Diaphragm loudspeaker and associated manufacturing process

Abstract

Membrane loudspeaker and associated embodiment. The invention relates to a loudspeaker (10) comprising: - a magnetic motor defining a first coaxial air gap and a second coaxial air gap; - a moving assembly comprising: a rigid diaphragm (50), adapted to emit sound waves; a first coil fixed to the diaphragm and located in the first air gap; a second coil fixed to the diaphragm and located in the second air gap; and - a device for powering the coils. The diaphragm comprises a plate (66) of thermosetting resin reinforced with ceramic fibers, and the power supply device comprises a first (92) and a second (94) strips deposited on said plate, each of the first and second strips being formed of a layer of conductive material, each strip being electrically connected to the coils. Figure for the abstract: Figure 1

Description

Title of the invention: Membrane loudspeaker and associated production method

[0001] The present invention relates to a loudspeaker arranged along a main axis and comprising: a magnetic motor defining a first air gap and a second air gap coaxial with the central axis, the second air gap being further from the main axis than the first air gap; an assembly axially movable relative to the magnetic motor, the movable assembly comprising: a rigid membrane, adapted to emit sound waves; a first coil fixed to the membrane and located in the first air gap; a second coil fixed to the membrane and located in the second air gap; and a device for electrically supplying the first and second coils.

[0002] The invention applies particularly to flat loudspeakers, that is to say of reduced thickness along the main axis.

[0003] Application FR2202297, in the name of the Applicant, not yet published, describes a flat loudspeaker comprising an injected plastic membrane, fitted with two metal blades intended to electrically supply the coils.

[0004] Such a membrane requires the overmolding of conductive blades in the plastic, which increases the production costs of the membrane. In addition, the plastic may have insufficient thermal resistance during the electrical connection steps between the blades and the coils, such connection steps being carried out in particular by welding or brazing.

[0005] In order to overcome these drawbacks, the invention relates to a loudspeaker of the aforementioned type, in which the membrane comprises a thermosetting resin plate reinforced with ceramic fibers and in that the electrical power supply device comprises at least a first and a second strip deposited on said thermosetting resin plate, each of the first and second strips being formed from a layer of electrically conductive material, each of the first and second strips being electrically connected to the first and second coil.

[0006] According to other advantageous aspects of the invention, the loudspeaker comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0007] - the first and second strips are arranged on the same first face of the thermosetting resin plate;

[0008] - the power supply device further comprises a third and a fourth strips deposited on a second face of the thermosetting resin plate, opposite the first face, each of the third and fourth strips being formed from a layer of electrically conductive material, each of the third and fourth strips being electrically connected to the first and second coils;

[0009] - the thermosetting resin of the membrane is an epoxy resin;

[0010] - the ceramic fibers of the membrane comprise glass fibers;

[0011] - ceramic fibers represent between 30% and 70%, preferably between 40% and 60%, more preferably close to 50% by mass of the reinforced thermosetting resin plate;

[0012] - the ceramic fiber reinforced thermosetting resin plate has a thickness between 0.8 mm and 1.6 mm, preferably between 0.8 mm and 1 mm.

[0013] The invention further relates to a method of producing a loudspeaker as described above, comprising the following steps:

[0014] - supply of a printed circuit element, of the PCB type, comprising a plate glass fiber reinforced epoxy resin composite, each face of said plate being coated with a laminated layer of copper or copper alloy;

[0015] - production of the first and second conductive strips on a first face said printed circuit element, by removing the laminated layer of copper around locations forming said first and second conductive strips.

[0016] According to one embodiment, said method further comprises a step of producing the third and fourth conductive strips on a second face of the printed circuit element, by removing the laminated layer of copper around locations forming said third and fourth conductive strips.

[0017] According to one embodiment, said method further comprises a step of machining the composite plate of the printed circuit element.

[0018] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example and made with reference to the drawings in which:

[0019] [Fig-1] [Fig.l] is a top view of a loudspeaker according to a method of realization lization of the invention;

[0020] [Fig.2] [Fig.2] is a sectional view of the loudspeaker of [Fig.l];

[0021] [Fig.3] [Fig.3] is a detail view of [Fig.2]; and

[0022] [Fig.4] [Fig.4] is a bottom view of an element of the loudspeaker of Figures 1 to 3.

[0023] Figures 1 to 4 show a loudspeaker 10 according to one embodiment of the invention.

