EP3008918B1 - Electroacoustic conversion chain with selectively powered coil - Google Patents

Description

The present invention relates to an electroacoustic conversion line, of the type comprising at least one loudspeaker, this loudspeaker comprising means for generating a magnetic field in a magnetic circuit having an air gap and a membrane secured to turns of conductive material capable of to move in this gap.

Such an electroacoustic conversion chain makes it possible to convert an electric signal to be broadcast into an acoustic signal.

Typically, the electroacoustic conversion chain comprises a loudspeaker. This comprises an axially polarized toroidal magnet inserted into a magnetic circuit. This magnetic circuit defines an annular gap where a magnetic field prevails.

The loudspeaker also comprises a coil of conductive material wound and secured around a tube extended by a membrane capable of generating an acoustic wave.

The coil is intended to receive a current depending on the signal to be diffused and extends partly into the gap in which it is axially movable.

The coil has an axial length such that, during operation of the loudspeaker, all or part of the coil is in the gap.

During the operation of the electroacoustic conversion chain, the entire coil is powered. The coils of the coil present in the gap undergo Laplace forces which make them move along the axis of the tube. The displacement of these turns causes the displacement of the membrane through the tube, causing the creation of sound.

This embodiment has a low electroacoustic output due to Joule losses in the coil.

Other speaker configurations are known documents US 2009/028371 A , US 2012/269378 A and GB 2 384 938 A .

The object of the invention is therefore to provide an electroacoustic conversion chain having a better performance.

For this purpose, the subject of the invention is an electroacoustic conversion chain of the aforementioned type, characterized in that it comprises at least one control module comprising at least one input for conveying a signal to be broadcast and at least one output connected to a turn, the control module being clean to apply to the or each output an excitation signal dependent on the position of at least one turn relative to the air gap, the applied excitation signal being all the lower as the turn is away from the gap.

By varying the value of the current passing through a turn according to its position relative to the air gap, so that this current is reduced or zero when said turn is outside the gap, the efficiency of the conversion chain Electroacoustics are improved by reducing or canceling the Joule losses of turns that are not able to contribute to the movement of the membrane since outside the gap.

• le module de commande est propre à appliquer un signal nul à toute ou partie des spires en dehors de l'entrefer ;
• le module de commande comporte au moins une entrée pour acheminer un signal de position par rapport à l'entrefer d'au moins une spire ;
• la chaîne comprend des spires disposées successivement le long de leur axe et reliées électriquement pour former au moins deux bobines disjointes disposées successivement ;
• chaque sortie du module de commande est reliée à une seule bobine ;
• la chaîne comporte des moyens de mesure sur le haut-parleur de la position par rapport à l'entrefer d'au moins une spire ;
• le module de commande est propre à commander le potentiel à au moins une de ses sorties ;
• le module de commande est propre à appliquer à au moins une de ses sorties un potentiel tel que la tension aux bornes de la bobine correspondante est nulle ;
• le circuit magnétique comporte au moins deux aimants disjoints, les aimants délimitant entre eux des espaces passe-fil dans lesquels des fils d'alimentation des bobines passent ; et
• le circuit magnétique comporte un noyau central comprenant des rainures longitudinales recevant partiellement chacune un fil d'alimentation des bobines.

According to particular embodiments, the invention has one or more of the following characteristics:

• the control module is able to apply a null signal to all or part of the turns outside the gap;
• the control module comprises at least one input for conveying a position signal with respect to the air gap of at least one turn;
• the chain comprises turns arranged successively along their axis and electrically connected to form at least two disjoint coils arranged successively;
• each output of the control module is connected to a single coil;
• the chain comprises means for measuring the position of the loudspeaker with respect to the air gap of at least one turn;
• the control module is adapted to control the potential at at least one of its outputs;
• the control module is adapted to apply to at least one of its outputs a potential such that the voltage across the corresponding coil is zero;
• the magnetic circuit comprises at least two disjoint magnets, the magnets defining between them wire-pass gaps in which the coil supply son pass; and
• the magnetic circuit comprises a central core comprising longitudinal grooves partially partially receiving a coil feed wire.

