HUP0105358A2 - Vibration exciter for creating bending wave vibration - Google Patents

Abstract

The talm ny t rgya oscillating coil vibration generator (1) for exciting the bending wave membrane. Its essence is that it contains a magnet that defines a cylindrical ring-shaped air gap, the oscillating coil unit (5) arranged in the cylindrical ring-shaped air gap, a fastening element (10) designed to strengthen the vibration generator (1) on the membrane, to which fastening element (10) the oscillating coil unit (5) is solidly attached, further arranged on the fastening element (10), connected to the magnet and in the cylindrical ring-shaped air gap, the oscillating coil unit (5) moves axially and provides flexible suspension in such an arrangement that the planar projection of the flexible suspension falls within the plane projection of the fixing element (10) or has the same extension as the latter.

Description

Pöl Ü5358. _; · _:: · / ο4 • Μ (Α2)

Voice coil transducer with bending wave diaphragm *

FOR EXCITATION

The present invention relates to vibration transducers, more particularly to voice coil vibration transducers that excite bending wave vibrations in bending elements to produce an acoustic output signal. Accordingly, the vibration transducers of the invention can be used as excitation units for resonant panel loudspeakers. Resonant panel loudspeakers are described, for example, in WO 97/09842; such devices are known in the art as distributed mode (DM) loudspeakers (DML).

EP-A-0,160,478 discloses a driving unit for a piston-type cone loudspeaker, which has a so-called reinforcing ring incorporated in the voice coil unit for connecting the rear suspension pin to the coil body and for connecting the piston-type conical diaphragm to the voice coil. In known voice coil vibration transducer assemblies used for driving resonant panel loudspeakers, a magnetic circuit can be connected to the voice coil unit by means of a flexible suspension element arranged between the flange-like extension of the outer shoe and the outer diameter of the voice coil. The said flexible element can be made in a known manner from a fabric from which a pleated region is formed, or from any suitable flexible or elastic material.

The disadvantage of such an arrangement is that, since the edge is located close to the resonant panel element, it creates a cavity that causes the enclosed air to excite cavity modes in the audible frequency range. Said cavity modes radiate from the open perimeter of the edge and produce an undesirable acoustic output signal that is extremely difficult to absorb.

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-2difficult. Some improvement can be achieved by sealing the area between the lug and the panel and not providing an air gap in the voice coil space, but even in this case the outer parts of the rim still excite cavity modes in the audible frequency range. ···

The centralization of the voice coil in the cylindrical air gap of the magnet is critical to performance, and apart from the efficiency degradation caused by large air gaps, it can be clearly demonstrated that extremely small amounts of voice coil misalignment or lack of uniaxiality lead to oscillation in the air gap, which is relatively undamped in the case of single-suspended vibrating transducer assemblies.

Equally important in the design of efficient transducers is the air gap size, which cannot be easily reduced unless the lateral deflection of the voice coil is severely limited. Foam suspensions allow equal deflection in the vertical and lateral directions, thereby increasing lateral stiffness to achieve proper coil centering, which increases the stiffness of the suspension in the active plane of deflection, thus limiting low-frequency extension.

It is clear that for certain applications, miniaturized vibration transducers require a suspension that allows free movement in and out of the air gap, but also allows extremely tight clearance in other directions to reduce the air gap size and increase efficiency.

Suspension in two planes leads to a piston-like motion with minimal tendency to swing. However, for DML-type operation, this basic requirement is slightly modified. The need for the transducer to ride the reflections of the bending waves it generates requires that the suspension located at the rear of the voice coil (behind the magnet) be much more flexible laterally than the suspension located in front of the magnet, so that the lateral deflection of the voice coil riding the reflected bending wave does not try to push the cup-shaped shoe sideways. For the same reason, the front suspension should be located as close to the resonant panel element as possible.

