US3067366A - Magnet system having little stray - Google Patents

Magnet system having little stray Download PDF

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US3067366A
US3067366A US845939A US84593959A US3067366A US 3067366 A US3067366 A US 3067366A US 845939 A US845939 A US 845939A US 84593959 A US84593959 A US 84593959A US 3067366 A US3067366 A US 3067366A
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magnet
housing
annular
top plate
stray
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US845939A
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Hofman Wytze
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US Philips Corp
North American Philips Co Inc
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US Philips 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
    • H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
    • H04R9/02—Details
    • H04R9/025—Magnetic circuit
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/02—Permanent magnets [PM]
    • H01F7/0273—Magnetic circuits with PM for magnetic field generation
    • H01F7/0289—Transducers, loudspeakers, moving coil arrangements
    • 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

  • the invention relates to a magnet system having little stray, particularly for use in loudspeakers, especially in television apparatus, in microphones and the like.
  • a system comprising a core with a bottom plate of soft magnetic material, at least one annular permanent magnet, preferably of an oxidic material and a top plate of soft magnetic material, in which system an effective annular air gap is formed between the top plate and the core, while on the free side of the bottom plate provision is made of a second permanent magnet preferably also of oxidic material, which is magnetized axially and in opposite direction relative to the first or annular permanent magnet, and a housing of soft magnetic material engages the free pole of the second magnet, this housing surrounding the system on three sides.
  • each of the two permanent magnets furnishes an essential part of the magnetic flux produced in the effective air gap.
  • the housing must have an adequate wall thickness to conduct the flux. This implies the disadvantage in a loudspeaker that, before the cone with the coil and the frame are arranged on the top plate, this housing must be compressed under a very high pressure to reduce the reluctance of the transition from the housing to the top plate to a permissible low value. Owing to this requirement it is not feasible to assemble the frame and cone beforehand.
  • magnets are to be magnetized before assembly since in the complete system (i.e. subsequent to compression) magnetization is no longer possible. It has been found from practice, that magnetizing the magneto before assembly of the cone involves a high loss of, for example, about 30% owing to very high magnetisable particles which get into the air gap during mounting so that the coil will establish a contact.
  • the annular magnet is proportioned so that it produces substantially the desired flux in the effective air gap for driving the cone, whereas between the top plate and the top side of the relatively thin-walled housing an additional annular gap of larger length than the effective air gap is left, while the second magnet is proportioned so that it eliminates at least for the major part the harmful stray flux in the additional gap.
  • the dimensions of both magnets can be calculated in a known manner dependent on the dimensions of the system and the magnetic values of the magnets.
  • This invention therefore provides various advantages over the above described prior art.
  • a thinwalled housing with the second magnet in accordance with one aspect of the invention, can be constructed in the form of a readily arranged unit, and the top part of the magnet system can also be constructed as a unit magnetized with cone and coil assembled, so that the aforesaid disadvantage of a high loss is obviated.
  • use may be made of permanent magnets which are first magnetized in a strong field, demagnetized in a reverse field and can be magnetized to saturation in a weak field as fully described in US. Patent 2,924,758.
  • the said top part unit may furthermore serve separately as a complete system, though the amount of stray is not particularly low. If a low-stray system is desired, the said unit (thinwalled housing and second magnet) may be slipped simply on the system or top part, since there is no contact with the top plate, the sleeve portion of the housing bearing on the outside of the annular magnet.
  • the magnet system according to the invention is therefore more universal.
  • the wall thickness of the housing is preferably not more than 2 mms., usually, however, 1.5 mms.
