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Publication numberUS3614335 A
Publication typeGrant
Publication dateOct 19, 1971
Filing dateJul 30, 1969
Priority dateAug 8, 1968
Also published asCA918798A1, DE1939837A1
Publication numberUS 3614335 A, US 3614335A, US-A-3614335, US3614335 A, US3614335A
InventorsLeslie Eugene Dymoke-Bradshaw, Norman William Tester
Original AssigneeInt Standard Electric Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electroacoustic transducer held together by thermoplastic clamping ring
US 3614335 A
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Description  (OCR text may contain errors)

iJnited States aterit lnventors Appl. No.

Filed Patented Assignee Priority Leslie Eugene Basil lliyrnolte-lfiradshnw Edgware;

Norman William Tester, London, both of England .lluly 30, 1969 Oct. 119, 19711 International Standard Electric Corporation New Yorlr, NY.

Aug. 8, 1968 Great Britain ELECTROACOUSTIC TRANSDUCER HELD References Cited UNITED STATES PATENTS 2/1952 Skelton 29/594 3/1932 Thuras... l79/115.5 6/1933 Giles 179/1 15.5 8/1942 Proctor 179/1 15.5 1/1949 Gileman 1. 179/179 9/1950 Zimmerman 179/1 15.5

FOREIGN PATENTS 8/1963 Germany 179/115.5 PC

1962 Germany 179/1 15.5

1966 Switzerland 179/1 15.5

Primary Examiner-llfiathleen l-l. Cllaffy Assistant Examiner-Thomas L. Kundert Att0rneysC. Cornell Remsen, Jr.,, Walter J. Baum, Percy P. Lantzy, .1. Warren Whitesel, Delbert P. Warner and James ABSTRACT: A moving coil electroacoustic transducer is held 'rocnrnnn m1 rnnniviormsric 13111111 11511; Radc nine 7 Claims, d Drawing Figs.

11.5.1131 .179/1155 R int. Cl HMr 9/02 ll' ield of Search...- 179/1 15.5,

115.5 ES, 178, 179, 11s; 1s1/31;175/115.5 PC;

together by a thermoplastic clamping ring. The ring has an in tegral flange which provides spaces between the magnetic system and the diaphragm. Acoustic damping is provided by a .nonmagnetic grid located behind a voice coil and coupled acoustically to the space behind the diaphragm.

ELEQTlllUACOUSTlC TRANSDUCER HELD TOGETHER WI THERMOPLASTTC ClLAMlPTNG MING This invention relates to electroacoustic transducers.

According to one aspect of the invention there is provided an electroacoustic transducer, in which the front cover, back cover and diaphragm are held together by a cylindrical thermoplastic clamping ring which has its two ends heat sealed over the front and back covers respectively.

According to this same aspect of the invention there is further provided a moving coil electroacoustic transducer, in which the magnetic structure consists of a solid cylindrical permanent magnet topped by an inner pole piece of soft magnetic material and encased concentrically by a cup-shaped yoke of soft magnetic material, in which a diaphragm carries a voice coil which rests in the annular airgap between the inner pole piece and the yoke, in which part of the yoke forms the back cover of the transducer, and in which the back cover, diaphragm and front cover are held together by a cylindrical clamping ring, with the diaphragm being located on an inwardly extending flange of the clamping ring and the two ends of the clamping ring being formed over the back and front covers of the transducer respectively.

According to another aspect of the invention there is also provided a moving coil clectroacoustic transducer, in which the magnetic structure consists of a solid cylindrical permanent magnet topped by an inner pole piece of soft magnetic material and encased concentrically by a cup-shaped yoke of soft magnetic material, in which a diaphragm carries a voice coil which rests in the annular airgap between the inner pole piece and the yoke, in which part of the yoke forms the back cover of the transducer, and in which sound equalization is achieved by a damping grid behind the moving coil having one or more holes leading to an otherwise closed space between the permanent magnet and the yoke, and by one or more holes in the front cover of the transducer which also serve for the ingress or egress of sound.

