EP2577992B1 - Acoustic loudspeaker - Google Patents

Description

TECHNICAL AREA

The invention relates to the field of acoustic loudspeakers, and more particularly compact speakers. It relates more particularly to a new architecture of loudspeakers that allows to very strongly reduce their thickness, that is to say, their dimension measured perpendicularly to the direction of emission of sound.

PRIOR TECHNIQUES

In general, a loudspeaker comprises a mobile membrane mechanically associated with a winding traversed by a current representative of the acoustic signal to be generated. The loudspeaker also comprises a magnetic field source, generally constant, which interacts with the current flowing through the winding to allow movement of the winding and therefore of the membrane.

Generally, the winding is disposed in a central zone of the membrane which is itself of generally conical shape, between polar parts that can channel the magnetic field generated by the magnetic field source, which is itself below of the membrane. It is understood that the stacking of these different elements is at the expense of the overall thickness of the speaker. In other words, when it is desired to make a conventional speaker of reduced thickness, it is necessary to reduce the angle of the cone of the membrane, or the dimensions of the magnetic field source, with inevitably a degradation. acoustic performance.

However, in some applications, it is necessary that the acoustic sources are the least thick possible. By way of nonlimiting example, the integration of loudspeakers in vehicle doors or in various furniture elements can be mentioned.

An example of a speaker of limited thickness is described in the documents JP53-129023 and EP 1 553 802 . In the document EP 1 553 802 such a loudspeaker comprises an annular magnetic assembly disposed on the periphery of the membrane. This set comprises several superimposed magnets, and whose magnetizations are radial for the central layer, and axial for the peripheral layers. Such an arrangement makes it possible to concentrate the field lines towards the inside of the ring formed by the magnetic assembly, but has the major disadvantage of limiting the height over which the magnetic field is useful. In other words, the excursion of the membrane is limited, which prevents the speaker from being effective at low frequencies.

SUMMARY OF THE INVENTION

• une membrane mobile ;
• une source de champ magnétique constant, orienté selon un plan sensiblement parallèle à la membrane,
• un bobinage mécaniquement solidaire de la périphérie de cette membrane, et interagissant avec le champ magnétique pour déplacer la membrane lorsque la bobine est parcourue par un courant alternatif

The invention therefore relates to an acoustic loudspeaker according to claim 1 which comprises:

• a mobile membrane;
• a source of constant magnetic field, oriented in a plane substantially parallel to the membrane,
• a winding mechanically secured to the periphery of this membrane, and interacting with the magnetic field to move the membrane when the coil is traversed by an alternating current

According to the invention, this loudspeaker is characterized in that the magnetic field source is formed of a set of magnetized elements disposed at the periphery of this membrane, around the winding. Each magnetized element has a cylindrical face facing the winding. The magnetic field generated by these magnetized elements has field lines that emerge from the full height of this inner face of the magnetic field source.

In other words, the invention consists in producing a loudspeaker by arranging the winding around the periphery of the membrane, and positioning the magnetic field source around the membrane, facing the winding. The magnetic field generated by the magnetic elements arranged in a ring is therefore radial, and acts directly on the winding without the need for a pole piece. The field lines generated by the magnets produce a homogeneous force (in direction and amplitude), on the winding, over the potential excursion of the membrane. Thus, the outer contour of the membrane, the coil and the magnetic field source are in the same plane, which provides a particularly compact and thin.

Thus, unlike conventional loudspeakers which comprise polar parts or complementary magnets channeling the magnetic field, the speaker according to the invention sees the magnetic field close naturally in the surrounding environment. This apparent disadvantage is offset by the fact that the mass of magnetic material required is globally important, since it occupies the entire periphery of the membrane. In addition, the gains in compactness form a largely preponderant advantage.

In practice, the shape of the membrane may be substantially flat, for example for applications in the low frequencies, or of more complex shape, for use at higher frequencies, where it is necessary to benefit from greater rigidity . This shape can for example be convex, concave, conical.

Advantageously, in practice, the various magnetized elements are arranged in a ring on the periphery of the membrane in a regular angular distribution, to balance the forces exerted on the coil.

Different geometries are possible for these magnetic elements. It is thus possible to have substantially rectilinear elements to form a polygonal global geometry. In this case, it is also possible for the winding to be wound into a polygonal shape corresponding to the shape of the magnetic field source, so as to maintain a substantially constant air gap. It is also possible to use magnetized elements having a curvature complementary to that of the winding, so as to provide a source which has a circular overall shape, and which is therefore at a quasi-constant distance from the winding.

