US2610259A - Electromagnetic vibratory device - Google Patents

Electromagnetic vibratory device Download PDF

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Publication number
US2610259A
US2610259A US767241A US76724147A US2610259A US 2610259 A US2610259 A US 2610259A US 767241 A US767241 A US 767241A US 76724147 A US76724147 A US 76724147A US 2610259 A US2610259 A US 2610259A
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United States
Prior art keywords
diaphragm
pole
magnet
main
gap
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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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US767241A
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English (en)
Inventor
Roberton James Samuel Paterson
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International Standard Electric Corp
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International Standard Electric Corp
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Publication date
Priority claimed from GB1873946A external-priority patent/GB624566A/en
Application filed by International Standard Electric Corp filed Critical International Standard Electric Corp
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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
    • H04R13/00—Transducers having an acoustic diaphragm of magnetisable material directly co-acting with electromagnet
    • 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
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/225—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only  for telephonic receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R11/00—Transducers of moving-armature or moving-core type
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R11/00—Transducers of moving-armature or moving-core type
    • H04R11/06—Telephone receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
    • H04R2499/10—General applications
    • H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/30—Against vector-borne diseases, e.g. mosquito-borne, fly-borne, tick-borne or waterborne diseases whose impact is exacerbated by climate change

Definitions

  • the invention consists of an electro-acoustie-transducer having a diaphragm, a single permanent magnet member, one or more pole-pieces one i enda 0f such potepi'ece, or-ofeach of them if-more than one; being" adjacent to the diaphragm and iormingone or more .gaps-respectivelybetween-the:- saidri one or more pole-piecesand thediaphragm, snoh one or: more pole-pieces co-operating with the eard Del manentmagnet member to'produce 'a magnetic flux in such 'one 'GlfimOl gaps, and having also an additional poleohpole pieces lac-operating with the said permanentmag-netmemben whereby not*all' ot' theflux 'which -traverses thesaid one or more gaps-traverses that part on those parts of the diaphrag
  • the invention consists of an electro-aooustic transdncer having a diaphragm andasingle permanent msgnet member, in which the magneto-motiye' force:
  • the said permanent magnetmember causes a polarising flux in one or more gapsbetween the diaphragm on the one hand andj the said permanent' magnet member-cr che or'n'iormpol'f pieces (ac-operating therewith on the other-hand; andin which a" portion ofthe said magn'etomotive force is used to-divert po1arising -fliix fromt a part or parts of the diaphragm-through which: all the po1arisingflux in the said oneor more gaps would-otherwise pass:
  • the additional flux produced by the auxiliary pole system is applied so that it traverses a gap or gaps, hereinafter called the auxiliary gap system, is pierced by a single hole in the centre for the ingress or egress of sound. It is possible of course for the depressed central portion to present a disc-like face to the diaphragm and for the sound aperture or apertures" to be located elsewhere on the plate.
  • FIG. 2 corresponding reference numerals to those used in Fig. 1 are used to denote corresponding things.
  • a pole piece 4, similar to pole piece '4 in Fig. 1 stands on top of the magnet.
  • FIG. 1 is a diagram of one embodiment of the invention in cross section
  • Fig. 2 is a diagram of another embodiment of the invention in cross section I
  • Fig. 3 is a diagram of another embodiment of theinvention incross section v V .
  • Fig, 4 is a circuit diagram representing an electrical analogy of the magnetic systems of the embodiments shown in Figs. 1, 2 and 3.
  • the embodiments in these figures have a pole piece of one polarity, representing the main pole system and such arrangement is hereinafter called a monopolar arrangement.
  • Fig. 5 is a diagram of an embodiment of the invention having two pole pieces of opposite polarity representing the main pole system and such anarrangement is hereinafter called a bipolar arrangement.