The invention provides, for example, a resonant, bending wave member:

• · we have implemented a voice coil vibration transducer for excitation, which comprises a magnetic circuit defining a cylindrical annular air gap, a voice coil unit arranged in the cylindrical annular air gap, a fixing element designed to fasten the vibration transducer to the membrane, to which fixing element the voice coil unit is firmly attached, and furthermore an elastic suspension arranged on the fixing element, connected to the magnetic circuit and ensuring the axial movement of the voice coil unit in the cylindrical annular air gap in such an arrangement that the planar projection of the elastic suspension falls within the planar projection of the fixing element, or has the same extent as the latter. The planar projection of the elastic suspension preferably falls within the planar projection of the magnet. Furthermore, the vibration transducer is preferably inertial.

The magnetic circuit preferably has an inner shoe coupled with a magnet and a cup-shaped outer shoe. The outer shoe preferably has an edge formed substantially without a rim. The edge of the outer shoe is preferably conical, terminating in a sharp tip.

Preferably, the fastening element has the same extension as the outer shoe, and the fastening element preferably has a ring or disc-like shape.

Preferably, the suspension is entirely located within the wall thickness of the outer shoe. The suspension is preferably formed to provide a coupling between the inner shoe and the fixing element fixed inside the voice coil unit. In another possible embodiment of the vibration transducer according to the invention, the suspension is formed to provide a coupling between the cup-shaped shoe and the fixing element.

The elastic suspension is preferably formed in the form of elements of elastic material fixed between the axially extending legs of the fastening element and the cutouts formed in the outer shoe. In another possible embodiment, the suspension preferably has an elastic element arranged in the axis of the disc-shaped fastening element and the inner shoe. In a further possible embodiment

In the case of the -4-shape, the elastic suspension preferably has an annular spring element. The : ·’· annular spring element preferably has arms, the free ends of which are attached to the outer circumference of the outer shoe. i*:*:

The outer shoe preferably has a separable disc-like back plate and a tubular ·’·' shaped part. The vibrating transducer according to the invention preferably has a second elastic suspension connected between the voice coil unit and the magnet in a position axially offset from the suspension. The back plate and the tubular part together define a recess for receiving the second suspension. Furthermore, the second elastic suspension is advantageously designed in the form of an elastic annular suspension, the second suspension is preferably arranged in a circular groove on the magnet.

The voice coil unit preferably comprises a voice coil wound on a bobbin. Preferably, the elastic suspension has electrical contacts formed on the voice coil unit connecting it to a power supply and thereby on the exciter.

By arranging the suspension in a plane perpendicular to the panel element, the presence of a suspension retaining flange on the cup-shaped shoe is eliminated, thus avoiding the entrapment of residual air. Preferred embodiments of the voice coil transducers of the invention reduce the potential edge areas which, if present, lead to the occurrence of undesirable cavity modes.

The invention will be described in detail below with reference to the attached drawing, where the

- Figure 1 is a perspective exploded partial view of one possible exemplary embodiment of an inertial voice coil vibration transducer for feeding bending waves into a panel loudspeaker;

- Figure 1a is a perspective view of the vibration transducer illustrated in Figure 1;

- Figure 2 illustrates another possible exemplary embodiment of an inertial voice coil transducer for feeding bending waves into a panel loudspeaker;

...· ·..· ·..· ··/· .-5-

- Figure 2a is a cross-section of the vibration transducer shown in Figure 2· a : ’ · ·

Figure 2b is a cross-section substantially identical to that illustrated in Figure 2a, but showing a modified suspension;

- Figure 3 is a cross-section of a possible further exemplary embodiment of an inertial '·’· voice coil vibration transducer for feeding bending waves into a panel loudspeaker; the

- Figure 4 is a cross-section of a possible further exemplary embodiment of an inertial voice coil vibration transducer for feeding bending waves into a panel loudspeaker;

- Figure 5 is a cross-section of a possible further exemplary embodiment of an inertial voice coil vibration transducer for feeding bending waves into a panel loudspeaker;

- Figure 6 is a cross-section of a possible further exemplary embodiment of an inertial voice coil vibration transducer for feeding bending waves into a panel loudspeaker; while the

- Figure 7 is a cross-section of a possible further exemplary embodiment of an inertial voice coil vibration transducer for feeding bending waves into a panel loudspeaker.