  • FIGURE 1 shows a magnet system according to the invention and FIGURE 2 shows a detail of FIGURE 1 on an enlarged scale.
  • the system comprises a cylindrical core 1 with a circular bottom plate or dish 2, both of soft magnetic material, an annular primary permanent magnet 33, a top annular plate 4 of soft magnetic material, defining an active annular gap 12 with the core 1, a disc-shaped auxiliary permanent magnet 5 (which may be annular, as an alternative) and the thinwalled cup-shaped housing 6 of soft magnetic material, while an annular air gap 7, which may be filled with a magnetically non-conductive material, is left between the housing 6 and the top plate 4.
  • the portion 14 (core 1, dish 2, magnet 3, and annular plate 4) is constructed in the form of a complete magnet system for use in loudspeakers, in which the magnet 3 of the system, completely with cone and accessories, can be magnetized.
  • the housing 6 shaped in the form of a sleeve (not shown) is arranged with the disc-shaped magnet 5, which serves substantially only for maximum elimination of the stray field of the top plate 4 and the uncovered top side of the magnet 3.
  • the magnet 5 will therefore have, as a rule, a smaller outside diameter than the magnet 3. Its height also is usually smaller.
  • the annular magnet 3 may also consist of two concentric rings (not shown), magnetized in the same axial direction and separated from each other by an air gap, the outer ring engaging the inner wall of the housing 6.
  • the inner ring provides the completion of the magnet system.
  • FIGURE 2 illustrates diagrammatically the at least partial compensation of the stray field.
  • the tendency to stray is indicated by the lines of force 8 and 9. This tendency is, however, suppressed for the major part by the lines of force 10 in opposite direction, originating from the magnet 5 of FIGURE 1.
  • the arrows in the figures indicate the direction of magnetization.
  • the internal diameter of the housing 6 is chosen to be equal to the outer diameter of the magnet 3, which in fact yields the best results, this cannot always be the case for practical reasons.
  • This embodiment has the disadvantage that the outer surface of the magnet 3, for example, in the case of cast magnets, and also in the case of ferroxdure magnets, must, as a rule, be ground which involves an increase in cost price. In certain cases it may therefore be more economical to provide a larger diameter for the housing 6 while the space between the housing 6 and the magnet 3 can be filled with a substance applied to the cylindrical surface of the magnet 3 and having a smooth outer sur face, for examplesynthetic resin. This substance is a magnetically non-conductive material.
  • the housing 6 may fit just around the unground outer surface of the magnet 3. It is neither always necessary to choose the diameter of the top plate 4 to be smaller than that of the magnet 3. In the case of equal diameters the top part of the housing 6 may be widened to an extent such that an annular air gap is obtained.
  • a magnetic system comprising at least one hollow permanent magnet, a core of soft magnetic material concentric within said magnet, a space between said magnet and said core, a bottom plate of soft magnetic material covering the opening in said hollow magnet, a top plate of soft magnetic material having an aperture concentric with said core, an eflective air gap defined by said core and top plate, said magnet extending beyond the marginal edges of said top and bottom plates, housing means of soft magnetic material and a magnet of opposite polarity relative to said hollow magnet disposed on the opposite "side of said bottom plate, from said opening, and a second air gap defined by the side walls of said housing and said top plate, whereby said magnet of opposite polarity reduces the flux in the air gap between said housing and said top plate.
  • a low stray magnetic system comprising a core piece and bottom plate each of soft magnetic material, at least one annular permanent magnet concentrically surrounding said core and contacting said bottom plate, a top plate of soft magnetic material having an annular opening surrounding said core and defining an effective air gap therewith, a second permanent magnet of opposite polarity relative to said annular magnet on the opposite side of said bottom plate, housing means concentrically surrounding said system on three sides, an air gap defined by said housing means and said top plate, said system characterized by said second magnet having a coercive force suflicient only to reduce the stray flux in said gap between said top plate and said housing means, and said annular magnet producing the flux in said effective air gap.