  • Fig. 6 isa circuit diagram representing an electrical analogy of the magnetic system of theembodiment shown in Fig. 5.
  • FIG. 7 is a diagram of a second bipolar embodiment of the invention.
  • Fig. 8 is a circuit diagram representing an electrical analogy of the embodiment shown in Fig. 7.
  • Fig.9 is a diagram of a third bipolar embodiment of the invention.
  • Fig. 10 is a circuit diagram representing an electrical analogy of the embodiment shown in Fig. 9.
  • Fig. 11 is a diagram of a fourth bipolar embodiment of the invention.
  • Figs. 12, 13 and 14 are top view, transverse cross sectionand bottom view, respectively of a telephone earpiece capsule following the arrangement shown diagrammatically in Fig. 1.
  • a cylindrical magnet l and a diaphragm 2 of magnetic material are arranged so that the diaphragm lies within the magnet a little distance from and in a plane parallel to that of one end face of the magnet.
  • the magnet is polarised axially, one end face being of north polarity and the other end face of south polarity.
  • an end plate 3 supporting a single cylindrical pole piece t around which are operatingwindings 5. Plate 3 and pole piece t are the main pole system.
  • a plate '6 rests onthe other end face or the magnet and is dished in the centre so as to approach close to the diain the form of a hollow truncated cone with an inward facing flange at its smaller end is fixed by this flange part way down the magnet, nearer to pole piece 4 than to cup 8.
  • the conical member 7 extends in a direction away from the bottom of cup 8 and towards its larger end, which carriesthe diaphragm, so as to leave a gap between the centre of the diaphragm and pole piece 4.
  • a member 8, similar to fi of Fig. 1, may be turned over. along its outer periphery so as to meet the upper rim of cup 8 or alternatively cup 8 could be extended upwardly and plate 6 could be as shown in Fig. 1.
  • pole piece 4 forms the main pole system as in Fig, 1, but the auxiliary pole system is constituted by cup 8 and plate 6.
  • Plate :8 in the Fig. 2 arrangement is capable of the same modifications of central pole face shape and sound aperture as are described in relation to Fig. 1.
  • a flat bar or disc magnet is used polar ised from centre to ends or circumference respectively.
  • a cylindrical member ID of permeable magnetic material rests, at two places on one of its end faces, on the outer ends of magnet I.
  • Another member 9, of permeable magnetic material which may be a cylinder of a part or parts of marked with the reference A, the auxiliary gap, system with the reference E, the part of the magnet associated with the main pole system, by the reference Vi, the part of the magnet associated with the auxiliary pole system by the reference V2 and the diaphragm by reference D. 1
  • VI and V2 are represented by batteries equivj alent to the magneto-motive forces of the respectlve' parts of the magnet, A (the reluctance V ofthe maingap system) by a resistance, E (the reluctance of the auxiliary gap system) by a resistance and D (the reluctance of the diaphragm) by a resistance. 7
  • V3 a source of alternating current, represents the alternating magneto-motive forces corresponding to the sounds to be transduced.
  • the alternating currents in the system are also partiallydiverted through and V2 which causes some loss but not inproportionto the gain resulting from 1 the increased current in A as compared with the maximum 'feas'ible figure for this in the conventional: type ot electro acoustic transducer.
  • Ad nta e ma begt ke r 01f.v e; pr n an mb rltways O urse. w en n e o ust nsdu r i b d ed. at. w th.
  • Fig. 5- illustrates diagrammaticallythe-mag: neticcircuitof a bipolar-electroacou-stic'transducerQh-aving am-ag'net" l-l, polarised longitudi nail-y; and with polepieces l2 andi3 attached to. its two ends and extending to the axis-0F themagnet towards a diaphragm I4, so as to" leave a gap between each pole piece; andthe diaphragmr. These gaps form "the main gap system.
  • Additional pole pieces #5 and I6 are attached to intermediate pointsalong the length of the magnet; equidistant from'theends and
  • Thegap's between l5 and I6 and the dia.-- phragm form the auxiliary gap system.
  • Interconnected coils are wound round l2 and I 3-, in which flow-alternating currentsreprescntingsounds. e
  • the diaphragm is mechanicallysupported by meansnot shown.
  • Fig. 6 showsan electrical analogy-ofthis ar rangement the similar letter referencesjdenotingf 1 the various circuit elements, to those used in Fig. 4, except that the main gap system and auxiliary gapsystemeach consist of two gaps instead of one, and areiepresenjted as two elements, A /l and two elements" E/ 2'; respectively and the: alternating current source is showna's;
  • Rig. 7 shows an extreme iorm of. the arrange ment' of'Fig. 5 and Fig. 3 shows an electrical analogy thereof; In'these figureslthesamenu Y merical and other. references. are. used as, thQ in Figsfi and 6,. to indicate corresponding ele ments.
