIC LOUDSPEAKER AND CORRESPONDING HIGH VOLTAGE AMPLIFIER Description

Technical Field

The present invention relates to the technical filed of electrical components, preferably but not exclusively for use within sound devices, and has particularly as its object a capacitor armature adapted to be used in a preferred but non-exclusive manner as a stator for electrostatic loudspeakers or diffusers, as well as an electrostatic loudspeaker comprising the stator.

The invention also relates to a high voltage amplifier, which can also be used in a preferred but non-exclusive manner inside an electrostatic loudspeaker or diffuser, as well as the electrostatic diffuser comprising such a high voltage amplifier.

State of the art

As known, electrostatic acoustic diffusers are particular diffusers characterized by the presence of a vibrating membrane placed inside a support frame that guarantees the right voltage and keeps it into position.

In particular, the vibrating membrane is usually composed of a film of insulating material suitably treated to reduce the surface resistivity and favour the diffusion of a surface electric charge.

As shown schematically in Fig. 1, the membrane is inserted between two stators, each defined generally by a perforated panel associated with respective conductive elements, for example properly insulated electric cables or layers of conductive material, so as to each constitute an electrostatic cell and wherein the membrane will be inserted.

The essential structure of the diffuser is completed by a voltage generator that generates a polarization voltage Vp, continuous and of the order of a few kV, applied to the conductive vibrating membrane to distribute an electric charge thereon.

The generator is also designed to produce a pair of alternating and opposed phase voltages Vs, also of the order of kV, to be applied to the stators to generate an electric field in the gap defined between the same stators and wherein the membrane is positioned. As the membrane is immersed in the electric field, the combined action of the polarization charge distributed on the membrane and the electric field generated by the stators creates a force that makes the membrane move.

In particular, the voltages that drive the stators are substantially an appropriately amplified audio signal, so that the membrane is stressed to move according to the audio signal itself.

The thus produced movement of the membrane generates pressure waves in the air, responsible for generating sound.

To this end, the membrane must be properly tensioned, so that the elasticity of the material guarantees the natural return to the rest position.

Consequently, there is no need for further suspension systems, since the membrane, stressed to move by the electrical forces that develop in the cell, tends to automatically return to the rest position, behaving substantially like a spring, with a displacement practically proportional to the applied force.

To obtain a correct vibration of the membrane it is also necessary that the stators are as rigid as possible and that their conductive part is distributed as uniformly as possible with respect to the membrane, to generate a uniform electric field, so as to have a uniform behaviour of the membrane.

Furthermore, it is also advisable that the full/empty ratio may be controlled and maintained precisely at the design value, possibly, but not necessarily, unbalanced in favour of the voids so that the sound energy generated is free to go outwards without obstacles.

Among the currently most commonly used solutions for the construction of stators is the one that provides for the use of perforated sheets treated with an insulating paint, which however does not guarantee an adequate degree of insulation.

Even the empty/full ratio is not optimal if a high rigidity is to be achieved.

A further solution involves the use of parallel iron rods, also treated with an insulating paint; however, this solution also does not guarantee an adequate degree of insulation and the empty/full ratio is always not optimal if a high rigidity is to be achieved.

Stators made of insulating material are also known which are provided with a layer of painted conductive material, usually copper, which are always limited by poor insulation and a non-optimal empty/full ratio.

For example, US8670581 describes an electrostatic acoustic diffuser wherein the stator panels comprise a metal core coated, after forming, with a high voltage resistant dielectric coating. In a second configuration, the stator panels are obtained by thermal moulding or forming and made of electrically conductive plastic which is subsequently coated with a dielectric insulating layer of the same shape.

Yet another solution provides that the stators have a honeycomb structure that defines the rigid part on which a conductor wire is spread which is fixed with points of hot glue or bicomponent or other material.

This solution, while ensuring good insulation thanks to the use of the conductor wire, is very laborious, in particular to maintain the parallelism between the wires, a necessary condition for having a uniform electric field.

US2008/307632 describes a stator for an electrostatic loudspeaker which comprises a frame made of electrically insulating material coupled by injection moulding to an electrically conductive grid.

