EP1593288B1 - Electrodynamic acoustic transducer - Google Patents

Abstract

The invention relates to an acoustic transducer generating a sound radiation by compression and expansion of an air mass situated between a mobile membrane and a fixed surface or between two mobile membranes. The present invention concerns a transducer or acoustic loudspeaker of electrodynamic type designed to emit sound waves from a modulated electrical signal. The particular arrangement of the constituent elements of the transducer as presented in the invention enables the generation of an acoustic radiation by compression and expansion of the air mass located between a mobile membrane and a fixed surface or anvil which are distinguished by being placed opposite one another. The direction of the resulting acoustical wave is perpendicular to the direction of displacement of the membrane. This manner of generating an acoustic wave enables the production of transducers with specific electroacoustic directivity characteristics.

Description

Technical area :

The present invention relates to an acoustic transducer or speaker type electrodynamic for the emission of sound waves from a modulated electrical signal.

Prior Art - Figures 1 to 4:

Traditional transducers or speakers (next Fig. 1 and 2 ) comprise a frame (13 and 23), generally metal on which are fixed the various active elements, movable membrane (17 and 27) and its suspension (18 and 28) and a motor (14-16 and 24-26) putting this membrane in motion. This motor can be of the electromagnetic, piezoelectric or electrostatic type. The mobile membrane generates a resulting acoustic wave (11 and 21) in the direction of its displacement (12 and 22) and according to the electric current modulating the sound signal to be reproduced. The figure 1 represents, in section, a transducer having a large diaphragm, more particularly intended for the reproduction of low frequencies to medium. The figure 2 represents, in section, a transducer more specialized in the reproduction of high frequencies and is characterized by a smaller membrane and generally comprising a voice coil located on the periphery of this membrane. To this transducer, can be added an acoustic flag that improves its performance by a better acoustic coupling between the membrane (solid) and the surrounding environment (air) by a gradual transition of pressure. These transducers, of which there is a very large number of variations, are mainly characterized by the direction of the resulting sound wave parallel to the direction of movement of the membrane. Their acoustic radiation is not homogeneous in all directions with the exception of special devices called "pulsating spheres" whose direction of the resulting sound radiation is always parallel to the direction of movement of the membrane.

Another type of transducer, the ESS loudspeaker, invented in the United States by Dr. Oscar Heil, (principle following the figure 3 ) consists of a pleated membrane (37) on which is printed a conductive strip (39), this membrane is located in the air gap of a magnet (66) via a circuit magnet (35) for distributing the magnetic induction over the entire membrane. This device allows, by a tightening or a spacing (32) of the folds of the membrane according to the modulation current, to obtain the suction and the alternative expulsion of the air located between these folds and thus the generation of a resulting acoustic wave (31). Despite the very high sound quality obtained, the sound radiation has a pronounced directivity, moreover, the very small amplitude of the fold movements of this membrane does not allow to obtain the reproduction of low frequencies.

A third type of transducer (next figure 4 ), invention of Sawafugi and Tadashi, is an extrapolation of an acoustic transducer operating by flexion of a flexible membrane. It uses two symmetrical flexible membranes (47), fixed at one end in a housing (43), and placed in compression and extension by a flat voice coil (49) located in the air gaps (46) of two magnets (44). The operating mode of this transducer, which is very compact, is dependent on the symmetrical bending operation of the membranes and does not make it possible to obtain particular directivity characteristics.

The spectrum that can be heard by humans, from around 20 to 20,000 hertz, is characterized by the very wide variety of different wavelengths involved (from millimeters to several meters). The reproduction of all these frequencies, with acceptable power, must be done using two or more speakers each of which supports a part of the spectrum. It follows from this necessity that the acoustic centers of these loudspeakers are separated by several decimetres. This degrades the precision and the spatial reproduction of the reproduced stereophonic signal and introduces a phenomenon of acoustic interference called directivity lobes resulting in large variations in the acoustic power emitted as a function of the position of the listener relative to the different transducers. This phenomenon aggravates the poor directivity characteristics inherent in traditional loudspeakers.

