EP0212840B1 - Geräuschreduzierungsvorrichtung - Google Patents

Geräuschreduzierungsvorrichtung Download PDF

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Publication number
EP0212840B1
EP0212840B1 EP86305415A EP86305415A EP0212840B1 EP 0212840 B1 EP0212840 B1 EP 0212840B1 EP 86305415 A EP86305415 A EP 86305415A EP 86305415 A EP86305415 A EP 86305415A EP 0212840 B1 EP0212840 B1 EP 0212840B1
Authority
EP
European Patent Office
Prior art keywords
noise
microphone
output
pick
cancelling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP86305415A
Other languages
English (en)
French (fr)
Other versions
EP0212840A3 (en
EP0212840A2 (de
Inventor
Robert Christopher Twiney
Anthony James Holden
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BAE Systems Defence Systems Ltd
Original Assignee
Siemens Plessey Electronic Systems Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Plessey Electronic Systems Ltd filed Critical Siemens Plessey Electronic Systems Ltd
Priority to AT86305415T priority Critical patent/ATE68903T1/de
Publication of EP0212840A2 publication Critical patent/EP0212840A2/de
Publication of EP0212840A3 publication Critical patent/EP0212840A3/en
Application granted granted Critical
Publication of EP0212840B1 publication Critical patent/EP0212840B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
    • G10K11/17825—Error signals
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17857—Geometric disposition, e.g. placement of microphones
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17875—General system configurations using an error signal without a reference signal, e.g. pure feedback
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3011—Single acoustic input
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3012—Algorithms
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3013—Analogue, i.e. using analogue computers or circuits
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3039—Nonlinear, e.g. clipping, numerical truncation, thresholding or variable input and output gain

