US3647969A - Motional feedback amplifier - Google Patents

Motional feedback amplifier Download PDF

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Publication number
US3647969A
US3647969A US853665A US3647969DA US3647969A US 3647969 A US3647969 A US 3647969A US 853665 A US853665 A US 853665A US 3647969D A US3647969D A US 3647969DA US 3647969 A US3647969 A US 3647969A
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bridge
amplifier
feedback
loudspeaker
frequency
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Expired - Lifetime
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US853665A
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English (en)
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Tadeusz Korn
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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
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/002—Damping circuit arrangements for transducers, e.g. motional feedback circuits
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback

Definitions

  • FIG.6 Sheets-Sheet 2 FIGA Patented March 7, 1972 3 Sheets-Sheet 5 I7 r I I I I I l I I I I I I I I I I I I I I 0 .l U Q a FIGLE FIG.6
  • This invention relates to the construction of a motional feedback amplifier whereby the mechanical resonance of the loudspeaker to which it is connected can be suppressed, said motional feedback being generated by an impedance bridge, one arm of which consists of a loudspeaker and which is balanced when the loudspeakers diaphragm is blocked.
  • the invention relates to the construction of means adapted to make such amplifiers reliable and suitable for mass production.
  • FIGS. 1 and 2 show a prior art motionalfeedback amplifier
  • FIG. 3 is a frequency-reactance graph of the amplifier of FIGS. 1 and 2;
  • FIGS. 4 to 6 illustrate a motional feedback amplifier in accordance with the present invention.
  • a motional feedback amplification method is already known of the type shown in FIG. 1 of the accompanying drawings, being based on the feedback principle comprising a bridge 2 with one arm formed by the loudspeaker 3, the said' bridge being prebalanced for the value of this arm equal to the electrical impedance of the coil of the loudspeaker with the diaphragm at rest.
  • the electromotive force induced in the coil by its vibrations in other words the appearance of the motional impedance of the loudspeaker-put the bridge off balanceand produces a reading voltage between the terminals 8 and 10.
  • This voltage which is assumed to be proportional to the velocity of the diaphragm, is applied as a negative feedback to the input of the amplifier 1 (terminal 8), in order to stabilize the velocity, i.e., suppress the mechanical resonance of the loudspeaker.
  • FIG. 2 illustrates the physical components forming the bridge 2.
  • the bridge 2 would readily operate in'accordance with the elementary principle set forth hereinbefore.
  • the electrical impedance of the coil of the loudspeaker 11 includes an inductive component 13 which seriously obstructs the required operation of the bridge 2.
  • the authors of known proposals had been aware of the existence of the element l3 but they have erroneously interpreted its obstructive action, i.e., they have considered it solely as a difficulty in correct prebalancing of the bridge 2 throughout the audio-frequency range (with the diaphragm blocked).
  • one of the other arms of the bridge 2 should contain adequate'reactive elements, e.g., an inductance in series in the arm 4 or 5, or a capacitor in parallel with a resistor in the arm 6.
  • the present invention is based on a careful investigation of the circuit shown in FIG. 2.
  • FIG. 3 is a frequency-reactance graph showing this concept.
  • the line f 0 relates to the frequency corresponding to the resonance of the loudspeaker where the motional feedback should be the most effective.
  • the amplifier according to this invention comprises an inseparable group of means which provide an efficient motional feedback action (at least 10 d.) at the resonant frequency f of the loudspeaker but which sufficiently suppresses the reading action of the bridge 2 in the frequency zone at which the false readings appear and which is very close to the said frequency f,,.
  • This group of means comprises the following elements (FIG. 4);
  • a transistor 18 for reading of the bridge 2 its input electrodes 19-20 being connected, according to the polarity of the required signal, respectively to the terminal 8 and the terminal 10 of the bridge 2, and the output electrode of which is shown at 21.
  • the object of the reading" transistor is not only to bring the reading signal into reference with respect to the ground, but also amplify it and to form a high-impedance source for the circuits following one another in the motional feedback loop.
  • the reading transistor is followed by a filter I7 comprising two capacitors 25 and 26 (FIG. 5) connected between the signal line and ground.
  • the filter also comprises a capacitor 27 in series in the signal line which attenuates the signal at the said very low frequencies.
  • the said series capacitor also corrects the phase-shift of the filter in the effective frequency zone.
  • the said filter with two capacitors to ground in other words with two RC networks, does not yet have sufficient slope to select the effective frequency zone in relation to the disturbing zone.
  • any increase in the number of RC networks results in a disturbing phase-shift which interferes with the operation of the system.
  • the amplifier has a third element which forms part of the group of means proposed in the invention and which is:
  • a low-frequency corrector 24 (FIGS. 4 and 6) disposed in the conventional negative feedback loop with which the amplifier according to this invention must be provided and which corrector consists, for example, of the resistor 29 and capacitor 28 in parallel.
  • the object of this corrector is to increase the amplifier gain at low frequencies, thus reinforcing discrimination between the effective zone and the disturbing zone of the motional feedback, because the said amplifier is situated in the loop of the latter.
  • a motional feedback amplifier comprising an impedance bridge for providing said feedback, one arm of said bridge including a loudspeaker, said bridge being balanced with a loudspeaker diaphragm blocked at the resonance frequency of the loudspeaker, a first feedback loop having a low-pass filter provided therein extending between reading terminals of the bridge and an amplifier input terminal for reading the feedback voltage to the amplifier, said amplifier being adapted to substantially suppress the feedback voltage in and above the frequency zone in which any false readings of the bridge appear, and a second feedback loop having a low-frequency corrector provided therein constituting a negative feedback loop of said amplifier, an active transistor element in said first feedback loop preceding said low-pass filter, said element including two control electrodes which form an emitter and a base of the element and which are supplied with a signal from the reading tenninals of the bridge, and an output electrode of the element adapted to deliver the feedback signal to the filter and to the amplifier.
  • said filter comprises at least two capacitors connected between a signal line and ground, and a capacitor connected in series in the signal line which attenuates the generated signal at very low frequencies and reduces the phase-shift in the operating zone of frequencies.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Amplifiers (AREA)
  • Circuit For Audible Band Transducer (AREA)
US853665A 1968-08-29 1969-08-28 Motional feedback amplifier Expired - Lifetime US3647969A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
BE720115 1968-08-29

