EP2524520B1 - Electrodynamic transducer having a dome and an inner hanging part - Google Patents

Description

The invention relates to the field of sound reproduction by means of loudspeakers, also called electrodynamic or electroacoustic transducers, which provide a function of converting electrical energy, generally provided by a power amplifier, into acoustic energy.

The acoustic energy is radiated by a membrane, the displacements of which cause variations in pressure of the surrounding air, which propagate in space in the form of an acoustic wave.

In the electrodynamic transducer of the Rice-Kellog type, the most common, the membrane is driven by a voice coil comprising a solenoid traversed by an electric current (from the amplifier) and immersed in a gap where there is a magnetic field produced by a permanent magnet. The interaction between the electric current and the magnetic field produces a force known as the "LAPLACE Force", which produces a displacement of the voice coil, which carries with it the membrane whose vibrations are the source of the acoustic radiation.

Many forms have been devised for the production of membranes; the most common are the cone (whose generator may be straight or curvilinear) and the dome, or a combination of both.

In the case of the cone, the voice coil is generally fixed on the periphery of an opening made in the center of the membrane. The size and mass of the moving equipment are relatively large, which makes this type of architecture particularly suitable for the production of transducers designed for the reproduction of the bass and the medium, requiring relatively low frequency membrane vibrations but large amplitude.

In the case of the dome, the voice coil is generally attached to a peripheral edge of the membrane. The bulk and mass of the moving equipment can be minimized, which makes this type of architecture particularly suitable for the realization of transducers designed for the reproduction of the treble, requiring high and low frequency membrane vibrations. amplitude.

• centrage et guidage axial de l'équipage mobile (comprenant la membrane et la bobine mobile) par rapport à l'entrefer,
• rappel de la membrane vers une position de repos,
• production d'un rayonnement acoustique secondaire, qui s'ajoute à celui de la membrane.

Whatever its shape, the membrane is generally attached to a frame of the transducer, via a peripheral suspension which, in addition to its primary function of maintaining the membrane, generally fulfills three functions:

• centering and axial guidance of the moving element (including the diaphragm and the voice coil) with respect to the gap,
• returning the membrane to a rest position,
• production of a secondary acoustic radiation, which is added to that of the membrane.

The centering of the diaphragm and its axial guidance represent an important function of the suspension. Indeed, it is essential to exclude, or at least minimize, the transverse movements (swinging, pitching) of the membrane, generating distortions in the sound signal emitted by it.

The spring return function, which acts on the diaphragm in the manner of a spring, must be calibrated so that the resonance frequency is located in the beginning of the frequency range to be reproduced. It is easily understood that, for the reproduction of the high frequencies, the excursion of the membrane must be weak, and the suspension relatively stiff.

In conical diaphragm transducers, because of the large deflections thereof, the peripheral suspension is generally not sufficient to guide the membrane relative to the air gap. It is therefore common recourse to complementary centering devices, especially spider type (see for example the French patent application FR 2,667,212 in the name of the plaintiff).

In the case of dome membranes, whose displacements are lower, the peripheral suspension is generally sufficient to effectively provide the three functions mentioned above. This topology is known for a long time, cf. for example the US patent US 2,442,791 (Edward C. Wente / Bell Laboratories), June 1948. A more recent example is set forth in US Patent Application US 2008/0166010 (Stiles et al. ).

However, the peripheral suspension has, in the case of a dome-shaped membrane, several disadvantages.

A first disadvantage is the creation of interference by the peripheral suspension (partly radiating, since driven in motion by the movement of the voice coil) with the radiation of the dome-shaped main part of the membrane. This phenomenon is particularly critical at high frequencies, where we observe for some frequency bands phase oppositions, destructive to the sensitivity level. Specifically, the response curve of the transducer shows hollows and bumps.

A second drawback is that a portion of the peripheral suspension is not radiating, since it is secured to the transducer frame by its outer periphery. More precisely, the radiating surface of the peripheral suspension represents only 50% of its apparent surface, which reduces the total emitting area of the diaphragm by about one sixth (about 17%), relative to its physical surface.

• la partie non rayonnante de la suspension périphérique, nécessaire à la fixation du dôme, s'étend radialement à l'extérieur de celui-ci et occupe par conséquent un espace périphérique non exploitable du point de vue de la genèse sonore ;
• la fixation de la suspension nécessite une pièce périphérique (exosquelette) qui accroît encore l'encombrement radial ;
• l'alimentation électrique de la bobine mobile est réalisée au moyen de fils, qui s'étendent à l'extérieur de la membrane, et nécessitent que l'exosquelette ménage un espace périphérique suffisant pour monter les cosses de raccordement des fils.

