US3891809A - Magnet system for an acoustic transducer - Google Patents

Magnet system for an acoustic transducer Download PDF

Info

Publication number
US3891809A
US3891809A US273299A US27329972A US3891809A US 3891809 A US3891809 A US 3891809A US 273299 A US273299 A US 273299A US 27329972 A US27329972 A US 27329972A US 3891809 A US3891809 A US 3891809A
Authority
US
United States
Prior art keywords
upper plate
core
magnet system
ferromagnetic
magnet
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
US273299A
Inventor
Derk Kleis
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.)
US Philips Corp
Original Assignee
US Philips Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by US Philips Corp filed Critical US Philips Corp
Application granted granted Critical
Publication of US3891809A publication Critical patent/US3891809A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • 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

  • ABSTRACT Magnet system for an acoustic transducer, in particular an electrodynamic microphone, which system comprises a main magnet and a ferromagnetic circuit the upper plate of which together with a centrally arranged core defines an annular effective air-gap, the upper plate being provided with a centering member which preferably comprises at least 3 re-entrant projections and is integral with, and is made of the same material as, the upper plate.
  • the re-entrant projections are moulded and calibrated in a single moulding operation during the manufacture of the upper plate.
  • the re-entrant projections may be in the form of bridge pieces joined to a disk which is made of the same material.
  • the invention relates to a magnet system for an acoustic transducer, in particular for an electrodynamic microphone, which system comprises a main magnet and a cooperating ferromagnetic circuit having a ferromagnetic upper plate which, together with a centrally arranged core, defines an annular effective airgap.
  • the core is centered with respect to the upper plate by means of a centering member which is joined to the upper plate and the larger part of which is located at the lower end of the effective air-gap.
  • This magnet system which is mounted in a microphone, comprises an annular main magnet provided with two pole pieces, a soft-iron upper plate and a soft-iron core rigidly secured to the lower plate. This core is centered by a separate centering ring made of a non-magnetic material which is glued to the lower surface of the upper plate.
  • a system according to the invention is characterized in that the centering member is integral with, and is made of the same material as, the upper plate.
  • the upper plate is provided with an inner edge formed with re-entrant projections during manufacture.
  • the centering member comprises at least three re-entrant projections on the inner edge of the upper plate.
  • the upper plate is stamped from a sheet in a single operation, the re-entrant projections being calibrated either in the same operation or in a subsequent operation.
  • a further advantage in comparison with the known magnet system consists in that in the centering process only one tolerance is significant, whereas in the use of a separate centering ring, as is the case in the known magnet system, the tolerance of the mounting thereof is to be added to the said tolerance.
  • a magnet system according to a further embodiment of the invention is characterized in that each re-entrant projection takes the form of a bridge piece which is joined to the ferromagnetic part of the core opposite the upper plate and is integral therewith.
  • the magnet system comprises a magnet core on which a ferromagnetic disk is placed at the level of the upper plate. Both the upper plate and the disk are made in a single moulding operation, the disk and the upper plate being joined to one another by narrow bridge pieces.
  • the crosssectional area of each of these elements is reduced so that the material is magnetically saturated at this point.
  • the reluctance is considerably increased so that the magnetic leakage via the projections is greatly reduced.
  • FIG. 1 is a cross-sectional view of an embodiment of a system according to the invention
  • FIG. 2 is a plan view of the upper plate used in this system
  • FIG. 3 is a cross-sectional view of the upper plate taken on the line [-1 in FIG. 2,
  • FIG. 4 is a cross-sectional view of another embodiment according to the invention.
  • FIG. 5 is a sectional view taken on the line V--V of FIG. 4.
  • the magnet system shown in FIG. 1 is a system which is used in many types of electrodynamic microphones. It comprises an annular magnet I made of an oxidic ceramic substance, for example, ferroxdure.
  • the magnet l is provided with an upper plate 2 and a lower plate 3 which is integral with a core 4.
  • the inner edge 5 of the upper plate 2 together with the upper edge 6 of the core 4 defines an effective air-gap 7. This air-gap serves to receive a moving coil, not shown, which is secured to a diaphragm, not shown.
  • the lower plate 3 and the core 4 are made of soft iron.
  • the upper plate 2 (see FIGS. 2 and 3), which is made of sintered iron, is provided with 3 re-entrant projections 8, the end of each projection having a reduced cross-sectional area.
  • the ends 8 are bent downward through a distance such as to allow sufficient space for the largest deflection which the moving coil may perform in operation.
  • the inner edges 10 of the ends 9 are calibrated.
  • the upper plate 2 is centered with respect to the core 4 by the three projections 8.
  • FIGS. 4 and 5 show another magnet system which comprises a centrally arranged permanent magnet 11 made of Ticonal. This magnet is provided with an upper plate 12 which through three re-entrant projections 18 is joined to a disk 14 which forms a pole piece for the magnet 11 on the upper surface thereof.
  • the projections 18 are in the form of bridge pieces which have parts of reduced cross-sectional area.
  • the ends 9 and the bridge pieces 19, respectively have portions the cross-sectional areas of which are reduced so that the centered material is saturated at these points, with a consequent very high reluctance.
  • the upper plate 2, and the upper plate 12 together with the disk 14, respectively, are moulded in one operation in which the inner edge 10 and 15, 16 respectively, are calibrated to have the required dimensions.
  • a magnet system for an acoustic transducer comprising, a main magnet and a ferromagnetic circuit which cooperates with the main magnet, said ferromagnetic circuit including a centrally arranged ferromagnetic core and a ferromagnetic upper plate having an opening therein which; together with the centrally arranged core, defines an annular effective air gap, said upper plate including a centering member integral therewith and made of the same ferromagnetic mate rial as the upper plate and comprising at least three circumferentially arranged reentrant projections on the inner edge of the upper plate with a part of each projection being dimensioned so that in operation said projection part is magnetically saturated, said core being centered wtih respect to the upper plate by means of the centering member the larger part of which is located at the lower end of the effective air gap.
  • a magnet system for an acoustic transducer comprising, a main magnet and a ferromagnetic circuit which cooperates with the main magnet, said ferromagnetic circuit including a centrally arranged ferromagnetic core and a ferromagnetic upper plate having an inner portion approximately coaxial with the core and adjacent to one end of said centrally arranged core and a peripheral portion with an opening that defines an annular effective air gap separating the inner and peripheral portions of the upper plate, said upper plate including a centering member for centering the core with respect to the upper plate and comprising at least three circumferentially spaced bridge members integral with the inner and peripheral portions so that the parts of the upper plate form a unitary piece and with all parts thereof made of the same ferromagnetic material.
  • a magnet system as claimed in claim 4 wherein a part of each bridge member is dimensioned so that in operation said part is magnetically saturated.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
  • Hard Magnetic Materials (AREA)