Definitions

  • This invention relates to arrangements for reducing the level of acoustic noise fields within the internal cavities or enclosures of so-called ear-defenders or earphone structures when being worn by personnel (e.g. pilots, vehicle drivers, industrial workers etc.) in high noise environments.
  • personnel e.g. pilots, vehicle drivers, industrial workers etc.
  • noise pick-up microphones produce electrical signal outputs in response to the acoustic noise fields within the aforesaid cavities and these signal outputs are phase inverted, filtered and amplified in a feedback loop arrangement for the production of noise-cancelling signals fed to the noise-cancelling transducers which accordingly produce noise-cancelling acoustic signals of substantially the same amplitude but of opposite phase to the acoustic noise field waveforms.
  • the noise pick-up microphones do not detect the incoming or ambient noise level but rather the reduced noise level within the cavities following acoustic noise reduction (ANR). It can be shown that such ANR arrangements produce a reduction in noise at a particular frequency given by:- (1 + 2 G cos 0 ⁇ + G2) ⁇ 1 ⁇ 2 where G is the total gain of the feedback loop arrangement and 0 ⁇ is the total loop phase change at the particular frequency concerned. From this expression it can readily be appreciated that the scale of noise reduction achieved is highly dependent upon the total loop gain. Due to the imperfect transfer functions of the noise pick-up microphones and noise-cancelling tranducers the acoustic noise reduction arrangements will, at certain frequencies, be feeding in-phase (i.e.
  • the overall loop gain of the system must be kept at less than unity at the frequencies concerned otherwise the noise levels in the cavities of the earphone structures will actually be increased rather than reduced by the positive feedback signals fed to the noise- cancelling transducers.
  • the loop gain must be kept below unity at the aforesaid frequencies in order to maintain stability the loop gain of the ANR must be sufficiently high to provide the optimum acoustic noise reduction.
  • Fixed loop gain control techniques could be used but for changes that occur in the characteristics of components of the ANR system with the passage of time. Such fixed loop gain techniques would not provide the requisite compensation for changes in sensitivity of the noise-cancelling transducers resulting from changes in the volume of the earphone structure cavities which occur when the earphone structures are worn by different persons or from small changes in earphone structure position caused by normal movements of the wearer's head.
  • Automatic loop gain control techniques would be capable of providing the requisite aforesaid compensation but the conventional procedure has hitherto been to utilise only the output signal from the noise pick-up microphone of the ANR arrangement for linear fedback automatic gain control purposes.
  • Changes in the microphone output can result from a change in loop gain (e.g. due to earphone movement) which requires the automatic gain control arrangement to act to adjust the gain and from a change in external noise spectrum/level in which case the automatic gain control arrangement is not required to act.
  • loop gain e.g. due to earphone movement
  • the automatic gain control arrangement to act to adjust the gain and from a change in external noise spectrum/level in which case the automatic gain control arrangement is not required to act.
  • the cause of these changes in loop gain cannot be distinguished in an active noise reduction system utilising noise pick-up microphone outputs only for gain control purposes. Consequently, such simple linear feedback gain control systems are inherently unstable and cause the loop gain to oscillate continuously about the requisite value.
  • an automatic gain active noise reduction arrangement for reducing the level of acoustic noise within the internal cavity or enclosure of an ear-defender or earphone structure, the arrangement having improved stability and comprising a noise pick-up microphone and a noise-cancelling transducer mounted within said cavity or enclosure, the noise pick-up microphone being adapted to produce an electrical signal output in response to an acoustic noise field within said cavity or enclosure, and phase inverter means, filtering means and amplifying means connected in a feedback control path extending between the noise pick-up microphone and the noise-cancelling transducer and effective in response to the generation of an electrical signal output by the noise pick-up microphone to produce a noise-cancelling signal output which is fed to the noise-cancelling transducer, characterised in that the output from the noise pick-up microphone is also applied to signal processing and control means for producing and electrical output dependent upon the microphone output and a predetermined non-linear control algorithm which is applied to variable loop gain control means coupled with the feedback control path for controlling
  • control means may comprise a microprocessor which introduces a non-linear control algorithm.
  • the microprocessor allows the parameter of the microphone output to vary over a finite range before any action is taken by the microprocessor to adjust the loop gain through the variable loop gain control means.
  • the signal processing means may be adapted to provide analogue processing (e.g. filtering) of the microphone output signal followed by analogue-to-digital conversion prior to applying the digital signal to the microprocessor.
  • the microprocessor itself may be arranged to perform the necessary processing of the microphone output signal.
  • an earphone 1 comprising a cup-shaped housing 2 fitted around its rim with compliant material 3 which in use of the earphone cushions the housing 2 against the wearer's head.
  • the earphone 1 is provided with an active noise reduction arrangement for reducing the overall level of noise within the earphone housing 2.
  • This arrangement comprises a sub-miniature microphone 4 which detects the acoustic noise within the earphone housing 2 and provides and electrical output which is fed through an electrical phase inverter 5 and a filter 6 before being applied to a variable loop gain control device 7 and a power amplifier 8.
  • the output from the power amplifier 8 is applied to a suitably supported noise-cancelling transducer 9 (e.g.
  • the noise-cancelling transducer 9 produces acoustic signals of the same amplitude but of opposite phase to the acoustic noise field waveforms within the earphone housing 2.
  • the gain control arrangement extending from the noise detecting microphone 4 to the noise-cancelling transducer 9 but excluding the variable loop gain device 7 constitutes a close loop linear feedback automatic gain control active noise reduction arrangement.
  • ANR active noise reduction
  • the output from the microphone 4 is applied to an analogue processing device 10 (e.g. filter) the output from which is fed into an analogue-to-digital converter 11.
  • the output from the converter 11 is then applied to a microprocessor 12 which is arranged to operate on the digital input thereto corresponding to a particular parameter of the microphone output so as to produce an output which is controlled in accordance with whether the parameter concerned is within a predetermined range of its desired value then no further change in the loop gain will be made unless the parameter again moves outside the desired range.
  • this shows two measured traces 13 and 14 which are derived from a known form of linear automatic gain control arrangement.
  • the lower trace 13 represents a derived microphone output parameter which the control arrangement is monitoring and controlling.
  • the parameter concerned is the level of enhanced frequencies within the control loop.
  • the upper trace 14 shows the loop gain. As can be seen, strong oscillation occurs in the loop gain as the control arrangement responds to changes in the parameter and vice versa thereby demonstrating the instability of the linear automatic gain control arrangement.
  • FIG 3 this demonstrates the action of the automatic gain control of the arrangement according to the present invention.
  • the upper trace 15 shows the output from the control loop or the loop gain whereas the lower trace 16 shows the level of the parameter being controlled. After an initial period following activation of the control arrangement it can be seen that stable control of the control parameter is achieved.
  • the random variation in the control parameter shown is due to the fact that the measurement was taken in the presence of external noise and on a longer time scale than in Figure 2.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
  • Input Circuits Of Receivers And Coupling Of Receivers And Audio Equipment (AREA)
  • Superconductors And Manufacturing Methods Therefor (AREA)
  • Diaphragms For Electromechanical Transducers (AREA)
  • Noise Elimination (AREA)
  • Surgical Instruments (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)

Claims (3)

