(19) TZZ____T

(11) EP 1 819 194 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.: of the grant of the patent: H04R 9/04 (2006.01) H04R 9/02 (2006.01) 28.11.2012 Bulletin 2012/48

(21) Application number: 07002539.0

(22) Date of filing: 06.02.2007

(54) centered voice coil speaker Lautsprecher mit ferrofluidzentrierter Schwingspule Haut-parleur à bobine mobile centrée par moyen d’un ferrofluide

(84) Designated Contracting States: • Rosensweig, Ronald E. AT BE BG CH CY CZ DE DK EE ES FI FR GB GR Summit, NJ 07901 (US) HU IE IS IT LI LT LU LV MC NL PL PT RO SE SI SK TR (74) Representative: von Hellfeld, Axel Wuesthoff & Wuesthoff (30) Priority: 14.02.2006 US 766831 P Patent- und Rechtsanwälte Schweigerstrasse 2 (43) Date of publication of application: 81541 München (DE) 15.08.2007 Bulletin 2007/33 (56) References cited: (73) Proprietor: FERROTEC CORPORATION WO-A1-03/107718 JP-A- 8 079 886 Tokyo 104-0031 (JP) JP-A- 2004 274 206 US-A- 4 414 437 US-A- 5 461 677 (72) Inventors: • Tsuda, Shiro Asahi, Chiba, 289-2515 (JP)

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 1 819 194 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 1 819 194 B1 2

Description signal without scraping against the metal pieces, e.g. pole piece and front plate, forming the gap. [0001] This application claims the benefit of US Provi- [0007] In a 1980 AES publication by Bottenberg et al., sional Patent Application No. 60/766,831, filed February titled "The Dependence of Design Param- 14, 2006. 5 eters on the Properties of Magnetic Fluids," which was presented at the 61st Convention of the Audio Engineer- BACKGROUND OF THE INVENTION ing Society, November 3-6, 1978, the authors derived a mathematical expression for the ferrofluid radial force for 1. Field of the Invention a 1 inch dome tweeter having the gap on both sides of 10 the coil filled with a ferrofluid. Many tweeter manufactur- [0002] The present invention relates to audio speak- ers now take advantage of the centering force of ferrofluid ers. Particularly, the present invention relates to audio by filling the gap on both sides of the coil and thus re- speakers that utilize liquid suspension mechanisms for quiring no mechanical centering device, i.e. a spider. the voice coils incorporated into audio speakers. [0008] Unfortunately, the use of ferrofluid in the air gap 15 causes other problems. The air gap is connected to a 2. Description of the Prior Art cavity between the speaker and various compo- nents of the magnetic structure. Ferrofluid in the air gap [0003] Audio speakers produce audible sounds by dis- acts like an O-ring seal between the voice coil and the placing air by way of the movement of a diaphragm. The magnetic structure. The cavity is essentially sealed off diaphragm is attached to and moves under the control 20 from the air space in front of the front plate. As the voice of a voice coil, through which electric currents associated coil moves or as the temperature rises, it tends to elevate with the sounds to be reproduced are driven. The voice the air pressure within this cavity. If the pressure builds coil is disposed in an annular air gap of a magnetic struc- up to a point where it exceeds the pressure capacity of ture. The magnetic structure includes a permanent mag- the ferrofluid O-ring seal, the air bursts through the seal net that provides radial flux in the air gap. Current through 25 and relatively large amounts of the ferrofluid may then the coil interacts with this radial flux to provide axial forces be blown or flow out of the gap. One solution to this prob- on the coil and causes displacement of the coil and the lem was addressed by U.S. Patent No. 5,335,287. attached diaphragm. [0009] U.S. Patent No. 5,335,287 (1994, Athanas) dis- [0004] The alignment of the voice coil in the air gap is closes a loudspeaker with a viscous magnetic fluid sus- crucial to the performance of an audio speaker. Any30 pension for the voice coil rather than the corrugated disk scraping of the voice coil against the sides of the air gap suspension that is conventionally used. Specially de- causes humming and distortion, which affects sound signed vent passages are formed in the magnet assem- quality. Additionally, scraping creates undesirable bly in order to prevent internal pressure from either build- stresses on the suspension system as well as removal ing up or creating sub- atmospheric conditions that could of the insulation from the coil windings. This leads to early 35 cause the magnetic fluid to be blown out of the magnetic speaker failure. Speaker manufacturers commonly em- gap. The patent also discloses that the mechanical ploy a flexible, fibrous element called a spider to align centering device can be eliminated even in more de- the voice coil in the air gap. The inclusion of a spider manding high excursion woofers by utilizing requires additional space in the speaker, which is not of high magnetization values such as 600-800 Gauss available in audio speakers such as tweeters and very 40 filling the gap on both sides of the voice coil. small full range speakers. [0010] Other problems that arise when using ferrofluid [0005] For over 25 years, air gaps in some audio in the air gap around the voice coil involve equalization speakers have been filled with magnetic fluids (also of the amount of ferrofluid on both sides of the voice coil called ferrofluids). These ferrofluids offer significant per- (because filing the entire gap can be problematic) and formance advantages in tweeters, midrangers, woofers, 45 equalization of the air pressure under the dust cap of the compression drivers, and automotive speakers. Ferroflu- voice coil. To address these problems, a plurality of vent ids are used for a wide variety of reasons such as damp- openings were incorporated in the voice coil adjacent the ing of the voice coil, heat transfer, reduction in harmonic dome end of the voice coil such as is disclosed in U.S. distortion, lubrication, and centering of the voice coil in Patent No. 4,414,437. the air gap. 50 [0011] U.S. Patent No. 4,414,437 (1983, Trauernicht [0006] A unique aspect of ferrofluid is its ability to exert et al.) discloses a moving coil dynamic transducer. The a radial force on the voice coil, which has come to be electromagnetic transducer (voice coil) includes a mem- known as the centering force. The magnitude of this force ber producing a and presenting an air gap depends on the magnetization of the ferrofluid and the traversed by the magnetic field, a mass of magnetic fluid magnetic flux density in the air gap of the speaker. The 55 extending across the air gap, and a moving coil mounted higher the magnetization and flux density, the greater the on a moving coil carrier supported for movement through radial force. The radial force keeps the voice coil properly the air gap. The moving coil carrier is provided with at aligned as it vibrates in the gap in response to an audio least one passage located to communicate with the mag-

