US3686511A - Speaker protective circuit - Google Patents

Speaker protective circuit Download PDF

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Publication number
US3686511A
US3686511A US134703A US3686511DA US3686511A US 3686511 A US3686511 A US 3686511A US 134703 A US134703 A US 134703A US 3686511D A US3686511D A US 3686511DA US 3686511 A US3686511 A US 3686511A
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US
United States
Prior art keywords
speaker
resistor
driving device
protective circuit
controlled rectifier
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
US134703A
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English (en)
Inventor
Walter W Pauly
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.)
Stanton Magnetics Inc
Original Assignee
Stanton Magnetics Inc
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Filing date
Publication date
Application filed by Stanton Magnetics Inc filed Critical Stanton Magnetics Inc
Application granted granted Critical
Publication of US3686511A publication Critical patent/US3686511A/en
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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
    • H02H9/041—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage using a short-circuiting device
    • 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
    • H04R3/007—Protection circuits for transducers

Definitions

  • a speaker protective circuit is provided designed to be interposed between the speaker transducer and driving signal source.
  • the protective circuit includes a silicon controlled rectifier shunted across the transducer adapted to fire in response to either repetitious, intermittent power surges or continuous high level surges and a circuit breaker in series connection with the driving signal source adapted to open circuit in response to long duration power surges or a series of closely spaced short duration surges.
  • the fuse or circuit breaker both of which are relatively slow acting devices, have been used to open circuit the speaker from its power source after a threshold level driving signal has been exceeded. Both these devices operate by heating a sensing element and thus, are more or less time dependent, having an inherent time lag determined by the heating time required.
  • the fuse type limiting device is effective for relatively longterm power control, it is ineffective for instantaneous control (i.e., where there is a short duration voltage surge).
  • the function of limiting the input voltage is performed by a device which, instead of opening a circuit, shunts the available current and short circuits the excitation potential.
  • These devices are available in various forms of biased diodes and they are frequently used to limit transients in noisy power lines.
  • the use of biased diodes produces very high levels of distortion, particularly if the input signal has high level transients which are relatively short in duration.
  • the use of biased diodes has proved to be economical and efficient.
  • aaspeaker protective circuit adapted to be interposed between the output of a speaker driving device and the input to a speaker transducer connected to the driving device.
  • the protective circuit comprises fuse means connected in series with the driving device and a silicon controlled rectifier shunted across the speaker input.
  • a first resistor series connected to a second resistor is shunted across the driving device output and the gate of the silicon controlled rectifier is connected to the junction of the first and second resistors.
  • the output signal of the speaker driving device is sampled by the voltage divider defined by the first and second resistors. If the potential at the junction of the resistors exceeds a predetermined threshold level, the silicon controlled rectifier will be fired, thereby shorting the speaker input substantially instantaneously. The silicon controlled rectifier remains conductive as long as the sampled signal exceeds the threshold level, thereby keeping the speaker shorted. If the speaker is shorted out for a sufficiently long time, the fuse (circuit breaker) will open thereby permanently disconnecting the speaker from the driving device.
  • a capacitance device may be shunted across one leg of the voltage divider to store part of the sampled signal for a short time duration so that the fuse will open by virtue of either a relatively long duration power surge or a closely spaced series of instantaneous peaks.
  • the protective circuit 10 of the present invention is shown interposed between the output of an audio amplifier l2 and a speaker 14. While the present protective circuit may be used with either dynamic or electrostatic speakers, it is particularly well suited for use with electrostatic speakers since such speakers are especially susceptible to damage from high voltage surges and such surges could do permanent damage to the speaker diaphragm.