A third drawback is the large radial size of the transducer, resulting from the large diameter of the membrane, while only part of it is radiating. The radial size of the transducer is even greater than:

• the non-radiating part of the peripheral suspension, necessary for fixing the dome, extends radially outside the latter and consequently occupies a peripheral space which can not be used from the point of view of sound genesis;
• fixing the suspension requires a peripheral piece (exoskeleton) which further increases the radial size;
• the power supply of the voice coil is made by means of wires, which extend outside the membrane, and require the exoskeleton to provide a sufficient peripheral space for mounting the connection terminals of the wires.

A fourth disadvantage is that the architecture of the membrane is not conducive to the evacuation of calories produced by Joule effect within the voice coil. In fact, to allow mounting of the connecting terminals of the power supply son of the voice coil, the exoskeleton is generally made of an electrically insulating material and thermally.

Solutions have been proposed to try to remedy the performance defects of the acute transducers, induced by the Peripheral suspension. The US patent US 5,471,437 for example, describes a dome transducer in which an annular portion of the vibrating membrane is received within the dome and also serves as an internal suspension of the dome.

This solution seems at first interesting, but if it effectively increases the space equal to the radiator surface of the transducer, it is however likely to generate interference in the same way as the architecture suspension device described above. In addition, the architecture described in the patent US 5,471,437 is conducive to the tilting of the membrane (pitching effect), detrimental to the proper functioning of the transducer.

The document DE 102 11 086 A1, published on October 16, 2003 , shows a dome speaker comprising a magnetic system, a voice coil interacting with the magnetic system and a membrane partially insulating a portion of the interior space of the outside air. To allow greater deflection of the membrane, it is expected that the acoustic coil assembly has at least one opening opening to the outside air. In addition, the mobile equipment is suspended from the magnetic system by means of an internal suspension. The speaker has no external suspension.

The document US 6,208,743, published March 27, 2001 , shows an electrodynamic acoustic converter comprising a coil which plunges into a gap crossed by an electromagnetic field, the air gap being sealed with a viscous medium or solid, for example, a ferrofluid. Thus, short circuits are avoided. The mobile equipment is suspended from the magnetic circuit of the converter by means of an internal suspension. The converter has no external suspension.

The invention aims to make a contribution to solving the problems mentioned above, by providing improvements to dome transducers.

For this purpose, the invention proposes, according to a first aspect, an electrodynamic transducer according to claim 1.

The use of an acoustically non-emissive material for the production of the suspension makes it possible to eliminate the acoustic interferences between the suspension and the dome-shaped diaphragm.

The fact that the suspension of the diaphragm extends inside the diaphragm and not on the outside allows the emitting surface to reach 100% of the overall diameter of the diaphragm.

The suspension is preferably spaced from a peripheral outer edge of the diaphragm, being shifted inwardly therefrom.

The suspension comprises a flat internal portion fixed to the plate, and a peripheral portion surrounding the inner portion and which extends freely relative to the plate and is fixed to the moving assembly by an outer peripheral edge.

The transducer may further include an electrical supply circuit of the voice coil, which comprises two electrical conductors passing through the magnetic circuit and opening into the internal volume of the diaphragm.

The plate comprises, for example, a rim and a central disk pierced with ventilation holes, a stripped end of each electrical conductor being connected to an eyelet set in one of the holes.

The electrical circuit may further comprise two flexible conductors which extend into the internal volume of the diaphragm and connect each eyelet to one end of the voice coil.

According to one embodiment, the transducer further comprises a waveguide mounted in the vicinity of the diaphragm, and having a face located opposite and in the vicinity thereof and delimiting a compression chamber.

The suspension is preferably made of a cross-linked polymer foam, such as melamine foam.

According to a second aspect, the invention proposes an at least two-channel coaxial loudspeaker system comprising a bass transducer designed for the reproduction of the bass and / or the medium, and an electrodynamic transducer as described above, designed for the reproduction of the treble, and mounted coaxially and frontally with respect to the bass transducer.

According to a third aspect, the invention proposes an acoustic enclosure comprising a transducer or a coaxial loudspeaker system as described above.

• la figure 1 est une vue en coupe montrant un transducteur d'aigu à dôme, selon un premier mode de réalisation préféré de l'invention ;
• la figure 2 est une vue en section d'un détail de la figure 1 ;
• la figure 3 est une vue similaire à la figure 2, selon un deuxième mode de réalisation ;
• la figure 4 est une vue de dessus du transducteur d'aigu ;
• la figure 5 est une vue en coupe montrant un système de haut-parleur coaxial comprenant un transducteur principal de grave, et le transducteur d'aigu de la figure 1, monté de manière coaxiale et frontale ;
• la figure 6 est une vue similaire à la figure 5, montrant un système de haut-parleur coaxial comprenant un transducteur principal de grave et un transducteur d'aigu selon une variante de réalisation, dans laquelle le transducteur d'aigu comprend un pavillon ;
• la figure 7 est une vue en perspective montrant une enceinte incluant un système de haut-parleur coaxial tel que représenté sur la figure 5.