Figures 1 and 1a show an inertial voice coil transducer 1 for generating bending wave vibrations in a panel element forming a loudspeaker, for example a resonant panel element of the type described in European Publication No. WO 97/09842. The vibration transducer 1 in question comprises a magnetic circuit with 2 magnets arranged between a disk-like inner lug 3 and a cup-like outer lug 4 defining a cylindrical annular air gap (not shown in the drawing), a voice coil unit 5 with a tubular coil body 6 carrying a grid-wound coil 7, and furthermore a suspension and fixing component 8, to which the voice coil is firmly attached - in order to ensure its axial deflection in the cylindrical annular air gap - for the purpose of connecting the magnet and the voice coil unit 5, and furthermore with which the vibration transducer 1 is attached to the resonant panel element (not shown separately in the drawing) awaiting excitation.

...· ·..· ··/· .-6As shown in Figures 1 and 1a, the cup-like shoe 4 is provided with three openings in the form of cutouts 9, spaced apart from each other, on its circumference. The suspension and fastening unit 8 is a fastening or mounting ring forming a fastening element 10 having dimensions substantially equal to the inner and outer diameters of the wall of the cup-like shoe 4.

The ring forming the fastening element 10 is provided with three axially extending projections or legs 11, which legs 11 form ears for attaching rectangular, flexible, for example rubber-like, suspension elements 12. The arrangement is such that the legs 11 forming the ears and the suspension elements 12 fit into the cutouts 9 formed in the cup-shaped shoe 4, and the suspension elements 12 in question are connected to the walls of the said cutouts 9 along the faces of the suspension elements 12 opposite the faces of the faces of the suspension elements 12 connected to the legs 11.

As a result of this design, the suspension is located within the thickness of the wall of the cup-like shoe 4, so that it is unnecessary to provide the shoe 4 with a rim extending along its circumference, thus reducing the difficulty described above.

The new embodiment of the vibration transducer 1 according to the invention illustrated in Figures 2 and 2a is generally very similar to the embodiment shown in Figure 1, since the vibration transducer 1 in question also includes a magnetic circuit with 2 magnets arranged between a disk-like inner lug 3 and a cup-like outer lug 4 in order to define a cylindrical annular air gap 20, a voice coil unit 5 carrying a grid-wound coil 7 and having a tubular coil body 6, and a suspension and fixing component 8. However, in the embodiment illustrated in Figures 2 and 2a, the suspension has a spring element 13, for example in the form of a tension ring 14 made of stainless steel, attached to the mounting ring forming the fastening element 10, the pieces of the tension ring 14 defining three arcuate spring arms 15, equidistant from each other, the free ends 16 of which spring arms 15 are attached to the edge of the cup-shaped shoe 4. The spring element 13 is schematically illustrated in Figure 2a.

...· ·..· ·..· ·..· ··/· .-7As in the embodiment illustrated in Figures 1 and 1a, the voice coil unit 5 is firmly attached to the ring forming the fixing element 10 in this embodiment, so that the tension ring 14 forms a suspension between the voice coil unit 5 and the cup-like shoe 4 of the magnet. As shown in Figure 2, the spring arms 15 are located on the outer edge of the tension ring 14, but it is obvious to a person skilled in ^the art that the said spring arms 15 can be located on either the inner or outer edge of the tension ring 14.

As shown in another embodiment of the vibration transducer 1 according to the invention, illustrated in Figure 2b, the spring element 13 can also form a suspension between the inner shoe 3 and a disc 30 attached to the coil body 6. The tension ring 14 is arranged concentrically on the shoe 3; for example, an opening (not shown in the drawing) can be formed in the tension ring 14, into which the projection (also not shown in the drawing) formed on the shoe 3 can penetrate. Since the tension ring 14 is arranged concentrically inside the coil body 6 and is tightly fitted into the coil body 6, the centering achieved in this way is also transmitted to the coil 7. As a result, the vibration transducer 1 shown in Figure 2b has a self-centering property, and the lateral compliance of the suspension will be sufficiently small to allow the air gap 20 to be formed with a relatively small size.

