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The moving iron speaker was the earliest type of electric loudspeaker. They are still used today in some miniature speakers where small size and low cost are more important than sound quality. A moving iron speaker consists of a ferrous-metal diaphragm or reed, a permanent magnet and a coil of insulated wire. The coil is wound around the permanent magnet to form a solenoid. When an audio signal is applied to the coil, the strength of the magnetic field varies, and the springy diaphragm or reed moves in response to the varying force on it.〔 The moving iron loudspeaker Bell telephone receiver was of this form. Large units had a paper cone attached to a ferrous metal reed. There are several types of moving iron speaker. Old undamped moving iron speakers have a characteristic sound, with probably the worst sound quality of any known type of speaker usable for speech. Modern damped moving iron mechanisms can provide respectable sound quality, and are used in headphones. The first moving iron transducer, the telephone receiver or earphone, evolved with the first telephone systems in the 1870s. Moving iron horn loudspeakers developed from earphones after the first amplifying device which could drive a speaker, the triode vacuum tube, was perfected around 1913. They were used in radio receivers and the first public address systems. Moving iron cone loudspeakers appeared around 1920. Around 1930 they were replaced by the moving coil cone loudspeaker developed in 1925 by Edward Kellogg and Chester Rice. Today the moving iron driver mechanism is still used in some earphones. == Design == There are several variations. Each speaker has one property from each of the following groups of characteristics: * Means of restraint of the moving member: * * Diaphragm * * Springy metal reed * Acoustic loading: * * Cone * * Disc * * Horn * * Resonant chamber * * None * Drive method: * * Single ended drive * * Balanced armature * * Inductor dynamic * Damping: * * Yes * * No 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Moving iron speaker」の詳細全文を読む スポンサード リンク
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