The invention relates to a conversion chain according to claim 1.

According to particular embodiments, the invention has one or more of the features of claims 2 to 10.

• la figure 1 est un schéma d'un exemple de réalisation d'un dispositif de restitution sonore comprenant une chaîne de conversion électroacoustique selon l'invention dont un haut-parleur est représenté en section ;
• la figure 2 est un détail d'une vue en section d'un mode de réalisation d'un haut-parleur selon l'invention ;
• la figure 3 est un schéma synoptique illustrant la structure générale d'un mode de réalisation d'une chaîne de conversion électroacoustique selon l'invention ;
• la figure 4 est un ensemble de courbes représentant les gains des amplificateurs reliés à trois groupes de spires durant leur déplacement à travers l'entrefer dans un mode de réalisation d'un haut-parleur selon l'invention ;
• la figure 5 est un détail d'une vue en section selon un plan orthogonal à l'axe X-X d'un autre mode de réalisation d'un haut-parleur selon l'invention ;
• la figure 6 est un détail d'une vue en section selon le plan VI-VI du haut-parleur de la figure 5 ; et
• la figure 7 est un détail d'une vue de dessus du circuit magnétique d'un autre mode de réalisation d'un haut-parleur selon l'invention.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings in which:

• the figure 1 is a diagram of an exemplary embodiment of a sound reproduction device comprising an electroacoustic conversion chain according to the invention, a speaker is shown in section;
• the figure 2 is a detail of a sectional view of an embodiment of a loudspeaker according to the invention;
• the figure 3 is a block diagram illustrating the general structure of an embodiment of an electroacoustic conversion chain according to the invention;
• the figure 4 is a set of curves representing the gains of the amplifiers connected to three groups of turns during their movement through the gap in one embodiment of a loudspeaker according to the invention;
• the figure 5 is a detail of a sectional view along a plane orthogonal to the axis XX of another embodiment of a loudspeaker according to the invention;
• the figure 6 is a detail of a section view according to the plane VI-VI of the loudspeaker of the figure 5 ; and
• the figure 7 is a detail of a top view of the magnetic circuit of another embodiment of a loudspeaker according to the invention.

The sound reproduction device 1 illustrated in FIG. figure 1 comprises the electroacoustic conversion chain 2 whose input is connected at the output of a signal source 3 to be broadcast.

The electroacoustic conversion chain 2 comprises a control module 4 adapted to process the signal to be broadcast and a loudspeaker 5. The control module 4 is connected to the loudspeaker for its excitation.

The loudspeaker 5 comprises a magnetic circuit 10 in which is disposed a toric magnet 15.

The magnetic circuit 10 comprises a yoke 16, comprising a central core 17, and an upper plate 18.

The magnet is sandwiched between the yoke 16 and the upper plate 18.

The volume of air between the central core 17 and the upper plate 18 defines an air gap 20, generally O-ring disposed along an axis X-X of the loudspeaker.

A moving element 25 comprising a guide tube 30 extended by a membrane 35 is slidably mounted along the X-X axis of the loudspeaker with respect to the magnetic circuit.

The membrane 35 is held by its outer edge to a chassis 40 of the loudspeaker by means of a peripheral suspension 45.

The moving element 25 also comprises a set of turns 46 of conductive material, wound around the tube 30 of which they are integral. The turns are intended to be traversed by a current depending on the signal to be broadcast, this current coming from the control module 4.

As it appears on the figure 2 the turns are electrically interconnected to form coils 60A, 60B, 60C, these coils being electrically independent. Each coil 60A, 60B and 60C is electrically connected by one of its ends to a point M, N, P respectively. The points M, N, P have, for example, different fixed electrical potentials.

