EP2177047A1

EP2177047A1 - Electrodynamic transducer, in particular of the loudspeaker type with ferrofluid suspension and related devices

Info

Publication number: EP2177047A1
Application number: EP08827304A
Authority: EP
Inventors: Gilles Milot
Original assignee: Individual
Current assignee: ACOUSTICAL BEAUTY
Priority date: 2007-08-09
Filing date: 2008-08-07
Publication date: 2010-04-21
Anticipated expiration: 2028-08-07
Also published as: US8280096B2; FR2919978B1; WO2009022085A1; FR2919978A1; EP2177047B1; US20110188698A1

Abstract

The invention relates to an electrodynamic transducer (1) with a membrane (2) including an electrodynamic motor in a carcass (7) and in which a coil (6) held by a mandrel (3) connected to the membrane is capable of movement, the mandrel having a shape generated by an essentially linear generatrix, the coil being arranged in an air gap of a vertical free space where it is capable of movement and defined, towards the centre of the transducer, by an inner magnetic structure (4) and, towards the periphery of the transducer, by an outer magnetic structure (5), at least one of the magnetic structures generating a static magnetic field, wherein the transducer does not include any peripheral nor inner suspension and the guiding of the mobile equipment and the pneumatic tightness between the front and rear faces of the membrane being ensured by a ferrofluid. The transducer is characterised in that the mandrel is maintained in the air gap by the ferrofluid applied on at least one of the two faces of the mandrel and entirely filling the air gap. Fluidic return/braking and ferrofluid-retaining means can also be used. The motor can be a Foucault-current one.

Description

Electrodynamic transducer, in particular of the speaker type, with ferrofluid suspension and associated devices

The present invention relates to the field of electrodynamic voice coil transducers, including speakers, without mechanical suspension but with ferrofluid suspension. It has applications in the field of the manufacture of measuring devices: including sound recording, vibration measurement, as well as sound reproduction devices, including speakers.

Already known from application FR05 / 53330 (FR-2,892,887) a speaker type transducer without mechanical suspension between the spooling mandrel or the membrane and the carcass, the guide of the mandrel being provided by at least two joints ferrofluids including a continuous to ensure acoustic sealing between the two faces of the membrane. It has also been shown in Application FR05 / 53331 (FR-2,892,886) that an ironless motor could be used with ferrofluid.

Conventionally, a voice coil electrodynamic loudspeaker comprises a membrane integral with a mandrel carrying a coil, the coil being immersed in a magnetic field of a gap. The gap is a narrowed area of a vertical free space of the electrodynamic motor of the speaker in which is disposed and can move the coil carried by the mandrel. When traversed by a variable current, the coil moves in the magnetic field that is generated by a permanent magnet type magnetic field generator.

If the means presented in the applications FR05 / 53330 and FR05 / 53331 make it possible to obtain loudspeakers with a relatively simple structure and having good performance with respect to their volume, it was realized that their operation could still be improved and that the techniques that were implemented there could be extended to various types of loudspeakers.

Among the means improving the operation of the transducers, especially loudspeakers, which are without mechanical suspension (without peripheral suspension between the periphery of the membrane and the carcass and without internal suspension between the membrane or mandrel and the carcass) but with a suspension ferrofluid (the mobile mandrel carrying the coil and secured to the membrane being maintained and guided in the air gap by ferrofluid), the ferrofluid is extended on at least one of the two faces of the mandrel and completely fills the gap. Of preferably, the ferrofluid overflows even the air gap so that during translational movements of the mandrel in the gap, the latter is always filled with ferrofluid on the (the) face (s) corresponding (s) of the mandrel. In addition to this complete filling of the air gap, the ferrofluid seal is continuous around the circumference of the mandrel and forms a sealing means between the front and rear faces of the membrane. If the ferrofluid can be maintained in the air gap thanks to the presence of a magnetic field (s) which is (are) more concentrated, it can furthermore predict or count on magnetic field confinement means, especially towards the ends of the gap (see outside in the vertical free space for the ferrofluid overflowing with the gap), to better retain the ferrofluid in the air gap. Indeed, besides specific magnetic field confinement means that can be realized, the ends / edges of magnets (motor without iron) or polar parts (conventional motor with iron) are areas where there is a field confinement which corresponds to a means of confining the magnetic field. Indeed, the ferrofluid tends to be placed where the magnetic field and / or the variation of the magnetic field are the highest.

Such a structure can be implemented in transducers of the microphone type or of the speaker type. For the latter type, this concerns both dome and cone type loudspeakers.

Thus, the invention relates to an electrodynamic diaphragm transducer comprising an electrodynamic motor in a carcass and in which a moving coil fixed on a mandrel integral with the diaphragm can move, the mandrel and the moving coil and the membrane forming a moving element, (The mandrel is a shape generated by a generally linear generatrix), the voice coil being placed in a gap of a vertical free space where it can move and which is delimited, towards the center of the transducer by an internal magnetic structure and, to the periphery of the transducer by an external magnetic structure, at least one of the magnetic structures generating a static magnetic field, the transducer having no peripheral suspension or internal suspension, the peripheral suspension being a suspension between the periphery of the membrane and the carcass, the inner suspension being a suspension between the membrane or the mandrel and the carcass, the guide of the coil and the pneumatic seal between the front and rear faces of the membrane being provided by a ferrofluid. According to the invention, the mandrel is maintained in the air gap by ferrofluid extended on at least one of the two faces of the mandrel and which completely fills the gap.

Because the ferrofluid completely fills the air gap, that is to say both in height and circumferentially on the mandrel, it can be noted that a seal is provided between the front and the rear of the mandrel. Sealing may be required between the front and the back of the membrane and therefore, in some types of transducers, the extended ferrofluid by its additional seal function provides an advantage. Note that the term joint is taken in the present context in the sense of connecting (one side of the mandrel to the adjacent face of the vertical free space, including the gap). Thus, a ferrofluid seal may or may not provide a pneumatic seal between the front and the rear of the mandrel for the corresponding face according to its shape: continuous seal on the circumference of the mandrel (such as one that completely fills the gap or as a circumferentially continuous low-profile joint) or discontinuous joint (such as vertical discrete joints extended over the entire height of the gap, see overflow). It should also be noted that the term "air gap" is used to denote a particular area of the vertical free space (vertical with reference to a motor representation whose cylindrical axis of symmetry is vertical) in which can translate (excursion ) the chuck, this zone is where a substantially radial magnetic field (s) are created and concentrated to act on the voice coil. This zone is related to a magnetic field generator (s) magnetic (s) static (s) or field guidance (s) with or without iron depending on the type of engine chosen: motor with iron or motor without iron. Thus, the term gap does not require the presence of iron (or other ferromagnetic material) for guiding the magnetic field in relation to said gap. It should also be noted that each motor comprises two magnetic structures (internal and external with respect to the mandrel), at least one of the two comprising at least one means for generating one or more magnetic fields (magnet (s) in particular) and the other being able to comprise one / such magnetic field generating means (s) or a part for looping the magnetic field (ferromagnetic part for example as in the case of a conventional iron motor) or a neutral piece vis-à-vis the magnetic field (part of plastic carcass for example) or still be air (lack of clean material element). In various embodiments of the invention, the following means can be used alone or in any technically possible combination are implemented:

preferably, the extended ferrofluid, which completely fills the air gap, is on only one of the two faces of the mandrel (on the other side there may or may not be ferrofluid and, if present, ferrofluid preferably does not completely fill the gap: can (can) be continuous or discontinuous (= discrete) whose discrete joints extended vertically)

the transducer is a microphone or geophone,

the transducer is a speaker,

- The ferrofluid is implemented on each of the two faces of the mandrel (including an extended seal and completely filling the air gap)

the mandrel is bored and the ferrofluid disposed on each side of said mandrel can pass through said mandrel,