2 3 EP 1 819 194 B1 4 netic liquid during at least part of the movement of the quirement for a mechanical centering device such as a coil carrier through the air gap. The passage permits flow spider. The magnetic fluid is positioned in the space on of magnetic liquid from one side to the other of the carrier the side of the voice coil having the higher magnetic flux in the direction of the air gap. This provides an equaliza- density. Another important aspect of the present inven- tion of the magnetic liquid on each side of the voice coil. 5 tion is the requirement to prevent the migration of the [0012] Document JP 08079886 A relates to a speaker. magnetic fluid from one side of the voice coil to the other. An air gap between an outer side face of a pole of a [0019] It should be noted that the magnetic gap or air magnetic circuit and an inner side face of a voice coil is gap may be thought of as having a gap portion of higher selected smaller than an air gap between an inner side magnetic field that diminishes in strength across the gap face of an upper plate and an outer side face of the voice 10 to a gap portion of lower magnetic field. Magnetic fluid coil to prevent the outer side face of the voice coil from will naturally reside in a gap portion of higher magnetic being in contact with the magnetic circuit. field. The magnetic fluid, however, will migrate to a gap [0013] Document JP 2004274206 A also relates to a portion of lower magnetic field located at the corners of speaker. An edge supporting an outer circumference of the pole piece that is situated in the lower magnetic field a diaphragm is constituted of a magnetic fluid and a voice 15 unless the gap portions are separated. The tubular form coil is coupled with the diaphragm. of the voice coil of the present invention is structured to [0014] Therefore, what is needed is an audio speaker maintain gap portion separation and prevent magnetic that uses ferrofluid for centering a voice coil without the fluid migration. need for ferrofluid equalizing vent openings. What is also [0020] In one embodiment, the magnetic structure of needed is an audio speaker that uses ferrofluid for center- 20 the driver unit is an assembly that includes a base plate ing a voice coil without the need for ferrofluid equalizing with a central magnetic post, an annular permanent mag- vent openings or the use of a spider. net and an annular top plate. The annular permanent magnet is sandwiched between the base plate and the SUMMARY OF THE INVENTION annular top plate. The base plate and the central mag- 25 netic post may be made from a single piece of magnetic [0015] It is an object of the present invention to provide material or may be two or more pieces integrally joined an audio speaker that uses ferrofluid for centering a voice together to form an inverted, T-shaped pole piece. The coil without the need for ferrofluid equalizing vent open- annular permanent magnet is axially polarized where one ings. It is another object of the present invention to pro- face of the magnet has one polarity and the other face vide an audio speaker that uses ferrofluid for centering 30 has the opposite polarity. a voice coil without the need for ferrofluid equalizing vent [0021] The central magnetic post extends from the openings or the use of a mechanical centering device base plate through the central space formed within the such as a spider. It is a further object of the present in- annular magnet and the annular top plate forming a cen- vention to provide an audio speaker that uses a ferrofluid trallylocated pole piece.The base plate, annulartop plate for centering a voice coil having low volatility and lower 35 and the central magnetic post are formed of a magnet- magnetization than previously required for high excur- izable material and together with the annular permanent sion woofers. magnet define a magnetic circuit having an annular gap. [0016] The present invention achieves these and other With the voice coil placed in position within the annular objectives by providing an audio speaker with the fea- gap, the space between the outer surface of the voice tures of claim 1 and a method of claim 9. 40 coil and the inner surface of the annular top plate has a [0017] The audio speaker has a driver unit, a vibration higher magnetic flux density than the space between the system and magnetic fluid disposed in an annular gap inner surface of the voice coil and the outer surface of only between one side of a voice coil and a surface of the central magnetic post. the annular gap. The driver unit includes a support frame [0022] In this embodiment of the present invention, the with a central portion forming a magnetic structure with 45 magnetic fluid is placed between the outer surface of the an annular gap around a central magnetic post. The vi- voice coil and the inner surface of the annular top plate. bration system has a diaphragm and a voice coil. The This position provides a larger centering force than the voice coil is attached to one side of the diaphragm and minimal centering force provided in audio speakers of movably mounted within the annular gap. The diaphragm the prior art where the magnetic fluid is placed on both is flexibly connected on its periphery to the support frame. 50 sides of the voice coil. The voice coil includes a tubular form with an electrical [0023] Inanother embodimentof thepresent invention, winding on the outer surface of the tubular form. The the magnetic structure of the audio speaker includes a electrical winding is preferably axially centered in the an- magnetic housing preferably with a cylindrical wall and nular gap. a bottom. The central magnetic post extends from the [0018] The major features of the present invention are 55 bottom through the central space formed by the cylindri- the placement of magnetic fluid on only one side of the cal wall of the magnetic housing forming a centrally-lo- voice coil to create a centering force to keep the voice cated pole piece that includes a permanent magnet and coil centered in the annular gap and the lack of the re- a top pole piece. Like the magnet in the previous embod-

