US3118972A - Acoustic apparatus - Google Patents

Acoustic apparatus Download PDF

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Publication number
US3118972A
US3118972A US163170A US16317061A US3118972A US 3118972 A US3118972 A US 3118972A US 163170 A US163170 A US 163170A US 16317061 A US16317061 A US 16317061A US 3118972 A US3118972 A US 3118972A
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United States
Prior art keywords
yoke
loudspeaker
pickup
magnetic
coil
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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
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US163170A
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English (en)
Inventor
Walczak Sylvester
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.)
RCA Corp
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RCA Corp
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Filing date
Publication date
Priority to NL287305D priority Critical patent/NL287305A/xx
Priority to BE626697D priority patent/BE626697A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US163170A priority patent/US3118972A/en
Priority to DER34085A priority patent/DE1183133B/de
Priority to GB48019/62A priority patent/GB1003150A/en
Priority to FR919286A priority patent/FR1350161A/fr
Application granted granted Critical
Publication of US3118972A publication Critical patent/US3118972A/en
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    • 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
    • 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
    • H03F1/36—Negative-feedback-circuit arrangements with or without positive feedback in discharge-tube amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
    • H03F3/183—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/26—Push-pull amplifiers; Phase-splitters therefor
    • 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
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
    • H04R9/02—Details
    • H04R9/025—Magnetic circuit
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2209/00—Details of transducers of the moving-coil, moving-strip, or moving-wire type covered by H04R9/00 but not provided for in any of its subgroups
    • H04R2209/022—Aspects regarding the stray flux internal or external to the magnetic circuit, e.g. shielding, shape of magnetic circuit, flux compensation coils