- The ferrofluid overflows the air gap at each of its two ends so that during excursions of the mandrel into the gap, the latter is always filled with ferrofluid on the (the) face (s) corresponding (s) of the mandrel,

the transducer comprises a fluidic return means at an equilibrium position of the moving and braking equipment, said fluidic booster / braking means causing a gradual reduction of the space in which the ferrofluid can be placed during excursions of the moving equipment out of its equilibrium position, said fluidic braking / return means being chosen in at least one of the following means and their combinations:

a high and / or low conicity (with respect to the coil) of the mandrel on the side of the ferrofluid,

at least one pattern of high and / or low excess (with respect to the spool) of the mandrel on the side of the ferrofluid,

at least one concavity of the mandrel,

the concavity of the mandrel is elongated axially and has front and rear ends (on either side of the coil) of smaller depth than towards its center (depending on the length),

the concavity of the axially elongated mandrel at a substantially constant depth in the zone of the gap, (area of the mandrel in the gap when the mandrel is at rest)

the concavity of the axially elongated mandrel overflows the air gap forwards and backwards (relative to the spool)

the mandrel comprises a set of concavities elongated axially, the restoring force (or braking force) created by the return / fluidic braking means is proportional to the excursion,

the restoring forces (or braking forces) created by the fluidic return / braking means for the two directions of excursion with respect to the equilibrium position of the moving equipment are symmetrical to each other (curves of variation of the force versus excursion with respect to the equilibrium / rest position, this is preferably obtained by implementing identical but symmetrical fluidic return / braking means on either side of the coil)

the pattern in excess thickness is substantially triangular with a point towards the ferrofluid (thus towards the air gap) and base towards the end of the mandrel (thus opposite the air gap),

- the edges between the tip and the base of the pattern in overthickness are straight,

the edges between the tip and the base of the thickened pattern are curved,

the thicknesses have a constant thickness,

the extra thicknesses have a thickness which increases toward the end of the mandrel

the maximum thickness of the conicity or the extra thicknesses is such that the conicity or the thicknesses can pass into the gap,

the maximum thickness of the conicity or of the excess thicknesses is such that their final parts towards the end of the mandrel can not pass into the gap, (in addition form one or more stops)

at rest (moving element at the equilibrium position), the return / fluidic braking means are already partly in the ferrofluid (so that fluidic return / braking forces of said means act even at rest),

at rest (moving element at the equilibrium position), the return / fluidic braking means are at a determined distance from the ferrofluid limit, outside the ferrofluid (so that any restoring force / fluidic braking of said means do not begin to act until after a certain start of the trip),

preferably, at rest (moving element at the equilibrium position), the return / fluidic braking means are at the limit of the ferrofluid (so that any restoring force / fluidic braking of said means does not begin to act until beginnings of excursions),

the corresponding wall of the gap or the adjoining vertical free space has towards its ends patterns in relief oriented towards the mandrel (overthickness) in relation to the spaces between the patterns in excess thickness of the mandrel, (may make it possible to limit the possibilities of rotation of the mandrel on itself, the extra thicknesses of the mandrel and the vertical free space between them with or without contact, preferably the ferrofluid limiting the engrainement )

the raised patterns facing the mandrel of the corresponding wall of the air gap or of the adjoining vertical free space are in addition of complementary shapes to those of the spaces between the mandrel thickening patterns, (the engraining is further advanced) in that the forms are complementary)

the conicity or the pattern (s) of the high and / or low end of the mandrel on the side of the ferrofluid are in a material or covered with a non-wettable material by the ferrofluid,

the conicity or the pattern (s) of the upper and / or lower end of the mandrel on the side of the ferrofluid are in a material or covered with a material that can be wetted by the ferrofluid,

the transducer comprises at least one of the two ends of the mandrel a collar, (besides a ferrofluid retention function if there is one on the side of the flange, the flange can also provide a stop function during excessive excursions since ferrofluid can abut against said collar if it is on the side of the ferrofluid or possibly abut against a rim of the air gap or the vertical free space in the absence of ferrofluid)

the transducer comprises at least one of the two ends of the mandrel a ferrofluid retaining means, said retaining means being a flange for, during excessive excursions of said mandrel, to maintain the ferrofluid on the side of the mandrel where it is situated initially,

- The collar is of such a width that it can pass into the gap, (allows to achieve a mandrel with flanges and then insert it into the vertical free space)

the flange is of a width such that it can not pass into the gap and forms a stop during excessive excursions of said mandrel, (mechanical stop in the absence of ferrofluid on the side of the flange or, in the presence of ferrofluid, fluidic stop since the ferrofluid can abut against said collar during excessive excursions)

- The flange is an insert on the mandrel, (it can be installed once the mandrel is placed in the air gap, useful when the flange can not pass into the gap because of its width)

- the collar is a flat piece, - The collar is bypassed in L (reference on the side of the gap),

the transducer comprises at least two means for confining the magnetic field in the vertical free space, the confinement means being stages in the vertical free space,

the at least two means for confining the magnetic field are at the gap,

the mandrel comprises concave deformations according to determined forms in which the ferrofluid forms an extra thickness with respect to the remainder of the mandrel,

the transducer further comprises at least one non-fluidic return means of the moving equipment (but still no mechanical suspension),

the non-fluidic return means of the moving equipment is chosen from one or more of the following means:

- charging the membrane by a closed volume at the rear of the dome, the internal magnetic structure being open to said closed volume;

- Loading of the membrane by a closed volume at the rear of the dome, the internal magnetic structure being open towards said closed volume which comprises a device for regulating its internal pressure, in particular by regulating the temperature of the air contained in said closed volume;

charge of the membrane by a quasi-closed volume at the rear of the dome, the internal magnetic structure being open towards said quasi-closed volume, said quasi-closed volume comprising a minimal pneumatic leak whose time constant is very long by relative to the frequencies to be reproduced, said leak being in particular in the form of a porous material or of a very small diameter orifice or of a fine tube towards the outside of the transducer;

- A mechanical spring means of spring or elastic material between the dome or mandrel and a fixed portion of the transducer;

an electronic servocontrol of the position of the coil;

a configuration of the coil and internal and external magnetic structures such that a restoring force is exerted on the coil by electromagnetic effect;

a configuration of the mobile equipment and internal and external magnetic structures such that a restoring force is exerted on said moving element by magnetic effect (in particular by placing small magnets (micro-magnets) in place (fixation) in particular) on the mandrel, preferably such micro-magnets are arranged opposite (at the same height, the moving equipment being at rest) of one or more ferromagnetic ferromagnetic rings of the motor's magnetic structure, in addition makes it possible to improve centering);

a set of magnets of small size (such size that they do not interfere with the excursions of the mandrel in the gap) is fixed on the mandrel, (for example equiangular distribution of these magnets along the circumference of the mandrel)

the transducer further comprises at least one other means for returning the moving equipment (but still no mechanical suspension), chosen from one or more of the following means:

a deformation of the mandrel in the zone of the ferrofluid or outside, said deformation extended along the periphery of the mandrel being defined so as to create a restoring force proportional to the movement of the moving element when ferrofluid is there;