Other objects and advantages of the invention will become apparent in the light of the description given hereinafter with reference to the appended drawings in which:

• the figure 1 is a sectional view showing an acute dome transducer according to a first preferred embodiment of the invention;
• the figure 2 is a sectional view of a detail of the figure 1 ;
• the figure 3 is a view similar to the figure 2 according to a second embodiment;
• the figure 4 is a top view of the acute transducer;
• the figure 5 is a sectional view showing a coaxial speaker system comprising a main bass driver, and the high frequency transducer of the figure 1 , mounted coaxially and frontally;
• the figure 6 is a view similar to the figure 5 showing a coaxial loudspeaker system comprising a main bass transducer and an acute transducer according to an alternative embodiment, wherein the treble transducer comprises a horn;
• the figure 7 is a perspective view showing a speaker including a coaxial speaker system as shown in FIG. figure 5 .

We have shown on Figures 1 to 6 , and in more detail on the Figures 1 to 4 , an electrodynamic transducer 1 adapted to the reproduction of high frequencies, that is to say around 1 kHz to about 20 kHz.

The transducer 1 comprises a magnetic circuit 2, which includes a central annular permanent magnet 3 , sandwiched between two pole pieces forming field plates, namely a rear pole piece 4 and a front pole piece 5, fixed on two opposite faces. of the magnet 3 by gluing.

The magnet 3 and the pole pieces 4,5 are symmetrical about a common axis A2 , forming the general axis of the transducer 1.

The magnet 3 is preferably made of a rare earth neodymium-iron-boron alloy, which has the advantage of offering a high energy density (up to 12 times greater than that of a permanent magnet of ferrite barium).

As is clearly visible on the figure 1 , the rear pole piece 4, called cylinder head, is in this case monobloc, and made of mild steel. It has a U-shaped cross sectional shape, and comprises a bottom 6 fixed to a rear face 7 of the magnet 3, and a peripheral side wall 8 extending axially from the bottom 6. The side wall 8 is ends, at a front end opposite the bottom 6, by an annular front face 9 . The bottom 6 has a rear face 10.

The pole piece before 5, called core, is also made of mild steel. It is of annular shape and has a rear face 12, by which it is fixed to a front face 13 of the magnet 3, and an opposite front face 14 , which extends in the same plane as the front face 9 of the side wall 8 of the cylinder head 4.

As is visible on the figure 1 , the magnetic circuit 2 is extra-flat, that is to say that its thickness is small compared to its overall diameter. Moreover, the magnetic circuit 2 extends to the outer diameter of the transducer 1. In other words, the size of the magnetic circuit 2 is maximized with respect to the overall diameter of the transducer 1, which increases its power handling. as well as the value of the magnetic field, and thus the sensitivity of the transducer 1.

The core 5 has an overall diameter smaller than the internal diameter of the side wall 8 of the yoke 4, so that between the core 5 and the side wall 8 of the yoke 4 is defined a gap 15 in which the major is concentrated. part of the magnetic field generated by the magnet 3.

At the air gap 15, the edges of the core 5 and the yoke 4 can be chamfered, or preferably and as illustrated in FIG. figure 1 , rounded, so as to avoid harmful burrs.

The transducer 1 further comprises a mobile unit 16 including a diaphragm 17 in the form of a dome and a moving coil 18 integral with the diaphragm 17.

The diaphragm 17 is made of a rigid and light material, thermoplastic polymer or in a light alloy based on aluminum, magnesium or titanium. It is positioned so as to cover the magnetic circuit 2 on the side of the core 5, and so that its axis of symmetry of revolution coincides with the axis A2.

Under these conditions, the apex of the diaphragm 17, located on the axis A2, can be considered as the acoustic center C2 thereof, that is to say the equivalent point source from which the acoustic radiation is emitted of the transducer 1.

The diaphragm 17 has a peripheral edge 19 circular slightly raised, to facilitate the attachment of the voice coil 18.

The voice coil 18 comprises a conductive wire solenoid (for example copper or aluminum), spirally wound to form a cylinder whose upper end is fixed by gluing to the peripheral edge 19 raised diaphragm 17. The voice coil 18 is without support, but it could include one.

• elle favorise le centrage de la bobine mobile 18 dans l'entrefer 15,
• elle a une fonction de lubrification dynamique, au bénéfice du silence de fonctionnement du transducteur 1,
• grâce à sa conductivité thermique très supérieure à celle de l'air, elle favorise l'évacuation vers le circuit magnétique 2, et en particulier vers la culasse 4, de la chaleur produite par effet Joule dans la bobine mobile 18.

The voice coil 18 is immersed in the air gap 15, which may be advantageous to fill a mineral oil filled with magnetic particles, for example of the type marketed by the company FERROTEC under the trade name Ferrofluid (registered trademark). Such a filling has the following advantages:

• it promotes the centering of the voice coil 18 in the gap 15,
• it has a dynamic lubrication function, to the benefit of the silence of operation of the transducer 1,
• thanks to its thermal conductivity much higher than that of the air, it promotes the evacuation to the magnetic circuit 2, and in particular to the yoke 4, of the heat produced by the Joule effect in the voice coil 18.