Description

United States Patent Ofiice 3,067,366 Patented Dec. 4, 1962 3,067,366 MAGNET SYSTEM HAVING LITTLE STRAY Wytze Hofman, Eindhoven, Netherlands, asslgnor to North American Philips Company, Inc., New York,
N.Y., a corporation of Delaware Filed Oct. 12, 1959, Ser. No. 845,339 Claims priority, application Netherlands Oct. 15. 1958 5 Claims. (Cl. 317-201) The invention relates to a magnet system having little stray, particularly for use in loudspeakers, especially in television apparatus, in microphones and the like. A system is known comprising a core with a bottom plate of soft magnetic material, at least one annular permanent magnet, preferably of an oxidic material and a top plate of soft magnetic material, in which system an effective annular air gap is formed between the top plate and the core, while on the free side of the bottom plate provision is made of a second permanent magnet preferably also of oxidic material, which is magnetized axially and in opposite direction relative to the first or annular permanent magnet, and a housing of soft magnetic material engages the free pole of the second magnet, this housing surrounding the system on three sides.
In this known system each of the two permanent magnets furnishes an essential part of the magnetic flux produced in the effective air gap. For this reason the housing must have an adequate wall thickness to conduct the flux. This implies the disadvantage in a loudspeaker that, before the cone with the coil and the frame are arranged on the top plate, this housing must be compressed under a very high pressure to reduce the reluctance of the transition from the housing to the top plate to a permissible low value. Owing to this requirement it is not feasible to assemble the frame and cone beforehand.
Moreover, in the prior art system the magnets are to be magnetized before assembly since in the complete system (i.e. subsequent to compression) magnetization is no longer possible. It has been found from practice, that magnetizing the magneto before assembly of the cone involves a high loss of, for example, about 30% owing to very high magnetisable particles which get into the air gap during mounting so that the coil will establish a contact.
In accordance with this invention the annular magnet is proportioned so that it produces substantially the desired flux in the effective air gap for driving the cone, whereas between the top plate and the top side of the relatively thin-walled housing an additional annular gap of larger length than the effective air gap is left, while the second magnet is proportioned so that it eliminates at least for the major part the harmful stray flux in the additional gap. The dimensions of both magnets can be calculated in a known manner dependent on the dimensions of the system and the magnetic values of the magnets.
This invention therefore provides various advantages over the above described prior art.
A thinwalled housing with the second magnet, in accordance with one aspect of the invention, can be constructed in the form of a readily arranged unit, and the top part of the magnet system can also be constructed as a unit magnetized with cone and coil assembled, so that the aforesaid disadvantage of a high loss is obviated. Moreover, use may be made of permanent magnets which are first magnetized in a strong field, demagnetized in a reverse field and can be magnetized to saturation in a weak field as fully described in US. Patent 2,924,758.
The said top part unit may furthermore serve separately as a complete system, though the amount of stray is not particularly low. If a low-stray system is desired, the said unit (thinwalled housing and second magnet) may be slipped simply on the system or top part, since there is no contact with the top plate, the sleeve portion of the housing bearing on the outside of the annular magnet.
The magnet system according to the invention is therefore more universal.
The wall thickness of the housing is preferably not more than 2 mms., usually, however, 1.5 mms.
The invention will be described, by way of example, more fully with reference to the accompanying figures.
FIGURE 1 shows a magnet system according to the invention and FIGURE 2 shows a detail of FIGURE 1 on an enlarged scale.
The system comprises a cylindrical core 1 with a circular bottom plate or dish 2, both of soft magnetic material, an annular primary permanent magnet 33, a top annular plate 4 of soft magnetic material, defining an active annular gap 12 with the core 1, a disc-shaped auxiliary permanent magnet 5 (which may be annular, as an alternative) and the thinwalled cup-shaped housing 6 of soft magnetic material, while an annular air gap 7, which may be filled with a magnetically non-conductive material, is left between the housing 6 and the top plate 4. The portion 14 (core 1, dish 2, magnet 3, and annular plate 4) is constructed in the form of a complete magnet system for use in loudspeakers, in which the magnet 3 of the system, completely with cone and accessories, can be magnetized. It is therefore possible to use a ferroxdure anisotropic oxidic magnet as described in US. Patent No. 2,762,778 with a much higher (BI-I) value than the isotropic permanent magnetic material as described in the US. Patent No. 2,762,777, since the first-mentioned material,-subsequent to magnetisation, is partly demagnetized outside the system or prior to assembly. Although the top plate 4 has a smaller diameter than the ring 3, between 70% and 90% of the diameter of the outside diameter of ring 3, preferably only thereof, the involved loss due to stray is negligible, since it amounts to only 1 or 1.5%.
