US3894333A - Electromechanical transducer and method of making same - Google Patents

Electromechanical transducer and method of making same Download PDF

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Publication number
US3894333A
US3894333A US359568A US35956873A US3894333A US 3894333 A US3894333 A US 3894333A US 359568 A US359568 A US 359568A US 35956873 A US35956873 A US 35956873A US 3894333 A US3894333 A US 3894333A
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Prior art keywords
diaphragm
stator
conductive
transducer
electret
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Expired - Lifetime
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US359568A
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English (en)
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Loh-Yi Chang
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UNIROYAL Ltd
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UNIROYAL Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/01—Electrostatic transducers characterised by the use of electrets
    • H04R19/013—Electrostatic transducers characterised by the use of electrets for loudspeakers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49005—Acoustic transducer

Definitions

  • This invention relates to electromechanical transducers and to methods of making the same. More particularly, the invention relates to electromechanical transducers utilizing a polarized dielectric material such as an electret in a construction suitable for push-pull operation without requiring an external direct-current bias voltage.
  • One prior transducer utilizes a diaphragm comprising a number of layers of thin electret material and a num' ber of conductive layers positioned between two electrodes for push-pull operation.
  • the dynamic mass of that diaphragm is usually higher than that of an electrostatic transducer of similar design which does not use electret materials but uses an external directcurrent bias voltage.
  • the higher dynamic mass of the electret diaphragm adversely affects the fidelity and conversion efficiency of the transducer.
  • the air gap space between the diaphragm and the stationary member of the transducer should be of the order of approximately mils.
  • the vibrational force on the diaphragm is a maximum when the thickness of the electret is greater than the air gap space, that is, when the thickness of the electret equals the dielectric constant of the electret multiplied by the air gap space.
  • the maximum vibrational force on the prior electret diaphragm described above cannot be realized practically because the electret diaphragm would be too thick to vibrate.
  • the equivalent direct current bias voltage may be at least one kilovolt. This is higher than the bias voltage of conventional electrostatic earphones, which is usually approximately 200 volts. Accordingly, high efficiency and stability can be obtained in transducers constructed in accordance with the invention without the high voltage hazard of an external bias voltage necessary for conventional electrostatic earphones.
  • an electromechanical transducer comprises a pair of electrostatically polarized dielectric stator means each having a conductive member and each having apertures therethrough.
  • the transducer also includes thin, vibratory diaphragm means comprising a layer of conductive material, means for supporting the diaphragm means between the stator means in spaced relation thereto, and means for individually connecting electrically to the conductive members of the stator means and the conductive layer of the diaphragm means.
  • the method of making an electromechanical transducer comprises assembling in spaced relation a pair of dielectric stator means each having a conductive member and each having apertures therethrough and thin, vibratory diaphragm means comprising a layer of conductive material between the stator means, and electrostatically polarizing the assembled stator means by applying a high potential difference from the conductive member of each stator means to the conductive layer of the diaphragm means.
  • an electromechanical transducer comprises electrostatically polarized dielectric stator means having a conductive member and having a dielectric constant.
  • the transducer also includes thin, vibratory diaphragm means comprising a layer of conductive material, means for supporting the diaphragm means in spaced relation to the stator means, the thickness of the dielectric stator means exclusive of the conductive member being approximately equal to the product of the dielectric constant times the distance between the diaphragm means and the stator means, and means for individually connecting electrically to the conductive member of the stator means and the conductive layer of the diaphragm means.
  • stator means means which is stationary within the transducer insofar as mechanical vibrations, for example, sound-reproducing or sound-responsive vibrations, within the transducer are concerned.
  • H6. 1 is a plan view, partly schematic, of a transducer suitable for use in an earphone and constructed in accordance with the invention
  • FIG. 2 is a fragmentary, sectional view, partly schematic, of the FIG. 1 transducer, taken along line 22 of FIG. 1, with the transducer drawn to an enlarged scale;
  • FIG. 3 is a plan view, partly schematic, of a stator of the FIG. I transducer
  • FIG. 4 is a perspective view, partly schematic, of the diaphragms and supporting frames of the H6. 1 transducer;
  • FIG. 5 is a fragmentary, sectional view, partly schematic, of the H0 4 diaphragms, drawn to an enlarged scale and taken along line 55 of FIG. 4;
  • FIG. 6 is a plan view of a frame utilized to space the diaphragms of FIG. 4;
  • FIG. 7 is a fragmentary sectional view, to an enlarged scale, of the FIG. 1 transducer, taken along line 7-7 of PK 1, representing means for connecting electrically to the conductive layers of the diaphragm means;
  • FIG. 8 is a diagram, partly schematic, of two earphone transducers constructed in accordance with the invention and electrical circuits connected thereto suitable for coupling to sources of electrical audiofrequency signals representing stereophonic sound.
  • an electromechanical transducer in accordance with the invention and suitable for use in an earphone is there represented.
  • the transducer may be housed in a conventional earphone casing (not shown) and may be attached thereto by any suitable means, for example, by contact cement.
  • the transducer comprises a pair of polarized dielectric stator means 10, 11 each having a conductive layer thereon and each having apertures 10a, 1 la therethrough.
  • the dielectric stator means preferably comprises a polarized electret sheet material, for example, a sheet of Lexan obtained commercially from General Electric Company which is believed to be polycarbonate of the following composition: poly[2,2-bis(4- hydroxyphenyl) propane carbonate].