[0024] The loudspeaker 10 extends around a main axis X. Along said main axis, the loudspeaker 10 has a small thickness, for example less than 20 mm, advantageously generously of the order of 1 cm.

[0025] The loudspeaker 10 comprises: a magnetic motor 12; a movable assembly 14; and an electrical device 16.

[0026] In the embodiment shown, the loudspeaker 10 further comprises a peripheral chassis 18, a suspension joint 19 and a rear partition 20.

[0027] The magnetic motor 12 has a shape substantially of revolution around the main axis X. In the embodiment shown, the magnetic motor 12 comprises a first pole piece 22, a second pole piece 24 and a permanent magnet 26.

[0028] The first polar part 22 has a substantially U-shaped section along a plane including the main axis X and corresponding for example to the section plane of figures 2 and 3. More precisely, the first polar part 22 comprises a bottom 28, an internal wall 30 and an external wall 32.

[0029] The bottom 28 is substantially planar and perpendicular to the main axis X. More precisely, the bottom 28 has the shape of a crown defined by a first internal edge and a first external edge, the first internal edge being closer to the main axis X than the first external edge.

[0030] Each of the inner 30 and outer 32 walls has a substantially cylindrical shape along the main axis X and is arranged to project relative to the same face of the bottom 28. The inner 30 and outer 32 walls extend respectively from the first inner edge and from the first outer edge of the crown forming the bottom 28.

[0031] Each inner wall 30 and outer wall 32 has an end 34, 36 formed by a circular edge. The ends 34 and 36 are substantially coplanar in a plane perpendicular to the main axis.

[0032] In the remainder of the description, it is considered that the face of the bottom 28 from which the inner 30 and outer 32 walls extend is oriented towards the front of the loudspeaker 10; and that the opposite face of said bottom 28 is oriented towards the rear of said loudspeaker. The terms “front” and “rear” are understood according to this orientation.

[0033] The second pole piece 24 is substantially planar and perpendicular to the main axis X. The second pole piece 24 has a crown shape defined by a second internal edge 38 and a second external edge 40. Perpendicular to the main axis X, a distance between the second internal 38 and external 40 edges is less than a distance between the first internal and external edges of the bottom 28 of the first pole piece 22.

[0034] The second polar piece 24 is arranged in a substantially coplanar manner at the ends 34 and 36 of the inner 30 and outer 32 walls of the first polar piece 22. A first air gap 42 is provided between the end 34 of the inner wall 30 and the second inner edge 38. A second air gap 44 is provided between the end 36 of the outer wall 32 and the second outer edge 40.

[0035] The permanent magnet 26 is substantially planar and perpendicular to the main axis X. The permanent magnet 26 has a crown shape with dimensions similar to those of the second pole piece 24. The permanent magnet 26 is sandwiched, along the main axis X, between the bottom 28 of the first pole piece 22 and the second pole piece 24.

[0036] The assembly 14 is movable in translation along the main axis X relative to the magnetic motor 12, according to a low amplitude movement allowing the emission of sound waves.

[0037] More specifically, the movable assembly 14 comprises: a membrane 50; and a first 52 and a second 54 coil fixed to said membrane.

[0038] In the embodiment shown, the assembly 14 further comprises a first 56 and a second 58 spool holder.

[0039] The membrane 50 is adapted to emit sound waves. Said membrane 50 is substantially flat and arranged on the front side of the magnetic motor 12. The membrane 50 comprises in particular a front face 60 and a rear face 62, said rear face being oriented towards the magnetic motor 12.

[0040] The membrane is formed of a central part 64 and a peripheral part 66, assembled to each other.

[0041] The central part 64 has substantially the shape of a disc arranged coaxially with the main axis X, opposite a space defined by the internal wall 30 of the first pole piece 22 of the magnetic motor 12. The central part 64 is defined by a contour 68.

[0042] The peripheral part 66 has substantially the shape of a crown defined by a third internal edge 70 and by a third external edge 72. The peripheral part 66 extends substantially opposite the first pole piece 22 of the magnetic motor 12. The third internal edge 70 is assembled to the contour 68 of the central part 64.

[0043] Preferably, each of the central 64 and peripheral 66 parts of the membrane 50 is made of an electrically insulating material. By “electrically insulating” is meant in particular that the resistivity of the material is greater than 1010 Qm

[0044] The central part 64 is for example made of metal, for example machined aluminum, or even of polymer material, in particular injectable, for example of the polycarbonate / acrylonitrile butadiene styrene type.