3 5 EP 1 819 194 B1 6 iment, the permanent magnet in the central magnetic BRIEF DESCRIPTION OF THE DRAWINGS post is axially polarized where one face of the magnet has one polarity and the other face has the opposite po- [0028] FIGURE 1 is a simplified, cross-sectional view larity. The magnetic housing and the top pole piece are of one embodiment of the present invention showing an formed of a magnetizable material. The magnetic hous- 5 audio speaker with an annular magnet. ing and central magnetic post define the magnetic circuit [0029] FIGURE 2 is a simplified, cross-sectional view having an annular gap between the outer surface of the of another embodiment of the present invention showing top pole piece and the inner surface of the cylindrical wall. an audio speaker with a magnet incorporated into the [0024] With the voice coil placed in position within the central post of the driver unit. annular gap, the space between the inner surface of the 10 voice coil and the outer surface of the top pole piece of DETAILED DESCRIPTION OF THE PREFERRED EM- the central magnetic post has a higher magnetic flux den- BODIMENT sity than the space between the outer surface of the voice coil and the inner surface of the cylindrical wall of the [0030] Thepreferred embodimentof the present inven- magnetic structure. This is due to the permanent magnet 15 tion is illustrated in Figs. 1-2. Figure 1 shows a simplified being part of the central magnetic post. In this embodi- cross-section of one embodiment of an audio speaker ment of the present invention, the magnetic fluid is placed 10. Audio speaker 10 includes a driver unit 20, a vibration between the inner surface of the voice coil and the outer system 60 and magnetic fluid 80. Driver unit 20 includes surface of the central magnetic post. a support frame 22 and a central portion 24. Central por- [0025] The magnetic fluid used in the present invention 20 tion 24 includes a magnetic structure 26 defining an an- has a magnetization preferably in the range of about 100 nular gap 28 around a central magnetic post 40. to about 600 Gauss. The choice of magnetization is de- [0031] In this embodiment, magnetic structure 26 is an pendent on the magnetic fluid that is most suited to assembly having a base plate 30 with the central mag- achieve an adequate centering force. For instance, audio netic post 40, an annular permanent magnet 32 and an speakers with high excursion voice coils and low mag- 25 annular top plate 34. Base plate 30 and central magnetic netic field require magnetic fluids with higher magnetiza- post 40 may be made from a single piece of magnetic tion values. Audiospeakers with low excursion voice coils material or may be two or more pieces integrally joined. and high magnetic field require magnetic fluids with lower Annular permanent magnet 32 is axially polarized where magnetization values. one face of magnet 32 has one polarity and the other [0026] It is also important that the magnetic fluid, once 30 face of magnet 32 has the opposite polarity. Magnet 32 positioned in the space on the side of the voice coil having is sandwiched between base plate 30 and annular top the greater magnetic flux density, is prevented from mi- plate 34. grating to the other side of the voice coil. One way to [0032] Central magnetic post 40 extends from base prevent magnetic fluid migration is to lengthen the tubular plate 30 through the central space formed within annular form that makes up the voice coil. The length of the tu- 35 magnet 32 and annular top plate 34 to form a centrally bular form should be sufficient so that the magnetic fluid located pole piece. Base plate 30, annular top plate 34 cannot migrate around the end of the voice coil during and post 40 are formed of a magnetizable material and the voice coil’s greatest excursion as it oscillates. In ad- together with annular magnet 32 define a magnetic circuit dition, where vent openings are incorporated through the having an annular gap 28 between a side surface 42 of wall of the tubular form to equalize air pressure, the vent 40 post 40 and an inner edge 35 of annular top plate 34. openings must be positioned so that the magnetic fluid [0033] Vibration system 60 includes a diaphragm 62 does not contact the edge of the vent openings during and a voice coil 64. Voice coil 64 includes a tubular form the voice coil’s greatest excursion as it oscillates. Allow- 66 and an electrical winding 70 wound on an outer sur- ing the magnetic fluid to migrate through the vent open- face 67 of tubular form 66. Voice coil 64 is connected to ings would also defeat the advantage of maximum45 diaphragm 62 at a proximal end 65a while a distal end centering force provided by the present invention. 65b surrounds central magnetic post 40. Electrical wind- [0027] It should be understood that the advantages of ing 70 is preferably axially centered in annular gap 28. the present invention can be successfully incorporated Winding 70 is shown in its de- energized state. When an in other speaker embodiments with magnetic air gaps. A.C. signal is applied to electrical winding 70, the voice One example is an embodiment having a radially polar- 50 coil 64 will oscillate axially in both directions from the ized magnet where an outer radial surface of the magnet neutral position. has one polarity and the inner radial surface has the op- [0034] A major feature of the present invention is the posite polarity. The key aspect of the present invention disposition of viscous magnetic fluid 80 in the annular is that, regardless of the speaker design, the magnetic gap 28 on only one side of voice coil 64. Magnetic fluid fluid is always added to the portion of the magnetic gap 55 80 has a magnetization in the range of about 100 to about on the side of the voice coil having the higher magnetic 600 Gauss, preferably, in the range of about 200 to about flux density. 500 Gauss, and, more preferably, in the range of about 300 to about 400 Gauss. In the embodiment shown in