  1. Eine automatische verstärkungsaktive Geräuschresp. Lärmreduktionsanordnung für die Reduktion des Pegels von akustischen Geräuschen resp. von Lärm innerhalb des internen Hohlraumes oder der Einfassung eines Gehörschutzes oder Kopfhörers (1), wobei die Anordnung ein Lärmaufnahmemikrophon (4) und einen Lärmunterdrückungsumwandler (9) umfasst, die innerhalb des besagten Hohlraumes resp. der Einfassung angeordnet sind, wobei das Lärmaufnahmemikrophon ausgelegt ist, um ein elektrisches Ausgangssignal als Antwort zu einem akustischen Lärm- resp. Geräuschfeld innerhalb des besagten Hohlraumes resp. der Einfassung zu erzeugen, und Phaseninvertermittel (5), Filtermittel (6) und Verstärkermittel (8), die, verbunden in einem Rückkopplungssteuerpfad, sich zwischen dem Lärmaufnahmemikrophon (4) und dem Lärmunterdrükkungsumwandler (9) erstrecken und wirksam in Antwort auf die Erzeugung eines elektrischen Ausgabesignals durch das Lärmaufnahmemikrophon (4) ein Lärmunterdrückungsausgabesignal erzeugen, das an den Lärmunterdrückungsumwandler (9) eingegeben wird, dadurch gekennzeichnet, dass die Ausgabe vom Lärmaufnahmemikrophon (4) ebenfalls an Signalbearbeitungs- und Steuerungsmittel (10, 11, 12) zugeführt wird für die Erzeugung einer elektrischen Ausgabe, die von der Mikrophonausgabe und einem vorbestimmten, nicht linearen Steueralgorithmus abhängig ist, die an variable Rückkopplungsschleifen-Verstärkersteuermittel (7) zugeführt wird, gekoppelt mit dem Rückkopplungssteuerpfad für die Steuerung des Rückkopplungsschleifenverstärkers, entsprechend, ob das Niveau der verstärkten Frequenzen innerhalb eines vorbestimmten Bereiches von erwünschten Wert ist.
  2. Eine automatische verstärkungsaktive Geräuschresp. Lärmreduktionsanordnung nach Anspruch 1, in welcher die Steuermittel einen Mikroprozessor umfassen, der den nicht linearen Steueralgorithmus in die Rückkopplungsschleifenverstärkung einführt.
  3. Eine automatische verstärkungsaktive Geräuschresp. Lärmreduktionsanordnung nach Anspruch 2, in welcher das Signalbearbeitungsmittel ausgelegt ist, um analoge Bearbeitung (z.B. Filtrierung) des Mikrophonausgangssignals vorzusehen, gefolgt von analog zu digital-Umsetzung vor dem Zuführen des digitalen Signals an den Mikroprozessor.
EP86305415A 1985-07-13 1986-07-14 Geräuschreduzierungsvorrichtung Expired - Lifetime EP0212840B1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT86305415T ATE68903T1 (de) 1985-07-13 1986-07-14 Geraeuschreduzierungsvorrichtung.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8517716 1985-07-13
GB858517716A GB8517716D0 (en) 1985-07-13 1985-07-13 Noise reduction arrangements

Publications (3)

Publication Number Publication Date
EP0212840A2 EP0212840A2 (de) 1987-03-04
EP0212840A3 EP0212840A3 (en) 1987-09-23
EP0212840B1 true EP0212840B1 (de) 1991-10-23

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ID=10582241

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86305415A Expired - Lifetime EP0212840B1 (de) 1985-07-13 1986-07-14 Geräuschreduzierungsvorrichtung

Country Status (4)

Country Link
EP (1) EP0212840B1 (de)
AT (1) ATE68903T1 (de)
DE (1) DE3682147D1 (de)
GB (1) GB8517716D0 (de)