However, this solution uses a rigid grid as a conductive element, i.e. a structure that limits the shapes that can actually be built, also considering the economic aspect.

As regards the aspect more strictly related to voltage supply, it must then be considered that historically the driving voltages for the stators are achieved with a system based on transformers, schematized in Fig. 2.

The input audio is applied to an amplifier that drives the step-up transformer characterized by a high turns ratio, as the audio amplifiers, whether solid-state or tube, are designed to drive dynamic loudspeakers, which require order of tens of volts.

For a long time, the step-up transformer has been the only method to obtain the high voltages required by the electrostatic panel and, at least in principle, the only limit to the voltage that can be supplied is given by the insulation of the wire used for winding. As matter of fact, modern electronic devices, such as MOSFETs or bipolar transistors, withstand maximum voltages of the order of hundreds of volts, with a maximum of a thousand, and would not be suitable for such purposes. Only relatively recently MOSFETs and IGBTs have been made available with maximum voltages of a few kV. However, the transformer, despite being used for a long time, is not the optimal solution since it is characterized by at least two parameters in contrast to each other: the maximum allowable magnetic flux from the core and the resonant frequency.

The magnetic flux is given by

0=Vi/(4.4 f Ni ) wherein Vi is the voltage applied to the primary, f is the frequency, Ni is the number of turns of the primary.

The magnetic core that makes up the transformer is characterized by a maximum allowable flux beyond which the core itself is saturated.

However, the transformer must operate with a flux lower than the saturation value: it follows that as the frequency decreases, the voltage applicable to the primary of the transformer also decreases and this determines, for practical purposes, a limit to the minimum frequency that can be treated by the assembly consisting of driver and transformer.

In principle, to reduce the minimum frequency the number of turns of the windings may be increased, but in this way the parasitic capacitance is increased which in turn determines the lowering of the resonant frequency of the transformer which effectively limits the maximum frequency that can be correctly applied to the transformer.

It is evident that the coupling transformer limits the bandwidth that can be reproduced by the whole electrostatic speaker system.

Scope of the invention

The scope of the present invention is to overcome the above drawbacks by providing a capacitor armature, suitable for use as a stator for electrostatic speakers, which is particularly effective and relatively cost effective.

A particular object is to provide a capacitor armature, suitable to be used also as a stator for electrostatic loudspeakers, which guarantees both an effective insulation and a high uniformity of the electric field, so as to allow, when inserted in an electrostatic loudspeaker, to have a uniform and well-controlled vibration of the membrane over the whole surface.

Still another object is to provide a capacitor armature, suitable to be used also as a stator for electrostatic speakers, which is characterized by an optimal full/empty ratio. Still another object is to provide a capacitor armature, suitable for use also as a stator for electrostatic speakers, which can be made in any shape and size while always maintaining the electric field uniform and well distributed over its whole surface.

A further object is to provide a high voltage amplifier, preferably but not necessarily of the type suitable to be used for electrostatic acoustic loudspeakers, which is particularly effective and which allows to overcome the above drawbacks of solutions using a transformer.

In particular, an object is to provide such a high voltage amplifier which is characterized by a high extension of the pass band, unlike transformers.

Still another object is to provide such a high voltage amplifier which is compact, efficient and light and which can be replicated in series also using commercially available components, if necessary.

Still another object is to provide a high voltage amplifier suitable for electrostatic loudspeakers which has reduced absorption and compact dimensions to be inserted inside the frame of the diffuser to have a slim and pleasing to the eye assembly, thus avoiding frames and bulky heat sinks.

These objects, as well as others which will become more apparent hereinafter, are achieved by a capacitor armature which, according to claim 1, comprises a supporting structure and electric power conduction means integral with said supporting structure, which conduction means comprise at least one electric conductor provided with an insulating sheath and integral with said supporting structure, said at least one electric conductor being adapted to be connected to high voltage electrical power supply means for generating an electric field.

According to a peculiar feature of the invention, said at least one electrical conductor is co-molded for its whole extension on said supporting structure to be integral therewith without the possibility of displacements.