Definitions

  • This invention relates to acoustic apparatus, and more particularly to improved acoustic transducers.
  • the invention is especially suitable for use in loudspeakers and provides loudspeaker apparatus which can be compensated for distortion and in which the fidelity of sound reproduction is improved.
  • Distortion in a loudspeaker may be attributable to nonlinearities in the mechanical suspension system of the loudspeaker and inhomogeneity of the magnetic flux in the voice coil air gap. Because of this distortion, the signals developed in the electrical driving system for the loudspeaker and the amplitude of the motion of the cone of the loudspeaker do not correspond linearly to each other.
  • lt is a still further object of the present invention to provide an improved device for picking up signals corresponding to the output of a loudspeaker, which device is low in cost and simple to install on the loudspeaker.
  • the leakage or fringe flux from a magnetic structure of a moving coil electromagnetic transducer corresponds to the motion of the coil.
  • the leakage flux from a loudspeaker magnetic structure thus corresponds to the loudspeaker acoustic output.
  • An acoustic transducer embodying the invention includes a magnetic structure. Another magnetic structure carrying a pickup coil is attached to the magnetic structure of the transducer so that leakage flux from the transducer magnet structure threads the pickup coil.
  • the signal derived by the pickup coil corresponds to the motion of the moving coil of the transducer and to the output of a loudspeaker type transducer. This signal is thus useful in providing distortion compensation and fidelity i iprovement by feedback.
  • FIG. l is a front View, partially in section, of loudspeaker apparatus of one type embodying the present invention.
  • FIG. 2 is a fragmentary front view, partially in section, of another type of loudspeaker apparatus embodying the invention.
  • FIG. 3 is a circuit diagram of a loudspeaker system embodying the invention.
  • a loudspeaker 8 having a cone-shaped diaphragm 10 connected at one end to a cylindrical voice coil structure 12 on which a Voice coil 14 is Wound.
  • the other end of the diaphragm 1l) is connected at its periphery to a frame 16, usually called a dishpan.
  • a magnetic field structure 18 supports the dishpan 16.
  • the field structure 18 includes a U-shaped (in crosssection) yoke 2t? of magnetic material, such as cold rolled steel, which is closed by a yoke plate 22, also of magnetic material.
  • the yoke plate 22 has a circular opening 2d therein.
  • a pole member, including a cylindrical magnet 2d and a pole piece 28, is centrally disposed in the yoke 20.
  • the magnet 26 may be of permanent magnet material, such as Alnico, which is an alloy of aluminum, nickel, cobalt, copper and iron.
  • the pole piece 2S is also centrally disposed with respect to the opening 24 in the yoke plate 22 by means of a centering and clamping ring 3u of non-magnetic material, such as brass.
  • the ring 30 also holds the magnet and pole piece in assembled relation in the yoke 20.
  • the pole piece 28 is cylindrical in shape and defines a cylindrical voice coil air gap 29 between the peripheral surface of the yoke plate opening 24 and the pole piece outer peripheral surface.
  • the voice coil 12 is centered within the voice coil air gap by means of a resilient centering disk 32, usually called a spider.
  • the loudspeaker described above is substantially similar in construction to a loudspeaker described in Cunningharn Patent 2,501,031, issued March 2, 1950.
  • a device 34 for picking up a signal corresponding to the sound output of the loudspeaker is attached to the exterior of the magnetic structure 18.
  • This device 34 includes a second magnetic structure having a U-shaped (in cross-section) yoke 36 of magnetic material, such as cold rolled steel, similar in shape to the loudspeaker yoke 2d but smaller in size.
  • a cylindrical pole member 38 Centrally disposed within this yoke is a cylindrical pole member 38, also of magnetic material.
  • This cylindrical pole member 38 may be secured to the yoke 3d by means of soldering,'ce inenting, or with a screw (not shown) extending through the bottom of the yoke 34 into the cylindrical pole member 3S.
  • the top of the cylindrical pole member 3S has a boss 4t! of reduced diameter thereon.
  • This boss is received into a hole 41 in the bottom of the yoke 15 of the loudspeaker.
  • the magnet structure 36--38 may be held on the loudspeaker yoke 18 by securing the boss 4d in the hole 41 by means of a force fit.
  • the boss tu may be swaged onto the loudspeaker yoke 29 before the loudspeaker magnet structure, including the magnet 26, the pole piece 28, the yoke plate 22 and the centering ring 3), is assembled.
  • the hole 41 in the bottom of the loudspeaker yoke 20 and the magnet 26 are desirably coaxial with each other.
  • the pole member 38 is disposed coaxially with respect to the magnet 26.
  • a pickup coil 42 is wound around the pole member 38 and serves to derive an output signal voltage.
  • the m-agnet 26 establishes magnetic flux along flux paths shown by the dashed line. These flux paths extend through the magnet 26, the pole piece 28, across the voice coil air gap and back to the magnet by Way of the yoke plate 22 and yoke 2i?. It will be appreciated that the flux passes through the voice coil air gap 29 and the pole plate 22 in a radial direction. It is ordinarily the practice to use a magnet 26 which provides a magnetic potential sufficient to establish a flux density in the yoke 20 and yoke plate 22 which is close to saturation. Thus, a signicant amount of fringe flux emanates from the yoke 20 and the pole plate 22. This fringe flux is intercepted by the yoke 36 of the pickup device 34 which directs the fringe ux along paths through the yoke 36 and pole member 38 of the structure. This fiux threads the coil 42.
  • an alternating current is established in the voice coil 14.
  • This alternating current establishes an alternating magnetic flux which interacts with the direct magnetic flux established by the magnet 26 and effectively modulates this direct magnetic flux.
