EP1734787B1 - Inertial loudspeaker without diaphragm - Google Patents

Description

The invention relates to the field of loudspeakers and loudspeakers used as sound transducer elements.

The invention relates in particular to the loudspeakers equipping home entertainment chains or theaters of theaters. But we could consider applying it to the radio channels equipping for example motor vehicles.

The choice of loudspeakers must, to reproduce the sound environment over a wide band of frequencies with sufficient fidelity and power, take into account the conditions of their fixation and their installation.

A loudspeaker typically includes a motor and a motor-driven diaphragm to vibrate to reproduce sounds in a certain band within the audible range between 30 and 16000 Hertz. The assembly is held together and protected by a housing.

The membrane is generally circular. Being fixed by its periphery to the housing and controlled at its center by the motor coil, it vibrates preferably at a frequency F corresponding to a vibration having a belly in the center and a node on its periphery, the belly and the distant node being at less than a quarter wavelength λ of the vibration.

c étant la vitesse du son.It is shown that the diameter D of the membrane corresponding to the vibration frequency F of wavelength λ is such that: $$\mathrm{D}=\mathrm{vs}/2*\mathrm{F}=\mathrm{\lambda }/2$$

where c is the speed of sound.

In order to widen the bandwidth of the membrane around the frequency F, on the one hand, a non-resonant material, such as paper, is provided and, on the other hand, the membrane is conformed so that it has at its periphery a ripple to isolate the best of the pavilion of the case and to blur the position of the nodes.

To cover a whole band of frequencies, one is moreover obliged to use loudspeakers of different diameters D1, D2,... Corresponding to central frequencies F1, F2, .... One thus defines loudspeakers called tweeters (D <8 cm), mediums (8 cm <D <16 cm), low (16 cm <D <25 cm), subwoofers (D> 25 cm), .... To reduce the volume, they can be arranged coaxially.

In addition, and regardless of the installation conditions, it must be ensured that the entire frequency band, thus covered by means of a plurality of loudspeakers, is diffused throughout the listening volume, for example a living room or office to serve as an auditorium, possibly in stereo, which doubles the number of speakers or speakers needed. It is this problem of diffusion which is solved by the invention, as will be seen below.

This is curiously not the one that the inventor sought to solve, but another problem in the very different setting of the realization of a device for therapy by body vibrations, usable in the medical field, in reverse operation of the stethoscope, to treat visceral organs affected by mechanical dysfunctions (incontinence, constipation, etc.).

To solve his medical problem, the inventor had the idea of drawing, in the know-how of at least twenty-five years ago, the solution then aborted of the problem of diffusion. This solution consisted of what can be called a speaker without a membrane.

This loudspeaker included an electromagnetic motor with a cylindrical magnetic core and an induction coil surrounding the core and secured to a set of two plates: a flexible suspension and centering plate, ensuring the radial positioning of the coil, around of the core while allowing the axial vibration of the coil and a rigid plate intended to be fixed for example to a partition of the auditorium. This last plate once fixed, it is the partition which replaces the membrane. But the performance of the engine and the acoustic quality of the speaker were far too inadequate. For a 35-watt motor, the sound was of poor quality and very low level, about 60 dB.

Seeking to realize a device for vibrating body tissue for its medical application, the inventor incidentally perfected the above device and then understood all its interest in the acoustic field.

The document US6618487 discloses a device for an excitation element having the capacity to support and propagate a vibratory energy supply comprising an engine coil assembly having a coil integral with a tubular coil, a magnet assembly arranged concentrically with relative to the motor coil assembly, and means suspending the magnet assembly for axial displacement relative to the motor coil assembly.

The document JP58,218296 describes a loudspeaker type acoustic device.

The document EP0553525 discloses a speaker body adapted to freely oscillate up and down in response to a variation of the magnetic field of a solenoid coil current conductor.

The document US2002 / 027999 discloses an acoustic device comprising an element extending transversely with respect to its thickness and capable of sustaining flexural waves.

The document US2001 / 017927 describes a flat panel incorporating several identical speakers.

Thus, the invention relates first of all to a speaker without a membrane, comprising a housing, a motor comprising a magnetic core and, around said core, an induction coil secured to a first rigid plate for transmitting vibrations to a support, the first plate being secured to the housing by means of flexible suspension means, the suspension means being arranged to ensure an elastic suspension of the first rigid plate to the housing, speaker characterized in that the means of flexible suspension comprise a second suspension plate and radial positioning of the coil.

