EP0272059A2 - Haut parleurs et leur réalisation - Google Patents

Haut parleurs et leur réalisation Download PDF

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Publication number
EP0272059A2
EP0272059A2 EP87310904A EP87310904A EP0272059A2 EP 0272059 A2 EP0272059 A2 EP 0272059A2 EP 87310904 A EP87310904 A EP 87310904A EP 87310904 A EP87310904 A EP 87310904A EP 0272059 A2 EP0272059 A2 EP 0272059A2
Authority
EP
European Patent Office
Prior art keywords
cone
loudspeaker
metal
aluminium
coil
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.)
Withdrawn
Application number
EP87310904A
Other languages
German (de)
English (en)
Other versions
EP0272059A3 (fr
Inventor
Philip Keith Glen Jones
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.)
Acoustic Energy Ltd
Original Assignee
Acoustic Energy Ltd
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 Acoustic Energy Ltd filed Critical Acoustic Energy Ltd
Publication of EP0272059A2 publication Critical patent/EP0272059A2/fr
Publication of EP0272059A3 publication Critical patent/EP0272059A3/fr
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • 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

Definitions

  • This invention relates to loudspeakers and their production and general objects of the invention include the provision of moving coil loudspeakers which are similar in basic construction to conventional loudspeakers but which can be made much more powerful than known loudspeakers of comparable sizes whilst having such low sound distortion characteristics as to be substantially distortion-free for all practical purposes.
  • the vast majority of known loudspeakers employ wood pulp/paper, card or a synthetic plastics material for the formation of their cones (diaphragms) but, unfortunately, when such a cone is subject to relatively large vibratory sound-producing movements (usually known as “excursions"), the cone is temporarily deformed and readily audible distortion of the sound results.
  • Some attempts have been made to use metallic or other more rigid materials to produce loudspeaker cones but, for various reasons, these attempts have met with only very limited success.
  • a method of producing a cone for use in a loudspeaker comprising the steps of forming said cone wholly or principally from aluminium and spinning the cone to harden the same.
  • the sheet metal blank 2 is preferably, but not essentially, formed from the almost (99% or more) pure grade aluminium that is known in the United Kingdom as "AA 1200". This material has a modulus of elasticity of 7.05 ⁇ 1010 Newtons per metre2 and a density of 2.71 ⁇ 103 per cubic metre.
  • AA 1200 the almost (99% or more) pure grade aluminium that is known in the United Kingdom as "AA 1200”.
  • This material has a modulus of elasticity of 7.05 ⁇ 1010 Newtons per metre2 and a density of 2.71 ⁇ 103 per cubic metre.
  • known alloys of aluminium which contain that metal as a major component may be employed but, generally speaking, aluminium with an absolute minimum of impurities gives the best results.
  • FIG. 1 of the drawings that Figure illustrates a metal spinning operation in which the initially circular blank 2 is spun by a lathe or like machine around an axis defined by a lathe shaft 4, a central region of the blank 2 being releasably clamped to a former 1 by a large securing nut 3 so that, when the nut 3 is tightened, the former 1, the sheet metal blank 2, the nut 3 and the shaft 4 will be temporarily united for rapid rotation around the longitudinal axis of the shaft 4.
  • Metal spinning is an art which is known per se and is a particularly effective method of making conically shaped items. Conventional metal spinning techniques may be used entirely successfully in putting the present invention into effect.
  • the sheet metal blank 2 may be forced into the required conical shape around the former 1 in much the same basic way as a potter moulds clay into a required shape on a potter's wheel.
  • the formed cone will usually be a so-called straight-sided cone since this configuration gives particularly low harmonic distortion characteristics.
  • Tempered steel or leather-faced wooden or other tools are the usual means by which pressure is applied to the blank 2 and, as shown in Figure 1 of the drawings, these may be employed manually.
  • the sheet aluminium or aluminium alloy that affords the blank 2 and, eventually, the cone of the loudspeaker that is being produced is necessarily thin and, in the case of a cone that is to have a diameter of about 91 millimetres, its thickness may advantageously be of the order of about 0.152 millimetres. Naturally, this thickness is variable having regard to the particular metallic formula in accordance with which the blank 2 is formed, the particular purpose for which the eventual loudspeaker is required, and the diameter of the cone that is being made. A large diameter cone will require a proportionately increased thickness of the aluminium from which it is formed whereas a smaller diameter cone will require a proportionately reduced thickness thereof.