  • Each polycarbonate sheet 10, 11 may have a thickness of, for example, 50 mils and preferably is in the range of 1 mil to k inch. Such a sheet material of 50 mils thickness has the mechanical strength, stability and rigidity suitable for the electret electrode.
  • the thickness of the conductive layer 10b, 1 lb on each electret may be, for example, 10 mils.
  • a layer of electrically insulating material 12, 13, for example, a coating of approximately /2 mil thickness may be applied to the conductive layers 10b, 1 lb.
  • a thin film electret could be laminated with a more rigid material, for example, a perforated metal plate to form the stator electrode of the desired mechanical strength and rigidity.
  • each stator 10, 11 a polycarbonate sheet may be, for example, sprayed, painted, or silk screened with a suitable conductive coating, for example, an adherent silver-loaded coating.
  • the coated sheet may be cut to the desired size, and perforated in the desired pattern as represented schematically in FIG. 3.
  • a conductive metal washer 14, which may be suitably cleaned, may be adhered with conductive epoxy to a projection 10c of the silver pattern surrounding an aperture in the stator to provide a suitable conductive connection between the silver coating and a terminal for making an electrical connection thereto to be described subsequently. After the conductive epoxy has set completely, the stator may be suitably cleaned.
  • the stators l and 11 preferably are of the same construction and silver pattern but the pattern 11b is positioned with its projection 11: extending in the opposite direction to the projection c as represented in broken line construction in FIG. 1.
  • the stator 10 has, for example, 90 apertures per square inch of 1/ 16 inch diameter in a pattern represented schematically in FIG. 3. That is, there are, for example, no apertures in the central region of, for example, one-half inch by one-half inch and no apertures in the edge region of, for example, /8 inch width of the silver pattern, to provide desired electromechanical conversion efficiency and sound transmission with little distortion in a frequency range of, for example, 50 hertz to 10 kilohertz.
  • the dimensions of the silver region of the stator may, for example, be 3 inches by 3.5 inches and may, for example, have the shape of an ellipse.
  • the aperture size, the number of apertures and their positions may be changed to change the efficiency, sound transmission and fidelity desired.
  • the apertures are uniformly distributed as represented and are not clustered in a single region.
  • the earphones with apertures per square inch of l/16 inch diameter can develop an output of over decibels (relative to 0.0002 dyne/cm with a flat frequency response, that is, plus or minus three decibels, over a frequency range from 50 hertz to 10 kilohertz.
  • a flat frequency response that is, plus or minus three decibels
  • Preliminary tests indicate that for apertures of 1/ 16 inch diameter approximately 50 apertures per square inch may provide maxiumum sound transmission with a flat frequency response, that is, plus or minus three decibels, over a frequency range from 50 hertz to 12 kilohertz.
  • Each stator may be polarized or charged, for example, by negative ion charge injection from an electrode at, for example, a negative 20 to 30 kilovolts across an air gap to the polycarbonate side of the stator while the silver side of the stator is grounded.
  • the charge period may be, for example, /2 minute to 20 minutes.
  • the stators preferably are charged simultaneously after assembly into a complete transducer in accordance with a preferred method of making the transducer to be described subsequently.
  • the transducer also includes vibratory diaphragm means comprising a layer of conductive material 17a and 17b and means for supporting the diaphragm means between the stator means in spaced relation thereto.
  • the diaphragm means comprises, for example, two stretched polyethylene terephthalate films 18a, 18b available under the trade mark Mylar.
  • Means for supporting the diaphragm means comprises, for example, cardboard frames 19, 20, 21 which are adhesively bonded in position in the transducer.
  • At least one Mylar film of the diaphragm has a conductive layer thereon formed by, for example, a vacuum deposited aluminum coating.
  • both films are conductively coated because better electronic and mechanical balance can be achieved in push-pull operations.
  • the films are preferably so arranged that their insulating sides face their respective stators and their conductive coatings 17a, 17b face each other.
  • Each of the Mylar films may have a thickness of, for example, one-half mil and each of the conductive coatings on the films a thickness of, for example, a few thousand Angstroms.
  • the cardboard spacer 20 preferably has a conductive metalized surface and has a thickness of, for example, 10 mils and is inserted between the conductive surfaces and 17b of the diaphragm films to maintain them at the same electrical potential and to prevent the films from rubbing against each other at high frequency.
  • the cardboard frames 19 and 21 may each have a thickness of, for example, 15 mils to provide an air gap of, for example, 15 mils thickness or distance between each diaphragm and the corre sponding stator.
  • the dielectric constant of the polycarbonate sheet material is 3.02.
  • the thickness of the electret sheet material of each stator 10, 11 preferably is greater than the thickness of the air gap and preferably is approximately equal to the product of the dielectric constant of the electret sheet material times the thickness of the air gap to provide maximum vibrational force on the diaphragm in response to an applied alternating-current voltage signal.
  • the thickness of the electret sheet material of each stator 10, 11 exd Kd,
  • d is the thickness of the electret
  • d is the thickness of the air gap between the electret stator member and the conductive layer of the diaphragm
  • K is the dielectric constant of the electret
  • e is the permittivity of air.
  • a is the area of the surface of the electret stator member cooperative with the diaphragm.
  • V is the alternating-current voltage signal applied between the stator electrode and the diaphragm.
  • the vibrational force F on the diaphragm is proportional to the product of the direct-current field strength E and the surface charge 0 induced on the diaphragm due to the alternatingcurrent signal and may be expressed:
  • stretched metalized film 170, 18a may be applied adhesively to a cardboard frame such as frame 19 represented in FIG. 5 by, for example, contact cement.
  • the frame 21 may be similar to the frame 19 and a stretched metalized film 17b, 18b may be applied thereto in a similar manner.
