Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R7/00—Diaphragms for electromechanical transducers; Cones
  • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
  • H04R7/12—Non-planar diaphragms or cones
  • H04R7/122—Non-planar diaphragms or cones comprising a plurality of sections or layers

Definitions

• the invention relates to a method for manufacturing a material absorbing mechanical surface waves, a material absorbing mechanical surface waves obtained by the implementation of this method, and the electroacoustic transducers thus obtained and used in restitution. sound.
• the sound reproduction tools that is to say essentially the electromechanical or electroacoustic transducers allowing the transmission of these signals digital and / or analog sound pressure waves have remained the poor parents of these developments.
• the object of the present invention is to eliminate or substantially reduce the drawbacks of electromechanical or electroacoustic transducers of the prior art by eliminating or at least significantly attenuating the above-mentioned coloring phenomenon.
• the subject of the present invention is the implementation of a process for manufacturing a material absorbing surface mechanical waves locally generated on the surface of this material, when the latter is subjected to mechanical excitation aimed at create a pressure wave to reproduce an acoustic wave.
• the object of the present invention is to provide a material absorbing surface mechanical waves generated locally on the surface of this material, when the latter is subjected to a mechanical excitation aiming to create a pressure wave restitution of a acoustic wave.
• the object of the present invention is to provide electromechanical or electroacoustic transducers comprising an electromagnetic motor and a membrane provided with an excitation coil, this membrane connected by a suspension being made of a material conforming to the object of the invention.
• the method of manufacturing an absorbent material of a surface mechanical wave generated by local waves is remarkable in that it consists in forming a support delimiting this surface from a continuous structure, this support having a determined rigidity in a direction substantially orthogonal to the surface of this support, and in forming, on at least one of the faces of this support, an absorbent coating of this surface mechanical wave and local waves, this coating having a plurality of obstacles to the propagation of this surface mechanical wave and local waves.
• the absorbent material of a mechanical surface wave generated by local waves capable of causing parasitic phenomena with respect to a pressure wave of direction substantially orthogonal to this surface, when this material is subjected to a mechanical action aiming to create a pressure wave to restore an acoustic wave, is remarkable in that it comprises a base constituted by a support delimiting this surface and formed from a continuous structure, this support having a determined rigidity in a direction substantially orthogonal to this support and an absorbent coating having a plurality of obstacles to the propagation of this mechanical surface wave and local waves.
• the electroacoustic transducer which is the subject of the invention comprises an electromagnetic motor and a membrane provided with an excitation coil, this membrane being able to be connected by a suspension to a rigid frame. It is remarkable in that the membrane is made of a material in accordance with the object of the invention.
• the material absorbing mechanical surface waves and local waves, the method of manufacturing this material and the electroacoustic transducers implemented in accordance with the object of the present invention find application in the manufacture of equipment and installations high quality high fidelity video and / or audio frequencies.
• FIG. 2a represents, by way of illustration, the essential stages of implementation the process for manufacturing a material absorbing mechanical surface waves and local waves which is the subject of the invention
• Figures 2b, 2c, 2d show different details of implementation of the method illustrated in Figure 2a
• Figures 2e, 2f and 2g represent, in a nonlimiting manner, a specific mode of implementation of the method which is the subject of the present invention
• FIGS. 1 relating to the prior art
• FIGS. 5a and 5b represent a diagram of amplitude of sound signal, time, frequency for a loudspeaker of conventional type respectively a loudspeaker of similar type, in which the conventional membrane has been replaced by a membrane obtained in accordance with the object of the invention
• FIGS. 6a and 6b represent a diagram of amplitude of sound signal, time, frequency for a tweeter of conventional type respectively a tweeter of similar type, in which the conventional membrane has been replaced by a membrane obtained in accordance with the object of the invention.
• an electroacoustic transducer such as a "tweeter” for example, comprising a membrane ME in the shape of a dome, connected by a suspension elastic SU to a rigid frame FR, the membrane being on the other hand provided with an excitation coil B by the analog audio signal representative of the sound signal, the excitation of the coil B by the aforementioned audio signal has the effect of cause the displacement of the membrane ME via the electromagnetic motor constituted by the magnetic core NM and the aforementioned coil B subjected to excitation. Under these conditions, the displacement of the membrane ME causes an acoustic wave of the plane or substantially plane wave type OP reproducing the aforementioned sound signal.