  • the wall thickness of the cone may be graduated from centre to outer edge, the greater thickness being in the central region and the minimum thickness being in the outer peripheral region. Due to the thinness of the blank 2, it is best to shape it around the former 1 in progressive stages using a shaping tool 5 and simultaneously supporting the rear or concave side of the cone that is being produced using, conveniently, a wooden or other stick 6 for this purpose. Once the metal of the blank 2 is sufficiently close to the former 1 to receive automatic support from the latter, the use of the support stick 6 is no longer required. As soon as the sheet metal blank 2 has taken the conical shape of the former 1, it is trimmed to size around its outer and inner peripheries, a relatively large central circular hole being left for the mounting of a voice/sound coil. The smoothly trimmed outer periphery of the cone will be accurately attached, in the finished loudspeaker, to a rubber or synthetic plastics or other foam roll surround as will be described with reference to Figure 2 of the drawings.
  • the spinning process increases the tensile strength of the aluminium or aluminium alloy by a factor of approximately two from substantially 80 megapascals to substantially 160 megapascals and this has the considerable advantage that the cone angle of the cone can be much greater or smaller than is conventional, without the metal tending to break, so that the design possibilities for a moving coil loudspeaker of this kind are greatly enhanced.
  • the aluminium or aluminium alloy of the formed cone is hard-anodised, advantageously on both sides.
  • an anodised layer of aluminium oxide having a thickness of 0.050 mms may be formed on each side of the metal, approximately half this thickness progressively replacing the metal itself so that a total wall thickness of about 0.254 mms is produced.
  • the method of shaping and tool-­hardening the alloy blank 2 that has been described with reference to Figure 1 of the drawings is a preferred manual method but that this method is by no means the only one that is possible. It will immediately be evident that automatic or semi-automatic mechanical ways of shaping the blank 2 could be substituted for the principally manual method that has been described. If high power handling of the loudspeaker that is to be produced is of great importance, the hard anodic layer of the cone may be permanently coloured black so as further to increase the heat-dissipation which it will effect in relation to the coil to which it is thermally coupled.
  • the spun metal cone (diaphragm) of the loudspeaker that is shown in these Figures is again denoted by the reference 2 so as to make it clear that it is the cone that has been formed in the manner already described above with reference to Figure 1 of the drawings.
  • the loudspeaker of Figure 2 of the drawings is traditionally constructed to a large extent, differing principally from most known loudspeakers in that, as well as the spun aluminium cone 2, it also comprises a spun metal centre dome 7 and advantageously a metallic voice or sound coil former 8.
  • Figure 3 of the drawings shows, to an enlarged scale, a region A in which the outer periphery of the centre dome 7 and the inner periphery of the spun metal aluminium 2 are secured to the voice or sound coil former 8.
  • This attachment is preferably effected by a strong adhesive having good heat conduction properties.
  • An epoxy resin adhesive containing a metallic powder filler is a good example of such an adhesive but is certainly not the only adhesive that could be employed.
  • an axial pole piece breather hole 10 extends through a combined pole piece and back plate assembly 18 into the space that is surrounded by the coil former 8 and the centre dome 7.
  • a circular row of ventilation holes 11 extends concentrically around the longitudinal axis of the loudspeaker, said holes 11 being formed through the back plate of the assembly 18 and opening into an annular space bounded internally by the pole piece of the assembly 18 and externally by the loudspeaker magnet which bears the reference 17.
  • An annular front plate 16 is in parallel relationship with the back plate of the assembly 18, its inner periphery closely surrounding the voice or sound coil 9 and its former 8.
  • the outer periphery of the spun metal cone 2 is flexibly connected to a very diagrammatically illustrated chassis 13 of the loudspeaker by the previously mentioned rubber or foam or other roll surround which is given the reference 12 in Figure 2 of the drawings.
  • a linen or like suspension of shape-enhanced flexibility 14 has a basically annular shape and is provided in such a position that its inner periphery is connected to the coil former 8 between the cone 2 and the voice or sound coil 9 whilst its outer periphery is connected to an angular rebate in the chassis 13 with the aid of a flexible sealing gasket 15.
  • the design of the loudspeaker is such as to maximise the performance of the spun aluminium alloy cone 2 and, to this end, the sizes and shapes of the various components, such as the magnet 17, the voice or sound coil 9 , the linen or like suspension 14 and the roll surround 12 will allow a considerably greater excursion of the cone 2 to take place, without any significant distortion of the produced sound, than occurs in any conventionally constructed loudspeaker of comparable size.
  • the wiring to the coil 9 is not shown but this wiring should also be such as to facilitate the large excursion of the cone 2 that has been referred to.
  • the wires that are employed throughout the loudspeaker may be of square or other ploygonal cross-section.
  • connection of the wires or other conductors to the voice coil 9 should preferably be located alongside the linen or other suspension 14 where that suspension 14 is secured to the coil former 8 and, in this area, they should be provided with surrounding electrical insulation in order to ensure that a short circuit cannot occur if they should touch the cone 2 and/or the preferably, but not essentially, metallic coil former 8.