  • metalized over its entire surface area by, for example, a conductive epoxy coating may then be positioned between the films and the components of the diaphragm assembly may be adhered together with contact cement with conductive contact being maintained between regions of the metalized spacer 20 and the conductive surfaces 17a, 17b of the diaphragm films.
  • the diaphragm assembly may be placed in a pre-heated oven at a temperature of, for example, C for a period of, for example, 2 minutes, until the Mylar film heat shrinks and suitable diaphragm tension results.
  • the metalized spacer has a slot 200 of, for example, 50 mils width, to allow gas pressure stabilization in the diaphragm assembly of FIG. 4.
  • the diaphragm assembly may then be adhesively bonded to the stators 10, 11 as represented in FIGS. 1 and 2 preferably with the apertures of both stators aligned in order to yield a higher acoustic transmissivity.
  • FIG. 7 is a fragmentary sectional view to an enlarged scale of the FIG. 1 transducer taken along line 7-7 of FIG.
  • an opening 10d in the stator 10 and similar openings 19d and 21d through the cardboard frames 19 and 21 are openings for means for connecting electrically to the center metalized spacer 20 and to the conductive layers 17a, l7b of the diaphragm means, comprising, for example, a suitable terminal or conductive solder lug 33a held in conductive contact with the spacer 20 by a screw 31a which extends through conductive washer 320, the spacer 20 and the other cardboard frame 21 and is fastened by a suitable washer 34 and nut 34a.
  • FIG. 2 of the drawings there is represented in the fragmentary sectional view, drawn to an enlarged scale, of the FIG. 1 transducer, means for connecting electrically to the stator surface 10a.
  • a screw 25 extends through a lock washer 26 and conductive solder lug 27 and through conductive washer l4 and silver projection 10c of the surface 100, through an insulating compressible washer 28 of, for example, rubber, through a lock washer 29 and nut 30 on the other side of the transducer. Electrical connection is thereby assured between the solder lug 27 and the silver coating 10b.
  • a generally similar connection may be made to the silver coating 11b of the other stator, as also represented in FIG. 2.
  • a conductive screw 31 extends through conductive lock washer 32, conductive solder lug 33, conductive washer 34, insulating compressible washer 35, silver coating projection 11c, conductive washer 36 and nut 37.
  • the means for individually connecting electrically to the conductive layers of the stator means and the diaphragm means comprises means for applying electrical signals to the conductive layers of the stator means and the diaphragm means.
  • the preferred method of making an electromechanical transducer comprises assembling in spaced relation a pair of dielectric stator means each having a conductive layer thereon and each having apertures therethrough and thin vibratory, diaphragm means comprising a layer of conductive material supported between the stator means.
  • the method comprises electrostatically polarizing the assembled stator means by applying a high potential difference from the conductive layer of each stator member to the conductive layer of the diaphragm means.
  • the step of polarizing the assembled stator means includes the step of applying the same high potential difference from the conductive layer of each stator means to the conductive layer of the diaphragm means.
  • the polarized dielectric stator means 10, ll develop direct-current electric fields of the same polarity relative to the layer of conductive material 17a, 17b of the diaphragm means.
  • Transducers utilizing electret stators polarized by this method have higher efficiency and lower distortion than transducers utilizing stators polarized prior to assembly in the transducer by the previously-described method because the potential differences between the center diaphragm and the conductive coatings of the electret stators due to the surface charges of the elec tret stators are approximately equal after the charging process.
  • the best electret stators are formed while an air space is maintained between one of the charging electrodes and the electret material.
  • air spaces are provided between the diaphragms and the electrodes comprising the silver coatings of the stators.
  • transducers constructed in accordance with the inven-' tion utilizing electrets charged prior to assembly in the transducers in the manner described previously also have high conversion efficiency because of the high equivalent direct current bias voltage of, for example, one kilovolt or more, and the transducers have low distortion because of push-pull operation, but the method of charging the transducer electrets after assembly is preferred to obtain even higher efficiency and lower distortion.
  • FIG. 8 of the drawings there is represented a circuit diagram, partly schematic, of two earphones each comprising a transducer constructed in accordance with the invention and suitable for push-pull operation, to be coupled to the output circuits of a stereophonic audio system.
  • the resistors 40 may individually have values of, for example, 10 megohms and are connected to the terminals of the stators 10, 11 and the diaphragm means 17a, 17b, 18a, 18b of each transducer as represented.
  • the resistors may physically be positioned at the rear side of each transducer.
  • the resistors 40 may not be necessary for some constructions and may be eliminated.
  • Suitable transformer windings 41, 42 individually coupled to the left and right channels of a stereophonic audio source (not shown), supply audiofrequency electrical signals which cause push-pull operation of each of the transducers.
  • Loudspeakers comprising transducers in accordance with the invention can be constructed by combining a group of transducers to get more radiation area.
  • the transducers in accordance with the invention can also be constructed as, for example, push-pull microphones and vibration pick-ups.
  • an electromechanical transducer comprising assembling in spaced relation a pair of electret stator means each having a conductive member thereon and each having apertures therethrough, and thin, vibratory diaphragm means comprising a pair of layers of conductive material individually on a pair of films of plastic material supported between said stator means with each of said plastic films being between the conductive layer thereon and the stator means adjacent thereto, and electrostatically polarizing the assembled stator means by applying a high potential difference from said conductive member of each stator means to said conductive layers of said diaphragm means.
  • step of polarizing the assembled stator means includes the step of applying the same high potential difference from said conductive member of each stator means to said conductive layer of said diaphragm