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Fig. 1, magnetic fluid 80 is disposed between the outer [0040] In this embodiment, magnetic structure 126 is surface 67 of voice coil 64 and the inner edge 35 of an- an assembly having a magnetic housing 127 preferably nular top plate 34. In the alternative, magnetic fluid 80 with a cylindrical wall 128 and a bottom 132. Central mag- may be disposed between the inner surface 68 of voice netic post 140 includes a permanent magnet 142 and a coil 64 and the outer surface 42 of magnetic post 40. 5 pole piece 144 on top of permanent magnet 142. Like its However, the space between outer surface 67 and inner counterpart in Fig. 1, permanent magnet 142 is axially edge 35 of annular top plate 34 in this embodiment has polarized where one face of magnet 142 has one polarity ahigher magneticflux density than theannular gap space and the other face of magnet 142 has the opposite po- between the inner surface 68 of tubular form 66 and side larity. Central magnetic post 140 extends from bottom surface 42 of magnetic post 40. 10 132 through the central space formed by cylindrical wall [0035] The inventors’ have discovered that placement 128 to form a centrally-located pole piece. Magnetic of magnetic fluid 80 on only one side of voice coil 64 housing 127 and pole piece 144 are made of magnetiz- having the higher magnetic flux density provides a great- able material and, together with magnet 142, define a er centering force on voice coil 64 than in audio speakers magnetic circuit having an annular gap 138 between out- that use magnetic fluid on both sides of the voice coil for 15 er surface 145 of pole piece 144 and an inner surface centering the voice coil. In fact in audio speakers that 129 of cylindrical wall 128. use magnetic fluid on both sides of the voice coil, the [0041] Vibration system 160 includes a diaphragm magnetic fluid provides minimal centering force. Further, 161, a dust cap 162 and a voice coil 164. Voice coil 164 placing the magnetic fluid on only the side of voice coil includes a tubular form 166 and a coil winding 170 wound 64 having the lower magnetic flux density provides no 20 on the outer surface 167 of tubular form 166. In this em- apparent centering force. bodiment, magnetic fluid 180 is disposed between the [0036] Another feature of the present invention is that outer surface 145 of pole piece 144 and the inner surface magnetic fluid 80 not be allowed to migrate from the high- 168 of voice coil 164. The space between the outer sur- er magnetic flux density side of the voice coil 64 to the face 145 of pole piece 144 and the inner surface 168 of lower magnetic flux density side of voice coil 64. Thus, 25 voice coil 164 is the side of voice coil 164 with the higher the tubular form 66 of voice coil 64 must be configured magnetic flux density. This is so because the permanent with a material and structure that prevents the magnetic magnet 142 forms a portion of central magnetic post 140. fluid from getting to the lower magnetic flux density side. The annular gap space between the outer surface 167 [0037] Conventional tubular forms are made from a flat of tubular form 166 and inner surface 129 of cylindrical piece of material formed into a cylindrical shape having 30 wall 128 has lower magnetic flux density. a longitudinal split between the opposing sides of the [0042] The present invention is applicable to all types material. In addition, some conventional tubular forms of audio speakers such as tweeters, midranges, woofers, include vent openings through the tubular form to allow full ranges, etc. The magnetic field in the air gap as well equalization of air pressure and/or equalization of mag- as voice coil excursion (i.e. the total oscillation distance netic fluid located on both sides of the voice coil. 35 of the voice coil) differs from one speaker type to another. [0038] In the present invention, the tubular form 66 It was found that magnetic fluids having a magnetization must be either a solid- walled tube or the longitudinal split in the range of about 100 to about 600 Gauss will be most must be covered with a material that will seal the split to suited to achieve an adequate centering force. As a gen- effectively form a solid surface so as to prevent magnetic eral rule, audio speakers with high excursion voice coils fluid 80 from migrating since it must be retained on only 40 and low magnetic field require magnetic fluids with higher one side of voice coil 64. In addition, the tubular form 66 magnetization values, i.e. magnetization values in the of the present invention must be long enough to prevent upper portion of the indicated range. Audio speakers with any accidental migration of magnetic fluid 80 from one low excursion and high magnetic field require magnetic side of voice coil 64 to the other during oscillation of voice fluids with lower magnetization values, i.e. magnetization coil 64. Vent openings may be used in the present inven- 45 values in the lower portion of the indicated range. tion, however, the vent openings must be positioned a [0043] Although the preferred embodiments of the sufficient distance from the magnetic fluid 80 so that mag- present invention have been described herein, the above netic fluid 80 will not reach the edge of the vent openings description is merely illustrative. Further modification of during the greatest oscillations of voice coil 64. Allowing the invention herein disclosed will occur to those skilled magnetic fluid 80 to migrate through the vent openings 50 in the respective arts and all such modifications are will defeat the advantages of the present invention. deemed to be within the scope of the invention as defined [0039] Turning now to Fig. 2, there is illustrated another by the appended claims. embodiment of the present invention. In this embodi- ment, audio speaker 100 includes a driver unit 120, a vibration system 160 and magnetic fluid 180. Driver unit 55 Claims 120 includes a support frame portion (not shown) and a magnetic structure 126 defining an annular gap 138 1. An audio speaker comprising: around a central magnetic post 140.