The coils are arranged successively along the length of the moving element extending along the axis X-X. Each coil has an axial length substantially equal to the height of the gap.

In one embodiment of an electroacoustic conversion chain according to the invention, the chain comprises means 65 for measuring on the loudspeaker the axial position relative to the air gap of at least one turn, visible on the figures 1 and 3 .

These measuring means 65 have an output 66, connected to an input 67 of the control module 4, represented on the figure 3 .

An input 71 of this control module is intended to receive the signal to be broadcast.

The control module 4 comprises a routing unit 72 for determining a supply signal specific to each coil 60A, 60B, 60C.

The routing unit comprises an input 73 connected to the input 71 of the control module 4, and an input 74 connected to the input 67 of the same control module.

The routing unit 72 also has three outputs 75A, 75B and 75C.

Each of these outputs 75A, 75B and 75C is followed by an amplifier, respectively 80A, 80B and 80C.

The output of each of these amplifiers 80A, 80B and 80C is respectively connected to one of the three outputs 81A, 81B and 81C of the control module 4.

The routing unit 72 is able to determine, as a function of the movement of the turns through the gap, the value of the electric current at each of the outputs of the control module 4 so that only the coils at least partially present in the gap are fed.

For this purpose, the routing unit 72 is able to control the gain K of the amplifier associated with the excitation signal coming from each of the outputs 81A, 81B and 81C of the control module 4.

For each of these outputs 81A, 81B and 81C of the control module 4, this gain K is maximum when the coil connected to this output, respectively 60A, 60B, 60C, is centered in the air gap along XX.

This gain K is even smaller than the coil considered is removed from this centered position.

On the figure 4 , the curves 85A, 85B and 85C respectively represent the evolution of the gain K for each of the coils 60A, 60B and 60C during their travel through the air gap.

"X" denotes the distance along the X-X axis between the cylinder head 16 and the end of the tube 30 closest to this cylinder head.

où P, A² et x₀ sont trois réels.For each of the outputs 81A, 81B and 81C of the control module 4, the gain K follows, for example, the law: $\mathrm{K}=\mathrm{P}*\exp \left[-\frac{\mathrm{<figure-callout\; id="2"\; label="ln"\; filenames="imgf0001.png"\; state="\{\{state\}\}">ln</figure-callout>}\left(2\right)*{\left(\mathrm{x}-{\mathrm{x}}_0\right)}^2}{{\mathrm{AT}}^2}\right],$

where P, A ² and x ₀ are three real.

x ₀ is a reality specific to each coil. In this case, it is the distance x for which the gain K for the coil considered is maximum.

P is a constant determining the maximum gain that each of the amplifiers 80A, 80B and 80C is likely to apply between its input and its output.

A ² is the square of half the distance between two successive coils.

For example, the gain of the amplifier 80B, represented by the curve 85B, is maximum when the coil 60B, to which this amplifier is connected, is centered in the gap at the position x _0B . As the tube moves away from the cylinder head, and the coil 60B leaves the air gap while the coil 60C is progressing, the gain of the amplifier 80B decreases while the gain of the amplifier 80C increases, as it appears on curve 85C.

According to another embodiment of the speaker, partially illustrated not Figures 5 and 6 , the central core 17 has longitudinal grooves 86 partially receiving each supply wire 87 of the coils 60A, 60B, 60C.

The supply wires 87 are disposed inside the guide tube 30, as shown on the figure 6 and passing through the guide tube 30 to feed the coils 60A, 60B, 60C.

A channel 88 passing through the central core 17 and the cylinder head 16 allows the supply wires 87 to be routed to the control module 4.

According to another embodiment of the loudspeaker according to the invention, partially illustrated by the figure 7 a magnetic circuit 90 of the loudspeaker 5 comprises at least two magnets, for example four disjoint magnets 95. A magnetic axis ZZ of each magnet 95 is substantially parallel to the axis XX of the loudspeaker 5.