In the same vein, the magnetized elements may have a face oriented on the side of the coil which is cylindrical, so as to maintain a constant air gap regardless of the relative position of the coil.

In practice, the magnetized elements can be mounted inside successive housings made in a frame, itself secured to a fixed point of the installation of the speaker.

According to another characteristic of the invention, the loudspeaker comprises a suspension member connected on the one hand to the frame of the magnetic field source, and on the other hand to the periphery of the membrane. This suspension element allows the displacement of the membrane relative to a fixed point.

Advantageously, the loudspeaker also comprises a second suspension member, also connected to the frame and the periphery of the membrane, but on the opposite side of the winding with respect to the first suspension member, so as to form a closed volume around the winding . In other words, the membrane is connected to the chassis of the loudspeaker by a set of two sheets defining an overall volume of substantially toroidal shape, inside which are enclosed the winding and the magnetic field source. Moisture tightness is thus ensured in particular vis-à-vis the winding. The presence of the second suspension member also makes it possible to improve the power handling by increasing the return force applied to the moving element. This second suspension member improves the guidance of the coil by creating a deformable parallelogram structure. Moreover, this double suspension makes it possible to balance the mechanical forces with respect to the two directions of movement of the moving equipment, as opposed to single suspension systems. However, the presence of this second suspension member is not mandatory because it adds weight to the moving equipment. This second suspension may therefore be omitted for loudspeakers in the ranges where the displaced mass considerations are preponderant.

SUMMARY DESCRIPTION OF THE FIGURES

• la figure 1 est une vue de dessus d'un haut-parleur conforme à l'invention, dans laquelle une partie d'un des organes de suspension a été masquée pour laisser apparaître la source de champ magnétique et le bobinage ;
• la figure 2 est une vue de détail d'une partie du châssis accueillant les éléments aimantés.
• la figure 3 est une vue en coupe transversale, et en légère perspective, du haut-parleur de la figure 1.
• La figure 4 est une vue en coupe transversale de détail d'un aimant et du bobinage en regard, sur laquelle les lignes de champ ont été représentées.

The manner of carrying out the invention, as well as the advantages which result therefrom, will emerge from the description of the embodiment which follows, in support of the appended figures in which:

• the figure 1 is a top view of a loudspeaker according to the invention, wherein a portion of one of the suspension members has been masked to reveal the magnetic field source and the winding;
• the figure 2 is a detail view of a part of the chassis hosting the magnetized elements.
• the figure 3 is a cross-sectional view, in slight perspective, of the loudspeaker of the figure 1 .
• The figure 4 is a detail cross-sectional view of a magnet and the facing coil on which the field lines have been shown.

DETAILED DESCRIPTION OF THE INVENTION

As already stated, the invention therefore relates to a loudspeaker which, as illustrated in FIG. figure 1 , essentially consists of a membrane 2 of circular shape and substantially flat geometry. This membrane also comprises a winding 3 of circular shape which is mechanically secured to the membrane. Around this winding 3, is the magnetic field source 4, which comprises a frame 5 supporting different magnetized elements 6. More specifically, the membrane 2 is made in a traditional manner with materials such as, among which may be mentioned, at examples: composite materials (combining glass, aramid or similar fibers, or carbon fibers), metals (especially aluminum, titanium and beryllium), cellulose pulp, polymers such as polypropylene, polyethylene terephthalate (Mylar®), or acrylonitrile butadiene styrene (ABS), or even synthetic textiles.

The shape of the membrane may be flat for use in the low frequencies, or even more complex (concave, convex, conical) to have a superior rigidity appreciable for operations at higher frequency.

The membrane 2 is peripherally extended by a zone 8 accommodating the coil 3 which is wound circularly around the periphery of the membrane 2. The wire used for the winding is of conventional characteristics, and for example based on various electrically conductive materials, and in particular copper, aluminum, and other alloys. The wire section can be optimized to minimize the overall resistance of the coil.

Complementarily, the magnetic source 4 consists essentially of magnetized elements 6 in the form of segments angularly distributed on the periphery of the coil 3. In practice, these elements 6 may be based on very strong magnetization materials, to compensate the absence of pole piece, and the fact that it is the creepage of these magnetized elements 6 which pass through the coil 3. The magnetization of these elements 6 is therefore chosen so that it is oriented radially, and passes through the winding 3 perpendicularly substantially along the plane of the membrane 2. Materials such as neodymium or the like have a magnetization compatible with these applications.