Figure 3 shows a possible further embodiment of the vibration transducer 1 according to the invention, similar to that illustrated in Figure 2b, in cross-section. This embodiment has a cup-like shoe 4 formed of a separable disc-like back plate 4a and a tubular part 4b, which together define 23 recesses for 17 pins at the rear of the coil 7, in order to provide a two-plane suspension with different degrees of lateral compliance in the front and rear planes, which can be assembled in two pieces.

This latter design has two additional features consistent with the simple self-centering design, namely:

(1) in order to ensure easy assembly and disassembly of the vibration transducer 1 according to the invention, it is possible to design the spring element 13 of the shoe suspension 3 in a form that can be attached to the disc 30 with a bayonet lock, and (2) the electrical connectors of the coil 7 can be connected to the electrical contacts 16' arranged on the disc 30, which, when the vibration transducer 1 comes into contact with the surface of the panel element, could electrically contact the electrically conductive contact points of the loudspeaker panel (also not shown in the drawing) in a vibration transducer mounting-contact structure (not shown in the drawing). As a result of such a design, the connection of the delicate coil wire to an external cable or earpiece could be eliminated, and the balance of the magnet would be improved. Furthermore, the design in question would result in the elimination of the need for wires leading to or passing through the panel element, as the electrical conductors could be embedded or incorporated into the outermost layer of the panel element in the form of a thin copper plate or a layer of electrically conductive paint.

The adoption of the principle that the cup-like shoe 4 can be assembled from several pieces opens up the possibility of realizing extremely compact, integrated suspensions, especially in the case of small vibration transducers. The vibration transducer 1 illustrated in Figure 4 is generally identical to the embodiments shown in Figures 2b and 3. Figure 4 also shows how the two circular grooves formed in the magnet 2 (but not separately indicated in the drawing) allow the use of a simple two-plane suspension, in which planar, flexible suspension rings 19 are inserted between the magnet 2 and the coil body 6. This design takes advantage of the presence of a wider cylindrical annular air gap 24 between the magnet 2 and the inner shell of the tubular part 4b. It should be noted here that the shoe 3 and the back plate 4a are both provided with a groove for centering the magnet 2, as a result of which the entire vibrating transducer 1, including the coil 7, has a self-centering property. In this latter embodiment, the front suspension is provided by a soft foam element 18 arranged concentrically on the disc 30 and the shoe 3.

Figure 5 illustrates another possible variant of the vibration transducer 1 according to the invention, outlined in Figure 4, which has a conventional, unmodified - i.e. free of circular grooves - magnet 2. In this embodiment

The cup-shaped shoe 4 is composed of three self-centering pieces 4a', 4b' and 4c', for example made of steel, which are separated from each other precisely at the suspension grooves that allow the suspension rings 19 to be pre-mounted on the bobbin case 6. In this embodiment, the uppermost, tubular self-centering piece 4c' is used to close the shoe 4 and is designed with a sharp tip 21 in order to reduce acoustic cavity phenomena. The actual air gap 20 is also created only where it is necessary for centering with the self-centering pieces 4a', 4b' and 4c'.

The further embodiment of the vibration transducer 1 according to the invention, illustrated in Figure 6, is generally similar to the embodiment illustrated in Figure 5. This design can be used for smaller vibration transducers, although the design can also be used for larger vibration transducers where the strong lateral centering resulting from the distance between the front and rear suspension would facilitate the intended design. The maximum oscillation of the coil in the shoe 4 must be limited in order to prevent the front support of the shoe 4 from colliding with the panel. In practice, a foam stop element 18 can be used for this purpose.

As shown in Figure 7, the structure of the embodiment of the vibration transducer 1 according to the invention, as shown in Figure 6, can be further simplified by sacrificing part of the space occupied by the magnet 2 and by placing an annular foam rear suspension 22 along the circumference of the magnet 2, which is also brought into contact with the inner shell of the coil body 6. The appropriate choice and tolerance of the foam allows the voice coil unit 5 to be simply pressed into place and to center itself at the rear. The front part of the voice coil unit 5 would be centered by the foam element 18 of the shoe 3 concentrically arranged on the disc 30 and on the shoe 3. The disc 30 is held in this embodiment by the ring forming the fixing element 10.