If a low-stray system is desired, the housing 6 shaped in the form of a sleeve (not shown) is arranged with the disc-shaped magnet 5, which serves substantially only for maximum elimination of the stray field of the top plate 4 and the uncovered top side of the magnet 3. The magnet 5 will therefore have, as a rule, a smaller outside diameter than the magnet 3. Its height also is usually smaller.
The annular magnet 3 may also consist of two concentric rings (not shown), magnetized in the same axial direction and separated from each other by an air gap, the outer ring engaging the inner wall of the housing 6. The inner ring provides the completion of the magnet system.
FIGURE 2 illustrates diagrammatically the at least partial compensation of the stray field. The tendency to stray is indicated by the lines of force 8 and 9. This tendency is, however, suppressed for the major part by the lines of force 10 in opposite direction, originating from the magnet 5 of FIGURE 1.
The arrows in the figures indicate the direction of magnetization. Although in FIGURE 1 the internal diameter of the housing 6 is chosen to be equal to the outer diameter of the magnet 3, which in fact yields the best results, this cannot always be the case for practical reasons. This embodiment has the disadvantage that the outer surface of the magnet 3, for example, in the case of cast magnets, and also in the case of ferroxdure magnets, must, as a rule, be ground which involves an increase in cost price. In certain cases it may therefore be more economical to provide a larger diameter for the housing 6 while the space between the housing 6 and the magnet 3 can be filled with a substance applied to the cylindrical surface of the magnet 3 and having a smooth outer sur face, for examplesynthetic resin. This substance is a magnetically non-conductive material.
As an alternative, however, the housing 6 may fit just around the unground outer surface of the magnet 3. It is neither always necessary to choose the diameter of the top plate 4 to be smaller than that of the magnet 3. In the case of equal diameters the top part of the housing 6 may be widened to an extent such that an annular air gap is obtained.
What is claimed is:
1. A magnetic system comprising at least one hollow permanent magnet, a core of soft magnetic material concentric within said magnet, a space between said magnet and said core, a bottom plate of soft magnetic material covering the opening in said hollow magnet, a top plate of soft magnetic material having an aperture concentric with said core, an eflective air gap defined by said core and top plate, said magnet extending beyond the marginal edges of said top and bottom plates, housing means of soft magnetic material and a magnet of opposite polarity relative to said hollow magnet disposed on the opposite "side of said bottom plate, from said opening, and a second air gap defined by the side walls of said housing and said top plate, whereby said magnet of opposite polarity reduces the flux in the air gap between said housing and said top plate.
2. A low stray magnetic system comprising a core piece and bottom plate each of soft magnetic material, at least one annular permanent magnet concentrically surrounding said core and contacting said bottom plate, a top plate of soft magnetic material having an annular opening surrounding said core and defining an effective air gap therewith, a second permanent magnet of opposite polarity relative to said annular magnet on the opposite side of said bottom plate, housing means concentrically surrounding said system on three sides, an air gap defined by said housing means and said top plate, said system characterized by said second magnet having a coercive force suflicient only to reduce the stray flux in said gap between said top plate and said housing means, and said annular magnet producing the flux in said effective air gap.
3. A magnet system according to claim 2 wherein the wall thickness of said housing means is not substantially greater than 2 mms.
4. A magnet system according to claim 2 wherein the ratio of the outside diameter of said top plate and the outside diameter of said housing means is 0.7 to 0.9 whereby the length of the gap defined thereby is determined.
5. A magnet system according to claim 2 wherein said second magnet is disk shaped and of a diameter appreciably less than the outside diameter of said annular magnet.
References Cited in the file of this patent UNITED STATES PATENTS 2,141,595 Cornwell Dec. 27, 1938 2,275,880 Arey Mar. 10, 1942 2,915,681 Troy Dec. 1, 1959 2,923,783 White Feb. 2, 1960 OTHER REFERENCES (1) Permanent Magnet Manual No. 2, the Indiana Steel Products Company, page 15.
(11) Permanent Magnet Manual No, 6, the indiana Steel Products Company, page 17.
US845939A 1958-10-15 1959-10-12 Magnet system having little stray Expired - Lifetime US3067366A (en)