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a driver unit (10) having a support frame (22) sion and lower magnetic field. with a central portion (24) forming a magnetic structure (26) defining an annular gap (28) 6. The audio speaker of claim 1 wherein said magnetic around a central magnetic post (40, 140), where- fluid (80) has a lower magnetization when said audio in the magnetic structure (26) includes a perma- 5 speaker has a voice coil (64) with lower excursion nent magnet (32; 142) that provides a radial and higher magnetic field. magnetic flux in the annular gap (28) and where- in the annular gap (28) has a gap portion of high- 7. The audio speaker of claim 1 wherein said voice coil er magnetic field that diminishes in strength (64) has a tubular form (66; 166) of sufficient length acrossthe gapto a gap portionof lower magnetic 10 to prevent the migration of said magnetic fluid (80) field; at a distal end of said voice coil (64) from said one a vibration system (60) having a diaphragm (62) side (67; 168) of said voice coil (64) to the second and a voice coil (64), said voice coil attached to side (68; 166) of said voice coil (64). one side of said diaphragm (62), wherein said vibration system (60) is fixed to said support15 8. The audio speaker of claim 7 wherein said tubular frame (22), wherein said voice coil (64) is mov- form (66; 166) of said voice coil (64) has a solid sur- ably mounted in said annular gap (28), and face. wherein the space between a first side (67; 168) of the voice coil (64), being either an outer side 9. A method of assembling a vibration system (60) to (67) or an inner side (168) of the voice coil (64), 20 a driver unit (10) of an audio speaker, said method and a first surface (35; 145) of the annular gap comprising: (28), being either an inner surface (35) of an annular top plate (34) of the magnetic structure providing the driver unit (10) with a support (26) or an outer surface (145) of a top pole piece frame(22) and with a central portion (24) forming (144) of the central magnetic post (40, 140), has 25 a magnetic structure (26) defining an annular a higher magnetic flux density than the space gap (28) around a central magnetic post (40), between on the one hand a second side (68; wherein the magnetic structure (26) includes a 166) of the voice coil (64), being opposite to the permanent magnet (32; 142) that provides a ra- first side (67; 168) of the voice coil (64) and being dial magnetic flux in the annular gap (28), where- either an inner surface (68) or an outer surface 30 in the annular gap (28) has a gap portion of high- (166) of the voice coil (64), and on the other hand er magnetic field that diminishes in strength a second surface (42; 129) of the annular gap acrossthe gap to a gap portion of lower magnetic (28), being opposite to the first surface (35; 145) field; of the annular gap (28) and being either an outer disposing a predetermined amount of a magnet- surface (42) of the central magnetic post (40, 35 ic fluid (80) only on a first side (67; 168) of a 140) or an inner surface (129) of a cylindrical voice coil (64) positioned in the annular gap (28) wall (128) of the magnetic structure (26); and of the driver unit (10), wherein the first side of a magnetic fluid (80) disposed in said annular the voice coil is either an outer side (67) or an gap (28) only in the space between the first side inner side (168) of the voice coil (64), and where- (67; 168) of said voice coil (64) and the first sur- 40 in the space between said first side (67; 168) of face (35; 145) of said annular gap (28) having the voice coil (64) and a first surface (35; 145) the higher magnetic flux density. of the annular gap (28), which first surface is either an inner surface (35) of an annular top 2. The audio speaker of claim 1 wherein said magnetic plate (34) of the magnetic structure (26) or an fluid (80) has a magnetization in the range of about 45 outer surface (145) of a top pole piece (144) of 100 to about 600 Gauss. the central magnetic post (40, 140), has a higher magnetic flux density than the space between 3. The audio speaker of claim 2 wherein said magnetic on the one hand a second side (68; 166) of the fluid (80) has a magnetization in the range of about voice coil (64), which second side is opposite to 200 to about 500 Gauss. 50 the first side (67; 168) of said voice coil (64) and which second side is either an inner surface (68) 4. The audio speaker of claim 3 wherein said magnetic or an outer surface (166) of the voice coil (64), fluid (80) has a magnetization in the range of about and on the other hand a second surface (42; 300 to about 400 Gauss. 129) of the annular gap (28), which second sur- 55 face is opposite to the first surface (35; 145) of 5. The audio speaker of claim 1 wherein said magnetic the annular gap (28) and which second surface fluid (80) has a higher magnetization when said au- is either an outer surface (42) of the central mag- dio speaker has a voice coil (64) with higher excur- netic post (40, 140) or an inner surface (129) of

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a cylindrical wall (128) of the magnetic structure gnetischen Aufbau (26) bildet, der einen ringför- (26), said voice coil (64) being configured to pre- migen Spalt (28) rund um einen mittigen Ma- vent said magnetic fluid (80) from migrating to gnetständer (40, 140) begrenzt, wobei der ma- the other side (68; 166) of said voice coil (64); gnetische Aufbau (26) einen Permanentmagne- aligning said vibration system (60) with said driv- 5 ten (32; 142) einschließt, der einen radialen Ma- er unit, wherein said voice coil (64) of said vi- gnetfluss in dem ringförmigen Spalt (28) vor- bration system (60) is movably mounted into sieht,und wobei derringförmige Spalt (28) einen said annular gap (28); and Spaltbereich von höherem Magnetfeld aufweist, fixing said vibration system (60) to said driver dessen Stärke quer über den Spalt zu einem unit (10). 10 Spaltbereich von geringerem Magnetfeld ab- nimmt; 10. The method of claim 9 further comprising obtaining einem Vibrationssystem (60) mit einer Membran a magnetic fluid (80) having a magnetization in the (62) und einer Schwingspule (64), wobei die range of about 100 to about 600 Gauss. Schwingspule an einer Seite der Membran (62) 15 angebrachtist, wobeidas Vibrationssystem(60) 11. The method of claim 10 further comprising obtaining an dem Stützrahmen (22) befestigt ist, wobei die a magnetic fluid (80) having a magnetization in the Schwingspule (64) in dem ringförmigen Spalt range of about 200 to about 500 Gauss. (28) beweglich montiert ist und wobei der Raum zwischen einer ersten Seite (67; 168) der 12. The method of claim 11 wherein said magnetic fluid 20 Schwingspule (64), die entweder eine Außen- (80) obtaining step includes selecting a magnetic flu- seite (67) oder eine Innenseite (168) der id (80) having a magnetization in the range of about Schwingspule (64) ist, und einer ersten Oberflä- 300 to about 400 Gauss. che (35; 145) des ringförmigen Spalts (28), die entweder eine Innenfläche (35) einer ringförmi- 13. The method of claim 9 wherein said magnetic fluid 25 gen Deckplatte (34) des magnetischen Aufbaus (80) obtaining step includes selecting a magnetic flu- (26) oder eine Außenfläche (145) eines ober- id (80) having a higher magnetization when said au- sten Polstücks (144) des mittigen Magnetstän- dio speaker has a voice coil (64) with higher excur- ders (40, 140) ist, eine höhere Magnetflussdich- sion and lower magnetic field. te aufweist als der Raum zwischen einerseits 30 einer zweiten Seite (68; 166) der Schwingspule 14. The method of claim 9 wherein said magnetic fluid (64), die der ersten Seite (67; 168) der (80) obtaining step includes selecting a magnetic flu- Schwingspule (64) gegenüberliegt und entwe- id (80) having a lower magnetization when said audio der eineInnenfläche (68) oder eine Außenfläche speaker has a voice coil (64) with lower excursion (166) der Schwingspule (64) ist, und anderer- and higher magnetic field. 35 seits einer zweiten Oberfläche (42; 129) des ringförmigen Spalts (28), die der ersten Ober- 15. The method of claim 9 further comprising forming fläche (35;145) desringförmigen Spalts (28) ge- said voice coil (64) with a tubular form (66; 166) of genüberliegt und entweder eine Außenfläche sufficient length to prevent migration of said magnet- (42) des mittigen Magnetständers (40, 140) oder ic fluid (80) at a distal end (65b) of said voice coil 40 eine Innenfläche (129) einer zylindrischen (64) from said one side (67; 168) of said voice coil Wand (128) des magnetischen Aufbaus (26) ist; (64) having a higher magnetic flux density to the sec- und ond side (68; 166) of said voice coil (64) having a einer magnetischen Flüssigkeit (80), die in dem lower magnetic flux density. ringförmigen Spalt (28) nur in dem Raum zwi- 45 schen der ersten Seite (67; 168) der Schwings- 16. The method of claim 9 further comprising forming pule (64) und der ersten Oberfläche (35; 145) said voice coil (64) having vent openings positioned des ringförmigen Spalts (28) mit der höheren sufficiently distant from said magnetic fluid (80) to Magnetflussdichte angeordnet ist. prevent migration of said magnetic fluid (80) during oscillation of said voice coil (64). 50 2. Lautsprecher nach Anspruch 1, wobei die magneti- sche Flüssigkeit (80) eine Magnetisierung im Be- reich von ungefähr 100 bis ungefähr 600 Gauß auf- Patentansprüche weist.