- further implementation of vertical ferrofluid joint segments, each vertical joint segment being in relation to a deformation along a vertical generatrix segment of the mandrel, the vertical deformations being defined so as to create a proportional return force moving the moving equipment;

one or more deformations in an area of ferrofluid joints, in particular deformations along segments of vertical generators of the mandrel, said deformations being defined so as to create a restoring force proportional to the displacement of the moving element,

the internal magnetic structure comprises at least one magnet,

the external magnetic structure comprises at least one magnet,

the engine is an iron motor, a ferromagnetic element looping the magnetic field outside the gap,

- the motor is a motor without iron, the magnetic field looping outside the gap in the air,

the motor is a motor without iron, the magnetic field looping outside the air gap in a non-ferromagnetic material,

the motor is a motor without iron, the magnetic field looping outside the gap in magnets,

- the transducer is a loudspeaker, the diaphragm is a dome, (the diaphragm is towards the center of the loudspeaker: only one pneumatic seal is enough) - the transducer is a loudspeaker, the diaphragm is a cone, (the diaphragm is external to the center of the loudspeaker: two pneumatic gaskets are required at both circumferential ends, towards the center and towards the outside , of the membrane)

the transducer is a loudspeaker, the diaphragm comprises a dome-shaped part and a cone-shaped part (only one pneumatic seal may be sufficient towards the outside of the membrane of the cone portion)

the transducer is a loudspeaker, the diaphragm is a cone, the said diaphragm being external to the center of the loudspeaker and a continuous ferrofluid seal (for pneumatic sealing) is furthermore arranged along the circumference of a lip of the membrane, said rim being along the edge of the membrane opposite to the edge of the membrane in relation to the mandrel, said ferrofluid seal being maintained by a magnetic field confinement means,

the flange comprises a means for retaining and biasing / fluidic braking (it is therefore a fluidic means of return to an equilibrium position of the membrane which ensures a return of the membrane to a position of equilibrium for the corresponding edge of the membrane) in the form of a curvature such that when the membrane is at its rest position (static equilibrium), the ferrofluid seal has a maximum of space to position relative to excursions out of the position rest,

the membrane comprises a dome part and another cone part,

the voice coil is an electrical short circuit and at least one of the magnetic structures comprises a fixed coil intended to receive a modulation current, the fixed coil being placed at the gap in the magnetic structure,

the engine comprises a single fixed coil,

the engine comprises two fixed coils, each in one of the magnetic structures,

- The coil of the spiral type electric short circuit is integrated in the mandrel, the mandrel being metallic and electrically conductive and forming said turn in short electric circuit.

The invention also relates to a fluidic coil return / braking device for an electrodynamic diaphragm transducer comprising an electrodynamic motor in a carcass and in which the coil carried by a mandrel integral with the diaphragm can move, the coil being placed in an air gap of a vertical free space where it can move and which is delimited, towards the center of the transducer by an internal magnetic structure and, towards the periphery of the transducer by an external magnetic structure, at least one of the magnetic structures generating a static magnetic field, the transducer having no peripheral suspension or internal suspension, the peripheral suspension being a suspension between the periphery of the membrane and the carcass, the internal suspension being a suspension between the membrane or the mandrel and the carcass, the guide of the moving element and the pneumatic sealing between the front and rear faces of the membrane being provided by a ferrofluid.

The fluidic return / braking device is characterized by a relief structure of the mandrel that can pass at least partly in a reduced section portion of the vertical free space (and in particular in the air gap, then also vertical) during excursions of the mobile team and which, during these excursions gradually reduces the space where the ferrofluid can be placed, said structure being chosen, alone or in combination, from a conicity or patterns in relief of the upper end and / or low chuck (in practice in any suitable position on the chuck for the expected function) on the side of the ferrofluid.

Preferably, the fluid return / braking device is specially adapted to the transducer according to one or more of the described modes, the ferrofluid completely filling the air gap, or even going beyond.

The invention also relates to a device for retaining ferrofluid and / or abutment (mechanical or fluidic excursion limiter according to the absence or presence of ferrofluid) for an electrodynamic diaphragm transducer comprising an electrodynamic motor in a carcass and in which a coil carried by a mandrel integral with the diaphragm can move, the coil being placed in a gap of a vertical free space where it can move and which is delimited, towards the center of the transducer by an internal magnetic structure and, towards the periphery of the transducer by an external magnetic structure, at least one of the magnetic structures generating a static magnetic field, the transducer having no peripheral suspension or internal suspension, the peripheral suspension being a suspension between the periphery of the membrane and the carcass, the inner suspension being a suspension between the membrane or mandrel and the carcass, the guidance of the moving equipment and pneumatic sealing between the front and rear faces of the membrane being provided by a ferrofluid. The ferrofluid retaining device is characterized in that it is a flange disposed towards at least one of the two ends of the mandrel (in practice in any suitable position on the mandrel for the expected function) in lateral overflow of said mandrel at least on the side mandrel where ferrofluid is located and intended to retain the same side ferrofluid during excessive excusions of the moving equipment.

Preferably, the ferrofluid retaining device is specially adapted to the transducer according to one or more of the described modalities, the ferrofluid completely filling the air gap, or even going beyond it.

The invention also relates to an eddy current motor for a diaphragm electrodynamic transducer in which a moving coil fixed on a mandrel integral with the diaphragm can move, the mandrel being a shape generated by a generatrix generally linear, the coil being placed in a an air gap of a vertical free space where it can move and which is delimited, towards the center of the transducer by an internal magnetic structure and, towards the periphery of the transducer by an external magnetic structure, at least one of the magnetic structures generating a field static magnet.

The eddy current motor (with or without iron) is characterized in that it comprises in at least one of the magnetic structures a fixed coil (there may be a fixed coil in the internal magnetic structure and another in the external ) for receiving a modulation current, the fixed coil being placed at the gap in the magnetic structure and in that the voice coil is a short circuit in electrical short circuit.

In a variant of the eddy current motor, the coil coil of the electrical short-circuit winding type is integrated in the mandrel, the mandrel being metallic and electrically conductive and forming said electric short circuit.

Preferably, the eddy current motor is an ironless motor.

Preferably, the eddy current motor is specially adapted to the transducer according to one or more of the described modes, said transducer having no peripheral suspension or internal suspension, the peripheral suspension being a suspension between the periphery of the membrane and the carcass, the inner suspension being a suspension between the membrane or the mandrel and the carcass, the guidance of the moving equipment and the pneumatic sealing between the faces front and rear of the membrane being provided by a ferrofluid, more particularly, the mandrel being maintained in the air gap by ferrofluid extended on at least one of the two faces of the mandrel and which completely fills the gap.

It should be noted that a loudspeaker intended to produce rather low frequencies of the audible spectrum must generally have a large excursion in order to produce sufficient acoustic energy and a loudspeaker intended to produce rather the high frequencies of the audible spectrum. do not need to have such an important excursion. Thanks to the invention, it is possible to realize a dome speaker for low frequencies and which can be relatively compact thanks to a large excursion.