Claims (20)

...· *..· ·..· ··/·.. · -10PATENT CLAIMS V i 1. A voice coil transducer for excitation of a bending wave diaphragm, characterized in that it comprises a magnetic circuit defining a cylindrical annular air gap (20), a voice coil unit (5) arranged in the cylindrical annular air gap (20), a mounting element (10) designed to mount the vibration transducer (1) on the diaphragm, to which mounting element (10) the voice coil unit (5) is firmly attached, and furthermore an elastic suspension arranged on the mounting element (10), connected to the magnetic circuit and ensuring the axial movement of the voice coil unit (5) in the cylindrical annular air gap (20) in such an arrangement that the planar projection of the elastic suspension falls within the planar projection of the mounting element (10) or has the same extent as the latter. 2. A vibration transducer according to claim 1, characterized in that the magnetic circuit has an inner shoe (3) coupled to a magnet (2) and a cup-like outer shoe (4). 3. A vibration transducer according to claim 2, characterized in that the outer shoe (4) has an edge formed substantially without a rim. 4. A vibration transducer according to claim 3, characterized in that the edge of the outer shoe (4) is conically formed, ending in a sharp tip (21). 5. The vibration transducer according to any one of claims 2-4, characterized in that the fixing element (10) has the same extension as the outer shoe (4). 6. Vibration transducer according to any one of claims 2-5, characterized in that the suspension is located entirely within the wall thickness of the outer shoe (4). 7. A vibration transducer according to any one of claims 1-6, characterized in that the fixing element (10) has a ring shape. 8. A vibration transducer according to any one of claims 2-6, characterized in that the suspension is designed to ensure coupling between the inner shoe (3) and the fixing element (10) fixed inside the voice coil unit (5). 9. A vibration transducer according to any one of claims 2-8, characterized in that the elastic suspension is axially mounted on the fixing element (10). -11 is formed in the form of elements (12) of elastic material fixed between the legs (11) extending from the outer shoe (4) and the cutouts (9). *·.*» • · 10. A vibration transducer according to any one of claims 1-7, characterized in that the fixing element (10) has a disc-like shape. *·· 11. A vibration transducer according to claims 2 and 10, ^{characterized} in that the suspension has an elastic element (18) arranged in the axis of the disk-like fixing element (10) and the inner shoe (3). 12. A vibration transducer according to any one of claims 1-11, characterized in that the elastic suspension has an annular spring element (13). 13. A vibration transducer according to any one of claims 1-12, characterized in that the elastic suspension has electrical contacts (16') formed on the voice coil unit (5) connecting it to a power supply and thereby exciting it. 14. A vibration transducer according to any one of claims 1-13, characterized in that it has a second elastic suspension connected between the voice coil unit (5) and the magnet core, in a position axially offset from the suspension. 15. A vibration transducer according to claim 14, characterized in that the second elastic suspension is in the form of an elastic annular suspension. 16. A vibration transducer according to claims 2 and 15, characterized in that the second suspension is arranged in a circular groove on the magnet (2). 17. A vibration transducer according to any one of claims 2-16, characterized in that the outer shoe (4) has a separable disc-like back plate (4a) and a tubular part (4b). 18. A vibration transducer according to claims 14 and 17, characterized in that the back plate (4a) and the tubular part (4b) together define a recess (23) receiving the second suspension. 19. The vibration transducer according to any one of claims 1-18, characterized in that it is inertial. - 12··♦ Μ) « ·» · » »1 . .· ^u ..'- -.* '·* ., 20. A vibration transducer according to any one of claims 1-19, characterized in that the planar projection of the elastic suspension falls within the planar projection of the magnet core. i’:’i Patent and Trademark Office Ltd. Our file number: 94896-8071/SZT-Ko Our administrator: Zsolt Szabó