1. Lautsprecher mit: 55 3. Lautsprecher nach Anspruch 2, wobei die magneti- sche Flüssigkeit (80) eine Magnetisierung im Be- einer Treibereinheit (10) mit einem Stützrahmen reich von ungefähr 200 bis ungefähr 500 Gauß auf- (22), wobei ein mittlerer Bereich (24) einen ma- weist.

7 13 EP 1 819 194 B1 14

4. Lautsprecher nach Anspruch 3, wobei die magneti- platte (34) des magnetischen Aufbaus (26) oder sche Flüssigkeit (80) eine Magnetisierung im Be- eine Außenfläche (145) eines obersten Pol- reich von ungefähr 300 bis ungefähr 400 Gauß auf- stücks (144) des mittigen Magnetständers (40, weist. 140) ist, eine höhere Magnetflussdichte auf- 5 weist als der Raum zwischen einerseits einer 5. Lautsprecher nach Anspruch 1, wobei die magneti- zweiten Seite (68; 166) der Schwingspule (64), sche Flüssigkeit (80) eine höhere Magnetisierung welche zweite Seite der ersten Seite (67; 168) aufweist, wenn der Lautsprecher eine Schwingspule der Schwingspule (64) gegenüberliegt und wel- (64) mit höherer Auslenkung und geringerem Ma- che zweite Seite entweder eine Innenfläche (68) gnetfeld hat. 10 oder eine Außenfläche (166) der Schwingspule (64) ist, und andererseits einer zweiten Oberflä- 6. Lautsprecher nach Anspruch 1, wobei die magneti- che (42; 129) des ringförmigen Spalts (28), wel- sche Flüssigkeit (80) eine geringere Magnetisierung che zweite Oberfläche der ersten Oberfläche aufweist, wenn der Lautsprecher eine Schwingspule (35; 145) des ringförmigen Spalts (28) gegen- (64) mit geringerer Auslenkung und höherem Ma- 15 überliegt und welche zweite Oberfläche entwe- gnetfeld hat. der eine Außenfläche (42) des mittigen Magnet- ständers (40, 140) oder eine Innenfläche (129) 7. Lautsprecher nach Anspruch 1, wobei die Schwings- einer zylindrischen Wand (128) des magneti- pule (64) eine Röhrenform (66; 166) ausreichender schen Aufbaus (26) ist; wobei die Schwingspule Länge aufweist, um die Migration der magnetischen 20 (64) dazu konfiguriert ist, zu verhindern, dass Flüssigkeit (80) an einem distalen Ende der die magnetische Flüssigkeit (80) zur anderen Schwingspule (64) von der einen Seite (67; 168) der Seite (68; 166) der Schwingspule (64) wandert; Schwingspule (64) zur zweiten Seite (68; 166) der Ausrichten des Vibrationssystems (60) mit der Schwingspule (64) zu verhindern. Treibereinheit, wobei die Schwingspule (64) des 25 Vibrationssystems (60) beweglich in dem ring- 8. Lautsprecher nach Anspruch 7, wobei die Röhren- förmigen Spalt (28) montiert ist; und form (66; 166) der Schwingspule (64) eine feste Befestigen des Vibrationssystems (60) an der Oberfläche hat. Treibereinheit (10).

