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WO1995024815A1 - Haut parleur electromagnetique - Google Patents

Haut parleur electromagnetique Download PDF

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Publication number
WO1995024815A1
WO1995024815A1 PCT/GB1995/000424 GB9500424W WO9524815A1 WO 1995024815 A1 WO1995024815 A1 WO 1995024815A1 GB 9500424 W GB9500424 W GB 9500424W WO 9524815 A1 WO9524815 A1 WO 9524815A1
Authority
WO
WIPO (PCT)
Prior art keywords
loudspeaker
sheet
magnets
spring means
damping
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.)
Ceased
Application number
PCT/GB1995/000424
Other languages
English (en)
Inventor
Jonathan Neil Smith
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.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Priority to GB9617999A priority Critical patent/GB2301507B/en
Priority to AU18176/95A priority patent/AU1817695A/en
Publication of WO1995024815A1 publication Critical patent/WO1995024815A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • H04R9/04—Construction, mounting, or centering of coil
    • H04R9/046—Construction
    • H04R9/047—Construction in which the windings of the moving coil lay in the same plane
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/16—Mounting or tensioning of diaphragms or cones
    • H04R7/24—Tensioning by means acting directly on free portions of diaphragm or cone

Definitions

  • This invention relates to an electromagnetic loudspeaker and particularly, but not exclusively, to a flat loudspeaker driven electromagnet!cally.
  • a movable element comprising a sheet of flexible material mounted by its edges so as to be substantially flat.
  • the sheet usually bears a conducting pattern which, when provided with a current from the system amplifier, drives the sheet to generate sound by interaction with the magnetic field of an array of magnets located behind the sheet.
  • Each magnet is typically of opposite polarity (N or S) to the magnets on either side adjacent thereto, and the magnets are spaced at various intervals in the prior art designs, for example in the order of half of the wavelength in air of sound to be produced or less in some designs, and in others much wider.
  • the sheet is typically polymer film between 1 and 25 microns thick.
  • any slackness in such a.film will give rise to serious sub-harmonic, non-linear motions at low frequencies. This is due to the varying spacing from the magnets resulting from the slackness and due to the effects of gravity or other factors. As the film is tightened, however, it starts to behave like the surface of a drum, with the edge constraints approaching the 'fixed' condition, such that acoustic modes across the surface dominate behaviour and the frequency response becomes very resonant.
  • Standard theory also shows how the frequency at which bass roll-off occurs increases in such thin sheet devices as the mass of the driven element approaches zero and air loading effects become more important.
  • a typical frequency at which bass roll-off becomes pronounced is 800 Hz.
  • One drawback is that the effectively 'free' edges implicit in a rigid element make the plate resonant. The high stiffness factor then makes it nearly impossible to get the damping up to an adequate level, so that any lateral vibration induced in the plate 'rings'.
  • an electromagnetic loudspeaker has an element movable for sound generation, the element comprising an electromagnetically driven sheet of untensioned material mounted by an array of mounting points attached to spring means, the mounting points being spaced inwardly of the sheet from its edges.
  • the mass of the driven sheet is preferably between 0.5 kg/m 2 and 2.0 kg/m 2 .
  • the sheet is also mounted by its edges, and where the speaker is to be enclosed to operate as a monopole radiator, edge mounting is a requirement.
  • this preferably comprises a 'roll surround' similar to that used in conventional cone speakers to permit 'semi-free' motion and to increase 'system' damping so as to help to control surface resonance in the movable element.
  • a roll surround is typically omega shaped in cross section, and is formed from a rubberised cloth which gives high damping.
  • the sheet is conveniently mounted so as to be substantially flat. However, for some applications it may be preferable to have an arrangement in which the sheet is curved in one or more dimensions.
  • the sheet is preferably electromagnetically driven by means comprising a conducting pattern provided on the sheet and co-operating with an array of magnets of corresponding pattern fixed behind the sheet adjacent magnets presenting opposite polarity (N or S), such that the sheet is driven by applying a suitable current to the conducting pattern.
  • the inventive mounting of the sheet by the array of mounting points, or by the array in combination with edge mounting of the sheet can approximate to an ideal case of 'all over' mounting which the prior art has been unable to achieve.
  • the more mounting points provided for a given sheet rigidity the closer the approximation.
  • the inventive mounting also allows the movable element to comply to a degree with local unevenness of drive force, without causing high amplitude resonances of the structure.
  • an electromagnetic loudspeaker has an element of untensioned sheet material of strip form which is movable for sound generation, an arrangement of discrete mounting points being provided along the lengthwise edges of the element for mounting the element, and the mounting points being attached to spring means.
  • the magnets are spaced at less than , and most preferably less than 1/10 of the wavelength in air of the sound to be produced.
  • a preferred movable element for the invention thus comprises polymer sheet material of thickness substantially in the range 0.2 to 2 mm.
  • the mass per unit area of the sheet and the spring stiffness and damping in the direction of movement are co-variant. They should preferably be scaled to achieve a 'Q' for the system substantially in the range 0.6 to 1.7, and most preferably substantially in the range 0.8 to 1.0.
  • the overall spring strength for the spring means is prefe ly in the range 33000 to 130000 S ⁇ 2 for each kilogram of the movable element.
  • the spring means incorporates damping, and this also reduces transmission of sound back to the fixed structure of the speaker.
  • the spring means comprises elastomeric material havi'i high inherent da- ng.
  • the rod members are preferably intec ly formed with the movable sheet as a unitary moulding, and tlu ⁇ conveniently be hollow.
