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unfortunate tendency to soften when hot. Hisco P450, developed in 1992 to address the softening issue in professional speakers, is a thermoset composite of thin glassfibre cloth, impregnated with polyimide resin, combining the best characteristics of polyimide with the temperature resistance and stiffness of glassfibre. It withstands brutal physical stresses and operating temperatures up to 300°C, while its stiffness helps maintain the speaker's 'cold' frequency response.
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response is required from a loudspeaker, aluminium wire may be substituted, to reduce the moving mass of the coil. While rather delicate in a manufacturing environment, aluminium wire has about one third of the mass of the equivalent gauge of copper wire, and has about two-thirds of the electrical conductivity. Copper-clad aluminium wire is occasionally used, allowing easier winding, along with a useful reduction in coil mass compared to copper.
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a portion of the coil remains within the gap at all times. The power handling is limited by the amount of heat that can be tolerated, and the amount that can be removed from the voice coil. Some magnet designs include aluminium heat-sink rings above and below the magnet gap, to improve conduction cooling, significantly improving power handling. If
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In the earliest loudspeakers, voice coils were wound onto paper bobbins, which was appropriate for modest power levels. As more powerful amplifiers became available, alloy 1145 aluminium foil was widely substituted for paper bobbins, and the voice coils survived increased power. Typical modern hi-fi
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is related to the heat resistance of the wire insulation, adhesive, and bobbin material, and may be influenced by the coil's position within the magnetic gap. The majority of loudspeakers use 'overhung' voice coils, with windings that are taller than the height of the magnetic gap. In this topology,
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Voice coils can be used for applications other than loudspeakers, where time force linearity and long strokes are needed. Some environments like vacuum or space require specific attention during conception, in order to evacuate coil losses. Several specific methods can be used to facilitate thermal
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The actual wire employed in voice coil winding is almost always copper, with an electrical insulation coating, and in some cases, an adhesive overcoat. Copper wire provides an easily manufactured, general purpose voice coil, at a reasonable cost. Where maximum sensitivity or extended high frequency
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Many hi-fi, and almost all professional low frequency loudspeakers (woofers) include vents in the magnet system to provide forced-air cooling of the voice coil. The pumping action of the cone and the dustcap draws in cool air and expels hot air. This method of cooling relies upon cone motion, so is
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Aluminium was widely used in the speaker industry due to its low cost, ease of bonding, and structural strength. When higher power amplifiers emerged, especially in professional sound, the limitations of aluminium were exposed. It rather efficiently but inconveniently transfers heat from the voice
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plastic film which did not suffer from aluminium's deficiencies, so Kapton, and later Kaneka Apical were widely adopted for voice coils. As successful as these dark brown plastic films were for most hi-fi voice coils, they also had some less attractive properties, principally their cost, and an
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coatings on other voice coil wire. This creates lightweight, low-inductance voice coils, ideally suited to use in small, extended range speakers. The principal power limitation on such coils is the thermal softening point of the adhesives which bond the wire to the bobbin, or the bobbin to the
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which assists in cooling the coil, by conducting heat away from the coil and into the magnet structure. Excessive input power at low frequencies can cause the coil to move beyond its normal limits, causing distortion and possibly mechanical damage.
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up to 150°C, or even 180°C. For professional loudspeakers, advanced thermoset composite materials are available to improve voice coil survival under severe simultaneous thermal (<300°C) and mechanical stresses.
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is produced. This magnetic field causes the voice coil to react to the magnetic field from a permanent magnet fixed to the speaker's frame, thereby moving the cone of the speaker. By applying an
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design which is used mostly in high-end speakers has the coil's height smaller than the gap's. The differences, advantages and disadvantages of both methods are listed below.
340:), voice coils are usually made as light weight as possible, making them delicate. Passing too much current through the coil can cause it to overheat (see
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coil into the adhesive bonds of the loudspeaker, thermally degrading or even burning them. Motion of the aluminium bobbin in the magnetic gap creates
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that positions the heads: an electric control signal drives the voice coil and the resulting force quickly and accurately positions the heads.
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Both topologies attempt the same goal: linear force acting on the coil, for a driver that reproduces the applied signal faithfully.
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ineffective at midrange or treble frequencies, although venting of midranges and tweeters does provide some acoustic advantages.
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within the material, which further increase the temperature, hindering long-term survival. In 1955 DuPont developed Kapton, a
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In 'underhung' voice coil designs (see below), the coil is shorter than the magnetic gap, a topology that provides consistent
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This method keeps the number of windings within the magnetic field (or flux) constant over the coil's normal excursion range.
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Overhung and underhung voice coils. Light grey is soft iron, dark grey is permanent magnetic material and the coil is in red.
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it may leave the gap, generating significant distortion and losing the heat-sinking benefit of the steel, heating rapidly.
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543:. In this application, a very lightweight coil of wires is mounted within a strong magnetic field produced by permanent
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The image above shows two ways in which the voice coil is immersed in the magnetic field. The most common method is the
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cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it.
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In particular, it is commonly used to refer to the coil of wire that moves the read–write heads in a moving-head
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design where the height of the voice coil is greater than the magnetic gap's height. The
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flat wire may be used, providing an insulating oxide layer more resistant to
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that the coil experiences, constant over the coil's normal excursion range.
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580:, 7th Edition, August 2001. Hisco, Anaheim, CA 92807. 714 777 2665.
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The term "voice coil" has been generalized and refers to any
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loudspeaker voice coils employ materials which can withstand
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to move an object back-and-forth within a magnetic field.
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A 7.5 cm diameter dual voice coil from a subwoofer driver.
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Because the moving parts of the speaker must be of low
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352:and collar materials so they may be immersed in a
344:). Voice coils wound with flattened wire, called
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84:but its sources remain unclear because it lacks
495:Gap's height is greater than the coil's height.
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313:to the voice coil, the cone will reproduce the
508:Hard non-linearity as the coil exceeds limits.
483:Soft non-linearity as the coil exceeds limits.
320:, corresponding to the original input signal.
474:Coil height is greater than the gap's height.
480:Higher coil mass, sensitivity low to medium.
282:such as those used to move the heads inside
50:Learn how and when to remove these messages
547:. The voice coil is the motor part of the
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505:Low coil mass, sensitivity medium to high.
375:over a limited range of motion, known as X
578:The Hisco Loudspeaker Voice Coil Handbook
235:Learn how and when to remove this message
217:Learn how and when to remove this message
115:Learn how and when to remove this message
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332:(to accurately reproduce high-frequency
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574:, A good paper on Voice Coil Actuators.
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278:The term is also used for voice coil
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366:all other conditions remain constant
155:adding citations to reliable sources
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336:without being damped too much by
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586:, Principle and Practice.
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393:operating temperatures
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600:Electromagnetic coils
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324:Design considerations
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584:Voice Coil Actuators
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373:electromotive force
545:rare-earth magnets
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72:list of references
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207:January 2008
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166:"Voice coil"
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149:Please help
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346:ribbon-wire
273:loudspeaker
97:introducing
594:Categories
567:References
541:disk drive
432:and coil.
381:overdriven
354:ferrofluid
257:voice coil
177:newspapers
36:improve it
458:underhung
406:polyimide
294:Operation
105:June 2017
42:talk page
555:See also
534:solenoid
454:overhung
311:waveform
436:drain.
338:inertia
300:current
290:(VCM).
269:winding
191:scholar
93:improve
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350:bobbin
334:sounds
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