Presentation of the invention

The particular arrangement of the constituent elements of the transducer according to the invention makes it possible to generate acoustic radiation, according to the current of modulation, by compression and expansion of the air mass located between a movably fixed membrane, by means of a suspension device, on a rigid frame and a rigid fixed anvil surface, also fixed rigidly to the same frame , this membrane and this anvil have the characteristic of being arranged face to face, the direction of the resulting acoustic wave is perpendicular to the direction of movement of the membrane. The distance separating the membrane and the fixed surface will be slightly greater than the maximum half excursion of the membrane in order to avoid any risk of direct contact between these two elements. This mode of generating an acoustic wave makes it possible to produce electroacoustic transducers with directivity characteristics different from those of conventional loudspeakers. The setting in motion of the membrane, according to the modulation current, can be done by means of an electromagnetic type motorization as shown in the drawings illustrating the invention, but this motorization can also be of piezoelectric type (following figure 10 ), electrostatic type or other.

Brief description of the drawings:

• The figure 1 represents, in section, a conventional transducer having a large diaphragm, more particularly intended for the reproduction of low frequencies to medium.
• The figure 2 represents, in section, a traditional transducer more specialized in high frequency reproduction and is characterized by a smaller membrane.
• The figure 3 shows schematically and axonometric view, the operating principle of a pleated diaphragm transducer, only part of the membrane, the electrical circuit and the magnetic circuit are shown.
• The figure 4 represents, in section, a transducer according to Sawafugi and Tadashi, and comprising two symmetrical flexible membranes.
• The figure 5 represents, in axonometric section, the transducer, object of the invention, in omnidirectional acoustic radiation configuration, provided with a dome-shaped membrane, this transducer allows the reproduction of low and medium frequencies.
• The figure 6 represents, the same transducer, seen in section.
• The figure 7 represents, in section, the transducer, object of the invention, in an omnidirectional acoustic radiation configuration with an annular membrane, more specifically intended for the reproduction of acute frequencies. The anvil 10 is shown in dashed line for a good understanding of the annular membrane device.
• The figure 8 represents this omnidirectional ring diaphragm transducer, seen in section.
• The figure 9 represents, in section, the superposition, along one axis, of two omnidirectional transducers, each being responsible for the reproduction of a part of the audible spectrum (low and low frequencies for the lower one and medium and high frequencies for the upper one). ).
• The figure 10 represents, in axonometric sectional view, the transducer, object of the invention, in acoustic radiation configuration with controlled directivity.
• The figure 11 represents, in section, the transducer of the figure 10 .

In order to designate, in the various figures, the elements, having the same function in different implementations, the reference numbers appearing in the drawings are preceded, in the description and the claims, by the number of the figure to which this reference refers. description. For example, the membrane (9) in the figure 5 is designated (59) in the description, the same membrane (9) in the figure 6 is designated (69) in the description.

Detailed description of the best implementations of the invention

• Un circuit magnétique (55 et 65) accouplé à un aimant (54 et 64), destiné à créer un champ magnétique dans un entrefer (56 et 66).
• Une membrane mobile en (57 et 67) montée sur une suspension souple périphérique (58 et 68) et comportant une bobine mobile (59 et 69) plongeant dans l'entrefer (56 et 66). Cette membrane, représentée ici sous forme de dôme convexe, pourra présenter une autre forme compatible avec une bonne rigidité. Cette membrane pourra comporter des plis ou corrugations destinée à former toute ou partie de sa suspension (58 et 68).
• Une surface fixe et rigide dite enclume (510 et 610), placée face à la membrane mobile (57 et 67) et raccordée (511 et 611) rigidement au châssis ou faisant partie intégrante de celui-ci.

Ce transducteur est caractérisé par la disposition de ses composants permettant d'obtenir un transducteur acoustique omnidirectionnel, c'est-à-dire générant un rayonnement sonore résultant (51 et 61) sur 360° dans le plan perpendiculaire au sens de déplacement (52 et 62) de sa membrane. La forme, le profil et le dimensionnement des différents éléments dépend de leurs caractéristiques électriques ou mécaniques ainsi que du spectre de fréquences à reproduire. Ce transducteur, s'il est destiné à reproduire des fréquences basses ou médium, pourra être couplé à un enceinte (621) destinée à récupérer ou amortir l'énergie acoustique générée par l'arrière de la membrane mobile.A first implementation is represented Figures 5 and 6 . The acoustic transducer according to the invention consists of a rigid chassis (53 and 63) on which are fixed:

• A magnetic circuit (55 and 65) coupled to a magnet (54 and 64) for creating a magnetic field in a gap (56 and 66).
• A movable diaphragm (57 and 67) mounted on a flexible peripheral suspension (58 and 68) and having a voice coil (59 and 69) immersed in the gap (56 and 66). This membrane, represented here as a convex dome, may have another form compatible with good rigidity. This membrane may comprise folds or corrugations to form all or part of its suspension (58 and 68).
• A fixed and rigid anvil surface (510 and 610), placed facing the movable diaphragm (57 and 67) and connected (511 and 611) rigidly to or integral with the frame.