  • the spring means comprises a respective separate element of the elastomeric material for each rod member, which is conveniently in the form of a washer.
  • each of the separate elements of elastomeric material is most preferably a washer of elliptical or similar shape, with the minor axis of the shape substantially vertical.
  • a spring means in the form of filaments or strips made into zig-zags, 'W', helix, coil, or other suitable shape could be used, and could be attached directly to the movable sheet.
  • the filament or strip is not made of a material which has suitable inherent damping, an additional damping means associated with said mounting points would be desirable.
  • the conducting pattern may comprise a single conducting wire or a number of single wires disposed in spaced-apart relationship, but in order to achieve a more desirable level of impedance for the speaker, a group or groups of two or more wires may be laid in place of a single wire arrangement, the wires w*" n any group being connected in series and laid next to each other, but with insulation between them.
  • the wire or wires of the conducting pattern are preferably attached to the sheet by a resilient adhesive having damping properties to improve the damping further.
  • the conducting pattern comprises a 'printed circuit', and damping means broadly equivalent to the resilient adhesive in damping effect is preferably provided with this.
  • the speaker is mounted in an enclosure.
  • the speaker may desirably be arranged as a dipole radiator.
  • a separate tweeter is provided and, if desired, a separate sub-woofer could be provided.
  • Figure 1 is a perspective view of the loudspeaker of the embodiment
  • Figure 2 is a front view showing the frame of the loudspeaker separately;
  • Figure 3 is a front view showing the mounting of the flat loudspeaker together with a tweeter
  • Figure 4 is a rear view of the movable element of the flat loudspeaker
  • Figure 5 is a section view of the movable element taken on line 5-5 of Figure 4, but omitting the conducting pattern;
  • Figure 6 s a view of the array of magnets of the embodiment from the front, that is to say, from the side facing the movable element;
  • Figure 7 is a side view of an assembly comprising a mounting rod, neoprene washer and mounting ring;
  • Figure 8 is a front view of the assembly of Figure 7
  • an electromagnetic loudspeaker has a timber plinth 1 with bevelled edges, and a frame 2, also of timber.
  • a handle 3 is provided on the frame and may be used for carrying the loudspeaker.
  • the loudspeaker is a dipole radiator, having sound coming from both front surface 15 and rear surface 16. These surfaces are therefore provided with a covering of cloth 7 which is substantially permeable to sound.
  • the rear of the loudspeaker would typically be enclosed by a rigid panel .
  • the space within the frame 2 is partitioned into a upper and lower portion by a cross-bar 8.
  • the loudspeaker has an element 14 movable for sound generation, comprising an electromagnetically driven sheet of untensioned material.
  • the movable element 14 is flat and is mounted by its edges in the lower portion o" the frame 2 by a 'roll surround' 13, as shown in Figures 4 and 5, whilst a separate tweeter is mounted in the upper portion.
  • the movable element 14 has a mass of 62 grams (0.675 Kg/m 2 ). It comprises a sheet 17 of COBEX polymer having thickness 0.5 mm. Upon the rear surface of sheet 17 a conducting pattern 18 is adhered ⁇ y a vinyl rubber adhesive proc, ced by 3M, whic ⁇ has suitable dampin properties.
  • the conducting pattern is fosmed from a single copper wire 11 which is laid in a convoluted arrangement of parallel lengths which are directed alternately upwards and downwards on the rear surface of the sheet. The lengths are equi-spaced except for two larger spaces ⁇ signated 12a. Leads 19 connect the ends of the wire to the system amplifier (not shown).
  • each magnet 20 comprises a ferrite strip (of about 3.0mm thickness) having opposite magnetic polarity to its nearest neighbour or neighbours.
  • the opposite polarity is indicated in Figure 6 by the alternation of hatching angle between the adjacent magnets.
  • the magnets are spaced so that each is disposed beneath a space between adjacent lengths of the wire 11, with the two wider spaces 12b between magnets being disposed beneath the wider spaces 12a of the conducting pattern 18.
  • the conducting pattern 18 and magnets 20 co-operate to provide electromagnetic means for driving the sheet 17.
  • the wider spaces 12a and 12b are to provide room for the middle two rows of an array comprising four rigid rod members 21, said rod members 21 being spaced inwardly of the sheet 17 of its edges.
  • Each rod member 21 is connected by one end to a mounting point on the sheet 17 (not shown), and by the other end, via an elastomeric washer 22 of neoprene located at the rear of the array of magnets 20, to a metal mounting ring 23 attached to the rear of the array of magnets 20. Twelve more rod members 21 shown are also spaced inwardly of the sheet 17 from its edges, and outwardly of the first-mentioned rod members 21 in spaces 12a and 12b.
  • the overall spring strength is approximately 67000 S -2 for each kilogram of the movable element 14, and the spring/damping arrangement achieves exceptionally low distortion for the loudspeaker, which is generally below 0.1% (allowing for material vagaries) and sometimes below 0.01%.
  • stiffness of suspension in displacement direction 180,000 N/metre to 720,000 N/metre per Kilogram driven sheet. This represents the sum of the stiffnesses for the individual mounts. For a 70g sheet the stiffness is substantially 40,000 N/metre.
  • the flat loudspeaker is desirably considerably more elongated than in the embodiment described, in order to achieve improvements such as a better horizontal radiation pattern of sound.
  • a flat loudspeaker in accordance wif- the invention might be made about 1 metre high, 2 centimetres thi.. f , and 8 centimetres wide.
  • Neodymium Iron Boron magnets may be employed instead of using ferrite bar magnets 20, an array of thin (say 1.0mm to 3.00mm) Neodymium Iron Boron magnets may be employed. Magnetic arrays may be placed on both sides of the sheet 17, or on only one side thereof.
  • the conducting pattern 18 may be replaced by wiring in parallel. Conducting patterns may be stacked in layers. Copper wiring may be replaced by wiring of aluminium, or another good conductor.