[0045] The peripheral part 66 is formed from a thermosetting resin plate reinforced with ceramic fibers. Preferably, the thermosetting resin is an epoxy resin and the ceramic fibers comprise glass fibers. The composition of the peripheral part 66 will be detailed below.

[0046] Each of the first 56 and second 58 coil holders has a substantially cylindrical shape of revolution around the main axis X. A first axial end of each of the first 56 and second 58 coil holders is fixed to the rear face 62 of the membrane 50, so that a second axial end of the first 56 and second 58 coil holders is arranged respectively in the first 42 and in the second 44 air gaps.

[0047] In the embodiment shown, each of the first 56 and second 58 coil holders is fixed to the peripheral part 66 of the membrane. The first coil holder 56 is fixed to the third internal edge 70. A coil holder 56, 58 is for example a fiberglass support impregnated with resin and covered with a polyimide insulating paper.

[0048] Each of the first 52 and second 54 coils is formed of an electrically conductive wire, said wire being wound, respectively around the first 56 and the second 58 coil holder. The first coil 52 is arranged in the first air gap 42 and the second coil 54 is arranged in the second air gap 44, between the first 22 and second 24 pole pieces of the magnetic motor 12.

[0049] The electrical device 16 is in particular intended to supply electricity to the first 52 and second 54 coils during operation of the loudspeaker 10.

[0050] The electrical device 16 comprises: at least a first 74 and a second 76 conductive strips; and a first 78 and a second 80 connection cables.

[0051] Each of the first 74 and second 76 conductive strips is formed from a layer of electrically conductive material deposited on the peripheral part 66. In the embodiment shown, the first 74 and second 76 conductive strips are arranged at the rear face 62 of the membrane 50, as visible in [Fig.4].

[0052] By "electrically conductive" is meant in particular that the conductivity of the material is greater than 30 Sm '. Preferably, each of the first 74 and second 76 conductive strips is formed from a layer of metal, for example copper, as detailed below.

[0053] The first 74 and second 76 conductive strips are arranged at a distance from each other on the peripheral part 66. In the embodiment shown, the first 74 and second 76 conductive strips are symmetrical to each other with respect to a plane of symmetry of the peripheral part 66, said plane of symmetry comprising the main axis X. Each of the first 74 and second 76 conductive strips extends between the third internal edge 70 and the third external edge 72 of the peripheral part.

[0054] In the embodiment shown, each of the first 74 and second 76 conductive strips comprises an oblong main portion 82 and an extension external 84. The external extension 84, for example square in shape, is arranged close to the third external edge 72. The main part 82 extends the external extension 84 continuously, towards the third internal edge 70.

[0055] As visible in [Fig. 3] for the first conductive strip 74, each end 86 of a wire of the first coil 52 is electrically connected to an internal end of the main part 82, respectively of the first 74 and of the second 76 conductive strips. By internal end, we mean an end of the main part 82 close to the third internal edge 70 of the peripheral part 66.

[0056] Similarly, as visible in [Fig. 3] for the first conductive strip 74, each end 88 of a wire of the second coil 54 is electrically connected to an external end of the main part 82, respectively of the first 74 and of the second 76 conductive strips. By external end, we mean an end of the main part 82 close to the external extension 84.

[0057] The ends 86, 88 of the wires of the first and second coils are for example welded or brazed onto the first 74 and second 76 conductive strips.

[0058] The first 52 and second 54 coils are thus electrically mounted in parallel on the first 74 and second 76 conductive strips.

[0059] The first 78 and second 80 connection cables, for example of the electrical braid type, are intended to electrically supply the electrical device 16. One end 90 of each of the first 78 and second 80 cables is electrically connected to the external extension 84, respectively of the first 74 and second 76 conductive strips. Said ends 90 are for example welded or brazed onto said external extensions.

[0060] In the embodiment shown, the electrical power supply device 16 further comprises a third 92 and a fourth 94 conductive strips, visible in [Fig. 1]. Each of the third 92 and fourth 94 conductive strips is formed from a layer of electrically conductive material deposited on the peripheral part 66. In the embodiment shown, the third 92 and fourth 94 conductive strips are arranged at the front face 60 of the membrane 50.

[0061] Preferably, each of the third 92 and fourth 94 conductive strips is formed from a layer of metal, for example copper, as detailed below.

[0062] The third 92 and fourth 94 conductive strips are arranged at a distance from each other on the peripheral part 66. More precisely, the third 92 and fourth 94 conductive strips are arranged opposite the main part 82, respectively the first 74 and the second 76 conductive strips, relative to the peripheral part 66. Each of the third 92 and fourth 94 conductive strips has substantially the same oblong shape as the corresponding main part 82.