  • pole pieces l5 and lfijare here conneetedj acrossj thewhole of magnet, II and inorder th t.
  • Figs. 9 and 10 in which the same numerical references as those used in Figs. and 6, are used to denote corresponding elements, show respectively another bipolar arrangement and an electrical analogy of. the magnetic system thereof.
  • the pole pieces l2 and 13 of the main pole system are in contact with intermediate parts of the magnet substantially equidistant from adjacent ends of the magnet and the pole pieces [5 and it of the auxiliary pole system are in contact with the ends of the magnet.
  • the polarisation of the magnet is such that the central portion between the points of contacts' with pole pieces i2 and I3. is of opposite polarity to that of the two ends, which themselves are polarised in the same direction as one another.
  • the polarity of the various points will therefore be such that one end will be, say, of north polarity, the intermediate portion in contact with the adjacent pole piece of the main pole system will be of south polarity, the portion in contact with the other pole piece of the main pole system will again be of north polartiy and the other extreme end of the magnet will be of south olarity.
  • pole pieces 15 and I6 are carried round the edge of the diaphragm and brought into proximity with the side of the diaphragm opposite to the side in proximity with pole pieces I2 and [3 but are not crossed over as in Figs. 5 and 7, since the polarisation of the magnet produces the same effect without this crossing over.
  • the magnet must be longer for the arrangement of Fig. 11 since the magneto motive force VI is furnished by' that of the two outer sections, opposed by that of the middle portion.
  • Figs. 12, 13 and 14 are top plan, side cross sectionvand bottom plan respectively of a practical construction of an electro acoustic transducer of the type illustrated in Fig. 1, for use as a telephone earpiece insert.
  • a cylindrical magnet l polarised axially, has a base plate 3 seated on one end face and a top plate 6 seated on the other end face.
  • a cylindricalcentre pole piece 4 Fixed to the centre of base plate 3 is a cylindricalcentre pole piece 4 carrying a bobbin l9 having windings, (not shown), to carry speech currents. Fitting closely within the magnet is a cylindrical spacing member 20, of an axial length less than that of the magnet. Member 20 must be of non magnetic material and if made of electrically conducting material, inust not be a continuous ring since such a ring would act as a short circuited turn on the speech coil. One end of 20 rests on base plate 3, and on the other end face of 20 the diaphragm'rests, being held in position by the pull of the polarising flux from pole piece 4. i
  • the diaphragm edge is in proximity with the magnet at a part of the latter spaced away from the junction of the magnet and top plate 6.
  • Top plate 6 rests on the end face of the magnet remote from base plate 3, and between I and 8 is clamped a membrane 2
  • the purpose of 2! is to keep moisture out of the interior of the receiver.
  • top plate 6 is dished inwards towards the diaphragm so as to present a disc-like pole surface thereto, substantially opposite to pole piece 4 on the other side of the diaphragm.
  • the sound apertures 23, four in number, are drilled into the sides of the depression in top plate 6.
  • the sizeand number of these holes should be chosen so that the acoustic mass of the plug of air within-them in combination with the acoustic stiffness of the air space between plate 6 and the diaphragm forms an acoustically resonant system having a resonant frequency at the upper end of the frequency range which the transducer is required to handle.
  • An acoustic arrangement of this type is described in British Patent No.
  • the .holes 25 are covered with porous material such as silk, to constitute an acoustic resistance between thesmall air space on one side of "the said bobbin flangeandjthe larger airspace on the other side of it.
  • the base plate 3 is pierced with holes 26 through drical covering 32 which projctsbeyondtopplate s and "disc 28, theprojec tin'g portions being pressed orspun over 6 andZB to hold; the components together axially.
  • An: electro-acoustic transducer comprising,