Landscapes

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

Abstract

Un haut-parleur électromagnétique (fig. 6) présente un élément (14, fig.4) mobile de reproduction sonore doté d'une feuille d'un matériau non tendu à pilotage électromagnétique. Cet élément (14) est plat et se monte par ses bords dans la partie inférieure du châssis (2), par un périmètre à arrondi (13, fig. 5). Cet élément mobile comporte une feuille (17) d'un polymère COBEX de 0,5 mm d'épaisseur. Un motif (18, fig. 4) conducteur et des aimants (20, fig. 6) coopèrent pour produire le dispositif électromagnétique pilotant cette feuille (17). Des espaces (12a et 12b) reçoivent deux rangs d'un ensemble comprenant quatre tiges (21) rigides réparties vers l'intérieur, entre les bords de la feuille. Chaque tige (21) est reliée par une extrémité à un point de montage placé sur la feuille (17) (non représenté), et par l'autre extrémité, par une rondelle (22, fig. 7) élastomère de néoprène placée à l'arrière de l'ensemble d'aimants (20). Douze autres tiges (21), représentées, sont également réparties vers l'intérieur entre les bords de la feuille (17), plus près des bords par rapport aux premières tiges (21) mentionnées propres aux espaces (12a et 12b). Dans cet exemple, les seize (21) tiges, combinées avec le perimètre arrondi (13), se rapprochent d'un montage intégral de la feuille (17). Les rondelles (22) de néoprène font office de ressorts et procurent un amortissement, et le périmètre à arrondi (13) procure au système un effet de ressort et d'amortissement supplémentaires.
PCT/GB1995/000424 1994-03-08 1995-02-28 Haut parleur electromagnetique Ceased WO1995024815A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB9617999A GB2301507B (en) 1994-03-08 1995-02-28 Electromagnetic loudspeaker
AU18176/95A AU1817695A (en) 1994-03-08 1995-02-28 Electromagnetic loudspeaker

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9404585A GB9404585D0 (en) 1994-03-08 1994-03-08 Loudspeaker
GB9404585.3 1994-03-08

Publications (1)

Publication Number Publication Date
WO1995024815A1 true WO1995024815A1 (fr) 1995-09-14

Family

ID=10751569

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1995/000424 Ceased WO1995024815A1 (fr) 1994-03-08 1995-02-28 Haut parleur electromagnetique

Country Status (3)