  • the modulation of the flux is related to the motion of the voice coil ⁇ 14 since the inliuence of the magnetic field set up by the coil 14 on the direct magnetic flux depends upon the position of the voice coil in its air gap. In other words, the coupling of magnetic flux from the voice coil into the magnetic structure 18 of the loudspeaker depends upon the position and the motion of the voice coil.
  • the excursions of the voice coil 14 will be greater relative to the voice coil gap than when the amplitude of the cone 10 is small.
  • the modulation of the magnetic flux in the magnetic structure 18 of the loudspeaker is, therefore, a function of the motion of the voice coil 14.
  • the modulated flux carries information as to distortion in the loudspeaker.
  • the fringe flux which is picked up by the pickup device 34 also contains modulation components due to the motion of the voice coil. Accordingly, the output of the pickup coil 42 is related to the motion of the voice coil 14.
  • the acoustic output of the loudspeaker is related to the motion of the voice coil.
  • the signal derived by the pickup coil 42 is related to the output of the loudspeaker.
  • the driving signal applied to the voice coil will also be inductively coupled to the coil 42 in the pickup device 34.
  • the voltage output of the pickup coil 42 carries information as to the distortion of the loudspeaker output which may be utilized in a feedback system for compensating such distortion.
  • FIG. 2 there is shown a portion of a cupshaped loudspeaker magnetic field structure of the type described in Hamson Patent 2,964,597, issued December 13, 1960.
  • This field structure includes a cylindrical, cupshaped, yoke structure 50.
  • a cylindrical magnet 52 is disposed centrally within the yoke structure 50 and is held in place therein by a deformed retaining ring 54.
  • a frame S6 supports the diaphragm 58 of the loudspeaker and is mounted on the open end of the yoke Si).
  • This frame carries a resilient centering disk or spider 60 which supports the truncated yapical end of the cone.
  • a voice coil form 62 is secured to the apical end of the cone and carries a voice coil 64.
  • the voice coil 64 is essentially disposed in an air gap defined between the outer periphery of the magnet 52 and the inner periphery of the cup-shaped yoke 50.
  • the bottom of the yoke 50 has an opening
  • a pickup device 68 is secured to the bottom of the yoke 50.
  • 'Ihis pickup device 68 includes a cup-shaped yoke 70 of magnetic material having a center pole member 72. This center pole can be formed by machining a cylindrical slot in the cup-shaped yoke 70.
  • a boss 74 is formed on the top of pole 72. This boss 74 may be secured in the hole 66 by a force fit, by swaging, or by other techniques, as described in connection with FIG. 1.
  • the device 68 and the yoke 5i) may be assembled readily by attachment of the boss 74 in the hole 66.
  • a coil 78 is wound around the pole 72. Flux established by the magnet 52 in the yoke 50 extends radially across the voice coil4 air gap and then downwardly through ⁇ the yoke, re ⁇
  • the diameters of the loudspeaker yoke structure 50 and the pickup yoke 70 are shown to be about equal to each other, the diameter of the pickup yoke may be smaller. Preferably, the diameter of the pickup yoke is larger than the diameter of the magnet 52.
  • a substantial amount of fringe flux emanates from the yoke 50, especially when the magnet has sufiicient magnetic potential to establish a ilux density in the yoke 50 close to magnetic saturation, ⁇ as is generally the practice.
  • This fringe ux extends downwardly into the yoke 76, radially across the bottom of the yoke, and then upwardly through the pole member 72 into the magnet 52.
  • the coil 78 derives an output signal voltage which corresponds to the motion of the coil 64 and to the output of the loudspeaker, in the same manner as does the coil 42 (FIG. l).
  • the disposition of the pickup devices at the bottom of the yoke 18 (FIG. 1) or the yoke 50 (FIG. 2) increases the fringe flux which threads the respective coils 42 and 78 because the yokes 36 and 70 of the pickup devices shape and direct the fringe field through the pickup coils 42 or 73.
  • the pickup coils 42 of FIG. 1 or 78 of FIG. 2 are also protected from damage, since they are surrounded by the yoke structures 36 and 70 of their respective pickup devices 34 and 68. Since the flux turns sharply from the yoke into the magnet at the bottom of ⁇ the yoke structures, the greatest fringing of flux occurs near the bottom of the yoke.
  • the pickup devices 42 and 78 are disposed in close proximity to the area of maximum leakage tiuX from the magnetic structures of their respective loudspeakers.
  • the magnetic coupling of audio signals applied to the voice coils I14 and 64 between these voice coils and their associated pickup coils 42 and 78 is relatively small, since the voice coils and pickup coils are substantially magnetically isolated from each other by the back part of the yoke structure 18 and 59. It will be observed that this isolation does not prevent the effective modulation due to the motion of the voice coil of the fringe flux to which the pickup coils 42 and 78 are responsive. Such isolation of the pickup coils and voice coils is believed to be responsible for the stability of feedback systems employing the pickup devices 34 and 68. Feedback systems including these devices 34 and 68 are not very susceptible to oscillation.
  • FIG. 3 A loudspeaker system employing feedback from such a speaker as that illustrated in FIG. l or 2 is shown in FIG. 3.
  • This loudspeaker system includes the audio stages of a transistor radio.
  • the illustrated audio stages alone, without the feedback feature are used in RCA Victor TX-l series transistor radios (chassis No. RC- 1196A), as described in a publication of Commercial Service, RCA Service Company, Camden 8, New Jersey, entitled, Service Data 1959 No. 20 (first edition, first printing, June 29, 1958).