  • the construction, position, insulation and length of these wires will take into account the exceptionally large excursions of the cone 2 that are a consequence of a construction in accordance with the invention.
  • the spun metal centre dome 7 of the loudspeaker has the shape of an outwardly tapering cone at one end of a cylinder and effectively affords a dust cover which, like the cone 2 itself, is of a substantially rigid construction. This shape and formation has proved to be a significant practical advantage, offering a still further reduction in sound distortion at peak wattage as compared with the use of conventional non-metallic and non-conical centre domes.
  • pole piece breather hole 10 is of relatively large diameter, as compared with a conventional construction, and this considerably facilitates heat dissipation and large excursions of the cone 2 in that ambient air is "pumped" into and out of the interior of the loudspeaker by the vibrating cone 2 and the parts to which it is secured, thus keeping the air in substantially constant movement whereby warmed air transports the heat which it receives to the afore-mentioned "heat sink” and is continuously replenished, by admixture, with fresh cool air entering the relatively large diameter breather hole 10.
  • At least one loudspeaker in accordance with the invention is installed in a cabinet or other enclosure, the large excursions of the or each cone 2 will greatly assist heat dissipation by substantially constantly vibrating the ambient air and conducting received heat to the walls of the cabinet or other enclosure which will usually, and advantageously, be ventilated.
  • At least one loudspeaker in accordance with the invention could advantageously be sited in a cast alloy enclosure that is thermally coupled to the or each magnet 17 by, for example, an epoxy resin adhesive containing a metallic powder filler or a cyanoacrylate adhesive.
  • a guitar or other instrument, a microphone, a tape player, a radio signal receiver, a conventional record player or a compact disc signal producer or other item could then be coupled directly to the amplifier/­loudspeaker unit without the use of a separate intervening amplifier.
  • a single loudspeaker of this kind having a substantially 91 millimetre diameter cone contained in a cabinet measuring substantially 159 by 159 by 203 millimetres will operate in a distortion-free manner with an amplifier producing up to 400 watts per channel, the loudspeaker having a sensitivity of 85 decibels per watt at a 1 metre spacing.
  • a commercially available contemporary loudspeaker assembly of modern design and generally comparable overall cabinet size will handle only approximately 150 watts per channel on a substantially continuous basis without significant sound distortion.
  • the aluminium cone 2 has the advantage that it provides a greater resistance to the propagation of reflected sound from the rear of the cone in the cabinet bearing in mind that the reflected sound can emanate through a conventional cone.
  • the aluminium cone 2 therefore provides a less boxy, more open, sound.
  • the cone 2 is also able to respond more quickly to movements of the voice coil 9 as the propagation delay is far shorter than that of a paper cone. Thus, the transient attack is more close to the electrical signal input.
  • Sonic velocity in aluminium is 6.32 mms per microsecond and in hard aluminium oxide 10 mms per microsecond.
  • the density of the anodic layer is 2.54 ⁇ 103 and the aluminium itself has a thermal conductivity of 226 watts per metre per degree Celsius/Centigrade.
  • the spun aluminium of its cone 2 may be between a minimum thickness of 0.075 mms and a maximum thickness of 1.015 mms. It is noted that any aluminium alloy having a high modulus of elasticity that may be employed for the cone 2 is advantageously heated by flame during the spinning process that has been described.
  • the large variation in cone angle which has been mentioned is possible following the metal spinning step because this greatly reduces the high notch resistivity of aluminium and many of its alloys which otherwise causes cracking and breakage unless the cone angle is within a relatively narrow range of values.
  • the greatly preferred hard anodising step considerably increases the cone rigidity with a consequent reduction of harmonic and intermodulation distortion.
  • the frequency limit of piston motion of the moving coil of a loudspeaker in accordance with the invention is improved, the speed of heat radiation is increased, the resistance to atmospheric and other corrosion is markedly improved and the thermal coupling with other metal parts of the loudspeaker is extremely good.
  • the operating temperature of the coil 9 is consistently low in relation to the ambient temperature so that increased power handling, without sound distortion, is possible by avoiding a significant increase in temperature-related coil impedance.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Diaphragms For Electromechanical Transducers (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
EP87310904A 1986-12-17 1987-12-11 Haut parleurs et leur réalisation Withdrawn EP0272059A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8630092 1986-12-17
GB868630092A GB8630092D0 (en) 1986-12-17 1986-12-17 Loudspeakers