This transducer is characterized by the arrangement of its components making it possible to obtain an omnidirectional acoustic transducer, that is to say generating a resultant sound radiation (51 and 61) over 360 ° in the plane perpendicular to the direction of movement (52 and 62) of its membrane. The shape, profile and dimensioning of the various elements depends on their electrical or mechanical characteristics as well as the frequency spectrum to be reproduced. This transducer, if it is intended to reproduce low or medium frequencies, may be coupled to an enclosure (621) intended to recover or dampen the acoustic energy generated by the rear of the mobile membrane.

• Un circuit magnétique (75 et 85) accouplé à un aimant (74 et 84), destiné à créer un champ magnétique dans un entrefer (76 et 86).
• Une membrane mobile annulaire (77 et 87) montée sur une suspension souple périphérique intérieure et extérieure (78 et 88) et comportant une bobine mobile (79 et 89) plongeant dans l'entrefer (76 et 86). Cette membrane pourra comporter des plis ou corrugations destinée à former toute ou partie de sa suspension, les figures 7 et 8 montrent un tel dispositif pour sa suspension périphérique externe.
• Une surface fixe et rigide dite enclume (710 et 810), placée face à la membrane mobile annulaire (77 et 87) et fixée (711 et 811) rigidement à l'ensemble des autres constituants non mobiles du transducteur.

Cette disposition avec membrane annulaire permet de conserver une surface effective de la membrane compatible avec une bonne puissance acoustique tout en évitant les oppositions de phase acoustique qui surviennent sur ce type de transducteur lorsque la longueur radiale de l'interface membrane et enclume est trop proche de la longueur d'onde des fréquences à reproduire. Cette disposition est plus spécialement destinée à la reproduction de fréquences aigues, de faible longueur d'onde.The Figures 7 and 8 represent another implementation of the omnidirectional transducer. It comprises a rigid frame (73 and 83) on which are fixed:

• A magnetic circuit (75 and 85) coupled to a magnet (74 and 84) for creating a magnetic field in a gap (76 and 86).
• An annular movable membrane (77 and 87) mounted on an inner and outer peripheral flexible suspension (78 and 88) and having a voice coil (79 and 89) dipping into the gap (76 and 86). This membrane may comprise folds or corrugations intended to form all or part of its suspension, the Figures 7 and 8 show such a device for its external peripheral suspension.
• A fixed and rigid anvil surface (710 and 810), placed facing the annular mobile membrane (77 and 87) and fixed (711 and 811) rigidly to all the other non-movable components of the transducer.

This arrangement with an annular membrane makes it possible to maintain an effective surface of the membrane compatible with good acoustic power while avoiding the acoustic phase oppositions that occur on this type of transducer when the radial length of the membrane and anvil interface is too close to the wavelength of the frequencies to be reproduced. This provision is more specifically intended for the reproduction of acute frequencies, of short wavelength.

With reference to the figure 9 , and to allow the reproduction of an extended frequency spectrum, it is possible to superimpose, along an axis parallel to the displacement of the mobile membranes (92), two or more of these omnidirectional transducers, each being responsible for the reproduction of a determined frequency range. The low height of each transducer allows a closer approximation of the acoustic centers of these different transducers and therefore the reduction of the directivity lobes inherent in the combination of several traditional transducers. All references in this figure relate to similar function elements in Figures 5 to 8 and previously described.