The transducer 1 further comprises a support 20 fixed to the magnetic circuit 2, and to which is suspended the moving element 16. This support 20, made of a diamagnetic and electrically insulating material, for example a thermoplastic material such as polyamide or polyoxymethylene (charged of glass or not), has a symmetrical general shape of revolution about an axis coincident with the axis A2, T-shaped section.

The support 20, in one piece, forms an endoskeleton for the transducer 1 and comprises an annular plate 21 applied against the front face 14 of the core 5, and a cylindrical rod 22 which projects rearwardly from the center of the platinum 21, and which is housed in a complementary cylindrical location 23 formed in the magnetic circuit 2 and formed by a succession of coaxial holes in the yoke 4, the magnet 3 and the core 5, which ensure the centering of the support 20 compared to the magnetic circuit 2.

As illustrated on the figure 1 , the endoskeleton 20 is rigidly fixed to the magnetic circuit 2 by means of a nut 24 screwed onto a threaded portion of the rod 22 and clamped against the yoke 4, inside a countersink 25 formed on the rear face 10 , in the center. In this way, the plate 21 is firmly pressed against the front face 14 of the core 5, without the possibility of rotation. This attachment may optionally be supplemented by the application of a film of glue between the plate 21 and the core 5.

Given its frontal location with respect to the magnetic circuit 2, the plate 21 extends into the lenticular internal volume delimited by the diaphragm 17.

The moving element 16 is mounted on the endoskeleton 20 by means of an inner suspension 26 which provides the connection between the diaphragm 17 and the plate 21. This suspension 26 is in the form of a piece of revolution made of a material light, elastic, and non-emissive acoustically (we can choose a porous material for this purpose). This material is preferably resistant to the heat prevailing in the transducer, and its elasticity is chosen so that the resonant frequency of the moving element 16 is lower than the lowest frequency reproduced by the transducer 1 (in this case 500 Hz at 2 kHz).

According to a first embodiment illustrated on the Figures 1 and 2 , the suspension 26 is of the "spider" type and made of a fabric of natural (for example cotton) or synthetic fibers (for example polyester, polyacrylic, nylon, and more particularly aramids, including Kevlar, registered trademark) or in a mixture of natural and synthetic fibers (for example cotton-polyester), these fibers being impregnated with a thermosetting or thermoplastic resin, which confers strength, stiffness and elasticity to the suspension 26.

The suspension comprises an annular, planar internal portion 27 fixed by gluing on an upper face 28 of the plate 21, and a peripheral portion 29 which extends around the inner portion 27. The peripheral portion 29 extends radially freely to beyond the plate 21 and comprises corrugations 30 which can be obtained by thermoforming.

By an outer edge 31, the suspension 26 is fixed, by gluing, on the inner surface of the diaphragm 17, near the peripheral edge 19 thereof. Alternatively, assuming that the voice coil 18 comprises a cylindrical support secured to the diaphragm 17 and on which the solenoid would be mounted, the suspension 26 could be fixed, by its outer edge, on the inner surface of this support.

It should be noted that the moving element 16 must be perfectly centered with respect to the magnetic circuit 2, and more precisely with respect to the gap 15 in which the voice coil 18 is housed. For this purpose, a centering assembly (or false breech) is used in which the endoskeleton 20 is positioned . The centering assembly comprises a bore (of a diameter equal to that of the housing 23 ) into which the rod 22 of the endoskeleton 20 is inserted . The gluing of the suspension 26 on the plate 21 is realized next. Before the glue has set, the internal diameter of the moving coil 18 is centered with respect to the bore of the centering assembly, which ensures the centering of the moving element 16 with respect to the endoskeleton 20 . After drying the adhesive, the assembly comprising the movable element 16 and the endoskeleton 20 can then be mounted by being perfectly centered in the magnetic circuit 2.

The suspension 26 provides a return function of the moving element 16 to a median position of rest, adopted in the absence of axial stress acting on the voice coil 18 (that is, in practice, in the absence of current running through it). It is in this median position that the transducer 1 is shown in the figures.

The suspension 26 also provides a function of maintaining the attitude of the diaphragm 17, that is to say of maintaining the peripheral edge 19 of the diaphragm 17 in a plane perpendicular to the axis A2, in order to avoid any tilting or pitch of the diaphragm 17 which would impair its operation.

The electric current is fed to the voice coil 18 by two electrical circuits 32 which connect the ends of the voice coil 18 to two electrical terminals (not shown) for supplying the transducer 1.