Abstract

Magnet system for an acoustic transducer, in particular an electrodynamic microphone, which system comprises a main magnet and a ferromagnetic circuit the upper plate of which together with a centrally arranged core defines an annular effective airgap, the upper plate being provided with a centering member which preferably comprises at least 3 re-entrant projections and is integral with, and is made of the same material as, the upper plate. The re-entrant projections are moulded and calibrated in a single moulding operation during the manufacture of the upper plate. The re-entrant projections may be in the form of bridge pieces joined to a disk which is made of the same material.

Description

United States Patent 11 1 Kleis June 24, 1975 I5 1 MAGNET SYSTEM FOR AN ACOUSTIC TRANSDUCER [75] Inventor: Derk Kleis, Emmasingel, Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New
York, NY.
[22] Filed: July 19, 1972 [21] Appl. No.: 273,299
[30] Foreign Application Priority Data 7/1966 Unitedf'Kingdom 179/180 163,965 2/1949 Austria l79/115.5 R 1,010,946 3/1952 France 179/117 336,913 4/l959 Switzerland 335/231 Primary Examiner-Kathleen H. Clafiy Assistant Examiner-George G. Stellar Attorney, Agent, or FirmFrank R. Trifari; Bernard Franzblau 7] ABSTRACT Magnet system for an acoustic transducer, in particular an electrodynamic microphone, which system comprises a main magnet and a ferromagnetic circuit the upper plate of which together with a centrally arranged core defines an annular effective air-gap, the upper plate being provided with a centering member which preferably comprises at least 3 re-entrant projections and is integral with, and is made of the same material as, the upper plate.
The re-entrant projections are moulded and calibrated in a single moulding operation during the manufacture of the upper plate.
The re-entrant projections may be in the form of bridge pieces joined to a disk which is made of the same material.
8 Claims, 5 Drawing Figures MAGNET SYSTEM FOR AN ACOUSTIC TRANSDUCER The invention relates to a magnet system for an acoustic transducer, in particular for an electrodynamic microphone, which system comprises a main magnet and a cooperating ferromagnetic circuit having a ferromagnetic upper plate which, together with a centrally arranged core, defines an annular effective airgap. The core is centered with respect to the upper plate by means of a centering member which is joined to the upper plate and the larger part of which is located at the lower end of the effective air-gap.
Such a magnetic system is described in Austrian Pat. No. 274,916. This magnet system, which is mounted in a microphone, comprises an annular main magnet provided with two pole pieces, a soft-iron upper plate and a soft-iron core rigidly secured to the lower plate. This core is centered by a separate centering ring made of a non-magnetic material which is glued to the lower surface of the upper plate.
The use of this additional ring, which must be mounted and glued, renders this magnetic system expensive and complicated.
It is an object of the invention to obviate this disadvantage, and a system according to the invention is characterized in that the centering member is integral with, and is made of the same material as, the upper plate.
The upper plate is provided with an inner edge formed with re-entrant projections during manufacture.
In a particularly advantageous embodiment the centering member comprises at least three re-entrant projections on the inner edge of the upper plate.
In this embodiment the upper plate is stamped from a sheet in a single operation, the re-entrant projections being calibrated either in the same operation or in a subsequent operation.
A further advantage in comparison with the known magnet system consists in that in the centering process only one tolerance is significant, whereas in the use of a separate centering ring, as is the case in the known magnet system, the tolerance of the mounting thereof is to be added to the said tolerance.
A magnet system according to a further embodiment of the invention is characterized in that each re-entrant projection takes the form of a bridge piece which is joined to the ferromagnetic part of the core opposite the upper plate and is integral therewith.
The magnet system comprises a magnet core on which a ferromagnetic disk is placed at the level of the upper plate. Both the upper plate and the disk are made in a single moulding operation, the disk and the upper plate being joined to one another by narrow bridge pieces.
To reduce the leakage of the magnetic flux via the projections or bridge pieces to a minimum, the crosssectional area of each of these elements is reduced so that the material is magnetically saturated at this point. As a result, the reluctance is considerably increased so that the magnetic leakage via the projections is greatly reduced.
Making the upper plate from sintered iron enables very close tolerances to be obtained during the moulding of the upper plate.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:
FIG. 1 is a cross-sectional view of an embodiment of a system according to the invention,