A moving coil, electroacoustic transducer according to the invention will now be described with reference to the accompanying drawings, in which:

FlG. 1 shows a cross section view, along the line A-A of FIG. 2 of a moving coil transducer according to the invention,

FlG. 2 shows a plan view of the moving coil transducer shown in FIG. ll,

FIG. 3 illustrates modification to the transducer shown in FIGS. 1 and 2 with regard to securing the permanent magnet of the assembly, and

FIG. A shows a section view of the clamping ring before it is used to hold together the assembly of parts of the transducer shown in F108. 1 and 2, or FIGS. 1 and 2 as modified by FIG. 3.

Referring now to the drawings, a solid cylindrical permanent magnet 111 of columnar material, such as Ticonal GX, is topped by an inner disc pole piece 11 of mild steel of greater diameter than the permanent magnet 10. A cup-shaped yoke of mild steel concentrically encases the permanent magnet the yoke being made up of a generally frustoconical pot 12, which forms the back cover of the transducer, and a flat annular pole piece 113.

A plastic diaphragm has a dome-shaped inner portion M and a flat rim 15. The diaphragm carries a voice coil 16 which rests in the annular airgap between the inner pole piece 111 and the outer pole piece 113. A damping grip 17, of nonmagnetic metal, is in the form of an annular trough behind the voice-coil 1b with its inner rim attached to the inner pole piece 11 and it outer rim attached to the outer pole piece 13 The damping grid 17, has one or more holes 171 leading to an otherwise closed space between the permanent magnet and the yoke.

The magnet 10 is secured by an adhesive to the pot 12. FIG. 3 shows a modification to the shape of the pct 12 in which the magnet is secured by making it a press fit. The larger end of the pot 12 has an outwardly extending flat lip 121 on which rests the flat annular outer pole piece 113. The pot 12 and the outer pole piece 13 are held together by a cylindrical clamping ring 18 (see also FIG. 1) of thermoplastic-insulating material,

being clamped between one side of an inwardly extending flange 1M of the clamping ring 1d and one end 1M of the clamping ring 1% which is heat sealed over the flat lip 121.

The flat rim 15 of the diaphragm is located on the outer side of the flange 1M. A fiat annular washer 19, e.g., of thermosetting plastic material, rests on the flat rim 15 of the diaphragm and a flat rim 201 of the front cover 20, e.g., of mild steel, rests on the washer 19. The other end 11131 of the clamping ring 1% is heat sealed over the flat rim 2111, thus clamping the diaphragm between the flange 1M and the washer 19 and holding the front cover 20 and diaphragm to the magnetic assembly of the transducer.

The clamping ring 13 has an outwardly extending rib WA into which the two terminals 21, e.g., of brass, are secured. Each electrical lead 161 of the voice coil 16 extends along a groove in the flange 1181 and through a hole or slot in the side of the clamping ring 18 and is laid over the top of the respective terminal 21 by locating it in a groove 1185 in the outer lip of the rib 11M. The leads 161 are soldered or welded to the terminals 21 and are protected by sealing material 22 in the upper surface of the rib 111 1.

A preferred method of manufacture of the diaphragm is to form it between heated male and female tools, followed by suitable cooling. The coil is made of solderable enameled copper wire coated with an adhesive and is self supporting, requiring no former.

Ticonal GX type-material is chosen for the permanent magnet working at its (Bl-1) maximum point, where B is the flux density in the permanent magnet and H is the magnetizing force in the permanent magnet. This material is chosen because it has a low value of A/(BH),,,,,,, where A is the density of the material, so as to achieve a low weight of magnet to provide a given flux density in a given airgap.