[0063] Furthermore, the peripheral part 66 comprises four through orifices 96, arranged at each end of each of the third 92 and fourth 94 conductive strips. The through holes 96 connect the front 60 and rear 62 faces of the membrane 50.

[0064] In the embodiment shown, as visible in [Fig. 3], each end 86, 88 of the wires of the first and second coils is arranged in a through orifice 96, and said orifice 96 is filled with a plug 98 of electrically conductive material. The plug 98 is for example formed by a brazing material.

[0065] The conductive plug 98 electrically connects the end 86, 88 of the corresponding wire with each of the conductive strips 74, 76, 92, 94 located on either side of the orifice 96. Preferably, the conductive plug 98 is produced by tin soldering.

[0066] More specifically, the first 74 and third 92 conductive strips are electrically connected to each other by the conductive plugs 98, which fill the orifices 96 opening onto each of said first and third strips. Similarly, the second 76 and fourth 94 conductive strips are electrically connected to each other by the conductive plugs 98, which fill the orifices 96 opening onto each of said second and fourth strips.

[0067] Preferably, the peripheral part 66 and the conductive strips 74, 76, 92, 94 are covered with an electrically insulating layer (not shown), for example a varnish.

[0068] According to a variant not shown, the electrical device 16 further comprises at least one additional electrical or electronic component, fixed to the peripheral part 66 and electrically connected to at least one of the conductive strips 74, 76, 92, 94. The at least one additional electrical or electronic component is for example chosen from a thermal sensor, a motion sensor, an accelerometer or an LED.

[0069] The peripheral chassis 18 is assembled to the magnetic motor 12. In the embodiment shown, the peripheral chassis 18 has a substantially annular shape, arranged along the main axis X, and the first pole piece 22 of the magnetic motor 12 is inserted into said chassis.

[0070] Preferably, the peripheral chassis 18 comprises eyelets 100 intended to assemble the loudspeaker 10 with a support (not shown) such as a housing.

[0071] In the embodiment shown, the membrane 50 is connected to the chassis 18. More precisely, the suspension seal 19 is made of flexible material of the rubber or nitrile (NBR) type and has a crown shape defined by a fourth internal edge 102 and a fourth external edge 104. The fourth internal edge 102 is fixed to the peripheral part 66 of the membrane 50 at the level of the front face 60. The fourth outer edge 104 is fixed to the frame 18.

[0072] The rear partition 20, in the form of a disc, is assembled to the first internal edge of the bottom 28 of the first pole piece 22 of the magnetic motor 12, so as to close the space defined by the internal wall 30 of said first pole piece. The rear partition 20 is for example made of machined aluminum.

[0073] A method of manufacturing the peripheral part 66 and the conductive strips 74, 76, 92, 94 will now be described.

[0074] Preferably, said peripheral part and said conductive strips are formed from a printed circuit element, of the PCB (printed circuit board) type. Preferably, said element corresponds to the FR-4 standard. More precisely, said element comprises a composite plate of epoxy resin reinforced with glass fibers, each face of which is coated with a laminated layer of copper or alloy comprising mainly copper.

[0075] Preferably, the percentage by mass of glass fibers represents between 30% and 70%, more preferably between 40% and 60%, even more preferably close to 50%, of the total mass of the composite.

[0076] Preferably, the composite plate has a thickness of between 0.8 mm and 1.6 mm.

[0077] In order to produce the peripheral part 66 from an FR-4 type element, the first and second 74, 76 conductive strips on the one hand, and the third and fourth conductive strips 92, 94 on the other hand, are produced on the appropriate face of said element by removing the copper layer around the locations forming said conductive strips. Such removal is carried out by a known method of the chemical etching type.

[0078] Then, the third inner 70 and outer 72 edges are machined in said element and the holes 96 are drilled at the appropriate locations of the conductive strips.

[0079] The peripheral part 66 provided with the conductive strips 74, 76, 92, 94 is thus obtained. Said peripheral part 66 has in particular better thermal resistance than the peripheral part obtained by plastic injection, described in the aforementioned application FR2202297.

[0080] In order to form the loudspeaker 10, the peripheral part 66 is then assembled to the other elements described previously. The thermal resistance of the PCB-based peripheral part 66 facilitates the assembly by welding or brazing of said part with the ends 90 of the first 78 and second 80 connection cables.