  • a diaphragm of magnetic material in combination: a diaphragm of magnetic material; a single permanent magnet memberj a main pole system including at leastone pole piece adjacent said diaphragm and a longitudinal portion of said diaphragm magnetically connected in series with at least a portion of said permanent magnet member; a main air gap system including a main air gap between each pole piece and the adjacent part of said diaphragm, said permanent magnet cooperating with said main pole system to produce a magnetic flux in said main air gap system and an auxiliary pole system including a magnetic path having at least one pole piece adjacent said diaphragm and magnetically connected in series with at least a portion of said permanent magnet member, said magnetic path being connected in series with a main air gap and in shunt with the longitudinal portion of the diaphragm adjacent said main air gap, said permanent magnet cooperating with said auxiliary pole system to produce an additional magnetic flux in said main air gap system to divert a portion of said first-mentioned magnetic flux passing through said adjacent part of the diaphra
  • An electro-acoustie transducer compi'ising, in combination: a diaphragm of'mag'netic material; a single permanent magnet member a main pole system including two polepieces positioned adjacent one side ofsaid-'diaphragmandieach magnetically connected with an opposite pole of said permanent magnet member; a main'air gap system including an air gap between each'pole piece and the adjacent part of said diaphragm, said permanent magnet cooperating with saidmain pole system to produce a magnetic flux in said main air gap system and an auxiliary pole system including two additional pole pieces positioned adjacent the other side of said diaphragm and each magnetically connected with an opposite pole of said permanent magnet member, said permanent magnet cooperating with said auxiliary pole system to produce an additional magnetic flux in said main air gap system to divert a portion of said first-mentioned magnetic flux passing through said adjacent part of the diaphragm.
  • said main pole system comprises two first pole pieces, each of which is magnetically connected with an opposite pole of said permanent magnet and arranged adjacent one side of said diaphragm
  • said auxiliary pole system comprises two further pole pieces each of which is connected with an. opposite pole of said permanent magnet and arranged adjacent the same side of the said diaphragm as the first pole pieces.
  • An electro-acoustic transducer comprising, in combination: a diaphragm of magnetic material; a single fiat permanent magnet member magnetized with consequent polarity along its length; a main pole system including two pole pieces adjacent said diaphragm and each magnetically connected with first opposite poles of said permanent magnet member; a main air gap system including an air gap between each pole piece and the adjacent part of said diaphragm, said permanent magnet cooperating with said main pole system to produce a magnetic flux in said main air gap system and an auxiliary pole system including two additional pole pieces adjacent said diaphragm and each magnetically :connected with additional opposite poles of said 11.
  • said permanent magnet is a fiat magnet polarized longitudinally
  • said main 'pole system comprises two first pole pieces each of which is magnetically connected to an opposite pole of said magnet and arranged adjacent said diaphragm
  • said auxiliary pole system comprises two additional pole pieces each of which is magnetically connected to parts of the magnet different from the parts to which the first pole pieces are connected and arranged adjacent said diaphragm in such maner that each of said 'additional pole pieces is nearest, at the end thereof adjacent said diaphragm, to that one of said first pole pieces from which it is furthest away at their respective connecting points with the permanent magnet, and in which the polarity of each additional pole piece is'opposite to that of the-one first pole piece which is nearest to it adjacent the diaphragm.
  • An electro-acoustic transducer as defined in claim 1, wherein said main pole system car- 'ries windings adapted to pass audio frequency currents, further comprising fixed external contact members; two plates mounted as an assembly 'in the same plane and each plate having portions concentric with portions of the other plate so that contact can be made with the two plates by means of said external contact members in any position of rotation of said assembly in said plate about the axis of the aforesaid concentricity, each plate having one or more re-entrant portionsso that connections at points which are equidistant from said axis can be made on said reentrant portions of both plates, and means for connecting the ends of said windings to said two plates respectively.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
  • Reciprocating, Oscillating Or Vibrating Motors (AREA)
US767241A 1946-06-21 1947-08-07 Electromagnetic vibratory device Expired - Lifetime US2610259A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1873946A GB624566A (en) 1948-10-22 1946-06-21 Improvements in or relating to electromagnetic vibratory devices
GB2745348A GB666408A (en) 1948-10-22 1948-10-22 Improvements in or relating to electro-magnetic vibratory devices