In addition, the flexible suspension means (115, 116, 117; 115, 116, 120) comprise resilient pads (116) between the second suspension plate (115) and the first transmission plate (114), said elastic pads (116) being fixed in peripheral portions (P1, P2) of the plates (115, 114). Pads (117) for attaching the suspension plate (115) to the housing (110) are fixed at the central portion (II) of the suspension plate (115).

A material is elastic as long as the force applied on the material and the displacements due to the deformations of this material, which result, remain proportional. This linearity property particularly promotes the acoustic resonance of the material at a vibrational stress.

The device of the prior art therefore already had a second flexible Bakelite plate, but which is a material which, like the paper used for the membranes, does not exhibit any acoustic quality or resonance and which, moreover, does not is not elastic. In addition, its mission is to center the coil while allowing the vibrations to spread, why would it have this quality, if not at the risk of introducing a parasitic resonance in passing?

Thanks to the elasticity of the suspension from the rigid plate to the housing, the vibrations generated by the coil propagate more freely between the motor and the plate or, more exactly here, between the plate and the motor.

In the preferred embodiment, the second radial positioning plate of the coil is of elastic material.

Advantageously, the second plate is made of composite material, for example epoxy resin reinforced with fiberglass or reinforced carbon or any other material capable of acoustic resonance.

Preferably still, the second plate, comprising a central portion and a peripheral portion, is perforated gills delimiting said central and peripheral portions and which are limited by bridges "hinges" giving them the ability to vibrate with respect to the other.

In the most preferred embodiment, the core of the coil has an axial symmetry, the two vibration and suspension transmission plates are substantially perpendicular to the axis of the core, the elasticity of the suspension means acting according to this axis, and the suspension plate is rigid in the direction perpendicular to this axis.

The speaker of the invention, once fixed for example on a partition, with a motor of 35 watts, provides an excellent noise level of 90 dB and high quality.

The invention also relates to an auditorium enclosure partition on which are fixed a plurality of loudspeakers according to the invention defined to transmit their vibrations in respectively different frequency bands.

Finally, the invention also relates to a body vibration therapy device comprising a loudspeaker according to the invention.

• la figure 1 est une vue en coupe axiale d'une première forme de réalisation du haut-parleur selon l'invention ;
• la figure 2 est une vue en coupe axiale d'une seconde forme de réalisation du haut-parleur selon l'invention ;
• la figure 3 est une vue en perspective éclatée des plaques de transmission et de suspension équipant le moteur du haut-parleur, avec le dispositif de fixation sur une cloison ;
• la figure 4 est une vue en coupe du haut-parleur de la figure 2, selon la ligne IV-IV, montrant les plaques vues de dessus, sans le dispositif de fixation et
• la figure 5 est un schéma de montage sur une surface support du moteur de haut-parleur selon l'invention.

The invention will be better understood with the aid of the following description of two embodiments of the speaker without membrane according to the invention, with reference to the appended drawing, in which:

• the figure 1 is an axial sectional view of a first embodiment of the loudspeaker according to the invention;
• the figure 2 is an axial sectional view of a second embodiment of the loudspeaker according to the invention;
• the figure 3 is an exploded perspective view of the transmission and suspension plates fitted to the loudspeaker motor, with the fixing device on a partition;
• the figure 4 is a sectional view of the speaker of the figure 2 along line IV-IV, showing the plates seen from above, without the fixing device and
• the figure 5 is a circuit diagram on a support surface of the loudspeaker motor according to the invention.

With reference to the figure 1 , the loudspeaker 100 comprises a cylindrical housing 110 of axis 1 protecting a motor 111. The motor 111 comprises a cylindrical magnetic core 112 of axis 1 integral with the housing 110 at its upper base. The upper base of the housing and the core are pierced with a coaxial cylindrical bore 1101 to pass an electrical connection cable 118. The cable 118 is secured to the housing by means of an elastic seal 119 cable pass thus closing the bore 1101 .

The lower base 1103 of the housing 110 is pierced with a circular opening 1102 centered on the axis 1 so as to pass an induction coil 113 freely sliding without contact along the axis 1 along the core 112 and receiving signals representative electric sound thanks to connection 118.