The antiresonant type of frequency response equalization is chosen for the transducer. This is achieved by the hole or holes 171 in the damping grid 17 behind the moving coil. The frequency response is also modified by one or more holes 202 in the front plate 20. The holes 171 and 202 may be damped by covering them with fabric or by making them in the fonn of louvres. The hole or holes 201 also serve for the ingress or egress of sound.

The magnetic efficiency factor G Z where G, the force factor, is defined as force per unit current or flux density in the airgap X conductor length and Z is the AC impedance of the winding, is optimized to achieve a flux density of the order of 7,500 lines per square cm. it is found that high sensitivity occurs for a magnet in the region of 5 to 10 grams and for an airgap 0.1 cm. long.

The weight of the complete transducer capsule is of the order of 18 grams, and the overall diameter and overall depth of the transducer capsule are approximately one inch and three-quarters of an inch respectively.

The above-described transducer is of small size and lightweight and can be used both as the transmitter and as the receiver of a telephone set. Modifications to the frequency response that may be required for these two different applications may be obtained by adjusting the acoustic mass and resistance of the holes in the associated mouthpiece or earcap and/or by adjusting the volume between the transducer front plate and the earcap or mouthpiece. if a cut in sensitivity at low frequencies is required this can be achieved by making one or more holes in the diaphragm.

As a receiver it has the advantages over the electromagnetic transducer of the rocking armature type at present used in telephones etc., of having a nearly constant impedance over the frequency band and of having no narrow airgaps which can cause failure of the transducer in service if they become blocked with dirt or if the armature poles.

The transducer has lower distortion than the rocking-armature type.

As a transmitter the transducer has the advantages of lower distortion than the carbon transmitter and does not suffer from burning noise. Because of its lower sensitivity than the carbon transmitter it must be used in conjunction with a transistor amplifier in the telephone set. However, the carbon transmitter, when subjected to much use, e.g., in public phone kiosks, and, more particularly when used in dirty locations such as railway stations and coal mines, becomes contaminated and replacement is frequent. The moving coil transducer (and amplifier) does not, of course, suffer from this defeet and, being inherently more reliable, ensures fewer replacements.

From a manufacturing point of view, the production spread of performance of this type of transducer is less than that of the moving iron type.

We claim:

I. An electroacoustic transducer, comprising a front cover, a back cover and a diaphragm, means holding said front cover, said back cover and said diaphragm together including a cylindrical thermoplastic-clamping ring, in which said thermoplastic-clamping ring includes two ends which are heat sealed over the front and back covers respectively, the diaphragm of the assembly is located on an inwardly extending flange of the clamping ring, the two ends of the clamping ring are formed over the back and front covers of the assembly respectively, and the clamping ring is of thermoplastic-insulating material and has an outwardly extending rib in which the terminals of the transducer are secured.

2. A moving coil electroacoustic transducer comprising a front cover, a magnetic structure, a diaphragm and a back cover, in which the front cover is formed of a flat piece of mild steel having a flat outer rim, the magnetic structure consists of a solid cylindrical permanent magnet topped by an inner pole piece of soft magnetic material and encased concentrically by a cup-shaped yoke of soft magnetic material, the diaphragm carries a voice coil which rests in an annular airgap between the inner pole piece and the yoke, the back cover is formed using part of the yoke, and the back cover, diaphragm, and the front cover are held together by a cylindrical clamping ring, the clamping ring is formed of thermoplastic-insulating material, the diaphragm is located on an inwardly extending flange integral to the clamping ring and the two ends of the clamping ring are formed over the back and front covers of the transducer respectively.

3. A transducer as claimed in claim 2, in which the transducerincludes terminals and electrical leads from the moving coil, and the clamping ring has an outwardly extending rib in which the terminals of the transducer are secured, and in which the electrical leads from the moving coil extend through holes in the clamping ring to said terminals.

4. A transducer as claimed in claim 3, in which antiresonant equalization is provided by modifying frequency response with a damping grid behind the moving coil having one or more holes leading to an otherwise closed space between the permanent magnet and the yoke, in which the frequency response is also modified by one or more holes in the front cover of the transducer which also serve for the ingress or egress of sound.