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
US359568A 1972-09-08 1973-05-11 Electromechanical transducer and method of making same Expired - Lifetime US3894333A (en)

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CA151,244A CA989514A (en) 1972-09-08 1972-09-08 Electromechanical transducer and method of making same

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US (1) US3894333A (de)
JP (1) JPS49101017A (de)
CA (1) CA989514A (de)
DE (1) DE2345285A1 (de)
FR (1) FR2199242B1 (de)
GB (1) GB1444763A (de)
NL (1) NL7312472A (de)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4382328A (en) * 1981-01-02 1983-05-10 Janszen Arthur A Method of making stationary electrodes for electrostatic transducers
WO1984004865A1 (en) * 1983-05-23 1984-12-06 Harold Norman Beveridge Electrode for electrostatic transducer and methods of manufacture
US6760462B1 (en) 2003-01-09 2004-07-06 Eminent Technology Incorporated Planar diaphragm loudspeakers with non-uniform air resistive loading for low frequency modal control
US20070189559A1 (en) * 2006-01-03 2007-08-16 Final Sound Internationale Pte Ltd. Electrostatic Loudspeaker Systems and Methods
US20110033079A1 (en) * 2009-08-10 2011-02-10 Industrial Technology Research Institute Flat loudspeaker structure
US20120002826A1 (en) * 2010-06-30 2012-01-05 Tsung-Hung Wu Electret electroacoustic transducer
CN102843628A (zh) * 2011-06-24 2012-12-26 富祐鸿科技股份有限公司 耳机发声结构及其组装方法
US20130022225A1 (en) * 2011-07-22 2013-01-24 Fortune Grand Technology Inc. Headphone sound-generating structure and method of assembling same
CN106341748A (zh) * 2015-07-17 2017-01-18 富祐鸿科技股份有限公司 静电耳机发声结构
US20170188158A1 (en) * 2015-12-23 2017-06-29 Sennheiser Electronic Gmbh & Co. Kg Electrostatic Headphones
US10697230B2 (en) 2018-02-27 2020-06-30 Taylor Made Group, Llc High strength window or door system
US11496838B2 (en) * 2020-04-18 2022-11-08 Audeze, Llc Electroacoustic transducer assembly