The figure 10 shows a variant of the first proposed implementation. Its particularity consists in motorizing the membrane (107) by a device comprising a single or composite crystal rod with piezoelectric properties (106b) which deforms according to the modulation current applied to the bar by the electrical connections (104b). The movements resulting from the deformations of the bar (106b) are mechanically transmitted to the membrane (107) by a rigid and light element (1 09b). The resulting sound radiation (101) is perpendicular to the direction of movement (102) of the membrane (107). The shape, profile and dimensioning of the various elements depends on their electrical or mechanical characteristics as well as the frequency spectrum to be reproduced. The other elements of the device according to the figure 10 are identical by their functions to the equivalent elements of the first implementation following Figures 5 and 6 .

• Un châssis (113 et 123) rigide.
• Un aimant (114 et 124), accouplé à un circuit magnétique (115 et 125) et destiné à créer un champ magnétique dans un entrefer (116).
• Une membrane mobile (117 et 127) montée sur une suspension souple (118) et comportant une bobine mobile (119 et 129) plongeant dans l'entrefer, cette bobine mobile est guidée par une deuxième suspension (1113 et 1213) destinée à assurer son centrage dans l'entrefer.
• Une surface fixe et rigide ou enclume (1110 et 1210), placée face à la membrane mobile et fixée rigidement au châssis ou faisant partie intégrante de celui-ci.
• Des baffles (1112 et 1212), rigides ou non, placées dans un plan perpendiculaire à la membrane et à l'enclume, dont le rôle est de limiter physiquement la masse d'air comprise entre la membrane et l'enclume, ces baffles peuvent faire partie intégrante du châssis (113 et 123).

Cette disposition permet d'obtenir une directivité précise du rayonnement acoustique résultant selon la forme, la géométrie et le dimensionnement de l'ensemble membrane, enclume, baffles et châssis et selon le spectre des fréquences à reproduire. Ce transducteur, s'il est destiné à reproduire des fréquences basses ou médium, pourra être couplé à un enceinte (1221) destinée à récupérer ou amortir l'énergie acoustique générée par l'arrière de la membrane mobile.Implementation following the Figures 11 and 12 consists of another arrangement of the various elements of the transducer operating by compression and expansion of the air mass located between a mobile membrane fixed loosely on a rigid frame and a fixed and rigid surface called anvil, also fixed rigidly to the same frame, this membrane and this anvil having the characteristic of being arranged face to face, the direction of the resulting acoustic wave (111 and 121) is perpendicular to the direction of movement of the membrane (112 and 122).
This implementation involves:

• A frame (113 and 123) rigid.
• A magnet (114 and 124) coupled to a magnetic circuit (115 and 125) for creating a magnetic field in an air gap (116).
• A movable diaphragm (117 and 127) mounted on a flexible suspension (118) and having a voice coil (119 and 129) immersed in the air gap, this voice coil is guided by a second suspension (1113 and 1213) to ensure its centering in the gap.
• A fixed and rigid surface or anvil (1110 and 1210), placed facing the movable membrane and fixed rigidly to the frame or forming an integral part thereof.
• Baffles (1112 and 1212), rigid or not, placed in a plane perpendicular to the membrane and the anvil, whose role is to physically limit the air mass between the membrane and the anvil, these speakers can be an integral part of the frame (113 and 123).

This arrangement makes it possible to obtain a precise directivity of the resulting acoustic radiation according to the shape, geometry and dimensioning of the membrane, anvil, baffle and chassis assembly and according to the frequency spectrum to be reproduced. This transducer, if it is intended to reproduce low or medium frequencies, may be coupled to an enclosure (1221) intended to recover or dampen the acoustic energy generated by the rear of the mobile membrane.

Possibility of industrial application and manufacture:

The manufacture of this type of transducer is identical to that of acoustic transducers or traditional loudspeakers.

• Châssis et enclume métalliques ou en matériaux de synthèse ou composites, en tôle pliée ou pressée ou obtenue par injection de métal ou de résine pouvant comporter des fibres de consolidation ou de renfort.
• Membrane en métal, en papier, traité ou non, en matériaux de synthèse ou composites, fibreux ou non.
• Suspension en caoutchouc naturel ou artificiel ou matériaux de synthèse. Cette suspension peut également comporter des plis ou corrugations formés dans la membrane du transducteur.
• Aimants, pièces de champs, circuits magnétiques et bobinages usuels.
• D'une manière générale tous les matériaux et modes de fabrication présents et à venir adaptés à la fabrication et à l'amélioration des performances de ce type de transducteur.