Different arrangements can be adopted to limit the gap, and optimize the performance of the speaker. Thus, as illustrated in figures 3 and 4 each of the segments has a face 10 which is curved, more precisely cylindrical, to be located at a constant distance from the winding. This face is cylindrical, that is to say that the distance to the coil 3 remains the same regardless of the position of the latter when moving with the membrane.

As illustrated in figure 4 the field lines 20 emerge from the flat face 10 of the magnetized element. These field lines are oriented inwardly of the loudspeaker in the direction of winding 3. In this way, during its movements, the coil 3 positively influenced by the magnetic field, including in its extreme positions 3 'which is shown by the dotted winding. Over the entire height of the face 10, the field lines 20 have an overall orientation in the direction of the winding, with a sufficiently homogeneous distribution, which helps to limit the phenomena of distortions.

In a particular embodiment illustrated in figure 2 these curved magnetized elements 6 are arranged inside a frame 4, which has appropriate housings 12. These housings 12 are formed between radial partitions 15 extending between two adjacent magnet elements 6 . Means for holding the magnetized elements may be arranged, for example in the form of a bulge 16 located at the end of the partition 15, and of complementary shape to a recess 17 formed on the short sides of the magnetized elements 6. In this way, a quasi-continuity of the magnetic field generated by the magnetized elements 6 is maintained at the boundary between two successive elements. The rear face 19 of the magnetized elements may be flat or curved depending on the type of material used. A wall 18 facing the rear face 19 of the magnetized elements, can advantageously improve the maintenance of these elements 6 on the frame 4. The frame 4 has a peripheral portion 20 for fixing the loudspeaker on its support.

According to another characteristic of the invention, the loudspeaker also comprises suspension members 30, 31 illustrated in FIG. figure 3 . Each suspension member 30,31 has an inner portion 32,33 which is substantially circular in shape and secured to one of the faces 34,35 of the membrane 2. The opposite end 36,37 forming the outer periphery of the 30.31 suspension member is itself secured to the frame 4 by various suitable means such as a commitment in a groove made for this purpose or a bonding, or any other suitable mechanical device. The portion 38,39 of the suspension member 30,31 located between its two ends 32,33; 36,37 adopts a curved shape, to generate a space 40 encompassing the magnetic field source and the winding. The shape of this central portion 38,39 is chosen to allow the maximum deflection of the membrane 2 without generating mechanical stress. Other forms, for example rectangular, can also give satisfaction. Materials conventionally used to make the suspensions may be employed, such as coated textiles or the like.

It follows from the foregoing that the loudspeaker according to the invention has multiple advantages, and in particular that of having a particularly reduced thickness with respect to its diameter. It can therefore be advantageously used for applications where congestion constraints are important, and while maintaining good acoustic performance, especially in low frequencies, thanks to the ability to move a relatively large volume of air.

Claims (7)

1. An acoustic loudspeaker (1) comprising:

   - a mobile membrane (2);

   - a magnetic field source (4),

   - a winding solidly attached to the periphery of said membrane (2), wound circularly around the outer periphery of the membrane (2) and interacting with the magnetic field to displace the membrane (2) when it conducts an A.C. current,

   characterized in that

   - the magnetic field source (1) is formed of a set of magnetized elements (6) distributed consecutively around the outer periphery of the winding (3), the magnetization of which is oriented radially and passes through the winding perpendicularly substantially along the plane of the membrane,

   - each magnetized element is curved and has a curved surface opposite to the winding, so that this curved surface is at a constant distance from the winding,

   - the magnetic field generated by said magnetized elements (6) has field lines emerging from said curved surface with a homogeneous distribution over the entire curved surface and an overall orientation towards the winding.
2. The loudspeaker of claim 1, characterized in that the membrane (2) is substantially planar.
3. The loudspeaker of claim 1, characterized in that the membrane is concave or convex.
4. The loudspeaker of claim 1, characterized in that the magnetized elements (6) are arranged in a ring around the periphery of the membrane (2).
5. The loudspeaker of claim 1, characterized in that it comprises a frame and that the magnetized elements (6) are assembled in consecutive housings (12) formed in the frame (4).
6. The loudspeaker of claim 1, characterized in that it comprises a suspension member (30) connected on the one hand to the frame (4) of the magnetic field source, and on the other hand to the periphery of the membrane (2).
7. The loudspeaker of claim 6, characterized in that it comprises a second suspension member (31), also connected to the frame (4) and to the periphery of the membrane (2), but on the opposite side of the winding with respect to the other suspension member (30), to form a closed volume (40) around the winding.

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