Thanks to this feature, it will be avoided that the electrical conductor can move from the supporting structure as a result of the vibrations produced by the specific use of the device wherein the armature is integrated, causing an irregularity of the electric field which would result in a worsening of the sound quality.

Advantageous embodiments of the invention are obtained in accordance with the dependent claims. Bnef disclosure of the drawings

Further features and advantages of the invention will become more apparent in the light of the detailed description of preferred but not exclusive embodiments of the various parts of the invention, shown by way of non-limiting example with the aid of the attached drawing tables wherein:

FIG. 1 is a schematic representation of an electrostatic acoustic diffuser;

FIG. 2 is a schematic representation of a transformer driving circuit according to the known art;

FIG. 3 shows a partial perspective view of an assembly sequence of an electrostatic loudspeaker made from two armatures according to the invention;

FIG. 4 is a perspective view of a step of construction of the reinforcement according to the invention;

FIG. 5 is a schematic representation of a driving circuit according to the present invention;

Fig- 6 is a schematic representation of the driving circuit configured as a CASCODE loaded by the SRPP circuit according to the present invention;

FIG. 7 is a graph that shows the trend of voltage and current within a known type SRPP circuit;

FIG. 8 is a graph that shows the trend of voltage and current within an SRPP circuit according to the present invention.

Best modes of carrying out the invention

A particular embodiment of a capacitor armature according to the present invention is disclosed in the following, which armature being adapted to be used to define a stator for an electrostatic speaker adapted to be integrated into electrostatic loudspeakers.

In particular, as can be seen from the assembly sequence of Fig. 3, an electrostatic loudspeaker, globally indicated with 1, will be composed of a pair of stators 2, 3 connected to high voltage power supply means for the generation of an electric field and a vibrating conductive membrane 4 placed in the gap 5 between the two stators 2, 3 and also fed by means of a bias voltage to be vibrated and generate sound.

However, it is understood that the armature according to the present invention may find an advantageous application in any electrical or electronic component that provides for the use of one or more capacitors, such as, by way of a not limiting example, to a TEM cell to be used in electromagnetic compatibility measurements.

In the preferred but not exclusive embodiment described below, the armature will define one of the two stators of the speaker and therefore will be defined below as the stator.

Furthermore, for reasons of conciseness of the exposure, in the following we will refer only to the stator indicated with 2, it being understood that everything that will refer to this stator will be found in a substantially similar or technically equivalent manner also in the other stator 3.

According to a particular embodiment, also preferred but not exclusive, the single stator 2 comprises a supporting structure 6 adapted to define an anchorage for the membrane 4 and having a front surface adapted to face, in use, towards the outside, and a rear surface adapted to face, in use, towards the membrane 4 itself.

The supporting structure 6 is provided with electric power conduction means connected to high voltage power supply means, not shown, which will allow the generation of an electric field, so that it can operate as one of the stators of the electrostatic loudspeaker 1.

In particular, the electric power conduction means comprise at least one electric conductor 7 provided with an insulating sheath and integral with one or more of the faces of the supporting structure 6.

In a peculiar way, the electrical conductor 7 will be co-molded for its whole extension on the supporting structure 6 to be integral with it for its entire longitudinal extension and without the possibility of displacements.

Conveniently, as exemplified in Fig. 4, the coupling between the electrical conductor 7 and the supporting structure 6 may be obtained by preparing a mold 8 having a molding cavity with a negative shape of the supporting structure 6, which must be provided with suitable housings of the electrical conductor 7.

Therefore, the mold 8 will have similar housings 9 with a shape complementary to those of the supporting structure 6 and wherein the electrical conductor 7 will be arranged.

In this way, once the electric conductor 7 has been positioned in the mold 8, according to the configuration that it will have to have after processing, it is possible to proceed with the co-molding.

In a first variant, the co-molding will be of the injection type and the material from which the supporting structure 6 will be formed will preferably be a thermoplastic polymeric material.

In this way, there will be a structural coupling by fusion and consequent adhesion between the two parts, also being possible to use a primer to facilitate the adhesion process.