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Cited By (24)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3134057A (en) * 1960-07-11 1964-05-19 Sumitomo Metal Ind Magnetic circuit for the deflection of flux leakage
US3387707A (en) * 1965-06-14 1968-06-11 Westinghouse Electric Corp Permanent magnet assembly
US3478289A (en) * 1968-02-12 1969-11-11 Robert A Parnell Permanent magnet assembly for a loudspeaker assembly
US3593239A (en) * 1968-03-01 1971-07-13 Philips Corp Magnetic system
US3805927A (en) * 1971-11-15 1974-04-23 Knorr Bremse Gmbh Electromagnetic rail brake for railroad vehicles
FR2443691A1 (en) * 1978-12-06 1980-07-04 Batham Ian DETECTOR FOR THE PRESENCE OF MAGNETIZABLE PARTICLES IN A FLUID MEDIUM
US4654486A (en) * 1983-11-03 1987-03-31 Kurt Adolph Poor-scatter pot magnet system for magnetic-dynamic loudspeakers or acoustic transducers
US5142260A (en) * 1991-03-08 1992-08-25 Harman International Industries, Incorporated Transducer motor assembly
US5197104A (en) * 1991-04-18 1993-03-23 Josef Lakatos Electrodynamic loudspeaker with electromagnetic impedance sensor coil
US5409236A (en) * 1993-12-23 1995-04-25 Therrien; Joel M. Magnetic game or puzzle and method for making same
US5452366A (en) * 1993-02-02 1995-09-19 Kabushiki Kaisha Kenwood Loudspeaker
US5565834A (en) * 1992-03-19 1996-10-15 Oxford Instruments Limited Magnetic assembly for a nuclear magnetic resonance imaging system
US5802191A (en) * 1995-01-06 1998-09-01 Guenther; Godehard A. Loudspeakers, systems, and components thereof
US5879549A (en) * 1997-09-13 1999-03-09 Caiozza; Joseph Filter cartridge magnetic attachment
US5883967A (en) * 1997-04-15 1999-03-16 Harman International Industries, Incorporated Slotted diaphragm loudspeaker
US6611606B2 (en) 2000-06-27 2003-08-26 Godehard A. Guenther Compact high performance speaker
US6654476B1 (en) 1999-08-13 2003-11-25 Godehard A. Guenther Low cost broad range loudspeaker and system
US20040071308A1 (en) * 2000-08-14 2004-04-15 Guenther Godehard A. Low cost broad range loudspeaker and system
US20040120826A1 (en) * 2002-12-18 2004-06-24 Charles Perkins Magnet assembly for sputter ion pump
US20060159301A1 (en) * 2004-09-09 2006-07-20 Guenther Godehard A Loudspeakers and systems
US20060215870A1 (en) * 2000-06-27 2006-09-28 Guenther Godehard A Low profile speaker and system
US20060239493A1 (en) * 1998-11-13 2006-10-26 Guenther Godehard A Low cost motor design for rare-earth-magnet loudspeakers
US20080292117A1 (en) * 2007-05-23 2008-11-27 Soundmatters International Inc. Loudspeaker and electronic devices incorporating same
US8588457B2 (en) 1999-08-13 2013-11-19 Dr. G Licensing, Llc Low cost motor design for rare-earth-magnet loudspeakers