• un conducteur 33 de forte section, comprenant un fil de cuivre isolé par une gaine plastique, traversant le circuit magnétique 2 en étant logé dans une rainure pratiquée longitudinalement dans la tige 22 de l'endosquelette 20, et dont une extrémité avant dénudée 34 débouche dans le volume interne au diaphragme 17 en faisant saillie du circuit magnétique 2 dans un trou 35 pratiqué dans la platine 21 ;
• un élément de jonction électrique, sous forme par exemple d'un oeillet 36 métallique (en cuivre ou en laiton) serti dans le trou 35 et auquel l'extrémité dénudée 34 du conducteur 33 est raccordée électriquement (par exemple par l'intermédiaire d'un point de soudure, non représenté) ;
• un conducteur 37 de faible section, sous forme d'une tresse métallique très souple et convenablement conformée qui s'étend dans le volume interne du diaphragme 17 en enjambant la platine 21 et la suspension 26, et dont une extrémité interne 38 est raccordée électriquement à l'oeillet 36 (par exemple par l'intermédiaire d'une soudure, non représentée), et dont une extrémité externe opposée est raccordée électriquement à une extrémité de la bobine mobile 18.

As illustrated on the figure 1 each electrical circuit 32 comprises:

• a conductor 33 of large section, comprising a copper wire insulated by a plastic sheath, passing through the magnetic circuit 2 being housed in a groove formed longitudinally in the rod 22 of the endoskeleton 20, and a bare front end 34 opens into the internal volume of the diaphragm 17 protruding from the magnetic circuit 2 in a hole 35 formed in the plate 21 ;
• an electrical joining element, in the form of, for example, a metal eyelet 36 (made of copper or brass) crimped into the hole 35 and to which the stripped end 34 of the conductor 33 is connected electrically (for example via a weld spot, not shown);
• a conductor 37 of small section, in the form of a very flexible and suitably shaped metallic braid which extends in the internal volume of the diaphragm 17 by stepping over the plate 21 and the suspension 26, and an inner end 38 is electrically connected to the eyelet 36 (for example by means of a weld, not shown), and an opposite external end of which is electrically connected to one end of the voice coil 18.

A single driver 37 of small section is visible on the figure 1 , the second conductor of small section, diametrically opposed to the first, being located in front of the sectional plane of the figure.

The arcuate shape (in U), added to the great flexibility of these conductors 37, allows them to deform without difficulty and to follow the movement movements of the diaphragm 17 accompanying the vibrations of the voice coil 18, without applying radial mechanical stress or axial that can compromise the positioning of the moving element 16 relative to the gap 15.

The transducer 1 finally comprises an acoustic wave guide 39 , integral with the magnetic circuit 2.

The waveguide 39 is in the form of a one-piece piece made of a material having a high thermal conductivity, greater than 50 Wm ^-1 .K ^-1 , for example aluminum (or in an aluminum alloy).

The waveguide 39, of revolution shape, is fixed directly on the yoke 4 and comprises a substantially cylindrical outer side wall 40 which extends in the extension of the side wall 8 of the yoke 4. The fastening is preferably performed by screwing, by means of a number of screws equal to or greater than 3. In order to maximize the thermal contact between the two parts, it is advantageous to complete this screwing by a coating of heat-conducting paste.

As can be seen in particular on Figures 1 and 2 , the waveguide 39 has, on a rear peripheral edge, a skirt 41 which fits on a recess 42 formed in the yoke 4, of complementary profile. This results in a precise centering of the waveguide 39 with respect to the yoke 4 and, more generally, with respect to magnetic circuit 2 and the diaphragm 17. In addition, the thermal conductivity between the two parts 4,39 is improved.

The waveguide 39 has a rear face 43 having a substantially spherical cap shape, which extends concentrically with the diaphragm 17, opposite and in the vicinity of an outer face thereof that it partially covers.

According to an embodiment illustrated on the figure 1 , the rear face 43 is perforated and comprises a continuous peripheral portion 44 which extends in the vicinity of the rear edge of the waveguide 39, and a discontinuous central portion 45 carried by a series of fins 46 projecting radially from the wall lateral 40 inward (that is to say towards the A2 axis of the transducer 1 ). The rear face 43 is delimited internally - that is to say on the side of the diaphragm 17 - by a petaloid-shaped ridge 47 (clearly visible on the figure 4 ).

As is visible on the figure 1 the fins 46 do not meet on the axis A2 but stop at an inner end located at a distance from the axis A2. At their apex, the fins 46 each have a curvilinear edge 48 .

The side wall 40 of the waveguide 39 is delimited internally by a discontinuous frustoconical front face 49 distributed over a plurality of angular sectors 50 which extend between the fins 46. This front face 49 forms a flag primer extending from the interior to the outside and from a rear edge, formed by the petaloid ridge 47 constituting a groove of the flag primer 49, to a front edge 51 which constitutes a mouth of the flag primer 49. The angular sectors 50 of the flag primer 49 are portions of a cone of revolution whose axis of symmetry coincides with the axis A2, and whose generator is curvilinear (for example according to a circular law, exponential or hyperbolic). The flag starter 49 ensures a continuous adaptation of acoustic impedance between the air medium delimited by the groove 47 and the air medium delimited by the mouth 51.