However, in a further variant it will be possible to have a co-molding, also of the injection type, such as to incorporate the electrical conductor 7 inside the supporting structure 6 without there being fusion or adhesion therewith, but still maintaining the conductor integral with the supporting structure 6 for its whole longitudinal extension, avoiding any possibility of displacements.

This technique will also make it possible to design and manufacture a panel or stator 2 of suitable rigidity and having any shape and size, both regular and irregular, as it will be sufficient to arrange the electrical conductor 7, which will be properly flexible, in the most correct possible way and maintaining the constant interspaces to create a uniform and well distributed electric field over the whole surface of the stator 2.

In turn, the electrical conductor 7 will follow the shape of the stator 2 to which it can be applied according to any configuration.

In particular, the electric conductor 7 will be a flexible electrically conductive element and therefore adapted to be shaped at will, following the 3D configuration adopted for the stator 2.

By way of example, the electrical conductor 7 will comprise an electric cable provided with one or more internal inner wires in a conductive material, such as copper, aluminum, graphite, carbon fiber or similar, wrapped in a sheath, film or other high insulation coating, made of thermoplastic polymeric material, for example PA, PMMA, ABS, PC, PP, PE or the like, which can be filled, for example with glass fiber, carbon fiber or similar or not filled.

According to a first embodiment, not exclusive for the present invention, the supporting structure 6 may be substantially flat and grid-shaped and will comprise a plurality of longitudinal ribs parallel to each other and equally spaced, joined by connecting crosspieces.

The longitudinal ribs each have an outer face designed to face, in use, towards the outside, and an internal face designed to face, in use, towards the membrane 4.

The electric conductor 7 will be arranged on the inner face of the longitudinal ribs, which will preferably be provided with suitable recesses defining a housing of the electric conductor 7, which will be made integral with the ribs for their entire longitudinal extension to define a plurality of longitudinal branches, parallel and equally spaced joined by respective curved sections.

The electrical conductor 7 will be applied on the rear surface of the grid without solution of continuity to at least partially cover also the connecting crosspieces in correspondence with its curved portions.

However, it will be possible to provide further variants wherein the electrical conductor 7 is arranged in a different way on the ribs, for example placed on the front face or, again, incorporated into the ribs themselves.

Further embodiments may provide that the electric conductor 7 is wound on the ribs with a spiral shape or with shapes different from the linear one, always applied by comolding.

The grid configuration will allow to obtain the greatest possible empty/full ratio in relation to the conductive material used, which preferably will not be less than 1, and to arrange it as precisely as possible while keeping the longitudinal branches of the electrical conductor 7 parallel and with a constant and repeatable distance, thus generating the right electric field.

Furthermore, this embodiment will allow to easily obtain the desired empty/full ratio and to keep it constant for the whole surface of the stator 2.

However, it is understood that the supporting structure 6 nay have any shape, without any limitation, and also the electrical conductor 7 may be applied to one or more faces of the supporting structure 6 according to any configuration, also in this case without any limitation at least theoretically.

According to a particularly advantageous variant, the electric power conduction means may comprise two or more electric conductors 7, in particular two or more electric cables as above, associated with respective portions of the supporting structure 6 and adapted to be supplied with high voltage independently with each other.

In this way it will be possible to have the advantage of defining distinct and separate sectors of the electrical conductor 7 within the same supporting structure 6 to drive them in a different way, for example by defining a sector with low frequencies and a sector with all frequencies.

The possibility of making the armature by co-molding also makes it possible to create a stator 2 formed by a plurality of modules mutually coupled at transverse and/or longitudinal side edges without solution of continuity, thus defining a unitary outer surface.

It will thus be possible to create modular structures which, when joined together, create even large reinforcements, regardless of the shape.

A further advantage is represented by the possibility of adding in the mold 8 of the supporting structure 6 one or more appendages which operates as support and positioning of the membrane 4, guaranteeing its correct distance from the inner surface of the grid.

In the following a particular configuration of a high voltage amplifier according to the present invention is disclosed, designed to be applied to an electrostatic acoustic diffuser, including an electrostatic diffuser of the type described above and in accordance with the present invention and therefore provided with one or more loudspeakers, each comprising a pair of stators connected to the high-voltage amplifier for the generation of an electric field and a conductive vibrating membrane placed in the gap between the two stators and also powered by a bias voltage to be vibrated and generate the sound.

