US3773984A - Electrostatic loudspeaker with constant current drive - Google Patents

Electrostatic loudspeaker with constant current drive Download PDF

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Publication number
US3773984A
US3773984A US00086614A US3773984DA US3773984A US 3773984 A US3773984 A US 3773984A US 00086614 A US00086614 A US 00086614A US 3773984D A US3773984D A US 3773984DA US 3773984 A US3773984 A US 3773984A
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sections
loudspeaker
input terminals
network
electrostatic loudspeaker
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US00086614A
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English (en)
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P Walker
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QUAD ELECTROACOUSTICS Ltd
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Individual
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Assigned to QUAD ELECTROACOUSTICS LIMITED, reassignment QUAD ELECTROACOUSTICS LIMITED, ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: WALKER, PETER J.
Assigned to QUAD ELECTROACOUSTICS LIMITED reassignment QUAD ELECTROACOUSTICS LIMITED ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ACOUSTICAL MANUFACTURING COMPANY LIMITED, THE
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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
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • H04R1/403—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers loud-speakers
    • 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
    • H04R19/02—Loudspeakers

Definitions

  • an electrostatic loudspeaker that is acoustically transparent over the frequency range of interest, for instance the audio frequency range, comprises separately accessible coplanar sections or individual units arranged to carry a common polarizing charge per unit area and which are connected as the parallel components of an electrical network so organized that the vector sum of the currents in the individual sections or units is always directly proportional to the total current at the input terminals of the network.
  • This invention concerns loudspeakers and is particularly concerned with high-quality electrostatic loudspeakers.
  • a cone or diaphragm meeting this area criterion is directional at high frequencies so that it is usual to employ a system of two or three cones or diaphragms or separate loudspeaker units, these being interconnected mechanically or electrically so that sound is radiated from a smaller area as the signal frequency increases.
  • this invention is concerned with the mitigation of these problems in an electrostatic loudspeaker.
  • any electrostatic loudspeaker element may take a variety of constructional forms but for the purposes of explaining the present invention it will be convenient to consider the construction that consists essentially of two perforated rigid plate electrodes in parallel relationship with a flexible membrane or diaphragm stretched or supported in the space between the electrodes. If a polarizing charge is fed to the diaphragm and an AC signal is applied between the electrodes there will be a force on the diaphragm proportional to the product of the AC and DC fields and the fold diaphragm will move in response to this force and radiate sound,
  • An electrostatic loudspeaker element of this construction is acoustically transparent over a wide frequency range between a low frequency limit determined by the stiffness or tension of the diaphragm and a high frequency limit determined by the mass of the diaphragm and any added mass due to the holes in the rigid electrodes. It is comparatively simple to arrange that these limits are beyond, or at the extremes of, the frequency range of interest, e.g. the audio frequency range.
  • an electrostatic loudspeaker that is at least substantially acoustically transparent over the frequency range of interest has separately accessible coplanar sections adapted to carry a common polarizing charge per unit area, these sections being so connected as the parallel components of an electrical network that, irrespective of the series branches of that network, the vector sum of the component currents in the individual sections will be equal to or proportional to the total current at the input terminals of the network.
  • Such a loudspeaker may have a single membrane or diaphragm with sub-divided signal electrode(s) or it may comprise a number of coplanar electrostatic loudspeaker units.
  • the series branches of the said network are preferably arranged to delay and/or attenuate the signal voltages applied to the individual parallel components so that the total radiating area and/or its effective phase contour varies with frequency, a well known technique to produce a desired directivity pattern.
  • a resistor may be connected to sample the current at the input terminals of the said network, the voltage developed being applied as feedback in accordance with known techniques to control the current, and hence the far field axis response, independent of changes of network impedance with frequency.
  • FIG. 1 diagrammatically shows in front elevation an electrostatic loudspeaker of the constructional form discussed but modified in accordance with the invention.
  • FIG. 2 illustrates the circuitry associated with the loudspeaker of FIG. 1.
  • the loudspeaker illustrated in the drawings comprises a circular diaphragm 1 supported between a pair of electrodes 2, 3 that are each divided into concentric sections with the various sections connected by impedances 4.
  • the arrangement is equivalent to that of a group of serially connected loudspeaker units with impedances therebetween, the purpose of which is both to provide an improved impedance match to the amplifier and to provide an improved directivity characteristic.
  • the objective of a level axis response is sought by a. designing each unit to cover a small part of the audio frequency range with a more or less level response and the required sensitivity in that range and then designing the network to distribute the frequency spectrum accordingly; and/or b.
  • a convenient method of controlling the vector sum of the currents in the individual sections is by means of a resistor 7 to sample the current flowing to the sections of one electrode, e.g. electrode 2., and to develop a voltage that may be applied via line 8 as feedback to the amplifier that feeds the loudspeaker through the usual transformer shown at 9. Care must be taken to keep stray capacitance to a minimum to ensure that the current through the resistor 7 is indeed proportional to the true vector sum of unit currents. In a practical loudspeaker, virtually complete and automatic control of axis response may be obtained from about 1001-12 to 10,000Hz. The high frequency limit is due to stray capacity and lack of acoustic transparency.
  • corrections can be applied either by replacing the feedback resistor by a more complex network or by applying an electrical correction circuit external to the loop.
  • the low frequency limit is due to lack of acoustic transparency. This is associated with the fundamental resonance of the diaphragm l at say 40 c/s and this must be damped electrically and/or mechanically as would be done with a conventional electrostatic loudspeaker.
  • An electrostatic loudspeaker system that is at least substantially acoustically transparent over a predetermined frequency range and comprising, a pair of loudspeaker terminals, a plurality of separately accessible coplanar voltage driven sections operatively connected to have a common polarising charge per unit area applied thereto, an electrical network connecting said sections to said terminals such as to improve the non-directionability of the loudspeaker at high audio frequencies, a pair of input terminals, constant-current driving means connected between said pair of input terminals and said loudspeaker terminals, the voltage across said loudspeaker terminals driving the loudspeaker in response to an audio signal applied to said input terminals, the far field axis-pressure response of said loudspeaker system being directly related to the driver current of said driving means, and means for controlling said driving means in a manner such that the vector sum of all the currents in said coplanar sections is made to follow the instantaneous amplitude of said audio signal applied to said input terminals.
  • said means connecting said sections to said input terminals comprise a network in which said sections are parallel-connected components, said network having series branches arranged in a manner to produce a predetermined directivity pattern.
  • said driving means includes a sampling resistor connected at said input terminals, the voltage developed across said resistor being applied as feedback to maintain the current independent of changes of the impedance with frequency.
  • controlling means includes means for monitoring the vector sum of all the currents in said coplanar sections, and a feedback connection to said driving means for maintaining said vector sum directly proportional to the voltage of said audio signal applied to said input terminals.
  • An electrostatic loudspeaker according to claim 6, wherein said sections are connected as parallel impedances in said network and said monitoring means comprise a single resistor connected in series in the network to carry the total current flowing in said sections, thereby to develop a feedback voltage thereacross proportional to said total current.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
US00086614A 1967-06-06 1970-11-03 Electrostatic loudspeaker with constant current drive Expired - Lifetime US3773984A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2615167 1967-06-06