According to one embodiment, the tangent to the horn primer 49 on the mouth 51 forms with a plane perpendicular to the axis A2 of the transducer 1 an angle of between 30 ° and 70 °. In the example illustrated in the drawings, this angle is about 50 °.

The fins 46, whose function in particular is to increase the exchange surface of the waveguide 39 to promote the radiation and convection dissipation of the heat produced at the moving coil 18, each laterally have two cheeks 52 which are connected externally to the angular sectors 50 of the flag primer 49 via leaves 53. The cheeks 52 contribute to guiding the wave generated by the diaphragm 17.

In the embodiment variant illustrated on the figure 6 , the waveguide 39 forms not a flag primer but a complete flag (for example symmetrical of revolution about the axis A2 ), whose groove 47 is circular in outline and whose mouth 51 has a diameter much greater than that of the throat 47.

• une zone interne 54 découverte, de forme pétaloïde, délimitée extérieurement par la gorge 47,
• une zone externe 55 couverte, de forme complémentaire de la zone couverte 54, délimitée intérieurement par la gorge 47.

The waveguide 39 defines on the diaphragm 17 two distinct and complementary zones, namely:

• an internal zone 54 discovered, petaloid-shaped, bounded externally by the groove 47,
• an outer zone 55 covered, of complementary shape to the covered area 54, delimited internally by the groove 47.

The rear face 43 of the waveguide 39 and the corresponding external covered area 55 of the diaphragm 17 define between them a volume of air 56 called a compression chamber, in which the acoustic radiation of the vibrating diaphragm 17 driven by the voice coil 18 moving in the gap 15 is not free, but compressed. The inner zone 54 uncovered communicates directly with the groove 47 opposite, which concentrates the acoustic radiation of the entire diaphragm 17.

The compression ratio of the transducer 1 is defined by the quotient of the emitting surface, corresponding to the plane surface delimited by the overall diameter of the membrane 17 (measured on the edge 19 ), by the surface delimited by the projection, in a plane perpendicular to the axis A2 of the groove 47. This compression ratio is preferably greater than 1.2: 1, and for example greater than or equal to 1.4: 1. Higher compression ratios, for example up to 4: 1, are conceivable.

We have shown on the figure 3 a second embodiment of the transducer 1, which differs from the first just described by the design of the suspension 26 and the shape of the endoskeleton 20.

Indeed, the suspension 26 has a substantially polygonal shape in section and comprises an inner edge 67 right, that is to say cylindrical of revolution about the axis A2, and a peripheral outer edge 68 substantially frustoconical.

The plate 21 substantially has the profile of a pulley and comprises a peripheral annular groove 69 which opens radially outwards, facing the inner surface of the diaphragm 17, near the edge 19 thereof.

The groove 69 separates the plate 21 into two flanges 70,71 facing each other, forming the side walls of the groove 69, namely a rear flange 70 bearing against the front face 14 of the core 5, and a front flange 71. The flanges 70,71 are connected by a cylindrical core 72 forming the bottom of the groove 69.

On the side of its inner edge 67, the suspension 26 is housed in the groove 69 (with a slight slight preload) by being fixed by gluing to the flanges 70, 71, during assembly of the moving assembly 16 in the manner described. above in the context of the first embodiment. For this purpose, a radial clearance 73 is provided between the inner edge 67 of the suspension 26 and the bottom of the groove 69.

By its frustoconical outer edge 68 , the suspension 26 is fixed to the inner surface of the diaphragm 17, close to the outer edge 19 thereof.

The suspension 26 can be made in one of the non-emissive materials already described, or in a cross-linked polymer foam (for example polyester or melamine) which has the advantage of being non-emissive and of having a high porosity while having a good resistance to heat.

The acute transducer 1 which has just been described can be used individually, or, as illustrated in FIGS. figures 5 and 6 coupled to a bass driver 57 for forming a multi-channel coaxial speaker system 58 designed to cover an extended acoustic spectrum, ideally the entire audible band.

In practice, the bass transducer 57 may be designed to reproduce the bass and / or the medium, and possibly part of the treble. For this purpose its diameter will preferably be between 10 and 38 cm. Although the main object of the present invention is not to define recommendations concerning the spectrum covered by the different transducers of the system 58, specify however that the spectrum covered by the bass transducer 57 can cover the bass, that is to say the band from 20 Hz to 200 Hz, or the medium, that is to say say the band from 200 Hz to 2 kHz, or at least part of the bass and medium (and for example the entire bass and medium), and possibly part of the treble. For example, the bass transducer can be designed to cover a band of 20 Hz to 1 kHz or 20 Hz to 2 kHz, or 20 Hz to 5 kHz.

The acute transducer 1 is preferably designed so that its bandwidth is at least complementary in the acute of that of the bass driver 57. Thus, it can be ensured that the bandwidth of the acute transducer 1 covers at least partly the medium and all of the treble, up to 20 kHz.