5. A transducer as claimed in claim 4, in which the inner pole piece is a disc of greater diameter than the permanent magnet, and in which the damping grid is in the form of an annular trough with its inner and outer rims attached to the inner pole piece and the yoke respectively.

6. A transducer as claimed in claim 3, in which the part of the yoke forming the back cover of the transducer is generally frustoconical with its smaller end fitting the back end of the permanent magnet.

7. A transducer as claimed in claim 2, in which one end of the clamping ring is sealed over one side of a flat rim of the front cover, in which the other side of the flat rim of the front cover rests on one side of a flat annular washer, in which a flat rim of the diaphragm is held between the other side of the flat annular washer and one side of the the inwardly extending flange of the clamping ring, in which the yoke consists of a pot forming the back cover of the transducer and having an outwardly extending flat lip with a flat annular outer pole piece resting on said flat lip, and in which said pot and said outer pole piece are held together between the other side of the inwardly extending flange of the clamping ring and the other end of the clamping ring which is sealed over the flat lip of said pot.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1847702 *May 2, 1931Mar 1, 1932Bell Telephone Labor IncSound translating device
US1915358 *Apr 11, 1930Jun 27, 1933Bell Telephone Labor IncElectrodynamic device
US2293078 *Dec 5, 1939Aug 18, 1942B A Proctor Company IncMicrophone
US2458158 *Nov 25, 1942Jan 4, 1949Permoflux CorpMagnetically shielded electrodynamic sound reproducer
US2523802 *Aug 6, 1949Sep 26, 1950Zimmerman Joseph DElectrodynamic pillow-type loudspeaker
US2585052 *Apr 21, 1949Feb 12, 1952Int Standard Electric CorpGranule type acoustic transducer
CH407233A * Title not available
DE1121654B *Aug 31, 1960Jan 11, 1962Siemens AgVerfahren und Zentrierring zum Zentrieren der Schwingspule eines elektroakustischen Wandlers mit Ringspaltmagnetsystem
DE1153421B *Jan 14, 1959Aug 29, 1963Peiker Acustic Fabrik ElektroaElektrodynamisches Schallgeraet
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4507800 *Jan 6, 1982Mar 26, 1985Analog & Digital Systems, Inc.Enclosed magnet loudspeaker
US5610989 *Dec 20, 1994Mar 11, 1997Knowles Electronics Co.Coil assemblies
US5708721 *Nov 25, 1996Jan 13, 1998Knowles Electronics Co.Coil assemblies
US6185809 *Jun 19, 1997Feb 13, 2001Akg Acoustics GmbhMethod of manufacturing a diaphragm for an electroacoustic transducer
US7266213 *Oct 15, 2002Sep 4, 2007Citizen Electronics Co., Ltd.Compact speaker with a protective cover
US7324658 *Nov 7, 2002Jan 29, 2008Sony CorporationSpeaker
EP1315400A2 *Oct 18, 2002May 28, 2003Citizen Electronics Co., Ltd.Speaker and method for manufacturing the speaker
Classifications
U.S. Classification381/398, 381/400, 381/354
International ClassificationH04R9/00, H04R9/02, H04R7/18
Cooperative ClassificationH04R9/025, H04R7/18, H04R9/02
European ClassificationH04R9/00, H04R9/02, H04R7/18
Legal Events
DateCodeEventDescription
May 28, 1987ASAssignment
Owner name: STC PLC, 10 MALTRAVERS STREET, LONDON, WC2R 3HA, E
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:INTERNATIONAL STANDARD ELECTRIC CORPORATION, A DE CORP.;REEL/FRAME:004761/0721
Effective date: 19870423
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:INTERNATIONAL STANDARD ELECTRIC CORPORATION, A DE CORP.;REEL/FRAME:004761/0721
Owner name: STC PLC,ENGLAND