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US3773984A true US3773984A (en) 1973-11-20

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US00086614A Expired - Lifetime US3773984A (en) 1967-06-06 1970-11-03 Electrostatic loudspeaker with constant current drive

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US (1) US3773984A (enrdf_load_stackoverflow)
DE (1) DE1762375C3 (enrdf_load_stackoverflow)
FR (1) FR1601302A (enrdf_load_stackoverflow)
GB (1) GB1228775A (enrdf_load_stackoverflow)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3892927A (en) * 1973-09-04 1975-07-01 Theodore Lindenberg Full range electrostatic loudspeaker for audio frequencies
EP0084608A1 (de) 1982-01-22 1983-08-03 Savod Sa Elektronni Preobrasuvatelni Elementi Elektrostatischer Schallwandler
US4703509A (en) * 1985-06-19 1987-10-27 Zavod Za Elektronni Preobrazuvatelni Elementi Electrostatic acoustic converter with stationary electrode having a progressively increasing surface resistance
US20080192953A1 (en) * 2004-10-04 2008-08-14 Holger Opfer Loudspeaker Arrangement in a Motor Vehicle
US20080212805A1 (en) * 2006-10-16 2008-09-04 Thx Ltd. Loudspeaker line array configurations and related sound processing
WO2010137988A1 (en) 2009-05-29 2010-12-02 Leiv Eiriksson Nyskapning As Loudspeaker arrangement
US20100322444A1 (en) * 2009-06-17 2010-12-23 Leiv Eiriksson Nyskapning As Loudspeaker arrangement
US20110019845A1 (en) * 2008-04-18 2011-01-27 Panphonics Oy Directing sound field of actuator
US20120033834A1 (en) * 2010-08-04 2012-02-09 Nokia Corporation Apparatus With Directivity Pattern

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT361555B (de) * 1979-02-12 1981-03-25 Akg Akustische Kino Geraete Kopfhoerer
GB2173068B (en) * 1985-02-08 1989-06-07 Furuno Electric Co Beam forming device
NL8601772A (nl) * 1986-07-08 1988-02-01 Philips Nv Inrichting voor het omzetten van een elektrisch signaal in een akoestisch signaal, voorzien van een elektrostatische omzettereenheid.
GB2520352A (en) * 2013-11-19 2015-05-20 Mellow Acoustics Ltd Loudspeakers and loudspeaker drive circuits
WO2021243367A1 (en) * 2020-05-29 2021-12-02 Shure Acquisition Holdings, Inc. Segmented stator plates for electrostatic transducers