The present invention, without being limited thereby, will now be exemplified with the following description of embodiments in connection with: Figure 1 which shows a vertical section through the anteroposterior axis of circular symmetry of a dome-shaped loudspeaker and with variants of means of return / fluidic braking and retaining / stop ferrofluid, and a non-fluidic return means of the moving element, Figure 2 which represents several examples of means of FIG. 3 which is a vertical section passing through the anteroposterior axis of symmetry of a conical loudspeaker schematically showing two embodiments of FIG. 3, which is a vertical section through one of the two ends of a mandrel; FIG. 'a motor, the first with a conventional voice coil driven by a modulation current and the second with a voice coil which is a shorted electric coil, ran it modulation device being sent in a fixed coil disposed in the gap, Figure 4 which shows a vertical section through the anteroposterior axis of circular symmetry of a mixed speaker having a dome-shaped portion of membrane and another cone-type portion and with, on the inner side of the cone and motor, return / fluidic braking and retaining / ferrofluid stop means, and with, on the outer side of the cone, a fluidic guide means with magnetic field confinement means, Figure 5 which shows a simplified enlargement of a posterior (lower) end of an air gap with an optional L-shaped flange and wall. In the following description, we will consider more particularly speaker-type transducers although the means of the invention can be applied to other types of devices including microphones or geophones, as long as these devices are electrodynamic type voice coil.

Ferrofluid suspension speakers considered as examples are dome or cone or mixed speakers (dome + cone).

The dome speakers have a central diaphragm and a single continuous pneumatic sealing ferrofluid seal along the peripheral circumference of the mandrel is sufficient to provide pneumatic isolation between the two faces of the diaphragm. The seal may be single and, preferably, extend over the entire height of the air gap (on at least one of the faces of the mandrel with total filling of the air gap with ferrofluid) or be associated with one or other Ferrofluid seals on the other face of the mandrel (for example: another seal, on the other face of the mandrel, extended over the entire height of the gap). In addition to the continuous joint extended in height in the air gap, the other possible ferrofluidic joints can be stages and / or any shape (s) including vertical joints.

The cone loudspeakers have a lateral membrane and at least two ferrofluid joints, two of which are continuous pneumatic sealing along the two inner and outer peripheral circumferences of the membrane (in practice along the circumference of the mandrel and the circumference of the cone). a rim of the membrane) are implemented to ensure the pneumatic insulation between the two faces of the membrane. On the mandrel side, the ferrofluid seal may be single and, preferably, extend over the entire height of the gap (on at least one of the faces of the mandrel with total filling of the gap with ferrofluid) or be associated with a or other ferrofluidic joints on the other face of the mandrel (the other ferrofluidic joints may be of any shape and / or shape (s) including vertical joints).

Finally, the mixed loudspeakers which have a cone-like membrane portion and another dome-like portion, approach the dome-type speakers in that a single continuous pneumatic sealing ferrofluid seal the circumferential outer periphery of the cone portion of the membrane may be sufficient to provide pneumatic insulation between the two faces of the membrane. In any case, the means for generating the magnetic field in the air gap, even if they are preferably of the ironless motor type, may also be more conventional and of the iron motor type.

Note that in the case of cone or mixed speakers, two motors (thus two mandrels and two conventional and / or eddy current coils) can be implemented and, thus, a first field generation means magnetic circuit for a first air gap of a first motor is on the inner periphery of the membrane (cone portion in the mixed case) and a second magnetic field generation means for a second air gap of a second motor is on the outer periphery of the membrane .

In a motor without iron, if a looping of the magnetic field must take place outside the gap, this looping is done by magnets. In other cases of motor without iron, the looping of the field takes place (generally outside the air gap) either in the air or through parts that do not guide the magnetic field. Thus, in a motor without iron, it is a magnet or they are magnets which ensure the creation of the magnetic field and which can also ensure the guidance of the static magnetic field (with one or more magnetic field senses in the gap) .

In the motor with iron, a ferromagnetic body is used to guide the magnetic field. Note that in a motor without iron, small pole pieces can be implemented, but in this case, they are mainly used to create magnetic field confinement zones where the ferrofluid can focus preferentially.

The motor comprises a magnetic field generator in at least one of its two magnetic structures (internal and external). The magnetic field generator may include a plurality of magnets for creating at least one magnetic field zone in the gap. In variants, the air gap comprises three zones of field direction with a median zone in one direction and two extreme zones in the other direction. In the latter case, a single coil can be implemented, the idle coil being in the middle zone (which corresponds to an electromagnetic braking end configuration due to the field reversal at both ends of the coil. air gap, effective braking during extreme excursions, the response to be substantially linear during normal excursions). Still in the latter case, several sense coils adapted to the field area considered can be implemented to add up their effects. The magnet (s) used in the magnetic field generator may be in one piece and / or each consist of smaller magnet assemblies. In the case where each of the internal and external magnetic structures (with respect to the coil) comprises a magnetic field generator (s), these are arranged in such a way as to optimize the distribution and the intensity of the areas of magnetic field in the air gap.

Preferably the engine (s) used is electromagnetically braking end configuration.

In the air gap, the magnetic field (at least one of the field directions in the case where there are several field sense zones) may be substantially uniform along the gap height or may include field reinforcement zones. magnetic (or zones of significant variation of the magnetic field) where the ferrofluid will preferentially be placed if it is in reduced quantity.

It should be noted that even if there are one or more zones of reinforcement of the magnetic field which may be locations for the formation of as many ferrofluidic joints in the air gap, the ferrofluid, if it is introduced in large quantities, will eventually fill completely, even in overflow, the gap. Thus, in an engine with at least two means of confinement of the magnetic field, it will form on one face of the mandrel where it is introduced and according to the amount of ferrofluid introduced, two joints and then only one when the quantity introduced is increased, (the two ferrofluid joints eventually merge). Conversely, if the ferrofluid is gradually removed, it may eventually be possible to leave only one / individual seals in the reinforcement zones (confinement) of the field.

For information on non-iron motors and ferrofluid suspensions, the applications FR05 / 53330 and FR05 / 53331 already mentioned may be consulted.

In a variant operating by eddy current, a fixed coil receiving a modulation current is arranged in a magnetic structure having a magnetic field generator, the voice coil then being an electrical short-circuit and, preferably, a metallic mandrel. electrical conductor (the mandrel then performs its chuck function and, in addition, the voice coil function which is a short circuit electric). Preferably, in the case of an extended seal which completely fills the air gap, the ferrofluid protrudes out of the air gap on each side so that during the excursion of the mandrel, it always bathes in the ferrofluid in the area where it is in the gap. Indeed, for best results, it is preferable that air does not enter the region of the air gap and that there is no air trapped in the extended ferrofluid joint completely filling the air gap. air gap.

In addition, especially in the case where one (of) seal is extended over the entire height of the air gap, it completely fills the air gap (it is also extended circularly) or not (case of discrete seal (s) ( s) extended vertically over the entire height of the air gap), in order to obtain a fluidic return effect at a position of equilibrium of the moving equipment and fluidic braking during excursions, the ends of the mandrel high and low (in practice in any suitable position on the mandrel for the expected function of reducing the space where the ferrofluid can be placed) can be conical (flare) on the side of the joint so that during excursions, the gap gap (or adjacent vertical clearance) between the wall of said gap (or the wall adjacent said vertical free space) and the mandrel is reduced gradually reducing the space where the ferrofluid can be placed, resulting in , in addition to "fluidic" braking, the creation of a return force of the mandrel and therefore of the moving element to a position of equilibrium during the suppression of the modulation current. This conical flare can also consist of a conical excess thickness of the end of the mandrel.