  • a loudspeaker 80 which may be similar to either one of the loudspeakers shown in FIG. 1 or FIG. 2, but having a center tapped voice coil 81, is equipped with a pickup device 82 similar to the pickup devices 34 or 63 of the loudspeakers shown in FIG. 1 or FIG. 2.
  • the electrical driving system for the loudspeaker receives an input signal, for example, from the detector of the radio receiver. This signal is coupled through a volume control 84 to a driver yamplifier stage 86.
  • the ⁇ driver amplifier drives a push-pull amplifier 88.
  • Output signals amplified by the amplifier 88 are applied directly across voice coil 81 of the loudspeaker 80.
  • the voice coil y is tapped, and no output transformer Lis used.
  • the pickup device 82 therefore, advantageously provides a feedback voltage even though an output transformer is not used.
  • the pickup device is connected between A.C. ground 91 and the near ground end 93 of the volume control 84.
  • the output signal from the device 82 is Itherefore applied through the control 84 to the base of the transistor in the driver stage 86.
  • a resistor is connected across the device 82 to attenuate the pickup signals somewhat.
  • a capacitor 92 is also connected across lthe device 82 to limit the high frequency components of the output signal from the device 82. These components 901 and 92 may or may not be needed, depending upon the type oef loudspeaker and the number ci turns in the coil of the device 82.
  • the pickup ooil 72 provides a feedback system which couples the output of the loudspeaker and the input of its driving system in negative feedback relationship.
  • the loudspeaker system including the feedback system is compensated for distortion due to nonlinearities in the motion of the loudspeaker voice coil.
  • the apparatus provides for the reduction of distortion due to nonlinearities in the operation of the loudspeaker in a convenient and economical manner.
  • the invention also provides for distortion compensating and frequency response improving feedback in loudspeaker systems without the 'danger of introducing oscillations in the system. While two embodiments olf the loudspeaker apparatus embodying the invention, and one embodiment of the electrical system including a loudspeaker embodying the invention have been illustrated, it will be appreciated that variations in the illustrated apparatus and system, Within the scope of the invention, Will undoubtedly suggest themselves to those skilled in the art. Accordinvly, the foregoing description shoulld be Itaken as illustrative and not in any limiting sense.
  • an acoustic transducer having a magnetic field structure inclu-ding ⁇ means for establishing magnetic ux in said structure, said stnucture also having an opening therein and having a coil movable in said opening, the improvement comprising another magnetic structure mounted on the outside of said first-named structure and exposed to portions off said magnetic iiux which fringe from said first-named structure, and a pickup coil Wound on said other structure for deriving an output voltage in response to changes in said fringe fiuX.
  • an acoustic transducer having a magnetic field structure including a yoke structure and a pole member defining -a voice coil air gap therebetween, said pole member including a magnet, said transducer also having a voice coil movable in said air gap and a diaphragm movable with said voice coil, the improvement comprising a pickup device comprising another magnetic field structure having a yoke structure and a pole member within said yoke, and a pickup coil Wound around said lastnamed pole member, said ilast-named yoke structure being mounted on said transducer yoke structure 'with said lastnamed pole member in alignment with said transducer pole member.
  • ln loudspeaker apparatus having a magnetic field structure including a U-shapcd yoke, a yoke plate on said yoke having an opening therein, a cylindrical pole member witnin said yoke centrally ydisposed with respect to said opening for defining with the periphery of said yoke plate opening a voice coil air gap, said pole member including a magnet, the improvement comprising a pickup device, a magnetic held structure including a U-shaped yoke smaller Athan said loudspeaker yoke, and a cylindrical pole member in said yoke ,and a pickup coil wound around said pole member, said pickup device field structure being mounted on the outside of sai-d loudspeaker field structure with the free ends of said device yoke and pole member in Contact with the outer surface of said loudspeaker yoke, said device pole member being disposed coaxially with said loudspeaker pole member.
  • loudspeaker apparatus including a magnetic lield structure having a cylindrical, cup-shaped yoke, and a cylindrical magnet centrally disposed in said yoke and attached thereto
  • the improvement comprising a pickup device including a cylindrical cup-shaped yoke having a central cylindrical pole member, said last-named yoke and pole member being mounted ion the outside of said loudspeaker yoke on the closed end theneoi with said device poie member coaxial with said magnet, and a pickup coil Iaround said device pole member.
  • a loudspeaker system comprising a loudspeaker having a magnetic field structure including a yoke of magnetic material, a pickup device including a pickup coil mounted on said yoke md responsive to fringe magnetic flux emanatingy fro-m said yoke, an electrical system responsive to electrical audio signals ⁇ for ⁇ driving said loudspeaker to reproduce sound corresponding tio said signals, and means for connecting said pickup coil and said electrical driving system in feedback relationship whereby to compensate for distontion in said loudspeaker.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
US163170A 1961-12-29 1961-12-29 Acoustic apparatus Expired - Lifetime US3118972A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL287305D NL287305A (xx) 1961-12-29
BE626697D BE626697A (xx) 1961-12-29
US163170A US3118972A (en) 1961-12-29 1961-12-29 Acoustic apparatus
DER34085A DE1183133B (de) 1961-12-29 1962-12-17 Elektroakustischer Wandler
GB48019/62A GB1003150A (en) 1961-12-29 1962-12-19 Acoustic apparatus
FR919286A FR1350161A (fr) 1961-12-29 1962-12-20 Appareil acoustique plus particulièrement haut-parleur