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US3647969A true US3647969A (en) 1972-03-07

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US853665A Expired - Lifetime US3647969A (en) 1968-08-29 1969-08-28 Motional feedback amplifier

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US (1) US3647969A (xx)
BE (1) BE720115A (xx)
FR (1) FR2016588A1 (xx)
GB (1) GB1276344A (xx)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0181608A1 (en) * 1984-11-07 1986-05-21 BBE Sound, Inc. Reference load amplifier correction systemand method
US4712247A (en) * 1984-04-03 1987-12-08 U.S. Philips Corporation Electro-acoustic system having a variable reflection/absorption characteristic
EP0332053A2 (en) * 1988-03-10 1989-09-13 Yamaha Corporation Acoustic apparatus
EP0340435A2 (en) * 1988-04-01 1989-11-08 Yamaha Corporation Acoustic apparatus
WO1989012432A1 (en) * 1988-06-24 1989-12-28 Sensor Electronics, Inc. Active noise reduction system
US4969195A (en) * 1988-05-06 1990-11-06 Yamaha Corporation Impedance compensation circuit in a speaker driving system
GB2234880A (en) * 1989-07-31 1991-02-13 David Robin Birt Controlling the Q factor of loudspeakers
US5031221A (en) * 1987-06-02 1991-07-09 Yamaha Corporation Dynamic loudspeaker driving apparatus
EP0801785A1 (en) * 1994-05-02 1997-10-22 Noise Cancellation Technologies, Inc. Industrial headset
WO1999059377A1 (fr) * 1998-05-12 1999-11-18 Centre Scientifique Et Technique Du Batiment (Cstb) Dispositif de controle actif d'impedance acoustique
US6396930B1 (en) 1998-02-20 2002-05-28 Michael Allen Vaudrey Active noise reduction for audiometry
US20030072462A1 (en) * 2001-10-16 2003-04-17 Hlibowicki Stefan R. Loudspeaker with large displacement motional feedback
US6683965B1 (en) 1995-10-20 2004-01-27 Bose Corporation In-the-ear noise reduction headphones
DE102007002920A1 (de) 2007-01-19 2008-07-31 Halang, Wolfgang A., Prof. Dr. Dr. Vorrichtung zum Einsatz in dynamischen Lautsprechern zur Vermeidung von Verzerrungsprodukten durch Regelung der Membranenbewegung
US11381908B2 (en) 2017-08-01 2022-07-05 Michael James Turner Controller for an electromechanical transducer
US11510286B2 (en) * 2017-11-30 2022-11-22 Koa Corporation Heater temperature control circuit and sensor device using the same