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE505752C2 (sv) * 1995-12-22 1997-10-06 Tore Fors Högtalare

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3389226A (en) * 1964-12-29 1968-06-18 Gen Electric Electrostatic loudspeaker
US3474197A (en) * 1964-10-24 1969-10-21 Tesla Np Electret microphone
US3646280A (en) * 1969-08-28 1972-02-29 Pioneer Electronic Corp Backplate for electret loudspeaker

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1639444B2 (de) * 1967-05-15 1972-08-03 Thermo Electron Engineering Corp., Waltham, Mass. (V.StA.) Elektroakustischer wandler
DE1952999A1 (de) * 1968-10-22 1970-08-13 Kureha Chemical Ind Co Ltd Elektrostatischer elektroakustischer Wandler
JPS4840084B1 (de) * 1969-11-19 1973-11-28
JPS4912598Y1 (de) * 1970-07-14 1974-03-28

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3474197A (en) * 1964-10-24 1969-10-21 Tesla Np Electret microphone
US3389226A (en) * 1964-12-29 1968-06-18 Gen Electric Electrostatic loudspeaker
US3646280A (en) * 1969-08-28 1972-02-29 Pioneer Electronic Corp Backplate for electret loudspeaker

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4382328A (en) * 1981-01-02 1983-05-10 Janszen Arthur A Method of making stationary electrodes for electrostatic transducers
WO1984004865A1 (en) * 1983-05-23 1984-12-06 Harold Norman Beveridge Electrode for electrostatic transducer and methods of manufacture
US4533794A (en) * 1983-05-23 1985-08-06 Beveridge Harold N Electrode for electrostatic transducer
US6760462B1 (en) 2003-01-09 2004-07-06 Eminent Technology Incorporated Planar diaphragm loudspeakers with non-uniform air resistive loading for low frequency modal control
US20070189559A1 (en) * 2006-01-03 2007-08-16 Final Sound Internationale Pte Ltd. Electrostatic Loudspeaker Systems and Methods
US8000483B2 (en) * 2006-01-03 2011-08-16 Transparent Sound Technology B.V. Electrostatic loudspeaker systems and methods
US8385586B2 (en) * 2009-08-10 2013-02-26 Industrial Technology Research Institute Flat loudspeaker structure
US20110033079A1 (en) * 2009-08-10 2011-02-10 Industrial Technology Research Institute Flat loudspeaker structure
US20120002826A1 (en) * 2010-06-30 2012-01-05 Tsung-Hung Wu Electret electroacoustic transducer
CN102843628A (zh) * 2011-06-24 2012-12-26 富祐鸿科技股份有限公司 耳机发声结构及其组装方法
CN102843628B (zh) * 2011-06-24 2015-01-07 富祐鸿科技股份有限公司 耳机发声结构及其组装方法
US20130022225A1 (en) * 2011-07-22 2013-01-24 Fortune Grand Technology Inc. Headphone sound-generating structure and method of assembling same
US8699740B2 (en) * 2011-07-22 2014-04-15 Fortune Grand Technology Inc. Headphone sound-generating structure and method of assembling same
CN106341748A (zh) * 2015-07-17 2017-01-18 富祐鸿科技股份有限公司 静电耳机发声结构
US20170188158A1 (en) * 2015-12-23 2017-06-29 Sennheiser Electronic Gmbh & Co. Kg Electrostatic Headphones
US10231060B2 (en) * 2015-12-23 2019-03-12 Sennheiser Electronic Gmbh & Co. Kg Electrostatic headphones
US10697230B2 (en) 2018-02-27 2020-06-30 Taylor Made Group, Llc High strength window or door system
US11496838B2 (en) * 2020-04-18 2022-11-08 Audeze, Llc Electroacoustic transducer assembly

Also Published As

Publication number Publication date
NL7312472A (de) 1974-03-12
CA989514A (en) 1976-05-18
FR2199242B1 (de) 1978-11-03
GB1444763A (en) 1976-08-04
JPS49101017A (de) 1974-09-25
FR2199242A1 (de) 1974-04-05
DE2345285A1 (de) 1974-03-21

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