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Quadraphonic (or ''Quadrophonic'' and sometimes ''Quadrasonic'') sound – similar to what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are (wholly or in part) independent of one another. Quadraphonic audio was the earliest consumer product in surround sound and thousands of quadraphonic recordings were made during the 1970s. It was a commercial failure due to many technical problems and format incompatibilities. Quadraphonic audio formats were more expensive to produce than standard two-channel stereo. Playback required additional speakers and specially designed decoders and amplifiers. ==Operation== Quadraphonic audio reproduction on vinyl records was problematic, because some systems were based on discrete sound channels (allowing for full separation of the four original recorded channels, albeit with restricted high-frequency response and reduced record life), while others were matrix encoded into two tracks that would also play back in standard, two-channel, stereo on normal audio equipment (so-called 'compatible' quadraphonic). Also, there were inexpensive "derived" solutions that only provided back ambiance channels, not a defined placement of individual instruments. Quadraphonic systems based on tape were also introduced, based on new equipment capable of playing four discrete channels. A full, four-channel (Quadraphonic) system will reproduce the Left Front, Left Back, Right Front, and Right Back audio signals in each of four separate speakers. Regardless of discrete or matrix formats, in four channel stereo the rear speakers should be of the same or almost same size or quality and have the same or almost same frequency range as the front speakers. 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「Quadraphonic sound」の詳細全文を読む スポンサード リンク
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