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GB1360080A (en) * 1971-12-22 1974-07-17 Melnikov J A Magnetic system

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US2923783A (en) * 1957-06-17 1960-02-02 Stanley F White Electro-acoustical transducer

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US2275880A (en) * 1939-10-05 1942-03-10 Gen Electric Magnetic structure
US2923783A (en) * 1957-06-17 1960-02-02 Stanley F White Electro-acoustical transducer
US2915681A (en) * 1957-11-20 1959-12-01 Indiana Steel Products Co Magnet assemblies

Cited By (42)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3134057A (en) * 1960-07-11 1964-05-19 Sumitomo Metal Ind Magnetic circuit for the deflection of flux leakage
US3387707A (en) * 1965-06-14 1968-06-11 Westinghouse Electric Corp Permanent magnet assembly
US3478289A (en) * 1968-02-12 1969-11-11 Robert A Parnell Permanent magnet assembly for a loudspeaker assembly
US3593239A (en) * 1968-03-01 1971-07-13 Philips Corp Magnetic system
US3805927A (en) * 1971-11-15 1974-04-23 Knorr Bremse Gmbh Electromagnetic rail brake for railroad vehicles
FR2443691A1 (en) * 1978-12-06 1980-07-04 Batham Ian DETECTOR FOR THE PRESENCE OF MAGNETIZABLE PARTICLES IN A FLUID MEDIUM
US4323843A (en) * 1978-12-06 1982-04-06 Batham Ian N Magnetic contamination detector
US4654486A (en) * 1983-11-03 1987-03-31 Kurt Adolph Poor-scatter pot magnet system for magnetic-dynamic loudspeakers or acoustic transducers
US5142260A (en) * 1991-03-08 1992-08-25 Harman International Industries, Incorporated Transducer motor assembly
US5197104A (en) * 1991-04-18 1993-03-23 Josef Lakatos Electrodynamic loudspeaker with electromagnetic impedance sensor coil
US5565834A (en) * 1992-03-19 1996-10-15 Oxford Instruments Limited Magnetic assembly for a nuclear magnetic resonance imaging system
US5452366A (en) * 1993-02-02 1995-09-19 Kabushiki Kaisha Kenwood Loudspeaker
US5409236A (en) * 1993-12-23 1995-04-25 Therrien; Joel M. Magnetic game or puzzle and method for making same
US5802191A (en) * 1995-01-06 1998-09-01 Guenther; Godehard A. Loudspeakers, systems, and components thereof
US8270662B2 (en) 1995-01-06 2012-09-18 Dr. G Licensing, Llc Loudspeakers, systems and components thereof
US7532737B2 (en) 1995-01-06 2009-05-12 Guenther Godehard A Loudspeakers, systems, and components thereof
US6876752B1 (en) 1995-01-06 2005-04-05 Godehard A. Guenther Loudspeakers systems and components thereof
US20060239492A1 (en) * 1995-01-06 2006-10-26 Guenther Godehard A Loudspeakers, systems, and components thereof
US20050232456A1 (en) * 1995-01-06 2005-10-20 Godehard A. Guenther Loudspeaker, systems, and components thereof
US5883967A (en) * 1997-04-15 1999-03-16 Harman International Industries, Incorporated Slotted diaphragm loudspeaker
US5879549A (en) * 1997-09-13 1999-03-09 Caiozza; Joseph Filter cartridge magnetic attachment
US20060239493A1 (en) * 1998-11-13 2006-10-26 Guenther Godehard A Low cost motor design for rare-earth-magnet loudspeakers
US6654476B1 (en) 1999-08-13 2003-11-25 Godehard A. Guenther Low cost broad range loudspeaker and system
US8588457B2 (en) 1999-08-13 2013-11-19 Dr. G Licensing, Llc Low cost motor design for rare-earth-magnet loudspeakers
US6611606B2 (en) 2000-06-27 2003-08-26 Godehard A. Guenther Compact high performance speaker
US7302076B2 (en) 2000-06-27 2007-11-27 Guenther Godehard A Low profile speaker and system
US7006653B2 (en) 2000-06-27 2006-02-28 Guenther Godehard A Compact high performance speaker
US20060215872A1 (en) * 2000-06-27 2006-09-28 Guenther Godehard A Compact high performance speaker
US20060215870A1 (en) * 2000-06-27 2006-09-28 Guenther Godehard A Low profile speaker and system
US20040076308A1 (en) * 2000-06-27 2004-04-22 Guenther Godehard A. Compact high performance speaker
US6993147B2 (en) 2000-08-14 2006-01-31 Guenther Godehard A Low cost broad range loudspeaker and system
US20040071308A1 (en) * 2000-08-14 2004-04-15 Guenther Godehard A. Low cost broad range loudspeaker and system
US6835048B2 (en) * 2002-12-18 2004-12-28 Varian, Inc. Ion pump having secondary magnetic field
US20040120826A1 (en) * 2002-12-18 2004-06-24 Charles Perkins Magnet assembly for sputter ion pump
US20060159301A1 (en) * 2004-09-09 2006-07-20 Guenther Godehard A Loudspeakers and systems
US7653208B2 (en) 2004-09-09 2010-01-26 Guenther Godehard A Loudspeakers and systems
US20100254564A1 (en) * 2004-09-09 2010-10-07 Guenther Godehard A Loudspeakers and systems
US8526660B2 (en) 2004-09-09 2013-09-03 Dr. G Licensing, Llc Loudspeakers and systems
US9060219B2 (en) 2004-09-09 2015-06-16 Dr. G Licensing, Llc Loudspeakers and systems
US20080292117A1 (en) * 2007-05-23 2008-11-27 Soundmatters International Inc. Loudspeaker and electronic devices incorporating same
US8189840B2 (en) 2007-05-23 2012-05-29 Soundmatters International, Inc. Loudspeaker and electronic devices incorporating same
US8929578B2 (en) 2007-05-23 2015-01-06 Dr. G Licensing, Llc Loudspeaker and electronic devices incorporating same

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CH376149A (en) 1964-03-31
DE1176768B (en) 1964-08-27
GB927545A (en) 1963-05-29
FR1247967A (en) 1960-12-09
NL111475C (en)
NL232314A (en)

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