FIG. 2 is a plan view of the upper plate used in this system,
FIG. 3 is a cross-sectional view of the upper plate taken on the line [-1 in FIG. 2,
FIG. 4 is a cross-sectional view of another embodiment according to the invention, and
FIG. 5 is a sectional view taken on the line V--V of FIG. 4.
The magnet system shown in FIG. 1 is a system which is used in many types of electrodynamic microphones. It comprises an annular magnet I made of an oxidic ceramic substance, for example, ferroxdure. The magnet l is provided with an upper plate 2 and a lower plate 3 which is integral with a core 4. The inner edge 5 of the upper plate 2 together with the upper edge 6 of the core 4 defines an effective air-gap 7. This air-gap serves to receive a moving coil, not shown, which is secured to a diaphragm, not shown. The lower plate 3 and the core 4 are made of soft iron.
The upper plate 2 (see FIGS. 2 and 3), which is made of sintered iron, is provided with 3 re-entrant projections 8, the end of each projection having a reduced cross-sectional area. The ends 8 are bent downward through a distance such as to allow sufficient space for the largest deflection which the moving coil may perform in operation.
The inner edges 10 of the ends 9 are calibrated. During the assembly of the magnet system the upper plate 2 is centered with respect to the core 4 by the three projections 8.
FIGS. 4 and 5 show another magnet system which comprises a centrally arranged permanent magnet 11 made of Ticonal. This magnet is provided with an upper plate 12 which through three re-entrant projections 18 is joined to a disk 14 which forms a pole piece for the magnet 11 on the upper surface thereof. The projections 18 are in the form of bridge pieces which have parts of reduced cross-sectional area.
[n the two magnet systems according to the invention, the ends 9 and the bridge pieces 19, respectively, have portions the cross-sectional areas of which are reduced so that the centered material is saturated at these points, with a consequent very high reluctance.
The upper plate 2, and the upper plate 12 together with the disk 14, respectively, are moulded in one operation in which the inner edge 10 and 15, 16 respectively, are calibrated to have the required dimensions.
What is claimed is:
l. A magnet system for an acoustic transducer comprising, a main magnet and a ferromagnetic circuit which cooperates with the main magnet, said ferromagnetic circuit including a centrally arranged ferromagnetic core and a ferromagnetic upper plate having an opening therein which; together with the centrally arranged core, defines an annular effective air gap, said upper plate including a centering member integral therewith and made of the same ferromagnetic mate rial as the upper plate and comprising at least three circumferentially arranged reentrant projections on the inner edge of the upper plate with a part of each projection being dimensioned so that in operation said projection part is magnetically saturated, said core being centered wtih respect to the upper plate by means of the centering member the larger part of which is located at the lower end of the effective air gap.
2. A magnet system as claimed in claim 1 wherein the cross-sectional area of said projection part is dimensioned to produce said magnetic saturation thereof.
3. A magnet system as claimed in claim 1, characterized in that the material of the upper plate comprises sintered iron.
4. A magnet system for an acoustic transducer comprising, a main magnet and a ferromagnetic circuit which cooperates with the main magnet, said ferromagnetic circuit including a centrally arranged ferromagnetic core and a ferromagnetic upper plate having an inner portion approximately coaxial with the core and adjacent to one end of said centrally arranged core and a peripheral portion with an opening that defines an annular effective air gap separating the inner and peripheral portions of the upper plate, said upper plate including a centering member for centering the core with respect to the upper plate and comprising at least three circumferentially spaced bridge members integral with the inner and peripheral portions so that the parts of the upper plate form a unitary piece and with all parts thereof made of the same ferromagnetic material.
5. A magnet system as claimed in claim 4 wherein a part of each bridge member is dimensioned so that in operation said part is magnetically saturated.
6. A magnet system as claimed in claim 5 wherein the larger part of the bridge member is located at the lower end of the effective air gap and its cross-sectional area is dimensioned at said part to produce the magnetic saturation thereof.
7. A magnet system as claimed in claim 4 wherein the magnet system comprises a permanent magnet core and the inner portion of the upper plate is shaped like a disk and is aligned with the core and all parts of the upper plate are formed as a single integral piece of the same material.
8. A magnet system as claimed in claim 4 wherein said bridge members extend in a generally radial direction bridging the lower parts of said air gap.