9. Verfahren zur Montage eines Vibrationssystems30 10. Verfahren nach Anspruch 9, ferner umfassend: Er- (60) an einer Treibereinheit (10) eines Lautspre- halten einer magnetischen Flüssigkeit (80), die eine chers, mit den folgenden Schritten: Magnetisierung im Bereich von ungefähr 100 bis un- gefähr 600 Gauß aufweist. Versehen der Treibereinheit (10) mit einem Stützrahmen (22) und mit einem mittleren Be- 35 11. Verfahren nach Anspruch 10, ferner umfassend: Er- reich (24), der einen magnetischen Aufbau (26) halten einer magnetischen Flüssigkeit (80), die eine bildet, welcher einen ringförmigen Spalt (28) Magnetisierung im Bereich von ungefähr 200 bis un- rund um einen mittigen Magnetständer (40) be- gefähr 500 Gauß aufweist. grenzt, wobei der magnetische Aufbau (26) ei- nen Permanentmagneten (32; 142) einschließt, 40 12. Verfahren nach Anspruch 11, wobei der Schritt zum der einen radialen Magnetfluss in dem ringför- Erhalten der magnetischen Flüssigkeit (80) das Aus- migen Spalt (28) vorsieht, wobei der ringförmige wählen einermagnetischen Flüssigkeit(80) mit einer Spalt (28) einen Spaltbereich von höherem Ma- Magnetisierung im Bereich von ungefähr 300 bis un- gnetfeld aufweist, dessen Stärke quer über den gefähr 400 Gauß beinhaltet. Spalt zu einem Spaltbereich von geringerem 45 Magnetfeld abnimmt; 13. Verfahren nach Anspruch 9, wobei der Schritt zum Anordneneiner vorgegebenen Mengeeiner ma- Erhalten der magnetischen Flüssigkeit (80) das Aus- gnetischen Flüssigkeit (80) nur auf einer ersten wählen einermagnetischen Flüssigkeit(80) mit einer Seite (67; 168) einer Schwingspule (64), die in höheren Magnetisierung beinhaltet, wenn der Laut- dem ringförmigen Spalt (28) der Treibereinheit 50 sprecher eine Schwingspule (64) mit höherer Aus- (10) positioniert ist, wobei die erste Seite der lenkung und geringerem Magnetfeld hat. Schwingspule entweder eine Außenseite (67) oder eine Innenseite (168) der Schwingspule 14. Verfahren nach Anspruch 9, wobei der Schritt zum (64) ist und wobei der Raum zwischen der ersten Erhalten der magnetischen Flüssigkeit (80) das Aus- Seite (67; 168) der Schwingspule (64) und einer 55 wählen einermagnetischen Flüssigkeit(80) mit einer ersten Oberfläche (35; 145) des ringförmigen geringeren Magnetisierung beinhaltet, wenn der Spalts (28), welche erste Oberfläche entweder Lautsprecher eine Schwingspule (64) mit geringerer eine Innenfläche (35) einer ringförmigen Deck- Auslenkung und höherem Magnetfeld hat.

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15. Verfahren nach Anspruch 9, ferner umfassend: Aus- la bobine acoustique (64), et d’autre part une bilden der Schwingspule (64) mit einer Röhrenform deuxième surface (42 ; 129) de l’espace annu- (66; 166) von ausreichender Länge zur Verhinde- laire (28), étant opposée à la première surface rung der Migration der magnetischen Flüssigkeit (35 ; 145) de l’espace annulaire (28) et étant soit (80) an einem distalen Ende (65b) der Schwingspule 5 une surface extérieure (42) du montant magné- (64) von der einen Seite (67; 168) der Schwingspule tique central (40, 140), soit une surface intérieu- (64) mit höherer Magnetflussdichte zur zweiten Seite re (129) d’une paroi cylindrique (128) de la struc- (68; 166) der Schwingspule (64) mit geringerer Ma- ture magnétique (26) ; et gnetflussdichte. un fluide magnétique (80) disposé dans ledit es- 10 pace annulaire (28) uniquement dans l’espace 16. Verfahren nach Anspruch 9, ferner umfassend: Aus- entre le premier côté (67 ; 168) de ladite bobine bilden der Schwingspule (64) derart, dass sie Belüf- acoustique (64) et la première surface (35 ; 145) tungsöffnungen aufweist, welche ausreichend ent- dudit espace annulaire (28) ayant la densité de fernt von der magnetischen Flüssigkeit (80) positio- flux magnétique plus élevée. niert sind, um eine Migration der magnetischen Flüs- 15 sigkeit (80) während der Schwingung der Schwings- 2. Haut-parleur audio selon la revendication 1, dans pule (64) zu verhindern. lequel ledit fluide magnétique (80) a une magnétisa- tion dans la plage d’environ 100 à environ 600 Gauss. Revendications 20 3. Haut-parleur audio selon la revendication 2, dans 1. Haut-parleur audio comprenant : lequel ledit fluide magnétique (80) a une magnétisa- tion dans la plage d’environ 200 à environ 500 une unité pilote (10) ayant un cadre support (22) Gauss. avec une partie centrale (24) formant une struc- 25 ture magnétique (26) définissant un espace an- 4. Haut-parleur audio selon la revendication 3, dans nulaire (28) autour d’un montant magnétique lequel ledit fluide magnétique (80) a une magnétisa- central (40, 140), dans lequel la structure ma- tion dans la plage d’environ 300 à environ 400 gnétique (26) inclut un aimant permanent (32 ; Gauss. 142) qui crée un flux magnétique radial dans 30 l’espace annulaire (28) et dans lequel l’espace 5. Haut-parleur audio selon la revendication 1, dans annulaire (28) a une partie d’espace de champ lequel ledit fluide magnétique (80) a une magnétisa- magnétique plus fort qui diminue en force au tion plus élevée lorsque ledit haut-parleur audio a travers de l’espace jusqu’à une partie d’espace une bobine acoustique (64) avec une excursion plus de champ magnétique plus faible ; 35 importante et un champ magnétique plus faible. un système de vibration (60) ayant un diaphrag- me (62) et une bobine acoustique (64), ladite 6. Haut-parleur audio selon la revendication 1, dans bobine acoustique fixée sur un côté dudit lequel ledit fluide magnétique (80) a une magnétisa- diaphragme (62), dans lequel ledit système de tion plus faible lorsque ledit haut- parleur audio a une vibration (60) est fixé sur ledit cadre support40 bobine acoustique (64) avec une excursion moins (22), dans lequel ladite bobine acoustique (64) importante et un champ magnétique plus fort. est montée de façon mobile dans ledit espace annulaire (28), et dans lequel l’espace entre un 7. Haut-parleur audio selon la revendication 1, dans premier côté (67 ; 168) de la bobine acoustique lequel ladite bobine acoustique (64) a une forme tu- (64), étant soit un côté extérieur (67), soit un 45 bulaire (66 ; 166) d’une longueur suffisante pour em- côté intérieur (168) de la bobine acoustique (64), pêcher la migration dudit fluide magnétique (80) à et une première surface (35 ; 145) de l’espace une extrémité distale de ladite bobine acoustique annulaire (28), étant soit une surface intérieure (64) dudit un côté (67 ; 168) de ladite bobine acous- (35) d’une plaque supérieure annulaire (34) de tique(64) jusqu’au deuxième côté (68 ;166) de ladite la structure magnétique (26), soit une surface 50 bobine acoustique (64). extérieure (145) d’une pièce polaire supérieure (144) du montant magnétique central (40, 140), 8. Haut-parleur audio selon la revendication 7, dans a une densité de flux magnétique plus élevée lequel ladite forme tubulaire (66 ; 166) de ladite bo- que l’espace entre d’une part un deuxième côté bine acoustique (64) a une surface pleine. (68 ; 166) de la bobine acoustique (64), étant 55 opposé au premier côté (67 ; 168) de la bobine 9. Procédé d’assemblage d’un système de vibration acoustique (64) et étant soit une surface inté- (60) sur une unité pilote (10) d’un haut- parleur audio, rieure (68), soit une surface extérieure (166) de ledit procédé comprenant :