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1983377A (en) * 1929-09-27 1934-12-04 Gen Electric Production of sound
GB537931A (en) * 1940-02-21 1941-07-14 Donovan Ernest Lea Shorter Improvements in electrostatic loudspeakers
US2302493A (en) * 1941-01-28 1942-11-17 Gen Electric Amplifying system
US2387845A (en) * 1943-06-24 1945-10-30 Bell Telephone Labor Inc Electroacoustic transducer
US2634335A (en) * 1948-12-18 1953-04-07 Ampex Electric Corp Magnetic recording system with negative feedback system
US2843671A (en) * 1954-05-19 1958-07-15 David Bogen & Company Inc Feed back amplifiers
US2905761A (en) * 1956-08-29 1959-09-22 Siegler Corp Control of amplifier source resistance
US3061675A (en) * 1958-09-09 1962-10-30 Texas Instruments Inc Loud speaker improvement
US3135838A (en) * 1958-12-10 1964-06-02 Wright St George Lab Inc Electrostatic loudspeaker
US3542952A (en) * 1967-05-18 1970-11-24 Chien San Wang Low distortion signal reproduction apparatus

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1983377A (en) * 1929-09-27 1934-12-04 Gen Electric Production of sound
GB537931A (en) * 1940-02-21 1941-07-14 Donovan Ernest Lea Shorter Improvements in electrostatic loudspeakers
US2302493A (en) * 1941-01-28 1942-11-17 Gen Electric Amplifying system
US2387845A (en) * 1943-06-24 1945-10-30 Bell Telephone Labor Inc Electroacoustic transducer
US2634335A (en) * 1948-12-18 1953-04-07 Ampex Electric Corp Magnetic recording system with negative feedback system
US2843671A (en) * 1954-05-19 1958-07-15 David Bogen & Company Inc Feed back amplifiers
US2905761A (en) * 1956-08-29 1959-09-22 Siegler Corp Control of amplifier source resistance
US3061675A (en) * 1958-09-09 1962-10-30 Texas Instruments Inc Loud speaker improvement
US3135838A (en) * 1958-12-10 1964-06-02 Wright St George Lab Inc Electrostatic loudspeaker
US3542952A (en) * 1967-05-18 1970-11-24 Chien San Wang Low distortion signal reproduction apparatus

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3892927A (en) * 1973-09-04 1975-07-01 Theodore Lindenberg Full range electrostatic loudspeaker for audio frequencies
EP0084608A1 (de) 1982-01-22 1983-08-03 Savod Sa Elektronni Preobrasuvatelni Elementi Elektrostatischer Schallwandler
US4703509A (en) * 1985-06-19 1987-10-27 Zavod Za Elektronni Preobrazuvatelni Elementi Electrostatic acoustic converter with stationary electrode having a progressively increasing surface resistance
US20080192953A1 (en) * 2004-10-04 2008-08-14 Holger Opfer Loudspeaker Arrangement in a Motor Vehicle
US8848938B2 (en) * 2004-10-04 2014-09-30 Volkswagen Ag Electrostatic planar loudspeaker arrangement in a motor vehicle
US8135158B2 (en) 2006-10-16 2012-03-13 Thx Ltd Loudspeaker line array configurations and related sound processing
US20080212805A1 (en) * 2006-10-16 2008-09-04 Thx Ltd. Loudspeaker line array configurations and related sound processing
US9414152B2 (en) 2006-10-16 2016-08-09 Thx Ltd. Audio and power signal distribution for loudspeakers
US20110019845A1 (en) * 2008-04-18 2011-01-27 Panphonics Oy Directing sound field of actuator
US8565454B2 (en) 2008-04-18 2013-10-22 Panphonics Oy Directing sound field of actuator
WO2010137988A1 (en) 2009-05-29 2010-12-02 Leiv Eiriksson Nyskapning As Loudspeaker arrangement
US20100322444A1 (en) * 2009-06-17 2010-12-23 Leiv Eiriksson Nyskapning As Loudspeaker arrangement
US20120033834A1 (en) * 2010-08-04 2012-02-09 Nokia Corporation Apparatus With Directivity Pattern
US8831248B2 (en) * 2010-08-04 2014-09-09 Nokia Corporation Apparatus with directivity pattern

Also Published As

Publication number Publication date
FR1601302A (enrdf_load_stackoverflow) 1970-08-17
GB1228775A (enrdf_load_stackoverflow) 1971-04-21
DE1762375C3 (de) 1973-10-04
DE1762375A1 (de) 1970-04-30
DE1762375B2 (de) 1973-03-15

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Owner name: QUAD ELECTROACOUSTICS LIMITED, ENGLAND

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ACOUSTICAL MANUFACTURING COMPANY LIMITED, THE;REEL/FRAME:005051/0720

Effective date: 19870813

Owner name: QUAD ELECTROACOUSTICS LIMITED,, ENGLAND

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:WALKER, PETER J.;REEL/FRAME:005051/0722

Effective date: 19880520