  • Amplifier 12 includes an output terminal 16 and return terminal 18 which is commonly maintained at ground potential.
  • Speaker 14 is provided with a pair of terminals 20 and 22 which ordinarily are connected to the amplifier output terminals 16 and 18.
  • the speaker protective circuit 10 of the present invention is interposed between amplifier l2 and speaker 14.
  • the protective circuit includes a fuse member 24 connected in series with the amplifier output terminal 16.
  • Fuse 24 may comprise any device which open circuits when the current passing through it exceeds a predetermined level. Although a conventional fuse comprising a strip of wire that melts when the level is exceeded may be used, an electromagnettype circuit breaker is preferred since the circuit breaker may readily be reset and the circuit completed without necessitating the replacement of a component.
  • the output of amplifier 12 is fed to speaker 14 through fuse 24 and speaker input terminal 20.
  • the resistance of fuse 24 is represented in the schematic by resistor 26.
  • a voltage divider formed of two series connected resistors 28 and 30, extends between the junction of fuse 24 and the-speaker input 20 and the return lead 32.
  • a capacitor 34, shunted across resistor 30, and a silicon controlled rectifier 36 complete the present protective circuit.
  • the anode 38 of the SCR is connected to the junction of resistor 26 and speaker terminal 20 and the cathode 40 is connected to the return lead 32.
  • the SCR gate terminal 42 is connected to the junction of resistor 30 and capacitor 34.
  • a diode 44 is provided in series with resistor 28 insuring the polarity of the voltage applied to capacitor 34.
  • the driving signal from amplifier 12 to speaker 14 is sampled via resistors 28 and 30. Part of the sampled signal is rectified and stored in capacitor 34. The value of the stored signal is determined by the ratio of resistors 28 and 30.
  • capacitor 34 charges to the point where it gates the silicon controlled rectifier 36, the SCR becomes conductive thereby shorting out the speaker. The current through fuse 24 will then rise sharply so that if the silicon controlled rectifier remains fired for a sufficiently long time, fuse 24 will open thereby disconnecting speaker 14 from amplifier 12.
  • a series of peaks spaced sufficiently close to one another to maintain the charge on capacitor 34 at a level to trigger SCR 36 will have the same effect, Thus, after a sufficient number of such peaks, fuse member 24 will also open circuit.
  • the response time for fuse member 24 and the signal level at which SCR 36 is triggered is determined by the value of the components which, in turn, are determined by the chosen threshold values.
  • the present circuit be designed so that the SCR fires in response to an output signal of approximately 110 dB sound pressure and the fuse member have a response time of approximately 500 mil-v liseconds.
  • the response of theSCR is substantially instantaneous so that the interruption of signals above the threshold level is sufficiently rapid that the shorted signal is virtually unheard by the listener.
  • a speaker protective circuit interposed between a speaker driving device and a speaker transducer element, said protective circuit being adapted to prevent audio signals from said driving device above 'a predetermined cumulative level from passing to said transducer element, said circuit comprising: fuse means connected in series with said driving device; a silicon controlled rectifier shunted across said speaker transducer element; a first resistor and a diode series connected to a second resistor connected in parallel with said driving device and said speaker transducer element, said diode having an anode connected to said first resistor and a cathode connected to said second resistor, the value of said resistors being such that the potential at the junction of said second resistor and said diode cathode is sufficient to gate said silicon controlled rectifier when the output level from said driving device reaches said predetermined level; connecting means extending between the gate terminal of said silicon controlled rectifier and said junction; and, a capacitor shunted across said second resistor whereby to maintain the potential at said junction for a predetermined time period.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Amplifiers (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Protection Of Static Devices (AREA)
US134703A 1971-04-16 1971-04-16 Speaker protective circuit Expired - Lifetime US3686511A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US13470371A 1971-04-16 1971-04-16

Publications (1)

Publication Number Publication Date
US3686511A true US3686511A (en) 1972-08-22

Family

ID=22464585

Family Applications (1)

Application Number Title Priority Date Filing Date
US134703A Expired - Lifetime US3686511A (en) 1971-04-16 1971-04-16 Speaker protective circuit

Country Status (9)