[0081] The assembly of the ends 86, 88 of the coils 52, 54 with the orifices 96, as well as the formation of the conductive plugs 98, are also facilitated by the properties of the PCB. These steps can in particular be carried out in an automated manner, which reduces the manufacturing costs of the loudspeaker 10.

[0082] Having conductive strips 74, 76, 92, 94 on both faces of the peripheral part 66 improves electrical conduction and facilitates the operations of assembling said strips with the ends 86, 88 of the coils. The tin soldering to form the plugs 98 can in particular be carried out from any of the two faces of the peripheral part, in particular the front face.

[0083] The peripheral part 66 made from a PCB-type element has acoustic properties comparable to those of the peripheral part described in the aforementioned application FR2202297.

[0084] Furthermore, the properties of the PCB make it possible to easily integrate additional electrical or electronic components such as described above into the peripheral part, for example a thermal sensor, a motion sensor, an accelerometer or an LED.

Claims

1. Claims Loudspeaker (10) arranged along a main axis (X) and comprising: - a magnetic motor (12) defining a first air gap (42) and a second air gap (44) coaxial along the main axis, the second air gap being further from the main axis than the first air gap; - an assembly (14) axially movable relative to the magnetic motor, the movable assembly comprising: a rigid membrane (50), adapted to emit sound waves; a first coil (52) fixed to the membrane and located in the first air gap; a second coil (54) fixed to the membrane and located in the second air gap; and - a device (16) for supplying electricity to the first and second coils; the magnetic motor comprising a first pole piece (22), a second pole piece (24) and a permanent magnet (26); the first pole piece (22) comprising: a bottom (28) having the shape of a crown defined by a first internal edge and a first external edge; and an internal wall (30) and an external wall (32), extending respectively from the first internal and external edges, each of said internal and external walls being substantially cylindrical along the main axis (X); the second pole piece having a crown shape defined by a second internal edge (38) and a second external edge (40) and being substantially coplanar with ends (34, 36) of the internal (30) and external (32) walls of the first pole piece; the first air gap (42) being provided between the end (34) of the internal wall (30) and the second internal edge (38), the second air gap (44) being provided between the end (36) of the external wall (32) and the second external edge (40); characterized in that the membrane comprises a plate (66) of thermosetting resin reinforced with ceramic fibers and in that the electrical supply device comprises at least a first (74) and a second (76) strip deposited on said plate of thermosetting resin, each of the first and second strips being formed of a layer of electrically conductive material, each of the first and second strips being electrically connected to the first and second coils.

2. Loudspeaker according to claim 1, wherein the first and second strips (74, 76) are arranged on the same first face (62) of the thermosetting resin plate.

3. A loudspeaker according to claim 2, wherein the power supply device further comprises a third (92) and a fourth (94) strips deposited on a second face (60) of the thermosetting resin plate, opposite the first face, each of the third and fourth strips being formed of a layer of electrically conductive material, each of the third and fourth strips being electrically connected to the first and second coils.

4. Loudspeaker according to one of the preceding claims, in which the thermosetting resin of the membrane (50) is an epoxy resin.

5. Loudspeaker according to one of the preceding claims, in which the ceramic fibers of the membrane (50) comprise glass fibers.

6. Loudspeaker (10) according to one of the preceding claims, in which the ceramic fibers represent between 30% and 70%, preferably between 40% and 60%, more preferably close to 50% by mass of the reinforced thermosetting resin plate.

7. Loudspeaker (10) according to one of the preceding claims, in which the thermosetting resin plate reinforced with ceramic fibers has a thickness of between 0.8 mm and 1.6 mm, preferably between 0.8 mm and 1 mm.

8. Method for producing a loudspeaker (10) according to one of the preceding claims, comprising the following steps: - providing a printed circuit element, of the PCB type, comprising a composite plate of epoxy resin reinforced with glass fibers, each face of said plate being coated with a laminated layer of copper or copper alloy; - producing the first and second conductive strips (74, 76) on a first face of said printed circuit element, by removing the laminated layer of copper around locations forming said first and second conductive strips.

9. A method of producing according to claim 8, a loudspeaker according to claim 3, said method further comprising a step of producing the third and fourth conductive strips (92, 94) on a second face of the printed circuit element, by removing the laminated layer of copper around locations forming said third and fourth conductive strips.

10. Production method according to one of claims 8 or 9, further comprising a step of machining the composite plate of the printed circuit element.

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