Alternatively, the mandrel can remain straight over its entire height and then extra thicknesses are made to both ends of the mandrel (in practice in any suitable position on the mandrel for the expected function of reducing the space where the ferrofluid can be placed ). These extra thicknesses which have a constant thickness or not (particularly thickness of the extra thickness gradually increasing towards the end of the mandrel), have a width which increases gradually as one approaches the end of the mandrel. For example, the shape of one of these extra thicknesses is a triangle pointed towards the air gap and base towards the end edge (upper or lower as the case) of the mandrel.

During the mandrel excursions, these extra thicknesses (as well as the conicity) which plunge into the ferrofluid (or which are already in the ferrofluid) come in a zone of reduced thickness of the air gap (or close to the gap in the vertical free space) and the ferrofluid then has less room to accommodate as the excursion, which creates a restoring force and fluidic braking of the mandrel during excursions.

Preferably, the progressive reduction of the space where the ferrofluid can be placed (tip of the conicity or the extra thicknesses) begins at the limit of the ferrofluid, a limit corresponding substantially to the position of the edge of the ferrofluid when the moving equipment is at rest ( static equilibrium). In other words, the braking / creation of a restoring force begins substantially from the beginning of an excursion of the moving equipment. This is true for each ferrofluid limit (high or forward, on the one hand, and low or rear, on the other hand, in the Figures) on either side of the air gap (overflowing ferrofluid) or at both ends. the air gap (ferrofluid air gap limit) to obtain a substantially symmetrical return / braking effect at least as regards its beginning.

It should be noted that this effect of return / fluidic braking by progressive reduction of the space in which the ferrofluid can take place when the excursion of the mandrel increases, can also work with ferrofluid joints that do not extend beyond the gap. Indeed, the taper and the extra thicknesses can have a maximum thickness which allows their passage in the gap. In the case where it is the ends of the mandrel which have a taper or thickenings, they may have (preferably) a maximum thickness which allows their passage in the gap or not and, in the latter case, it can also serve as stop during excessive excursions: the conicity of the mandrel or the overthicknesses will eventually hit the edge of the air gap or the constricted part of the vertical free space.

In addition, especially in the case of joint (s) extended (s) over the entire height of the air gap (which completely fills the air gap or which are discrete) and possibly overflowing, in addition or not to the devices of return / braking fluidically, the ends of the mandrel may comprise flanges (ring or ring these terms being also equivalent) ferrofluid retaining at the end edge of the mandrel (in practice in any suitable position on the mandrel for the expected function of the mandrel). retaining and / or abutment), preferably only on the side of the ferrofluid, but in other variants, on both sides of the mandrel. These collars make it possible to retain the ferrofluid on the chuck side where it is normally located and to prevent it from being able to pass on the other side of the chuck during excessive excursions. In a particular embodiment, these flanges are of a width such that they can not pass into the gap or, more generally, a portion of reduced width of the vertical free space. Thus, in addition, the flanges may have a mechanical stop function (they abut against the edge of the air gap or a reduced width portion of the vertical free space) or fluidic stop (they abut against the ferrofluid) during excessive excursions. In the case where the flanges have a width greater than the width of the air gap, it is understood that one of the flanges must be put in place after insertion of the mandrel into the air gap of the vertical free space unless walls of the air gap can be mounted at a later stage of the manufacture of the engine. In addition, the flange is a reinforcing means of the mandrel and improves its mechanical strength (avoids possible deformations of the mandrel, including folds or other).

The ferrofluid is chosen in particular on the one hand for its longevity to withstand the high temperatures that can be encountered in the loudspeakers and, on the other hand, depending on its viscosity. By way of example, the ferrofluid APG S12n from FERROTEC of the United States can be used. As already indicated and in order to obtain better results, it is preferable that there is no air bubble or air pocket in the extended ferrofluid which completely fills the gap. For this, it may be useful to degas the ferrofluid before introduction into the air gap (and, as already indicated, preferable that the ferrofluid overflows the ends of the gap on both sides so that during the mandrel excursion of the air can not enter the gap).

The electrodynamic motor of the speaker 1 to dome 2 of Figure 1 comprises a coil 6 on a mandrel 3 and external magnetic structures 5 and internal 4 of which at least one has a magnetic field generation means (s) (s) ( s) in the air gap. The coil 6 is placed in an air gap of a vertical free space in which the mandrel can move during the excursions of the moving equipment. In this example, magnetic field confinement means 11 are shown and are intended to create, in the vertical free space (in or outside the gap), magnetic field concentrations / variations where the ferrofluid tends to focus preferably. These containment means are optional and their number and location (s) may be different depending on the embodiment of the speaker. Ferrofluid 14 has been introduced into the air gap on the opposite side outer mandrel 3 to completely fill the air gap between the outer face of the mandrel and the external magnetic structure 5. In addition, the amount of ferrofluid is such that it overflows up and down the air gap so that during excursions of the mobile equipment (at least for normal excursions) the air gap is always filled with ferrofluid on the corresponding face of the mandrel 3. It is understood that the ferrofluid 14 extended over the entire height of the air gap and which completely fills The air gap is also extended all the way around the mandrel, which also ensures a pneumatic / acoustic seal between the two faces (front-rear) of the dome 2.

In a variant, ferrofluid is also introduced on the internal face of the mandrel either to form one or more independent ferrofluidic joints (at the level of the means of confinement of the field) when the amount of ferrofluid is small or to fill completely (preferably overflow) the air gap on this internal side. Note that the possible joints on the other face of the mandrel (the other face that of the ferrofluid completely filling the gap) can be of various shapes and, for example instead of horizontal: vertical, oblique or other forms of which circumvented (the means of confinement of the field will be adapted accordingly).

It is understood that the provisions of some of the elements of Figure 1 can be reversed, for example the ferrofluid filling the entire height of the air gap is only internal side of the mandrel. Note that since it is necessary to pneumatically isolate (sealing function) the front of the back of the membrane, in this case a dome 2, it will be ensured that in the structure realized the ferrofluid completely filling the air gap or any associated joints ensures this function. Indeed, the lower part of the vertical free space is not necessarily closed and can be open to the air or in a rear tire load. Likewise, the position of the spool 6 (which may in fact be a set of spools) can be reversed with respect to FIG. 1 and be positioned on the outside face of the mandrel 3.

The motor is in a rigid bowl of which only a portion 7 has been shown to the front with a means for fixing to a support (screwthread) which may be a face of an enclosure for example. In addition to the fact that the two external and internal magnetic structures can both be active (include means for generating magnetic field (s)), alternatively, one of the external magnetic structures 5 or internal 4 may be passive; to say that it contains only means for guiding a magnetic field created in the other structure or does not have any and can then made of a material that is neutral with respect to the magnetic field or else be air (absence of clean material element).

As a variant, the two internal and external magnetic structures may be active, that is to say each comprise one or more static magnetic field generating means (one or more magnets: ring / pellet / composite / monoblock). .), or, again, may be mixed, that is to say comprise a magnetic field generating means / means and a magnetic field guiding means. Thus, the motor of Figure 1 can be iron type or ironless type (with only one / magnets).

In Figure 1 there is also shown two non-fluidic return means of the moving element to a predefined position when the coil is no longer electrically excited (or following the removal of an accidental external stress). These non-fluidic return means given by way of example in this simplified Figure 1 are, on the one hand, a pneumatic load of the rear face of the dome and, on the other hand, a mechanical means of the spring type. Note that the taper 12 and the extra thicknesses 16 are also return means but fluidic type.