It is preferable that the linear parts of the 1.57 transducer responses partially overlap and that the sensitivity level of the acute transducer 1 is at least equal to that of the bass transducer 57, in order to avoid a fall in the overall response of the system 58 at certain frequencies corresponding to the upper part of the spectrum of the low-frequency transducer 57 and the lower part of the spectrum of the acute transducer 1.

The bass driver 57 is of conventional architecture and we will not describe it in detail. Note however that it comprises a magnetic circuit 59 having a symmetry of revolution about an axis A1 forming the general axis of the bass transducer 57.

The bass transducer 57 also comprises a mobile unit 60 including a conical membrane 61 of revolution about the axis A1 (with a curvilinear generatrix, for example according to a circular law, exponential or hyperbolic) and a voice coil 62 comprising a solenoid 63 wound on a cylindrical support 64 integral with the membrane 61.

In its center, the membrane 61 defines an opening 65 on the inner edge of which the support 64 is fixed by a front end, by gluing. The geometric center of the opening 65 is considered, as a first approximation, to be the acoustic center C1 of the bass transducer 57, that is to say the virtual point source from which the acoustic radiation of the transducer 57 is emitted. main.

As illustrated on the figures 5 and 6 , the acute transducer 1 is housed in the bass transducer 57 by being received in a frontal central space (that is to say on the front side of the magnetic circuit 59 ) defined rearwardly by the magnetic circuit 59, and laterally by the inner wall of the support 64.

• de manière coaxiale, c'est-à-dire que l'axe A1 du transducteur de grave 57 et l'axe A2 du transducteur d'aigu 1 sont confondus,
• de manière frontale, c'est-à-dire que le transducteur 1 est placé à l'avant du circuit magnétique 59 (autrement dit du côté du circuit magnétique 59 où s'étend la membrane 61).

As shown on the figures 5 and 6 , the acute transducer 1 can be mounted in the bass transducer 57 at a time:

• in a coaxial manner, that is to say that the axis A1 of the bass transducer 57 and the axis A2 of the acute transducer 1 coincide,
• frontally, that is to say that the transducer 1 is placed in front of the magnetic circuit 59 (that is to say on the side of the magnetic circuit 59 where the membrane 61 extends).

This assembly, described as "frontal" as opposed to rear mounting in which the transducer is mounted on the rear face of the cylinder head (see for example the patent Tannoy US 4,164,321 ), is made possible thanks to the particular architecture of the treble transducer 1 .

In addition to the front coaxial positioning of the transducer 1 with respect to the bass transducer 57, their respective geometries, in particular (but not only) the thicknesses of the magnetic circuits 2.59 and the curvature (and consequently the depth) of the membrane 61, are preferably adapted to allow at least approximate coincidence of the acoustic centers C1 and C2 of the transducers 1.57, such that the time difference between the acoustic radiation of the transducers 1.57 is imperceptible (this is called temporal alignment of the transducers 1 , 57 ). The system 58 can then be considered as perfectly coherent despite the duality of the sound sources.

In addition, in the embodiment illustrated on the figure 5 , the axial positioning of the acute transducer 1 relative to the bass transducer 57, and the geometry of the waveguide 39, are such that the membrane 61 extends in the extension of the flag primer 49. In other words, the tangent to the horn primer 49 on the mouth 51 coincides with the tangent to the membrane 61 on its central opening 65. In this configuration, the waveguide 39 and the diaphragm 61 of the bass transducer 57 together form a complete horn for the transducer 1, and allowing both 1.57 transducers to have homogeneous directivity characteristics.

In the variant embodiment of the figure 6 , the waveguide 39 forming a complete horn is independent of the diaphragm 61 of the bass transducer 57. In this configuration, the directivity characteristics of the two transducers 1.57 are distinct and can be optimized separately, which is advantageous in some applications such as stage return speakers.

The system 58 can be mounted on any type of acoustic loudspeaker, for example a stage return speaker 66 , with an inclined end face, as illustrated by way of example on FIG. figure 7 .

The architecture of the transducer 1 described above, associated with the acoustic properties of the suspension 26, provides the following advantages.

First, the location of the suspension 26 within the dome-shaped diaphragm 17 and the production of the suspension 26 in an acoustically non-emissive material suppresses acoustic interference between the suspension 26 and the diaphragm 17.

Secondly, the fact that the suspension 26 extends inside the diaphragm 17 and not outside thereof makes it possible to increase the emitting surface to 100% of the overall diameter of the diaphragm 17.

This increase in the emissive surface of the diaphragm 17 allows a substantial gain in sensitivity of the transducer 1, since this is proportional to the square of the emitting surface. In practice, the architecture of the transducer 1 allows, with an overall diameter of the equal transducer, an increase in the emitting surface of up to 17%. This results in a gain in sensitivity of about 1.4 dB for this value.