Publications (2)

Publication Number Publication Date
EP0272059A2 true EP0272059A2 (fr) 1988-06-22
EP0272059A3 EP0272059A3 (fr) 1990-03-21

Family

ID=10609132

Family Applications (1)

Application Number Title Priority Date Filing Date
EP87310904A Withdrawn EP0272059A3 (fr) 1986-12-17 1987-12-11 Haut parleurs et leur réalisation

Country Status (2)

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EP (1) EP0272059A3 (fr)
GB (1) GB8630092D0 (fr)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3925626A (en) * 1974-02-22 1975-12-09 Jr Robert John Stallings Dynamic speaker having dome diaphragm and basket frequency
EP0244087A2 (fr) * 1986-04-26 1987-11-04 Northern Telecom Europe Limited Capteur à distance de pression compensé en température

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3925626A (en) * 1974-02-22 1975-12-09 Jr Robert John Stallings Dynamic speaker having dome diaphragm and basket frequency
EP0244087A2 (fr) * 1986-04-26 1987-11-04 Northern Telecom Europe Limited Capteur à distance de pression compensé en température

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
JOURNAL OF THE AUDIO ENGINEERING SOCIETY, vol. 25, no. 5, May 1977, pages 294-299, New York, US; J.R. GILLIOM et al.: "Design problems of high-level cone loudspeakers" *
TOOLING & PRODUCTION, vol. 46, no. 4, July 1980, pages 75-77, Solon, OH, US; T. HUDSON: "CNC comes to METAL SPINNING" *

Also Published As

Publication number Publication date
EP0272059A3 (fr) 1990-03-21
GB8630092D0 (en) 1987-01-28

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