Claims (8)

1. A magnet system for an acoustic transducer comprising, a main magnet and a ferromagnetic circuit which cooperates with the main magnet, said ferromagnetic circuit including a centrally arranged ferromagnetic core and a ferromagnetic upper plate having an opening therein which; together with the centrally arranged core, defines an annular effective air gap, said upper plate including a centering member integral therewith and made of the same ferromagnetic material as the upper plate and comprising at least three circumferentially arranged reentrant projections on the inner edge of the upper plate with a part of each projection being dimensioned so that in operation said projection part is magnetically saturated, said core being centered wtih respect to the upper plate by means of the centering member the larger part of which is located at the lower end of the effective air gap.
2. A magnet system as claimed in claim 1 wherein the cross-sectional area of said projection part is dimensioned to produce said magnetic saturation thereof.
3. A magnet system as claimed in claim 1, characterized in that the material of the upper plate comprises sintered iron.
4. A magnet system for an acoustic transducer comprising, a main magnet and a ferromagnetic circuit which cooperates with the main magnet, said ferromagnetic circuit including a centrally arranged ferromagnetic core and a ferromagnetic upper plate having an inner portion approximately coaxial with the core and adjacent to one end of said centrally arranged core and a peripheral portion with an opening that defines an annular effective air gap separatingg the inner and peripheral portions of the upper plate, said upper plate including a centering member for centering the core with respect to the upper plate and comprising at least three circumferentially spaced bridge members integral with the inner and peripheral portions so that the parts of the upper plate form a unitary piece and with all parts thereof made of the same ferromagnetic material.
5. A magnet system as claimed in claim 4 wherein a part of each bridge member is dimensioned so that in operation said part is magnetically saturated.
6. A magnet system as claimed in claim 5 wherein the larger part of the bridge member is located at the lower end of the effective air gap and its cross-sectional area is dimensioned at said part to produce the magnetic saturation thereof.
7. A magnet system as claimed in claim 4 wherein the magnet system comprises a permanent magnet core and the inner portion of the upper plate is shaped like a disk and is aligned with the core and all parts of the upper plate are formed as a single integral piece of the same material.
8. A magnet system as claimed in claim 4 wherein said bridge members extend in a generally radial direction bridging the lower parts of said air gap.
US273299A 1971-07-29 1972-07-19 Magnet system for an acoustic transducer Expired - Lifetime US3891809A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL7110445A NL7110445A (en) 1971-07-29 1971-07-29