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US163170A US3118972A (en) 1961-12-29 1961-12-29 Acoustic apparatus

Publications (1)

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US3118972A true US3118972A (en) 1964-01-21

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US163170A Expired - Lifetime US3118972A (en) 1961-12-29 1961-12-29 Acoustic apparatus

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US (1) US3118972A (xx)
BE (1) BE626697A (xx)
DE (1) DE1183133B (xx)
GB (1) GB1003150A (xx)
NL (1) NL287305A (xx)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3530244A (en) * 1967-02-13 1970-09-22 Martin G Reiffin Motional feedback amplifier systems
US3798374A (en) * 1972-04-03 1974-03-19 Rene Oliveras Sound reproducing system utilizing motional feedback
US3928723A (en) * 1973-07-02 1975-12-23 Kazuo Kai Telephone set with built-in loudspeaker
US3937887A (en) * 1969-05-15 1976-02-10 Ben O. Key Acoustic power system
US4465905A (en) * 1982-04-28 1984-08-14 International Jensen Incorporated Loudspeaker assembly
US4565905A (en) * 1982-04-28 1986-01-21 International Jensen Incoporated Loudspeaker construction
US5493620A (en) * 1993-12-20 1996-02-20 Pulfrey; Robert E. High fidelity sound reproducing system
US20060133637A1 (en) * 2004-12-16 2006-06-22 Jl Audio, Inc. Loudspeaker with integrated spider standoff ring
US8401207B2 (en) 2009-03-31 2013-03-19 Harman International Industries, Incorporated Motional feedback system