• the ME membrane is subjected locally, at the level of surface elements dS to microdeformations which are due to local imperfections of the aforementioned membrane as well as to the structure of this membrane when this membrane is constituted by an element woven by example in which the woven structure has periodic weakening zones or not.
• each elementary surface area dS can be the seat of microdeformations, which generate local waves
• each local wave OL in the direction orthogonal to the surface of the membrane ME may appear negligible, this contribution, along the surface of the membrane ME and of any equipression plane in the vicinity of this is no longer negligible, which results in the creation of an equivalent surface wave.
• the object of the present invention is to remedy the propagation of this mechanical surface wave and, in particular, of the local waves previously mentioned in relation to FIG. 1.
• the object of the invention is to provide a material provided with a coating making it possible to absorb, or at the very least to attenuate significantly, the propagation of the mechanical surface wave and of the waves.
• a more detailed description of a method for manufacturing an absorbent material of a mechanical surface wave capable of generating parasitic phenomena with respect to a pressure wave of direction of propagation substantially orthogonal to this surface will now be given in connection with FIG. 2a.
• the process which is the subject of the present invention consists in forming a support S delimiting the above-mentioned surface from a continuous structure.
• continuous structure is meant either a solid structure in the form of a sheet or thin layer, or a periodic structure which may have recesses, the maximum dimension of the recesses being much less than the wavelength of the pressure wave OP and of the acoustic wave to be restored.
• step 2a The aforementioned step is then followed by a step consisting in forming on at least one of the faces of the support S a coating absorbing the mechanical surface wave and the local waves previously mentioned.
• the coating is noted R and shown in dotted lines due to the structure of the latter which will be described later in the description.
• the absorbent coating R presents a plurality of obstacles to the propagation of the above-mentioned mechanical surface wave and local waves.
• the support S can advantageously be formed by a continuous structure, a composite structure, a woven or non-woven structure of fibers chosen from the group of plant or synthetic fibers such as nylon fibers or the like.
• the support S can be shaped by forming, thermoforming, molding or stamping, cutting or trimming of plate, according to a predetermined forming profile.
• the support S consisting of a continuous cap C of metal, such as aluminum for example, and formed by stamping, a cap formed by a fabric of nylon fibers for example, shaped by thermoforming, and a support made of NT nonwoven material, formed for example from vegetable fibers or the like.
• the shaping by stamping of a sheet F is shown in FIG. 2c, using OF tools.
• the step consisting in forming an absorbent coating consists in applying, to at least one of the faces of the support S, a structure chosen from the group of fluff, velvets, cellular foams for example, under the conditions which will be explained below.
• the step consisting in forming the absorbent coating may, by way of nonlimiting example, consist in subjecting the support S to a surfactant substance accompanied by a wetting agent, the support S being for example soaked in a Sol solution consisting of the surface-active substance and the aforementioned wetting agent.
• the so-called wetting operation is carried out for a few minutes.
• the support S after wetting, can be subjected to a step consisting in depositing at least one layer of resin, Res, comprising an acrylic layer on at least one of the faces of the support S. It is understood in particular that the deposition of the resin layer can be carried out by spreading on the face of the support S considered.
• the resin deposition step is itself followed by a so-called expansion step, consisting in subjecting the assembly constituted by the support provided with the resin layer Res, this in order to allow the surface of the aforementioned resin layer and of the support a surface structure of the plush, velvet or cellular foam type previously mentioned.
• the expansion step may consist of a step of heating the assembly constituted by the support S and the resin Res, this assembly being subjected to a heat treatment at a temperature between 120 ° and 250 ° depending on the nature of the support S and the aforementioned resin Res.
• Various tests have been carried out in order to determine the best operating mode for carrying out the expansion step previously cited and described in connection with FIG. 2e. Referring to FIG.
• the previously mentioned expansion step may consist first of all in subjecting the assembly constituted by the support S and the resin Res to a drying step, the aforementioned assembly being subjected to a ventilation air flow FA in a closed enclosure for example for an appropriate duration of a few minutes.
• the aforementioned drying step can then be followed by a heat treatment step proper, the assembly consisting of the support S and the resin Res being placed in an oven at a temperature between 120 ° and 250 ° for example.