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2887532A (en) * 1956-10-31 1959-05-19 Rca Corp Audio frequency amplifier
US3047661A (en) * 1957-01-18 1962-07-31 Daniel E Winker High fidelity audio system
US3525812A (en) * 1969-05-08 1970-08-25 James E Verdier Transducer circuit and method of operation
US3530244A (en) * 1967-02-13 1970-09-22 Martin G Reiffin Motional feedback amplifier systems

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2887532A (en) * 1956-10-31 1959-05-19 Rca Corp Audio frequency amplifier
US3047661A (en) * 1957-01-18 1962-07-31 Daniel E Winker High fidelity audio system
US3530244A (en) * 1967-02-13 1970-09-22 Martin G Reiffin Motional feedback amplifier systems
US3525812A (en) * 1969-05-08 1970-08-25 James E Verdier Transducer circuit and method of operation

Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4712247A (en) * 1984-04-03 1987-12-08 U.S. Philips Corporation Electro-acoustic system having a variable reflection/absorption characteristic
EP0181608A1 (en) * 1984-11-07 1986-05-21 BBE Sound, Inc. Reference load amplifier correction systemand method
EP0293806A3 (en) * 1987-06-02 1991-07-17 Yamaha Corporation Dynamic loudspeaker driving apparatus
US5031221A (en) * 1987-06-02 1991-07-09 Yamaha Corporation Dynamic loudspeaker driving apparatus
EP0332053A2 (en) * 1988-03-10 1989-09-13 Yamaha Corporation Acoustic apparatus
EP0332053A3 (en) * 1988-03-10 1991-04-17 Yamaha Corporation Acoustic apparatus
EP0340435A3 (en) * 1988-04-01 1991-04-24 Yamaha Corporation Acoustic apparatus
EP0340435A2 (en) * 1988-04-01 1989-11-08 Yamaha Corporation Acoustic apparatus
US4969195A (en) * 1988-05-06 1990-11-06 Yamaha Corporation Impedance compensation circuit in a speaker driving system
WO1989012432A1 (en) * 1988-06-24 1989-12-28 Sensor Electronics, Inc. Active noise reduction system
GB2234880A (en) * 1989-07-31 1991-02-13 David Robin Birt Controlling the Q factor of loudspeakers
EP0801785A1 (en) * 1994-05-02 1997-10-22 Noise Cancellation Technologies, Inc. Industrial headset
EP0801785A4 (en) * 1994-05-02 1999-08-04 Noise Cancellation Tech INDUSTRIAL HELMET
US6683965B1 (en) 1995-10-20 2004-01-27 Bose Corporation In-the-ear noise reduction headphones
US6396930B1 (en) 1998-02-20 2002-05-28 Michael Allen Vaudrey Active noise reduction for audiometry
FR2778741A1 (fr) * 1998-05-12 1999-11-19 Scient Et Tech Du Batiment Cst Dispositif de controle actif d'impedance acoustique
WO1999059377A1 (fr) * 1998-05-12 1999-11-18 Centre Scientifique Et Technique Du Batiment (Cstb) Dispositif de controle actif d'impedance acoustique
US20030072462A1 (en) * 2001-10-16 2003-04-17 Hlibowicki Stefan R. Loudspeaker with large displacement motional feedback
US20030086576A1 (en) * 2001-10-16 2003-05-08 Hlibowicki Stefan R Position sensor for a loudspeaker
US7260229B2 (en) 2001-10-16 2007-08-21 Audio Products International Corp. Position sensor for a loudspeaker
DE102007002920A1 (de) 2007-01-19 2008-07-31 Halang, Wolfgang A., Prof. Dr. Dr. Vorrichtung zum Einsatz in dynamischen Lautsprechern zur Vermeidung von Verzerrungsprodukten durch Regelung der Membranenbewegung
US11381908B2 (en) 2017-08-01 2022-07-05 Michael James Turner Controller for an electromechanical transducer
US11510286B2 (en) * 2017-11-30 2022-11-22 Koa Corporation Heater temperature control circuit and sensor device using the same

Also Published As

Publication number Publication date
BE720115A (xx) 1969-02-03
FR2016588A1 (xx) 1970-05-08
GB1276344A (en) 1972-06-01

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