The coil 113 is free in its upper part and is integral with a first rigid plate 114 substantially square and perpendicular to the axis 1. This plate 114 comprises fixing means on a support, not shown in this figure, but will be described later. The plate 114 is a vibration transmission plate.

The plate 114 is also secured to the housing 110 by means of flexible and resilient suspension means that keep the induction coil 113 in place relative to the core 112, while allowing it to vibrate under the action of the induction forces created by the electrical signals mentioned above.

These suspension means comprise a second plate 115 substantially parallel to the first plate 114, plate 115 which is a plate for suspending and positioning the coil radially, pads 116 for elastic fixing of the first plate 114 to the second plate 115, and fastening means 117 (120 on the figure 2 ), the second plate 115 to the housing 110. These means may be rubber pads 117, as the pads 116 for fixing the two plates together.

To make the second plate 115, a composite material card was used, here made of epoxy resin reinforced with fiberglass, but it would have been possible to choose the reinforced carbon, or any other material allowing a plane rigidity and a perfectly elastic axial behavior favoring the acoustic resonance.

This card is arranged to vibrate along the axis 1 and yet remain rigid perpendicular to this axis, as will be explained later.

The description above corresponds to the first embodiment of the figure 1 . The figure 2 corresponds to a second embodiment not distinguishable from this first form (the homologous elements bear the same references) as by the choice of a crown here in PVC 120 in place of the pads 117 and by the addition of a crown of foam 121 between the two plates making it possible to isolate the motor 111 from the external environment and to limit the intrusion of dust between the core 112 and the coil 113.

The set of suspension means will now be described more precisely with reference to the Figures 3 and 4 .

The second suspension plate 115, substantially of the same shape as the first plate 114, is perforated according to four louvers a, b, c, d circular along a quadrant of a common circle of axis 1 but which remain separated by bridges, or connecting zones, e acting as hinges increasing the elasticity of the plate 115. The gills a, b, c, d divide the plate 115 into a central portion I1 and a peripheral portion P1 which are capable thanks to hinges to vibrate relative to each other along axis 1, but not in their plane.

The pads 116 for fixing the two plates 114 and 115 to each other are cylindrical with an axis parallel to the axis 1, rubber, are glued and arranged at their four corners so as to be as far away as possible from the hinges e to disrupt their elasticity as little as possible.

The elastic shoes 117, also cylindrical with an axis parallel to the axis 1, are bonded to the central portion I1 in zones 1154 regularly spaced ( figure 3 ) and facing the lower base of the housing 110, here removable from this housing. They can also be rubber. The PVC ring 120 is glued on the periphery of this central part I1 ( figure 4 ) and on the housing 110.

The coil 113 is crimped by tabs (not shown) in notches 1143 of the central portion I2 of the transmission plate 114. These notches allow proper centering of the coil.

It is possible to provide notches 1142 distributed symmetrically according to an axial symmetry at the periphery of the rigid transmission plate 114 to increase the bandwidth of the sound vibrations.

It will be noted that the fixing pads 116 are distributed at the periphery P1, P2 of the second and first plates 115, 114 in an axial symmetry arrangement of axis 1, and that the pads 117 or the ring 120 are located between the central portion I1 of the second plate 115 and the housing 110 so that only the hinges mechanically connect the housing 110 to the first plate 114. This gives the first transmission plate 114 the ability to vibrate relative to the housing 110 along the axis 1, so that when the plate 114 is attached to a partition and that electrical signals are sent into the coil 113 attached to the plate 114, it is the core 112, so the motor 111 and its housing 110, which vibrate relative to the wall which then forms an enclosure.

A loudspeaker of this type, with a 35 watt motor, provides a high-quality 90 dB sound level.

Suspension means with pads 116 have been described between the two plates 114 and 115. Naturally, it would also be possible to envisage having springs between these two plates or other elastic means.

The attachment to a partition 300 will now be explained, with reference to figures 3 and 5 .

The first transmission plate 114 can be attached to the wall 300, in particular by using two different fixing means.

The first means consists of a fastening for directly fixing the plate 114 on the surface of the partition 300. A set of screws 202 is then provided ( figure 3 ) passing through the pads 116 and the two plates 114 and 115 along axes A1, A2, A3, A4.