The magnets 95 are arranged in the magnetic circuit 90 by defining between them grommet spaces 100.

The grommet spaces 100 are suitable for allowing the passage of electrical wires, for example the electrical wires for supplying coils 105 of the loudspeaker 5.

The coils 105 advantageously have a polygonal section in a plane orthogonal to the X-X axis, for example a square section.

A central core 110 of the magnetic circuit 90 advantageously has the same polygonal section as the coils 105.

According to another non-represented embodiment of a conversion chain according to the invention, the routing unit 72 is able to impose a specific electrical potential at the output 81A, 81B, 81C of the corresponding amplifier, 80A, 80B , 80C respectively, when the coil connected thereto, 60A, 60B, 60C respectively, is not powered.

The electric potential imposed on each output 81A, 81B, 81C is such that the electrical voltage between the output 81A, 81B, 81C, and the point M, N, P respectively, is substantially opposite to the voltage induced at the terminals of the coil corresponding, 60A, 60B, 60C respectively, by the displacement of this coil in the magnetic field generated by the magnet or magnets of the speaker.

Indeed, the electrical voltage induced by the displacement of the coils in the magnetic field in the loudspeaker generates an induced electric current. This induced electric current creates a counter-driving force opposing the displacement of the moving element, which reduces the electroacoustic output of the electroacoustic conversion chain.

By canceling the voltage induced by a substantially opposite voltage imposed by the routing unit 72, the counter-motive force is canceled and the electroacoustic efficiency of the electroacoustic conversion chain is increased.

Claims (10)

1. An electroacoustic conversion chain (1) comprising at least one loudspeaker (5), this loudspeaker comprising means (15) for generating a magnetic field in a magnetic circuit (10; 90) having an air gap (20) and a membrane (35) secured to the turns (46) of conducting material which may be moved in this air gap, the electroacoustic conversion chain (1) comprising at least one control module (4) comprising at least one input (71) for conveying a signal to be broadcast and at least one output (81A, 81B, 81C) connected to a turn, the control module (4) being able to apply to said or each output (81A, 81B, 81C) an excitation signal depending on the position of at least one turn relatively to the air gap (20), characterized in that the control module (4) is able to apply on each turn (46), an excitation signal all the weaker when this turn is moved away from the air gap.
2. The chain according to claim 1, characterized in that the control module (4) is able to apply a zero signal to all or part of the turns (46) outside the air gap.
3. The chain according to claim 1 or 2, characterized in that the control module (4) comprises at least one input (67) for conveying a position signal relatively to the air gap of at least one turn (46).
4. The chain according to any one of the preceding claims, characterized in that the chain comprises turns (46) positioned in succession along their axis (X-X) and electrically connected so as to form at least two disconnected coils (60A; 60B; 60C; 105) positioned in succession.
5. The chain according to claim 4, characterized in that each output (81A, 81B, 81C) of the control module (4) is connected to a single coil (60A; 60B; 60C; 105).
6. The chain according to any one of the preceding claims, characterized in that the chain comprises means (65) on the loudspeaker for measuring the position relatively to the air gap (20) of at least one turn 46).
7. The chain according to any one of preceding claims, characterized in that the control module (4) is able to control the potential of at least one of its outputs (81A, 81B, 81C).
8. The chain according to claim 7, characterized in that the control module (4) is able to apply to at least one of its outputs (81A, 81B, 81C) a potential such that the voltage at the terminals of the corresponding coil (60A; 60B; 60C; 105) is zero.
9. The chain according to any one of the preceding claims, characterized in that the magnetic circuit (90) comprises at least two disconnected magnets (95), the magnets (95) delimiting between them grommet spaces (100) in which pass power supply wires (105) for the coils.
10. The chain according to any one of claims 1 to 8, characterized in that the magnetic circuit (10) comprises a central core (17) comprising longitudinal grooves (86) partly receiving each a power supply wire (87) of the coils (60A; 60B; 60C).

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