The pneumatic load corresponds to an implementation of a closed volume 8 behind the membrane, this enclosed volume closed by a wall 9 is in this case almost closed because a minimal leak in the form of an orifice 10 has been performed. The time constant of the orifice (time required to balance the pressures between the two sides of the orifice) is very long compared to the frequencies to be reproduced by the loudspeaker. The orifice therefore has a very small diameter or can be replaced / supplemented by a porous material or by a thin tube (capillary tube type or needle).

It may be noted that in order to charge the rear of the dome with this quasi-closed volume arranged essentially behind the engine, the central core of the motor is hollow towards the rear of the loudspeaker. It is possible to note at the bottom (bottom) of the vertical free space two zones 31 delimited by dotted lines, they correspond to a variant embodiment with an opening (or openings) directly between the bottom of the vertical free space and the volume 8 closed or near-closed rear tire load. In the absence of this (these) opening 31, the communication between the bottom of the vertical free space and the rear volume 8 of load is carried forward upward along the mandrel and through the opening central speaker. It is understood that this (these) aperture 31 improves the operation in the case where a continuous seam (s) on the circumference of the mandrel would also be implemented on the side opposite to the extended joint 14 and which completely fills the air gap because otherwise it There would then be more communication possible between the bottom of the vertical free space and the rear load volume 8.

It should be noted that it is preferable to obtain better results than the vertical space towards the rear is the best possible decompressed (role of the opening 31) towards the pneumatic load (closed volume or quasi-closed back) and therefore the surface of the opening must be maximum to improve the circulation of the air. Since the various elements of the loudspeaker must be held together, the internal and external magnetic structures of the engine in this case, spacers must be implemented through the continuous circumferential opening 31 and these spacers may be fins of the type 22 implemented in the speaker of Figure 3 (which connect other internal and external elements of the other speaker).

Similarly, it is best to remove sharp edges on loudspeaker elements in areas where there may be air movement. This is particularly why the edges 32 forward and rearward of the internal magnetic structure 4 are rounded. These roundings are preferably the widest possible.

The non-fluidic return means is a spring 15 between the dome 2 and the central stationary part of the engine, in this case the internal magnetic structure 4. Other non-fluidic return means can be implemented in variants of FIG. production. In particular embodiments, none, only one or more non-fluidic return means are implemented.

Means of return / fluidic braking 12, 16 and retaining / abutment 13 of ferrofluid are implemented in order to limit the amplitude of the excursions and to avoid that they become too important at the risk of "dissociating" the static elements and movable motor and which are maintained and guided between them by fluidic means, in this case ferrofluid, fluidic guide means which do not in themselves limit the amplitude of excursions in contrast to the mechanical means to type of conventional suspensions.

The fluidic return / braking means acts during the excursions of the moving equipment causing a decrease in the space in which the ferrofluid can be placed during said excursions. In the example shown, this action is permitted at the air gap which is already a zone of reduced thickness but in variants, a specific narrowing zone / zones can be implemented at a distance from the air gap and in connection with elements (conicity of the mandrel or overthickness in particular) which will now be described

In order to obtain this reduction of the space in which the ferrofluid can be placed, a reduction of preferably progressive space as the amplitude of the excursion increases, it is possible to implement a conicity 1 2 and / or thicknesses 1 6 of / on the end (or in any other suitable position for the expected function) of the mandrel.

In Figure 1, there is shown at the top of the mandrel 3 the conicity 1 2 of said mandrel (of mandrel construction or by an insert) and, bottom, patterns in overthickness 1 6 (mandrel construction or by patches ). Various types of overthickness are shown in Figure 2 as being viewed frontally on a lower portion (cut) around the mandrel. The first overthickness 1 6a is substantially triangular top / tip upwards, ferrofluid side, base towards the lower end of the mandrel and side edges (between the tip and the base) straight. The second oversize 1 6b is equivalent to the first except that its side edges are concave. The third oversize 16c is equivalent to the first except that its lateral edges are convex. The first three oversizes 16a, 16b, 16c are of constant thickness. The fourth oversize 1 6d is of thickness which increases the closer we get to the lower end of the mandrel and is similar to the conicity mentioned above. This fourth extra thickness 1 6d is of the type of the first 1 6a with respect to its general triangular shape but in variants it could be in other general forms including those of 1 6b and 1 6c. It is understood that because of these different variants of extra thickness, the variation of the effects of return and fluidic braking will be different and one can choose the form of the function of return / fluidic braking according to the type of overthickness implemented.

Note that, preferably, it implements only one type of these forms for extra thickness on a mandrel. Similarly, it is preferable that the functions of return / fluidic braking are identical at both ends of the mandrel, which is easier if the fluidic return / braking means are identical (but symmetrical) to these two ends, or identical conicities, either oversizes (same number and then type) identical. Thus, preferably, one implements conicities or extra thicknesses which make it possible to obtain a restoring force (symmetrical with respect to the rest position) proportional to the displacement in a linear operating zone of the loudspeaker and corresponding to normal excursions. Apart from these normal excursions, during extreme excursions, greater variations can be implemented up to the effects of abutment or near-stop.

The ferrofluid retaining / stop means 13 are flange-type rims disposed towards the upper and lower ends of the mandrel 3 (or in any other position suitable for the expected function) at least on the side of the ferrofluid which completely fills the gap . This collar prevents the passage of the ferrofluid on the other side of the mandrel (or on the membrane in this case) during excessive excursions of the moving equipment. If, preferably, the collar has a width such that it can pass into the air gap (especially to simplify the mounting of the motor), in a variant, this width may be such that it can not pass into the air gap . In addition to the retaining effect of the ferrofluid, an abutment effect is provided, the fluidic abutment effect in the case of Figure 1 because the ferrofluid abuts against this flange and remains trapped on the corresponding side of the mandrel. Note that, as shown in dashed lines with reference 17 in FIG. 1, a "wall" may, in a variant, be made to prevent the ferrofluid from escaping on the sides, which could occur because it can not escape by passing on the other side of the mandrel (or the membrane) because of the collar.

FIG. 3, not to scale, will now be described as an example of a cone-type membrane speaker 27. This speaker, which is cylindrically symmetrical, comprises a motor with a single field generator static magnetic device disposed here in the internal magnetic structure 4. This internal magnetic structure comprises on an inner portion 21 of the bowl a first and a second magnets 18 and 19 (pellet or ring) vertical and opposite internal magnetic fields. These magnets, which have their polar faces opposite and of the same sign, are separated by a space preferably comprising a material that is neutral with respect to the magnetic fields of the magnets and the result is that a radial field (horizontal in the Figure) is created in the gap where there is a coil 6 secured to a mandrel 3 itself integral with the cone membrane 27. The ferrofluid forming a first seal 29 is disposed in the gap between the inner face of the mandrel and the wall internal air gap. It should be noted that the air gap here corresponds to an area outside the internal magnetic structure 4 which is in front of the space between the two magnets 1 8 and 1 9 and therefore, as shown, the ferrofluid seal extends over the entire height of the gap and overflows even up and down. In addition, the external magnetic structure is here air (absence of own material element).

The loopback outside the gap of the magnetic field created by a static magnetic field generator in the internal magnetic structure 4 is carried out in the air. No structure based on "iron" is implemented and so here we have a motor without iron.