For this, the pads 116 are each pierced with a hole 1163 along their axis and the plates 114 and 115 of four holes 1141 and 1151 along the axes A1, A2, A3, A4, to let each pass a screw 202, here to hexagonal head. The heads of the screws 202 tighten the plate 115 by means of a washer 203 and an elastic O-ring 204, as shown in FIG. figure 3 .

The pads 116 further comprise shoulders 1161 and 1162 to the diameters of the holes 1151 and 1141 of the plates 115 and 114 both lower than their outer diameter which keeps the two plates 114 and 115 parallel and at a predetermined distance. Thus, the pads 116 also serve as spacers.

In order to fix the loudspeaker on the partition, the lower base 1104 of the housing 110, which remains fixed to the elastic suspension plate 115, is removed by means of an ordinary assembly device, not shown. By a hole 1103 provided in this base 1104 to give access to the head of the screw 202, the screw 202 corresponding to each of the axes A1, A2, A3, A4 is screwed into the partition 300, and the housing 110 is raised to its lower base 1104 by the same device. assembly mentioned above.

The second way, also illustrated on the same figure 5 , consists of a flange 200 screwed, by screws 201, in the wall 300 and the housing 110 against the wall 300. When screwed, it bears elastically on the cable 119 and maintains the housing 110 sufficiently flexible not to prevent it from vibrating relative to the partition 300.

Of course, these two fastening means can be used simultaneously.

The invention not only makes it possible to eliminate the volume otherwise necessary for the placement of loudspeaker speakers in an auditorium, but also to obtain a perfect ambience effect since the sound is diffused by the same partitions of this auditorium , forming themselves pregnant. Moreover, several speakers of respectively different frequency bands can be attached to the partitions to further improve this ambience effect. In general, the invention makes it easy to transform a room into an auditorium.

Claims (9)

1. Loudspeaker (100) without membrane, comprising a housing (110), a motor (111) having a magnetic core (112) and around said core (112), an induction coil (113) secured to a first rigid plate (114) for transmitting vibrations to a support (300), the first plate (114) being integral with the housing (110) via flexible suspension means (115, 116, 117; 115, 116, 120), the suspension means being arranged to provide a resilient suspension of the first rigid plate (114) to the housing (110), loudspeaker, the flexible suspension means (115, 116, 117; 115, 116, 120), comprising a second plate (115) for suspension and radial positioning of the coil (113), characterised in that the flexible suspension means (115, 116, 117; 115, 116, 120) comprise resilient pads (116) between the second suspension plate (115) and the first transmitting sheet (114), said resilient pads (116) being fixed in peripheral parts (P1, P2) of the plates (115, 114), and of the pads (117) for fixing the suspension plate (115) to the housing (110) being fixed in a central part (11) of the suspension plate (115).
2. Loudspeaker according to Claim 1, wherein the second suspension plate (115) for radial positioning of the coil (113) is of elastic material.
3. Loudspeaker according to Claim 1 or 2, wherein the second suspension plate (115) is of composite material.
4. Loudspeaker according to Claim 3. wherein the material of the suspension plate (115) is selected from the group comprising an epoxy resin reinforced with glass fibre and reinforced carbon.
5. Loudspeaker according one of Claims 1 to 4, wherein the second suspension plate (115) having a central portion (11) and a peripheral portion (P1), is perforated with louvers (a, b, c, d) defining said central (11) and peripheral (P1) portions and which are limited by hinge bridges (e) conferring the ability to vibrate relative to each other.
6. Loudspeaker according to one of Claims 1 to 6, wherein the core (112) of the coil (113) has an axial symmetry, both vibration transmission (114) and suspension (115) plates are substantially perpendicular to the axis (1) of the core (112), the elasticity of the suspension means acting along said axis (1), and the suspension plate (115) is rigid in the direction perpendicular to said axis (1).
7. Loudspeaker according to one of Claims 1 to 6, wherein the periphery (P2) of the transmission plate (114) comprises notches (1142) to increase the bandwidth of the sound vibrations.
8. Wall (300) forming an auditorium enclosure on which are fixed a plurality of loudspeakers according to one of Claims 1 to 7 and set to transmit their vibrations in respectively different frequency bands.
9. Apparatus for body vibration therapy comprising a membrane-free loudspeaker according to one of Claims 1 to 7.

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