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5379525A (en) * 1976-12-23 1978-07-14 Sony Corp Compound diaphtagm for speakers

Citations (7)

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Publication number Priority date Publication date Assignee Title
US1734944A (en) * 1927-10-11 1929-11-05 Celebritone Ltd Sound-amplifying system
US1901331A (en) * 1929-05-15 1933-03-14 Magnavox Co Electrodynamic loud-speaker
US2860183A (en) * 1954-02-01 1958-11-11 Conrad Ivan Willard Sound reproducing system
US2964597A (en) * 1954-12-10 1960-12-13 Rca Corp Loudspeaker magnetic field structure
US3047661A (en) * 1957-01-18 1962-07-31 Daniel E Winker High fidelity audio system
US3057961A (en) * 1959-01-08 1962-10-09 Security First Nat Bank Self-correcting, high fidelity, sound reproducing apparatus
US3061675A (en) * 1958-09-09 1962-10-30 Texas Instruments Inc Loud speaker improvement

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Publication number Priority date Publication date Assignee Title
DE719459C (de) * 1938-04-26 1942-04-09 Arthur Anders Sicherheitsvorrichtung fuer Fahrzeugbrennkraftmaschinen
DE853298C (de) * 1950-08-01 1952-10-23 Bernhard Philberth Rueckgekoppelter dynamischer Lautsprecher
DE967169C (de) * 1952-06-20 1957-10-17 Werner Holle Dr Ing Gegenkopplungsanordnung fuer elektrodynamische Lautsprecher
US2948778A (en) * 1956-05-07 1960-08-09 Warner W Clements Sound reproducing means

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1734944A (en) * 1927-10-11 1929-11-05 Celebritone Ltd Sound-amplifying system
US1901331A (en) * 1929-05-15 1933-03-14 Magnavox Co Electrodynamic loud-speaker
US2860183A (en) * 1954-02-01 1958-11-11 Conrad Ivan Willard Sound reproducing system
US2964597A (en) * 1954-12-10 1960-12-13 Rca Corp Loudspeaker magnetic field structure
US3047661A (en) * 1957-01-18 1962-07-31 Daniel E Winker High fidelity audio system
US3061675A (en) * 1958-09-09 1962-10-30 Texas Instruments Inc Loud speaker improvement
US3057961A (en) * 1959-01-08 1962-10-09 Security First Nat Bank Self-correcting, high fidelity, sound reproducing apparatus

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3530244A (en) * 1967-02-13 1970-09-22 Martin G Reiffin Motional feedback amplifier systems
US3937887A (en) * 1969-05-15 1976-02-10 Ben O. Key Acoustic power system
US3798374A (en) * 1972-04-03 1974-03-19 Rene Oliveras Sound reproducing system utilizing motional feedback
US3928723A (en) * 1973-07-02 1975-12-23 Kazuo Kai Telephone set with built-in loudspeaker
US4465905A (en) * 1982-04-28 1984-08-14 International Jensen Incorporated Loudspeaker assembly
US4565905A (en) * 1982-04-28 1986-01-21 International Jensen Incoporated Loudspeaker construction
US5493620A (en) * 1993-12-20 1996-02-20 Pulfrey; Robert E. High fidelity sound reproducing system
US20060133637A1 (en) * 2004-12-16 2006-06-22 Jl Audio, Inc. Loudspeaker with integrated spider standoff ring
US7379558B2 (en) 2004-12-16 2008-05-27 Jl Audio, Inc. Loudspeaker with integrated spider standoff ring
US8401207B2 (en) 2009-03-31 2013-03-19 Harman International Industries, Incorporated Motional feedback system

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GB1003150A (en) 1965-09-02
NL287305A (xx)
BE626697A (xx)
DE1183133B (de) 1964-12-10

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