However, it is understood that the amplifier according to the present invention may find advantageous application in any electrical or electronic component that provides for the use of the amplifier, such as, by way of a non limiting example, a TEM cell to be used in electromagnetic compatibility measurements.

Generally speaking, the amplifier will be provided with voltage generation means suitable to supply the conductive membrane with a continuous bias voltage Vp and to apply to the stators a pair of voltages Vs in phase opposition to generate a potential difference suitable for establish an electric field in the interspace and bring the conductive membrane into vibration for the generation of sound.

Regardless of the structure of the stators and of the respective electrical energy conduction means, the high voltage generation means, defined by the high voltage amplifier according to the present invention, are characterized by the fact that they do not provide for the use of transformers, instead of which there will be, for each stator, driving circuits of the SRPP type suitably modified to increase the output current.

In particular, the aforesaid driving circuits, illustrated more clearly in Fig. 5, are modified to operate in class AB.

To this end, the driving circuits each comprise an input branch provided with a first solid-state active component and a first resistor for the passage of a first current and an output branch, placed in series with the input branch, and provided with a second active component and a second resistor for the passage of a second current.

In a peculiar way, the SRPP driving circuit is of the modified type and has a third branch placed in parallel to the portion of the first circuit comprising the first resistor and is designed to introduce a non-linearity adapted to produce an increase in the first current and allowing the section output of the output branch to deliver all the current required by the load.

In this way the SRPP circuit is characterized by the fact that the maximum deliverable current is equal to the quiescent current.

Therefore, in the event that the load requires a high current, it will be necessary to provide a suitably high quiescent current, which in turn determines a strong power dissipation and the need for abundant means for heat dissipation.

The addition of the third branch allows the input branch to increase the quiescent current to automatically adapt to the load requirements. The power absorbed at rest will remain low and will only increase if required by piloting requirements. This allows to drive the load perfectly, while keeping the dissipation at rest relatively low.

Preferably, the third branch comprises a third resistor placed in parallel with the first resistor and having a lower value thereof.

Furthermore, the third branch comprises a diode placed in series with the third resistor and a voltage reference adapted to supply a fixed or variable voltage higher than the rest voltage on the first resistor.

In an exemplary and non-limiting manner, the voltage supplied by the reference may be equal to a value substantially equal to one and a half times the value of the voltage at rest.

For example, the voltage reference could be a voltage generator placed downstream of the third resistor.

The active components will be selected from the group comprising bipolar transistors, IGBTs, MOSFETs and the like.

According to a further particularly advantageous aspect, which will become clearer hereinafter, these components will be powered by the source (if MOSFET) or by the emitter (if IGBT or bipolar transistors) instead of by the gate, creating a structure that can be defined as CASCODE-SRPP, schematized in Fig. 6.

When sizing the driving circuit, it is also necessary to consider that the current II develops the voltage R1 * Il on the first resistance R1

DI begins to conduct when the current II circulating in the first component XI determines on R1 a voltage drop greater than El .

Since DI begins to conduct, the equivalent resistance seen by the first component XI will be given by the parallel between R1 and R3. This entails the possibility of increasing the current in XI much faster than with the first resistor R1 alone.

The addition of the third branch allows a strong increase of the impulse current in the first active component, which translates, in fact, into the temporary increase of the quiescent current which, in turn, allows the circuit to deliver a much greater current than the current static rest.

To demonstrate the above, consider a hypothetical classic biased SRPP with 7.5mA at rest, called to deliver sinusoidal voltage on a 2nF capacitor.

With reference to the graph of Fig. 7, wherein the trace T1 represents the voltage delivered to the load, the trace T2 represents the current Ii in the lower MOSFET X2 and trace T3 represents the current b in the upper MOSFET X2, it is observed that the supplied voltage is strongly distorted with respect to the reference sinusoid and that the delivered current is strongly asymmetrical, a consequence of the different capacity of supplying current of the two MOSFETs which make up the SRPP. It is also evident that the lower MOSFET XI, due to the operation in class A, works a sinusoidal current with amplitude equal to the quiescent current (7.5mA peak).