Publications (1)

Publication Number Publication Date
US3891809A true US3891809A (en) 1975-06-24

Family

ID=19813706

Family Applications (1)

Application Number Title Priority Date Filing Date
US273299A Expired - Lifetime US3891809A (en) 1971-07-29 1972-07-19 Magnet system for an acoustic transducer

Country Status (7)

Country Link
US (1) US3891809A (en)
AT (1) AT316668B (en)
DE (1) DE2233656C3 (en)
FR (1) FR2147288B1 (en)
GB (1) GB1386358A (en)
IT (1) IT963399B (en)
NL (1) NL7110445A (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1957765A (en) * 1934-05-08 Magnetomotive force circuits
US2048222A (en) * 1931-10-08 1936-07-21 Deutsche Edelstahlwerke Ag Improvements, in or relating to magnets
US2216961A (en) * 1937-09-30 1940-10-08 Rca Corp Sound translating apparatus
US3462559A (en) * 1964-08-03 1969-08-19 Dallas Richard Wilder Two-piece loudspeaker

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1957765A (en) * 1934-05-08 Magnetomotive force circuits
US2048222A (en) * 1931-10-08 1936-07-21 Deutsche Edelstahlwerke Ag Improvements, in or relating to magnets
US2216961A (en) * 1937-09-30 1940-10-08 Rca Corp Sound translating apparatus
US3462559A (en) * 1964-08-03 1969-08-19 Dallas Richard Wilder Two-piece loudspeaker

Also Published As

Publication number Publication date
GB1386358A (en) 1975-03-05
NL7110445A (en) 1973-01-31
AT316668B (en) 1974-07-25
FR2147288B1 (en) 1980-03-14
IT963399B (en) 1974-01-10
FR2147288A1 (en) 1973-03-09
DE2233656C3 (en) 1979-12-06
DE2233656B2 (en) 1979-04-05
DE2233656A1 (en) 1973-02-08

Similar Documents

Publication Publication Date Title
US3919498A (en) Electroacoustic transducer
US3067366A (en) Magnet system having little stray
GB2085694A (en) Balanced armature transducers
JPH0671360B2 (en) Loudspeaker
GB1514095A (en) Electron beam apparatus
US3830986A (en) Magnetic circuit for an electro-acoustic converter
US3783311A (en) Magnetic device for use in acoustic apparatus
US3922501A (en) Moving voice coil electro-acoustic converter with laminated magnetically anisotropic poles
US3593239A (en) Magnetic system
US3632904A (en) Moving coil loudspeaker with eddy current suppression
US2249160A (en) Acoustic device
GB513895A (en) Improvements in telephone instruments
US3763334A (en) Magnet assembly
US3891809A (en) Magnet system for an acoustic transducer
US3129298A (en) Electro-dynamic conical loudspeaker
US3549830A (en) Magnet configuration for a loudspeaker
US1795948A (en) Reproducing device
US3790724A (en) Electromagnetic microphone including at least one acoustic resistance
US2506609A (en) Ring armature telephone receiver
US2957053A (en) Audio-electric translating device
US3851118A (en) Electroacoustic transducer having a preformed non-magnetic gentering sleeve
US2171733A (en) Acoustic device
US1632332A (en) Electromagnetic sound reproducer
US1630380A (en) Loud-speaker unit
JPH08317489A (en) Speaker device