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US2610259A true US2610259A (en) 1952-09-09

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BE (1) BE476263A (en))
FR (2) FR951325A (en))
GB (3) GB606012A (en))

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2754373A (en) * 1952-08-22 1956-07-10 Harry B Shaper Miniature hearing-aid receiver
US2830240A (en) * 1954-09-23 1958-04-08 Hoffman Electronics Corp Electromagnetically controlled capacitors or the like
US2869049A (en) * 1954-04-13 1959-01-13 Baso Inc Electromagnetic control device
US2882459A (en) * 1954-06-04 1959-04-14 Berglund Nils Knut Edvard Polarised relay
US2957053A (en) * 1956-02-21 1960-10-18 Gen Phones Corp Audio-electric translating device
US3763335A (en) * 1971-02-23 1973-10-02 Matsushita Electric Ind Co Ltd Pickup cartridge with magnet armature having opposite axial sides of like polarity and central portion of opposite polarity
US20130170674A1 (en) * 2011-08-15 2013-07-04 Suzhou Hearonic Electronics Moving iron unit for loudspeakers
US20230007401A1 (en) * 2019-12-02 2023-01-05 Goertek Inc. Vibration sound device for electronic product and electronic product

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE500297A (en)) * 1951-10-31
US2848560A (en) * 1954-09-20 1958-08-19 Beltone Hearing Aid Company Hearing aid receiver
US11197099B2 (en) * 2019-06-12 2021-12-07 AAC Technologies Pte. Ltd. Screen sounding device

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US679405A (en) * 1901-03-22 1901-07-30 Emil Volkers Microtelephone.
US1660864A (en) * 1923-01-05 1928-02-28 Westinghouse Electric & Mfg Co Telephone device
US1721217A (en) * 1926-05-20 1929-07-16 Rca Corp Telephone receiver
US1830160A (en) * 1928-03-19 1931-11-03 French Electric Company Telephone receiver
US2069817A (en) * 1933-09-26 1937-02-09 Bell Telephone Labor Inc Acoustic device
US2099727A (en) * 1934-04-05 1937-11-23 Archibald A Duncan Telephone receiver
US2249158A (en) * 1939-05-19 1941-07-15 Bell Telephone Labor Inc Electroacoustic transducer
US2360796A (en) * 1940-11-29 1944-10-17 Int Standard Electric Corp Electroacoustic device
US2396135A (en) * 1942-05-06 1946-03-05 Terry Robert Saint George Electromagnetic device

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US679405A (en) * 1901-03-22 1901-07-30 Emil Volkers Microtelephone.
US1660864A (en) * 1923-01-05 1928-02-28 Westinghouse Electric & Mfg Co Telephone device
US1721217A (en) * 1926-05-20 1929-07-16 Rca Corp Telephone receiver
US1830160A (en) * 1928-03-19 1931-11-03 French Electric Company Telephone receiver
US2069817A (en) * 1933-09-26 1937-02-09 Bell Telephone Labor Inc Acoustic device
US2099727A (en) * 1934-04-05 1937-11-23 Archibald A Duncan Telephone receiver
US2249158A (en) * 1939-05-19 1941-07-15 Bell Telephone Labor Inc Electroacoustic transducer
US2360796A (en) * 1940-11-29 1944-10-17 Int Standard Electric Corp Electroacoustic device
US2396135A (en) * 1942-05-06 1946-03-05 Terry Robert Saint George Electromagnetic device

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2754373A (en) * 1952-08-22 1956-07-10 Harry B Shaper Miniature hearing-aid receiver
US2869049A (en) * 1954-04-13 1959-01-13 Baso Inc Electromagnetic control device
US2882459A (en) * 1954-06-04 1959-04-14 Berglund Nils Knut Edvard Polarised relay
US2830240A (en) * 1954-09-23 1958-04-08 Hoffman Electronics Corp Electromagnetically controlled capacitors or the like
US2957053A (en) * 1956-02-21 1960-10-18 Gen Phones Corp Audio-electric translating device
US3763335A (en) * 1971-02-23 1973-10-02 Matsushita Electric Ind Co Ltd Pickup cartridge with magnet armature having opposite axial sides of like polarity and central portion of opposite polarity
US20130170674A1 (en) * 2011-08-15 2013-07-04 Suzhou Hearonic Electronics Moving iron unit for loudspeakers
US8861754B2 (en) * 2011-08-15 2014-10-14 Suzhou Hearonic Electronics Moving iron unit for loudspeakers
US20230007401A1 (en) * 2019-12-02 2023-01-05 Goertek Inc. Vibration sound device for electronic product and electronic product
US11979725B2 (en) * 2019-12-02 2024-05-07 Goertek Inc. Vibration sound device for electronic product and electronic product

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Publication number Publication date
GB677225A (en) 1952-08-13
GB677235A (en) 1952-08-13
BE476263A (en))
FR951325A (fr) 1949-10-29
FR61602E (fr) 1955-05-16
GB606012A (en) 1948-08-04

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