Third, thanks to the absence of external suspension to the diaphragm, the diameter of the voice coil 18 can be increased, being made equal to the diameter of the diaphragm 17. This results in an increase in the admissible power of the voice coil 18, proportional to increase its diameter. More specifically, an increase in the diameter of the voice coil of 20% induces an equivalent gain in power handling.

Fourthly, the fixation of the moving element 16 being carried out inside the diaphragm 17, via the suspension 26 and the endoskeleton 20, the transducer 1 is delivered from the radial space of a support external to the diaphragm 17. Given the emissivity at 100% of the diaphragm 17, the ratio Emitting surface / Radial overall dimensions (equal to the quotient) is thus significantly increased. squares of the radii of the diaphragm and the transducer), which can be about 70%.

This ratio makes it possible to carry out a short axle primer 49 axially, which allows the mounting of the transducer 1 axially and frontally in a bass transducer 57, with tangential connection of the horn primer 49 to the profile of the membrane 61 of the bass transducer 57.

In addition, the absence of exoskeleton avoids the thermal confinement of the magnetic circuit 2. This aspect, combined with the direct thermal contact between the yoke 4 and the waveguide 39, made of a material that is a good conductor of heat, makes it possible to significantly improve the heat dissipation capacity of the transducer 1, and therefore its power handling.

As already indicated, the transducer 1 is delivered from the radial space of a support external to the diaphragm 17 since this support is produced by means of an endoskeleton 20. This aspect, combined with the increase in the diameter of the voice coil 18, equal to that of the diaphragm 17, makes it possible to increase the diameter of the magnetic circuit 2, which can equal the overall diameter of the transducer 1, as it appears on FIG. figure 1 .

This results in a gain in product BL (product of the magnetic field in the air gap 15 by the length of wire of the solenoid 18, to which is proportional the Laplace force generating the displacements of the moving element 16 ), hence a gain In practice, one can obtain with the architecture of the transducer 1 an increase of the product BL of greater than about 40%, and therefore a gain in sensitivity that can be achieved in terms of the sensitivity of the transducer (proportional to the square of the increase of the product BL). raise to about 3 dB.

Claims (9)

1. An electrodynamic transducer (1) comprising:

   - a magnetic circuit (2), defining an air gap (15);

   - a movable element (16), comprising a dome-shaped diaphragm (17), integral with a movable coil (18) dipped into the air gap (15);

   - a support (20), to which the movable element (16) is suspended;

   - a suspension (26), providing the connection between the movable element (16) and the support (20);

   - the support (20) extends at least partly in an inner volume of the movable element (16), this support (20) comprises a plate (21), on which the suspension (26) is attached, and a rod (22) integral with the plate (21) and by which the support (20) is attached to the magnetic circuit (2)

   - the suspension (26) comprises a planar inner portion (27) attached to the plate (21) and a peripheral portion (29) surrounding the inner portion (27) and which freely extends with respect to the plate (21), this electrodynamic transducer (1) being characterised in that:

   - the suspension (26) is made of an acoustically non-emissive material,

   - the peripheral portion (29) comprises corrugations (30), the peripheral portion (29) being attached to an inner face of the diaphragm (17) by an external peripheral edge (31) of said corrugations (30).
2. The electrodynamic transducer (1) according to the preceding claim, wherein the movable element (16) is devoid of a suspension external to the diaphragm (17).
3. The electrodynamic transducer (1) according to the claim 1, which comprises an electric circuit (32) for supplying the movable coil (18) comprising two electric conductors (33) passing through the magnetic circuit (2) and opening into the volume internal to the diaphragm (17).
4. The electrodynamic transducer (1) according to the claim 3, wherein the plate (21) is pierced with holes (35), and wherein stripped ends (34) of the electric conductors (33) are connected to two eyelets (36) crimped in said holes (35).
5. The electrodynamic transducer (1) according to the claim 4, wherein the electric circuit (32) comprises two flexible conductors (37) which extend in the volume internal to the diaphragm (17) and connect the eyelets (36) to one end of the movable coil (18).
6. The electrodynamic transducer (1) according to one of the preceding claims, which comprises a waveguide (39) mounted in the vicinity of the diaphragm (17), and having a face (43) facing and in the vicinity thereof and delimiting a compression chamber (56).
7. A coaxial loudspeaker system (58) with at least two ways, comprising a low-frequency sound transducer (57) designed for reproducing a low frequency and/or mid-frequency sound, and an electrodynamic transducer (1) according to one of the preceding claims, designed for reproducing a high-frequency sound, and possibly at least part of a mid-frequency sound.
8. The coaxial loudspeaker system (58) with at least two ways according to claim 7, wherein the high-frequency transducer (1) is mounted coaxially and frontally with respect to the low-frequency transducer (57).
9. A speaker enclosure (66) comprising an electrodynamic transducer (1) according one of claims 1 to 6, or a coaxial loudspeaker system (58) with at least two ways according to one of claims 7 or 8.

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