Country Link
AU (1) AU1817695A (fr)
GB (1) GB9404585D0 (fr)
WO (1) WO1995024815A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998026630A1 (fr) * 1996-12-11 1998-06-18 The Secretary Of State For Defence Haut-parleur en forme de panneau
EP1532838A4 (fr) * 2002-05-02 2005-11-23 Harman Int Ind Haut-parleurs planaires electro-dynamiques
US7146017B2 (en) 2002-05-02 2006-12-05 Harman International Industries, Incorporated Electrical connectors for electro-dynamic loudspeakers
US7203332B2 (en) 2002-05-02 2007-04-10 Harman International Industries, Incorporated Magnet arrangement for loudspeaker
US7316290B2 (en) 2003-01-30 2008-01-08 Harman International Industries, Incorporated Acoustic lens system
EP1269793A4 (fr) * 2000-03-03 2009-03-25 American Tech Corp Haut-parleur magnetique plat a extremite unique
EP1366636A4 (fr) * 2001-01-26 2009-03-25 American Tech Corp Haut-parleurs magnetiques plans avec une structure magnetique secondaire

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB468624A (en) * 1934-12-03 1937-07-05 Joseph Massolle G M B H Improvements in or relating to electrostatic sound receivers and reproducers
DE1161591B (de) * 1962-08-14 1964-01-23 Isophon Werke G M B H Statischer Lautsprecher
US3674946A (en) * 1970-12-23 1972-07-04 Magnepan Inc Electromagnetic transducer
FR2335118A1 (fr) * 1975-12-11 1977-07-08 Rank Organisation Ltd Transducteur electro-acoustique, notamment pour haut-parleur et ecouteurs
US4081626A (en) * 1976-11-12 1978-03-28 Polaroid Corporation Electrostatic transducer having narrowed directional characteristic
US4480155A (en) * 1982-03-01 1984-10-30 Magnepan, Inc. Diaphragm type magnetic transducer
JPS6390300A (ja) * 1986-10-03 1988-04-21 Matsushita Electric Ind Co Ltd スピ−カ用振動板
US4803733A (en) * 1986-12-16 1989-02-07 Carver R W Loudspeaker diaphragm mounting system and method

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB468624A (en) * 1934-12-03 1937-07-05 Joseph Massolle G M B H Improvements in or relating to electrostatic sound receivers and reproducers
DE1161591B (de) * 1962-08-14 1964-01-23 Isophon Werke G M B H Statischer Lautsprecher
US3674946A (en) * 1970-12-23 1972-07-04 Magnepan Inc Electromagnetic transducer
FR2335118A1 (fr) * 1975-12-11 1977-07-08 Rank Organisation Ltd Transducteur electro-acoustique, notamment pour haut-parleur et ecouteurs
US4081626A (en) * 1976-11-12 1978-03-28 Polaroid Corporation Electrostatic transducer having narrowed directional characteristic
US4480155A (en) * 1982-03-01 1984-10-30 Magnepan, Inc. Diaphragm type magnetic transducer
JPS6390300A (ja) * 1986-10-03 1988-04-21 Matsushita Electric Ind Co Ltd スピ−カ用振動板
US4803733A (en) * 1986-12-16 1989-02-07 Carver R W Loudspeaker diaphragm mounting system and method

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 012, no. 328 (E - 0654) 6 September 1988 (1988-09-06) *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998026630A1 (fr) * 1996-12-11 1998-06-18 The Secretary Of State For Defence Haut-parleur en forme de panneau
GB2334402A (en) * 1996-12-11 1999-08-18 Secr Defence Panel-form loudspeaker
GB2334402B (en) * 1996-12-11 2000-10-11 Secr Defence Panel-form loudspeaker
AU728609B2 (en) * 1996-12-11 2001-01-11 Qinetiq Limited Panel-form loudspeaker
US6215882B1 (en) 1996-12-11 2001-04-10 The Secretary Of State For Defence Panel-form loudspeaker
CZ297254B6 (cs) * 1996-12-11 2006-10-11 Qinetiq Limited Rezonancní mnohovidový radiacní prvek a reproduktor ve tvaru panelu
EP1269793A4 (fr) * 2000-03-03 2009-03-25 American Tech Corp Haut-parleur magnetique plat a extremite unique
EP1366636A4 (fr) * 2001-01-26 2009-03-25 American Tech Corp Haut-parleurs magnetiques plans avec une structure magnetique secondaire
EP1532838A4 (fr) * 2002-05-02 2005-11-23 Harman Int Ind Haut-parleurs planaires electro-dynamiques
US7146017B2 (en) 2002-05-02 2006-12-05 Harman International Industries, Incorporated Electrical connectors for electro-dynamic loudspeakers
US7203332B2 (en) 2002-05-02 2007-04-10 Harman International Industries, Incorporated Magnet arrangement for loudspeaker
US7316290B2 (en) 2003-01-30 2008-01-08 Harman International Industries, Incorporated Acoustic lens system

Also Published As

Publication number Publication date
AU1817695A (en) 1995-09-25
GB9404585D0 (en) 1994-04-20

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