Country Link
US (1) US3686511A (enExample)
BE (1) BE781432A (enExample)
CA (1) CA931513A (enExample)
CH (1) CH551728A (enExample)
DE (1) DE2217523A1 (enExample)
FR (1) FR2133639B1 (enExample)
GB (1) GB1380151A (enExample)
IT (1) IT957276B (enExample)
NL (1) NL7204045A (enExample)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS50117735U (enExample) * 1974-03-10 1975-09-26
JPS5177828A (en) * 1974-12-27 1976-07-06 Matsushita Electric Industrial Co Ltd Ijokodenatsuyokuseikairo
US4242713A (en) * 1979-10-25 1980-12-30 Goodrich Edward W Triac output asymmetry detector
US4406921A (en) * 1981-06-15 1983-09-27 Electro Audio Dynamics, Inc. Apparatus for improving linearity of electromechanical transducers
US4410924A (en) * 1981-09-10 1983-10-18 The Gorman-Rupp Company Motor protection control circuit
WO1995001668A1 (en) * 1993-07-02 1995-01-12 Nokia Telecommunications Oy Method and apparatus for protecting an electric circuit
US20080044045A1 (en) * 2006-08-15 2008-02-21 Dobbs-Stanford Corporation Externally fused speaker terminal cup

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2415816C3 (de) * 1974-04-01 1981-10-29 Arndt 7500 Karlsruhe Klingenberg Verfahren zur Begrenzung der maximalen Belastung von elektroakustischen Wandlersystemen
DE2641079C3 (de) * 1976-09-11 1986-07-31 Telefunken Fernseh Und Rundfunk Gmbh, 3000 Hannover Lautsprecherschaltung
WO1980002477A1 (en) * 1979-05-08 1980-11-13 Fortieth Benelux Nominees Pty Protection device or circuit for loudspeakers
EP0095902A1 (en) * 1982-05-28 1983-12-07 British Broadcasting Corporation Headphone level protection circuit

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3215896A (en) * 1962-10-04 1965-11-02 Gen Electric Fast response overload protection circuit
FR1477358A (fr) * 1965-04-26 1967-04-14 Stone J & Co Ltd Agencement perfectionné de circuits électriques qui assure la protection d'appareils utilisant des organes semi-conducteurs
US3317792A (en) * 1964-03-20 1967-05-02 Westinghouse Electric Corp Load protection circuit

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3549808A (en) * 1967-10-09 1970-12-22 Marantz Co Protective circuit for speaker windings
DE1762472C3 (de) * 1968-06-22 1975-03-06 Grundig, E.M.V.-Elektro-Mechanische Versuchsanstalt-Max Grundig, 8510 Fuerth Überlastungsschutzschaltung für die Transistoren eines mit einer eisenlosen Gegentaktstufe versehenen Verstärkers

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3215896A (en) * 1962-10-04 1965-11-02 Gen Electric Fast response overload protection circuit
US3317792A (en) * 1964-03-20 1967-05-02 Westinghouse Electric Corp Load protection circuit
FR1477358A (fr) * 1965-04-26 1967-04-14 Stone J & Co Ltd Agencement perfectionné de circuits électriques qui assure la protection d'appareils utilisant des organes semi-conducteurs

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS50117735U (enExample) * 1974-03-10 1975-09-26
JPS5177828A (en) * 1974-12-27 1976-07-06 Matsushita Electric Industrial Co Ltd Ijokodenatsuyokuseikairo
US4242713A (en) * 1979-10-25 1980-12-30 Goodrich Edward W Triac output asymmetry detector
US4406921A (en) * 1981-06-15 1983-09-27 Electro Audio Dynamics, Inc. Apparatus for improving linearity of electromechanical transducers
US4410924A (en) * 1981-09-10 1983-10-18 The Gorman-Rupp Company Motor protection control circuit
WO1995001668A1 (en) * 1993-07-02 1995-01-12 Nokia Telecommunications Oy Method and apparatus for protecting an electric circuit
US20080044045A1 (en) * 2006-08-15 2008-02-21 Dobbs-Stanford Corporation Externally fused speaker terminal cup

Also Published As

Publication number Publication date
NL7204045A (enExample) 1972-10-18
IT957276B (it) 1973-10-10
FR2133639B1 (enExample) 1978-05-26
GB1380151A (en) 1975-01-08
BE781432A (fr) 1972-09-29
CA931513A (en) 1973-08-07
CH551728A (fr) 1974-07-15
FR2133639A1 (enExample) 1972-12-01
DE2217523A1 (de) 1972-10-26

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