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la prévision de l’unité pilote (10) avec un cadre viron 600 Gauss. support (22) et avec une partie centrale (24) for- mant une structure magnétique (26) définissant 11. Procédé selon la revendication 10, comprenant en un espace annulaire (28) autour d’un montant outre l’obtention d’un fluide magnétique (80) ayant magnétique central (40), dans lequel la structure 5 une magnétisation dans la plage d’environ 200 à en- magnétique (26) inclut un aimant permanent viron 500 Gauss. (32 ; 142) qui crée un flux magnétique radial dans l’espace annulaire (28), dans lequel l’es- 12. Procédé selon la revendication 11, dans lequel ladite pace annulaire (28) a une partie d’espace de étape d’obtention d’un fluide magnétique (80) inclut champmagnétique plus fort quidiminue en force 10 la sélection d’un fluide magnétique (80) ayant une au travers de l’espace jusqu’à une partie d’es- magnétisation dans la plage d’environ 300 à environ pace de champ magnétique plus faible ; 400 Gauss. la disposition d’une quantité prédéterminée d’un fluide magnétique (80) uniquement sur un pre- 13. Procédé selon la revendication 9, dans lequel ladite mier côté (67 ; 168) d’une bobine acoustique 15 étape d’obtention d’un fluide magnétique (80) inclut (64) positionnée dans l’espace annulaire (28) la sélection d’un fluide magnétique (80) ayant une de l’unité pilote (10), dans lequel le premier côté magnétisation plus élevée lorsque ledit haut- parleur de la bobine acoustique est soit un côté extérieur audio a une bobine acoustique (64) avec une excur- (67), soit un côté intérieur (168) de la bobine sion plus importante et un champ magnétique plus acoustique (64), et dans lequel l’espace entre 20 faible. ledit premier côté (67 ; 168) de la bobine acous- tique (64) et une première surface (35 ; 145) de 14. Procédé selon la revendication 9, dans lequel ladite l’espace annulaire (28), laquelle première sur- étape d’obtention d’un fluide magnétique (80) inclut face est soit une surface intérieure (35) d’une la sélection d’un fluide magnétique (80) ayant une plaque supérieure annulaire (34) de la structure 25 magnétisation plus faible lorsque ledit haut-parleur magnétique (26), soit une surface extérieure audio a une bobine acoustique (64) avec une excur- (145) d’une pièce polaire supérieure (144) du sion moins importante et un champ magnétique plus montant magnétique central (40, 140), a une fort. densité de flux magnétique plus élevée que l’es- pace entre d’une part un deuxième côté (68 ; 30 15. Procédé selon la revendication 9, comprenant en 166) de la bobine acoustique (64), lequel outre la formation de ladite bobine acoustique (64) deuxième côté est opposé au premier côté (67 ; avec une forme tubulaire (66 ; 166) d’une longueur 168) de ladite bobine acoustique (64) et lequel suffisante pour empêcher une migration dudit fluide deuxième côté est soit une surface intérieure magnétique (80) à une extrémité distale (65b) de (68), soit une surface extérieure (166) de la bo- 35 ladite bobine acoustique (64) dudit un côté (67 ; 168) bine acoustique (64), et d’autre part une deuxiè- de ladite bobine acoustique (64) ayant une densité me surface (42 ; 129) de l’espace annulaire (28), de fluide magnétique plus élevée jusqu’au deuxième laquelle deuxième surface est opposée à la pre- côté (68 ; 166) de ladite bobine acoustique (64) mière surface (35 ; 145) de l’espace annulaire ayant une densité de fluide magnétique plus faible. (28) et laquelle deuxième surface est soit une 40 surface extérieure (42) du montant magnétique 16. Procédé selon la revendication 9, comprenant en central (40, 140), soit une surface intérieure outre la formation de ladite bobine acoustique (64) (129) d’une paroi cylindrique (128) de la struc- ayant des ouvertures d’aération positionnées suffi- ture magnétique (26), ladite bobine acoustique samment distantes dudit fluide magnétique (80) pour (64) étant configurée pour empêcher que ledit 45 empêcher une migration dudit fluide magnétique fluide magnétique (80) ne migre jusqu’à l’autre (80) pendant une oscillation de ladite bobine acous- côté (68 ; 166) de ladite bobine acoustique (64) ; tique (64). l’alignement dudit système de vibration (60) avec ladite unité pilote, dans lequel ladite bobine acoustique (64) dudit système de vibration (60) 50 est montée de façon mobile dans ledit espace annulaire (28) ; et la fixation dudit système de vibration (60) à ladite unité pilote (10). 55 10. Procédé selon la revendication 9, comprenant en outre l’obtention d’un fluide magnétique (80) ayant une magnétisation dans la plage d’environ 100 à en-

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REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• US 60766831 B [0001] • JP 08079886 A [0012] • US 5335287 A [0008] [0009] • JP 2004274206 A [0013] • US 4414437 A [0010] [0011]

Non-patent literature cited in the description

• BOTTENBERG et al. The Dependence of Loud- speaker Design Parameters on the Properties of Magnetic Fluids. 61st Convention of the Audio Engi- neering Society, 03 November 1978 [0007]

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