By its materials and its manufacture:

• Anvils and anvils made of metal or of synthetic or composite materials, in folded or pressed sheet metal or obtained by metal or resin injection, which may comprise reinforcing or reinforcing fibers.
• Membrane of metal, of paper, whether or not treated, of synthetic materials or composites, fibrous or not.
• Suspension made of natural or artificial rubber or synthetic materials. This suspension may also comprise folds or corrugations formed in the membrane of the transducer.
• Magnets, field parts, magnetic circuits and usual windings.
• In a general manner all the present and future materials and methods of manufacture adapted to the manufacture and the improvement of the performances of this type of transducer.

• Elle devra répondre et s'adapter aux caractéristiques et au fonctionnement particulier de ce type de transducteur. Les motorisations du type électromagnétique, piézo-électrique, électrostatique ou autres, ainsi que tous les procédés de contrôle, d'assistance et de pilotage des pièces mobiles par méthode analogique ou numérique peuvent être appliqués à ce type de transducteur.
• Le type de transducteur selon l'invention, pourra comporter un dispositif dit « pavillon acoustique» qui permet d'améliorer son rendement par un meilleur couplage acoustique entre la membrane (solide) et le milieu ambiant (air) par une transition progressive des pressions.
• Le type de transducteur selon l'invention pourra être mis en oeuvre dans d'autres fluides, gazeux ou liquides, que l'air ambiant.

By its implementation and its use:

• It will have to respond and adapt to the characteristics and the particular functioning of this type of transducer. Motorizations of the electromagnetic, piezoelectric, electrostatic or other types, as well as all the methods of controlling, assisting and controlling moving parts by analog or digital method can be applied to this type of transducer.
• The type of transducer according to the invention may include a device called "acoustic flag" which improves its performance by a better acoustic coupling between the membrane (solid) and the surrounding environment (air) by a gradual transition of pressure.
• The type of transducer according to the invention may be implemented in other fluids, gaseous or liquid, than the ambient air.

Claims (9)

1. An electroacoustical transducer comprising :

   - A chassis (3);

   - A rigid surface (10) rigidly attached to the said chassis (3);

   - A moving membrane (7), attached flexibly to the said chassis (3) and positioned to face the said rigid surface (10), with an air mass between the said rigid surface (10) and the said moving membrane (7) and the distance between the said rigid surface (10) and the said moving membrane (7) increases from the center to the periphery ;

   - A driving device (4, 5, 9, 9b) to displace the said moving membrane (7) in the direction of the said rigid surface activated by a modulating electric current ;

   Accordingly, the displacement of the said membrane (7) generates, by compression and expansion of the said air mass, an acoustic wave, of which the direction of propagation (1) is essentially perpendicular to the direction (2) of the displacement of the said membrane (7).
2. An electroacoustical transducer as set forth in claim 1 in which the said rigid surface (10) and the said moving membrane (7) are configured in cylindrical symmetry about an axis that is parallel to the direction (2) of displacement of the said moving membrane (7), accordingly, the resulting sound radiation is omnidirectional in a plane perpendicular to the said direction (2) of displacement of the said moving membrane (7).
3. An electroacoustical transducer as set forth in one of the above claims in which the said rigid surface (10) is shaped in the form of a convex dome.
4. An electroacoustical transducer according to claim 3 in which the said moving membrane (7) also is shaped in the form of a convex dome.
5. An electroacoustical transducer as set forth in claim 3 in which the said moving membrane (7) is ring shaped.
6. An electroacoustical transducer according to claim 1 comprising also acoustic screens or baffles (12) arranged to be in a plane that is perpendicular to the said moving membrane (7) and the said rigid surface (10), in such a way as to limit the air mass contained between them. Accordingly the resulting sound radiation is directional.
7. An electroacoustical transducer as set forth in one of the claims 1, 2 or 6 comprising similarly an acoustic horn that enables the improvement of the acoustic coupling between the moving membrane (7) and the ambient air.
8. An electroacoustical transducer as set forth in one of the preceding claims in which the said means of driving is electromagnetic (4, 5, 9), piezoelectric, (9b) or electrostatic types.
9. An array consisting of multiple electroacoustical transducers as set forth in claims 1 to 5, each adapted to the reproduction of a determined range of frequencies, stacked on an axis that is parallel the direction of displacement of the said moving membrane (7).

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