On the other hand, the upper MOSFET X2, which basically functions as a follower of the voltage developed on its source resistance due to the current modulated by the lower MOSFET XI, is adapted to supply all the current required by the load.

The result is a strongly distorted output current and, consequently, a very distorted voltage delivered to the stator and a voltage that could be supplied that is limited by the “slew rate" imposed by the maximum deliverable current (equal to the quiescent current) divided by the capacity of the stator to be driven.

By adding to the classic SRPP the network formed by diode DI, resistor R3 of much lower value than R1 and voltage E3 higher than the rest voltage on Rl, in the same operating conditions of the previous circuit (therefore same load and same input voltage), we obtain the graph of Fig. 8 wherein the trace T4 represents the voltage delivered to the load, the trace T5 represents the current h in the upper MOSFET X2 and the trace T6 represents the current Ii in the lower MOSFET Xi.

From this graph it can be observed that the current in the lower MOSFET Xi has a “sinusoidal-like” trend only below the quiescent current. For currents higher than the quiescent current, the current in the lower MOSFET grows very fast, while the upper MOSFET continues to work as in the previous case.

The result is that the SRPP stage is now adapted to supply all the current required by the load.

Considering that the lower MOSFET Xi never reaches complete cut-off, because the current must not be completely zero, however, or the output will be saturated, it can be said that the new SRPP works substantially in class AB.

The SRPP circuit thus modified is however characterized by a strong non-linearity, due precisely to the presence of the third branch, which introduces a strong distortion which effectively prevents its use in an open loop.

It is therefore necessary to close a reaction loop that keeps the gain of the entire stage under control, ensuring the linearity of the system. By way of non-limiting example, it is proposed to feed the input branch from the source through an operational amplifier. The circuit of Fig. 6 is now configured as a CASCODE loaded by the new SRPP, wherein the operational amplifier sets the gain, defined as usual as the ratio between the reaction resistors RF1/RF2, compensates for the non-linearity and smoothes the response in frequency.

The final result is a driver that delivers thousands of Volts to the electrostatic panel, with all the current required by the panel and keeping the dissipated power very low at rest.

Claims

1. A capacitor armature, comprising: a supporting structure (6); electric power conduction means integral with said supporting structure (6); wherein said electric power conduction means comprise at least one electric conductor (7) provided with an insulating sheath and integral with said supporting structure (6), said at least one electric conductor (7) being adapted to be connected to high voltage electric power supply means for the generation of an electric field; characterized in that said at least one electrical conductor (7) is a flexible electrical cable provided with an insulating coating which houses one or more wires of electrically conductive material, said at least one electrical conductor (7) being comolded on said supporting structure (6) to be integral therewith without the possibility of displacements.

2. Armature as claimed in claim 1, characterized in that said at least one electrical conductor (7) is applied on said supporting structure (6) by injection co-molding inside a proper mold (8).

3. Armature as claimed in claim 1 or 2, characterized in that said supporting structure (6) is made of plastic material and is grid-shaped and comprises a plurality of longitudinal ribs parallel to each other and equally spaced joined by connection crosspieces, said longitudinal ribs each having an outer face adapted to be directed, in use, towards the outside, and an inner face.

4. Armature as claimed in claim 3, characterized in that said longitudinal ribs are parallel to each other and equally spaced.

5. Armature as claimed in claim 3 or 4, characterized in that said at least one electrical conductor (7) is arranged on the inner faces of said grid-shaped supporting structure (6) for their whole longitudinal extension to define a plurality of longitudinal branches joined by respective curved sections.

6. Armature as claimed in claim 5, characterized in that said longitudinal branches are parallel and equally spaced with each other.

7. Armature as claimed in any claim from 3 to 6, characterized in that said at least one electrical conductor (7) is arranged on the outer faces of said grid-shaped supporting structure (6) or is incorporated thereinto.