• the resin Res can advantageously be formed by a paint comprising an acrylic base.
• an acrylic base marketed under the designation PRINTOFIX FLOCK LW and under the product code 254210-100 by the company CLARIANT S.A. in France.
• this acrylic base consists of acrylic binders and thickeners with a blowing agent.
• Another paint has proved to be particularly suitable for implementing the process and the material which are the subject of the invention, it is the paint sold worldwide under the designation "brod 'express" by the company PÉBÉO.
• the companies LEFRANC & BOURGEOIS and PÉBÉO are domiciled in France.
• the processing step thermal previously described in fact allows to cause the expansion of air microbubbles contained in the resin Res and thus the formation of open microcavities, forming the plurality of obstacles to the propagation of the mechanical surface wave and local waves.
• These open microcavities constitute a layer of air in direct contact with the ambient air, which also causes a boundary layer improving the coupling of the membrane with the ambient air, when the relative movement of the latter takes place. opposite the latter.
• the process which is the subject of the invention consists in forming the support from a continuous structure of a determined material, then in forming on at least one of the faces of the support an absorbent coating of this mechanical wave. surface and local waves from the same material, the coating however being expanded and then having an apparent density lower than that of the support.
• a solution may consist, as shown in FIG. 2g, of forming a temporary support S 'and, on one face of this temporary support S', forming a coating R ′ of material such as the acrylic base previously mentioned in the description.
• the coating R 'on the support S' is shown in 2) in Figure 2g.
• the coating R ′ can be produced by several successive layers of the acrylic base mentioned above marketed by CLARIANT.
• the temporary support S ′ can be formed by bamboo cellulose paper, with a grammage of between 10 and 12 g / m 2 , or silicone.
• Step 2 is then followed by a step 3 in which the assembly formed by the support S 'and the coating R' is then, in step 3, subjected to compression P in order to stiffen the assembly and in particular to densify the coating R '.
• the assembly constituted by the support S 'and the densified coating R' can then be subjected to a mechanical treatment process making it possible to remove the support S ', this mechanical treatment thus making it possible to obtain, from the single coating R' , a support S made of the compressed material formed by the acrylic base previously mentioned.
• the mechanical removal treatment can be carried out by take-off under controlled ventilation FA, as shown in point 4) of FIG. 2g.
• the aforementioned material comprises a base constituted by a support S delimiting the previously mentioned surface, this support being formed from a continuous structure.
• the support S has a rigidity determined in a direction substantially orthogonal to the surface of the support.
• the support may consist of paper, metal such as aluminum, titanium, a structure woven from nylon threads, these various supports advantageously being able to be formed in the form of a sheet.
• the rigidity of the aforementioned sheets, in the direction orthogonal to the surface of these sheets, can advantageously correspond to a value of Young's modulus E such that Ix10 9 Pa ⁇ E ⁇ HOOx10 9 Pa.
• the range of values of the Young's modulus of the materials used covers materials as diverse as: cellulose pulp; - polycarbonate; glass-reinforced polymer; graphite polymer; 1 aluminum; titanium; - ceramics.
• the material as shown in FIG. 3a comprises an absorbent coating of a surface mechanical wave and local waves arranged on at least one of the faces of the support S.
• the absorbent coating R has a plurality of obstacles to the propagation of the mechanical surface wave and local waves. These obstacles are shown in a nonlimiting manner in FIG. 3a by a granular structure, denoted G in the above-mentioned figure.
• the coating R can be constituted by a structure chosen from lint, velvet, cellular foam for example.
• FIG. 3b represents a photograph, with a magnification of 100, of a preferred embodiment of the coating R when the latter is produced from the acrylic base previously mentioned in the description.
• the structure constituting the absorbent coating R comprises a plurality of protuberances regularly distributed inside and on the surface of the coating, these protuberances extending in a direction substantially orthogonal to the inside and on the external surface of the coating, over a height of between 2 ⁇ m and 500 ⁇ m, in successive layers for example.
• the air microbubbles contained in the microbeads granular of the structure shown are subjected to an expansion phenomenon which causes the partial destruction of the part of the aforementioned microbeads, this destruction creating the previously mentioned growths, which extend in a direction substantially orthogonal to the external surface of the coating.