Still in FIG. 3, it is possible to notice the presence in the space separating the two magnets 18 and 19 of a fixed winding (fixed coil) inserted therein for operation of the loudspeaker by eddy current ( inductor winding). Indeed, this Figure 3 shows two embodiments. In the first, conventional mode, the voice coil 6 is intended to receive a modulation current that will allow the excursions of the membrane driven by the mandrel integral with said moving coil, these three elements forming the moving element. In this first mode, the fixed coil 20 can be omitted. In the second mode, Foucault current operation, the voice coil is a short-circuit electrical and preferably corresponds to the mandrel 3 which is then metallic and electrically conductive and forming the circular electrical short circuit. In this second mode, the modulation current is sent in the fixed coil 20. It is understood that this second eddy current mode of operation can be used in any other type of loudspeaker and especially in those described above in connection with the Figure 1, in which have then implemented a fixed coil at the gap receiving the modulation current and a voice coil which is an electric short circuit and preferably corresponds to an electrically conductive metal mandrel.

In another variant type motor without iron, the motor has an external magnetic structure also generating a magnetic field with magnets whose orientations are compatible with those of the internal magnetic structure (can be usefully consulted the FR05 / 53331 application already mentioned for examples of such engines). In another variant, the static magnetic field generator is only external instead of internal. In yet another variant, the motor is of the conventional iron type.

Since the membrane 27 is here external, two ferrofluid seals 29 and 30 continuous on the circumference of the membrane are necessary to ensure pneumatic sealing between the two faces of the membrane 27. A first internal seal 29 ferrofluid already reported is disposed in the air gap between the inner face of the mandrel 3 and the outer face of the internal magnetic structure 4 (central ) of the speaker. This first seal 29, which is disposed in a field confinement zone, is therefore continuous on the circumference of the mandrel 3. A second outer ferrofluid seal 30 is disposed on the outer face of a flange 28 of the membrane 27. The second Ferrofluid seal 30 is held in place by a magnetic field confinement means disposed outwardly of flange 28 relative to the central symmetry axis 29 of the loudspeaker. The confinement means disposed on an outer portion 23 of the salad bowl comprises a magnet 26 and two field plates 25, each on one of the polar faces of said magnet. Thus, the second seal is extended between a field plate 25 and the flange 28 while extending continuously over the circumference of the flange 28. The flange 28 comprises a means for retaining the ferrofluid and return / fluidic braking in the form of a curve, concavity towards the ferrofluid, such that when the membrane is at its rest position, the ferrofluid seal 30 has the maximum space to position itself. It is understood that during excursions of the membrane 27 and thus of the flange 28, this space will decrease hence the return / fluidic braking effect.

In addition to this return function of the second ferrofluid seal, it is also an external guide structure of the moving element via the rim 28 of the diaphragm which is the equivalent of the mandrel 3 of the corresponding internal guide structure. at the first ferrofluid joint. It will be understood that, with regard to the guidance and the reminder of the moving equipment, these external structures (non-driving (passive) from the point of view of excursions of the moving equipment and with means of confinement of the magnetic field) and internal (motor itself ensuring the excursions of the mobile equipment and with magnetic structure (s) generator (s) of magnetic field and air gap) are equivalent: one finds there (at least) a zone of concentration of field magnetic (air gap of the motor or the magnetic field confinement means), the ferrofluid and a piece integral with the membrane (flange 28, 28 'or mandrel 3). As a result, the mobile assembly may comprise, in addition to a mandrel, a rim 28, 28 'of membrane.

The inner portion 21 and the outer portion 23 of the salad bowl are held together by a series of fins 22 distributed over the circumference of the speaker. In the example, 6 fins of determined thickness are distributed over the 360 ° of the circumference. It may be noted that at the rear of the loudspeaker, which has not been shown all the elements for simplification, there is a pneumatic load to pneumatically charge the rear face of the membrane, only the beginning of the charging tube. having been represented.

In alternative embodiments, return / fluidic braking means (conicities and / or thicknesses) and / or retaining the ferrofluid (flanges) according to the characteristics described above are implemented on the mandrel 3. Note that these same means restoring / fluidic braking and / or retaining the ferrofluid can also be implemented at the high and low ends of the flange 28.

Still in the context of a cone loudspeaker, if in FIG. 3, the motor comprises only means for generating a static magnetic field in the internal magnetic structure (toward the center of the loudspeaker), in variants, this generating structure may be external to the mandrel or be external to the membrane or, in still other variants, two coils (or series of coils) may be implemented: one (of) inwards by relative to the membrane (as shown in FIG. 3), but also outwardly relative to the membrane with the equivalent of a mandrel in place of the flange 28 and a structure / structures for generating static magnetic field to create a second gap on the same side of the membrane. In the latter case, it is understood that the coils work in phase with one another for a coherent displacement of the membrane which is driven at each of its edges (external via the flange and internally via the mandrel).

FIG. 4 will now be described by way of example of a mixed-type cone 27 '+ dome 2' membrane loudspeaker. This speaker which is symmetrical cylindrical, comprises an internal motor with internal magnetic structures 4 and external 5 which is not detailed here the structure that can be of any type suitable (with or without iron, with one or two magnetic structures materialized ...). In the air gap of this motor is a coil 6 integral with a mandrel 3 itself integral with the cone type membrane 27 '+ dome 2'. Ferrofluid forming a first seal 14 is disposed in the gap between the outer face of the mandrel and the outer wall of the air gap. The first ferrofluid seal 14 completely filled the air gap overflow and thus ensures in addition to the guiding function, a pneumatic seal (not essential however in the context of Figure 4 because the dome is watertight by itself). The mandrel comprises a taper-type return / braking means 12 at the two upper (front) and lower (rear) ends of the mandrel 3. It may be noted that the mandrel 3 is straight in the air gap zone (moving element at rest, at equilibrium) and that the conicity of the mandrel (bilateral) starts at the upper or lower limit of the ferrofluid joint 14. In addition, the mandrel 3 comprises at its ends a ferrofluid retention means flange type 13 clearly visible towards the lower end of the mandrel. At the upper end, the flange is attached to the membrane and may be optional because the membrane alone can prevent the passage of the ferrofluid on the other side of the mandrel during extreme excursions of the moving assembly.

Still Figure 4, but on the outer periphery of the cone portion 27 'of the membrane, a ferrofluid guide means is also implemented in connection with a flange 28' of the membrane. A ferrofluid joint 30 is implemented in a guide structure comprising at least one magnetic field confinement means (or an air gap in the case where the flange comprises a voice coil in another motor, this time external, of the loudspeaker ). This guidance structure, which may be of the type of (and its variants) implemented in FIG. 3, is not more detailed. As before, the loudspeaker of FIG. 4 may thus comprise a motor (external or internal). ) or two motors. For simplicity, the other elements of the loudspeaker have not been detailed, for example the fins between the external and internal parts of the loudspeaker and the associated salad bowl or the rear pneumatic load.

Figure 5, simplified, gives an embodiment of a flange at the lower end of a mandrel 3 (or flange type 28, 28 '). This flange 13 is L-shaped and is slightly inclined in order to make the fluidic thrust effect which, in FIG. 5, has begun to occur more progressively, the moving element being in a forward excursion position towards the high (front of the speaker). The width of the collar is such that it can pass into the gap (especially during the assembly of the engine). The L-shape of the flange 13 is here implemented in combination with a wall 17 which extends laterally (here downwards, therefore the rear of the loudspeaker) the part of reduced width of the free space corresponding to the air gap. It follows that the ferrofluid will be constrained, in addition to the flange 13, but also by the wall 17, to remain on the same side of the mandrel (or rim), this even during extreme excursions. This wall 17, shown in dashed lines in FIG. 5, is optional but when it is present, it improves the retaining effects of the ferrofluid and fluidic stop. It is understood that this wall may be a clean room, attached to the ends of the air gap or a simple lateral extension of the reduced width portion of the vertical free space corresponding to the gap (this extension having no function magnetic in contrast to the elements at the gap). It is also understood in connection with Figure 5 simplified that return / braking means (not shown) can be implemented.