8. Armature as claimed in any claim 3 to 7, usable as stator (2, 3) inside an electrostatic loudspeaker (1) comprising a pair of said armatures mutually facing and spaced apart to define a gap (5) housing an electrically conductive vibrating membrane (4), characterized in that said supporting structure (6) has a front surface adapted to face, in use, towards the outside, and a rear surface adapted to be face, in use, towards said membrane (4), said at least one electric conductor (7) being applied on said rear surface of said grid without solution of continuity to cover at least partially also said connection crosspieces at said curved sections.

9. Armature as claimed in any preceding claim, characterized in that said electric power conduction means comprise two or more of said electrical conductors (7) associated with respective portions of said supporting structure (6) and adapted to be electrically powered with a high voltage independently from each other.

10. Armature as claimed in any preceding claim, characterized in that said at least one electric conductor (7) or each of said two or more electric conductors (7) comprise an inner wire made of conductive material, such as copper, aluminum, graphite, fiber carbon or similar, wrapped in a sheath, film or other high insulation coating, made of filled or unfilled thermoplastic polymeric material.

11. Armature as claimed in any preceding claim, characterized in that said supporting structure (6) is formed by a plurality of modules mutually coupled at side transverse and/or longitudinal edges without solution of continuity to define a unitary outer surface.

12. An electrostatic loudspeaker comprising a pair of stators (2, 3) adapted to be connected to high voltage power supply means for the generation of an electric field and a conductive membrane (4) anchored to said stators (2, 3) to be immersed in said electric field and vibrated by it for the generation of sound, characterized in that each of said stators (2, 3) comprises or is defined by an armature according to one or more of the preceding claims.

13. A high voltage amplifier, comprising voltage generation means suitable for being applied to at least one load and having an SRPP type driving circuit made with solid state devices, wherein said driving circuit comprises an input branch provided with a first solid-state active component and a first resistor for the passage of a first current and an output branch placed in series with said input branch and provided with a second solid-state active component and a second resistor for the passage of a second current; characterized in that said SRPP driver circuit has a third branch placed in parallel to the portion of said first circuit comprising said first resistor and having a third resistor placed in parallel with said first resistor and a voltage reference adapted to provide a fixed or variable voltage higher than the rest voltage on said first resistor to introduce a non-linearity adapted to produce an increase in said first current and allow the output section of said output branch to deliver all the current required by the load.

14. Amplifier as claimed in claim 13, characterized in that said third resistor is lower than said first resistor.

15. Amplifier as claimed in claim 14, characterized in that said third branch comprises a diode in series with said third resistor and wherein said voltage reference is adapted to supply a fixed or variable voltage higher than said rest voltage.

16. Amplifier as claimed in claim 15, characterized in that said voltage reference is a voltage generator.

17. Amplifier as claimed in any claim 13 to 16, characterized in that said active components are selected from the group comprising bipolar transistors, IGBTs, MOSFETs and the like.

18. Amplifier as claimed in claim 17, characterized in that said active component is powered by the source.

19. An electrostatic loudspeaker, comprising: a pair of stators facing each other and spaced apart to define a gap; a conductive membrane placed in said gap; voltage generation means adapted to be applied to at least one load to supply said conductive membrane with a continuous bias voltage (Vp) and to apply to said stators a pair of alternating voltages in phase opposition to generate a voltage suitable to establish an electric field in said interspace and bring said conductive membrane into vibration for the generation of sound; wherein said voltage generation means comprise, for each of said stators, a respective

17 driving circuit of the modified SRPP type made with solid state devices to increase the output current and the voltage gain; wherein said driving circuit comprises an input branch provided with a first solid-state active component and a first resistor for the passage of a first current and an output branch in series with said input branch and provided with a second active component and a second resistor for the passage of a second current; characterized in that said SRPP driver circuit has a third branch placed in parallel to the portion of said first circuit comprising said first resistor and having a third resistor placed in parallel with said first resistor and a voltage reference adapted to provide a fixed or variable voltage higher than the rest voltage on said first resistor to introduce a non-linearity adapted to produce an increase in said first current and allow the output section of said output branch to deliver all the current required by the load.

18