• each expanded and degraded microbead constitutes, with respect to the surface mechanical wave and local waves, a network of mass-spring type shock absorbers absorbing the mechanical energy of the surface mechanical wave and local waves. generating these.
• the surface condition of the coating R consists of asperities and microcavities trapping air, these cavities being essentially open.
• Such a surface state creates, on the surface of the coating R, and of the membrane, an air layer which substantially improves the coupling of the membrane with the air which it sets in motion. This phenomenon can thus be compared to the notion of boundary layer of flows. This improved coupling allows better reproduction of the wavefront emitted by the membrane.
• the support S and the coating R are constituted by a single and same material as the acrylic base previously mentioned in the description.
• the expanded coating R has an apparent density p 2 lower than the apparent density pi of the support S.
• the electroacoustic transducer constitutes the "tweeter” or tweeter of a loudspeaker
• a motor constituted by a magnet, pole pieces and in the air gap.
• This motor of the conventional type, is, for this reason, not shown in detail in the drawing.
• the membrane ME is integral with the coil B, which is connected to the excitation wire by the audio signal.
• a molded material cover having a central recess is intended to be placed on the FR frame, the ME membrane and the SU suspension, so as to allow free travel. of the ME membrane in the central recess of the cover, when the latter is moved by the motor.
• the ME membrane is made of a material as defined and described above in conjunction with Figures 3a to 3c.
• the electroacoustic transducer described in connection with FIG. 4 can be implemented in accordance with the object of the present invention for any type of acoustic transducer other than a "tweeter", the membrane under these conditions however being shape according to a surface of revolution with respect to an axis of symmetry.
• the electroacoustic transducer which is the subject of the present invention can also be used in the form of flat transducers or loudspeakers, with a flexible or rigid membrane, this type of loudspeaker or transducer may even have no rigid frame ensuring the suspension.
• the material which is the subject of the invention appears to be well suited for coating the walls and membranes of horn speakers or compression chambers.
• the membrane ME has a substantially homogeneous rigidity corresponding to that of the material object of the invention, regardless of the zone of deformation of this membrane with respect to this axis of symmetry. This allows, thanks to the suppression or significant attenuation of mechanical surface waves and local waves as well as the creation of a substantially uniform deformation of the membrane, in the absence of significant microdeformation, to improve the phase coherence of the acoustic waves restored by the electroacoustic transducer object of the invention.
• the audio signal causes an almost random excitation of the membrane ME via the magnetic motor formed by the magnetic core NM and the coil B, the randomness being able to be understood as depending on the succession of sounds and the intensity of these sounds as a function of the type of acoustic signal reproduced, the pulsations generated at the level of the ME membrane in fact excite all the resonance modes and micromodes of the aforementioned membrane, all of these modes and micromodes corresponding in fact to the coloring phenomenon linked to the nature of the material and of the structure of the membrane used.
• the material object of the present invention used to produce such a membrane then behaves as an absorbent of the surface and local mechanical waves generated at the aforementioned membrane. It also provides better coupling with ambient air, due to the phenomenon comparable to that of a boundary layer, previously mentioned.
• Comparative tests for a loudspeaker and a tweeter have been carried out when the diaphragm of a loudspeaker of a conventional tweeter is replaced by a diaphragm, called a treated diaphragm, in accordance with the object of the present invention.
• the treated membrane was a cellulose pulp + binder membrane.
• the results of comparative tests are reported below in conjunction with Figures 5a, 5b and 6a, 6b.
• the amplitude in dB, scale from 0 to -30 dB, of the sound signal is represented on the ordinate, and in horizontal 2D abscissa, the time in milliseconds and the frequency in Hz.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Diaphragms For Electromechanical Transducers (AREA)

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• 1999
  • 1999-12-16 FR FR9915877A patent/FR2802759B1/fr not_active Expired - Fee Related
• 2000
  • 2000-12-18 WO PCT/FR2000/003578 patent/WO2001045462A1/fr not_active Application Discontinuation
  • 2000-12-18 EP EP00988951A patent/EP1238568A1/de not_active Withdrawn
  • 2000-12-18 US US10/148,754 patent/US20030075382A1/en not_active Abandoned

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