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1989000746A1 (en) * 1987-07-20 1989-01-26 Plessey Overseas Limited Improvements relating to noise reduction systems
WO1990002513A1 (en) * 1988-09-16 1990-03-22 Noise Cancellation Technologies, Inc. Active attenuation system for medical patients
US4953217A (en) * 1987-07-20 1990-08-28 Plessey Overseas Limited Noise reduction system
EP0385713A2 (de) * 1989-03-01 1990-09-05 Sony Corporation Empfangsvorrichtung zur Reduzierung von Rauschen
EP0412902A2 (de) * 1989-08-10 1991-02-13 Mnc, Inc. Elektroakustische Anordnung für Hörgeräte mit Lärmunterdrückung
US5001763A (en) * 1989-08-10 1991-03-19 Mnc Inc. Electroacoustic device for hearing needs including noise cancellation
WO1991013429A1 (en) * 1990-02-21 1991-09-05 Noise Cancellation Technologies, Inc. Noise reducing system
WO1992018975A1 (en) * 1991-04-09 1992-10-29 Active Noise And Vibration Technologies Inc. Active noise recuction
EP0468610A3 (en) * 1990-07-27 1992-12-23 Mnc, Inc. Method and apparatus for performing noise cancelling in headphones
US5182774A (en) * 1990-07-20 1993-01-26 Telex Communications, Inc. Noise cancellation headset
US5313945A (en) * 1989-09-18 1994-05-24 Noise Cancellation Technologies, Inc. Active attenuation system for medical patients
GB2289960A (en) * 1994-06-03 1995-12-06 Mazda Motor Adaptive gain control
US5524058A (en) * 1994-01-12 1996-06-04 Mnc, Inc. Apparatus for performing noise cancellation in telephonic devices and headwear
US5675658A (en) * 1995-07-27 1997-10-07 Brittain; Thomas Paige Active noise reduction headset
US6118878A (en) * 1993-06-23 2000-09-12 Noise Cancellation Technologies, Inc. Variable gain active noise canceling system with improved residual noise sensing

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2274757A (en) * 1993-01-28 1994-08-03 Secr Defence Ear defenders employing active noise control
CN1427988A (zh) * 2000-03-07 2003-07-02 新西兰商史莱柏Dsp公司 有源噪声抑制系统

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2097629B (en) * 1981-04-15 1984-09-26 Nat Res Dev Methods and apparatus for active sound control

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4953217A (en) * 1987-07-20 1990-08-28 Plessey Overseas Limited Noise reduction system
WO1989000746A1 (en) * 1987-07-20 1989-01-26 Plessey Overseas Limited Improvements relating to noise reduction systems
WO1990002513A1 (en) * 1988-09-16 1990-03-22 Noise Cancellation Technologies, Inc. Active attenuation system for medical patients
EP0385713A3 (de) * 1989-03-01 1991-08-21 Sony Corporation Empfangsvorrichtung zur Reduzierung von Rauschen
EP0385713A2 (de) * 1989-03-01 1990-09-05 Sony Corporation Empfangsvorrichtung zur Reduzierung von Rauschen
US5091954A (en) * 1989-03-01 1992-02-25 Sony Corporation Noise reducing receiver device
EP0412902A2 (de) * 1989-08-10 1991-02-13 Mnc, Inc. Elektroakustische Anordnung für Hörgeräte mit Lärmunterdrückung
US5001763A (en) * 1989-08-10 1991-03-19 Mnc Inc. Electroacoustic device for hearing needs including noise cancellation
EP0412902A3 (en) * 1989-08-10 1992-07-01 Mnc, Inc. Electroacoustic device for hearing needs including noise cancellation
US5313945A (en) * 1989-09-18 1994-05-24 Noise Cancellation Technologies, Inc. Active attenuation system for medical patients
WO1991013429A1 (en) * 1990-02-21 1991-09-05 Noise Cancellation Technologies, Inc. Noise reducing system
AU639761B2 (en) * 1990-02-21 1993-08-05 Noise Cancellation Technologies, Inc. Noise reducing system
US5182774A (en) * 1990-07-20 1993-01-26 Telex Communications, Inc. Noise cancellation headset
EP0468610A3 (en) * 1990-07-27 1992-12-23 Mnc, Inc. Method and apparatus for performing noise cancelling in headphones
WO1992018975A1 (en) * 1991-04-09 1992-10-29 Active Noise And Vibration Technologies Inc. Active noise recuction
US6118878A (en) * 1993-06-23 2000-09-12 Noise Cancellation Technologies, Inc. Variable gain active noise canceling system with improved residual noise sensing
US5524058A (en) * 1994-01-12 1996-06-04 Mnc, Inc. Apparatus for performing noise cancellation in telephonic devices and headwear
GB2289960A (en) * 1994-06-03 1995-12-06 Mazda Motor Adaptive gain control
US5675658A (en) * 1995-07-27 1997-10-07 Brittain; Thomas Paige Active noise reduction headset

Also Published As

Publication number Publication date
GB8517716D0 (en) 1985-08-21
DE3682147D1 (de) 1991-11-28
EP0212840A3 (en) 1987-09-23
EP0212840A2 (de) 1987-03-04
ATE68903T1 (de) 1991-11-15

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