It is understood that the invention can be declined in various ways without departing from the general scope of the claims. Thus, a simplified loudspeaker according to the invention preferably comprises a motor with an external magnetic field generator (with respect to the coil) without a magnetic field generator on the inner side. The generator preferably comprises a radial magnetic ring formed of a circular juxtaposition of elementary radial magnets (which may eventually lead to the formation of vertical joints if an insufficient amount of ferrofluid is used). More generally, any type of engine can be implemented, conventional motor iron or motor without iron and, this with or without hardware loopback (by iron or magnets) of the field outside the gap, generator (s) magnetic field unilateral (internal or external to the coil) or bilateral. The engine in all its variations can also be eddy current. The shape and distribution of the field in the gap can be arbitrary, for example substantially uniform field, multiple fields (alternating directions for electromagnetic braking effect and / or operation with several coils). Specific magnetic field confining means may or may not be implemented in the vertical free space where the mandrel moves to facilitate the retention of the ferrofluid in the gap and said vertical free space. In addition to the motors with circular symmetry (circular membrane), other types of symmetries are possible in the context of the invention and, for example, elliptical. The transducer may comprise one or two motors depending on its type (for example a cone or mixed speaker may comprise an internal motor and an external motor relative to the ends of the membrane). The return / braking means (taper and oversize) and retaining / abutment (flange) can be combined into a single integrated structure or reported on the mandrel (or flange). We have seen that the maintenance of ferrofluidic joints was obtained by the existence of magnetic fields, both of the air gap and specific confinement means and it is understood that the distinction between the two as regards the creation of magnetic fields for the maintenance of ferrofluidic joints does not occur. to be if we consider the functional aspect. Finally, if preferably, at least one extended seal is used over the entire height of the gap (and possibly overflowing) and also extended over the entire circumference of the mandrel to completely fill the air gap on the corresponding side of the mandrel, a alternative may correspond to a series of independent vertical joints extended over the entire height of the gap (and possibly overflowing) and distributed over the circumference of the mandrel (preferably equiangularly), substantially parallel to each other. We understand that in the latter case, if we increase the amount of ferrofluid these vertical joints, the ferrofluid will eventually completely fill the gap on the corresponding side of the mandrel which will ensure a seal. Indeed, still in the latter case, this series of independent vertical joints (with the just necessary amount of ferrofluid so that these vertical joints are independent), does not ensure pneumatic sealing and that if it is necessary and that the it is not desired to increase the amount of ferrofluid to interconnect the vertical joints by the ferrofluid, an independent sealing means will have to be implemented (continuous seal circularly on the other face of the mandrel or other pneumatic sealing means more classic).

Claims

Electrodynamic transducer (1) with membrane (2) comprising an electrodynamic motor in a carcass (7) and in which a coil (6) movable fixed on a mandrel (3) integral with the membrane can move, the mandrel and the moving coil and the movable-line membrane, the mandrel being a shape generated by a generally linear generatrix, the voice coil being placed in a gap of a vertical free space where it can move and which is delimited, towards the center of the transducer by an internal magnetic structure (4) and, towards the periphery of the transducer by an external magnetic structure (5), at least one of the magnetic structures generating a static magnetic field, the transducer having no peripheral suspension or internal suspension, the peripheral suspension being a suspension between the periphery of the membrane and the carcass, the inner suspension being a suspension between the membrane or the mandrel and the carcass, the guidance of the moving equipment and the pneumatic sealing between the front and rear faces of the membrane being provided by a ferrofluid, characterized in that the mandrel is maintained in the air gap by extended ferrofluid on at least one of the two faces of the mandrel and said ferrofluid fills the gap on all the (the) corresponding face (s) of the mandrel.

2. Transducer according to claim 1, characterized in that the ferrofluid is extended on only one of the two faces of the mandrel.

3. Transducer according to claim 1 or 2, characterized in that the ferrofluid protrudes from the air gap at each of its two ends so that during excursions of the mandrel in the gap, the latter is always filled with ferrofluid on the (the corresponding face (s) of the mandrel.

4. Transducer according to claim 1, 2 or 3, characterized in that it comprises a fluid return means at an equilibrium position of the moving and braking equipment, said biasing means / fluidic braking causing a decrease of progressive preference of the space in which the ferrofluid can be placed during excursions of the moving element out of its equilibrium position, said fluidic return / braking means being chosen in at least one of the following means and their combinations:

a high and / or low conicity of the mandrel on the side of the ferrofluid, at least one pattern of high and / or low excess thickness of the mandrel on the side of the ferrofluid,

at least one concavity of the mandrel.

5. Transducer according to any one of the preceding claims, characterized in that it comprises at least one of the two ends of the mandrel means for retaining the ferrofluid, said retaining means being a collar for, during excessive excursions of said mandrel maintain the ferrofluid on the side of the mandrel, where it is located initially.

6. Transducer according to any one of the preceding claims, characterized in that it comprises at least two means of confinement (11) of the magnetic field in the vertical free space, the confinement means being stages in the vertical free space. .

7. Transducer according to any one of the preceding claims, characterized in that it further comprises at least one non-fluidic return means of the moving element.

8. Transducer according to claim 7, characterized in that the non-fluidic return means of the moving element is selected from one or more of the following means:

an electronic servocontrol of the position of the coil; a configuration of the coil and internal and external magnetic structures such that a restoring force is exerted on the coil by electromagnetic effect;

a configuration of the mobile equipment and internal and external magnetic structures such that a restoring force is exerted on the mobile equipment by magnetic effect.

9. Transducer according to any one of the preceding claims, characterized in that it is a speaker, the membrane is a dome.

1 0. Transducer according to any one of claims 1 to 8, characterized in that it is a speaker, the membrane is a cone (27) and in that said membrane being external to the center of the high- In addition, a continuous ferrofluid seal (30) is disposed along the circumference of a flange (28) of the membrane, said flange (28) being along the edge of the membrane opposite the edge of the membrane. relationship with the mandrel (6), said ferrofluid joint (30) being held by at least one magnetic field confining means (25, 26).

1 1. Transducer according to claim 1 0, characterized in that the rim (28) comprises a retention and return / fluidic braking means in the form of a curvature such that when the membrane is at its rest position, the ferrofluid seal ( 30) at maximum space to position relative to excursions out of the rest position.

2. Transducer according to claims 9 and 1 0 or 9 and 1 1, characterized in that the membrane comprises a dome portion and another cone portion.

3. Transducer according to any one of the preceding claims, characterized in that the voice coil is an electrically short-circuited coil and that at least one of the magnetic structures comprises a fixed coil (20) intended to receive a modulation current. , the fixed coil being placed at the gap in the magnetic structure.

14. Transducer according to claim 1 3, characterized in that the coil coil of the electric short-circuit type is integrated in the mandrel, the mandrel being metallic and electrically conductive and forming said short-circuit coil.