The term Quadrophonic, or Quadraphonic, either are correct, was coined in the early 1970s to describe a four-channel sound presentation used in the recording and broadcast industries.
The speaker placement is frontLeft, frontRight, rearLeft and rearRight (fL,fR,rL,rR), with the listener sitting equidistant from all speakers for the optimum Quadrophonic experience. All speakers were intended to be uniform in their audio response characteristics. This is unlike the surround speaker adopted in Dolby® matrixed stereo of the 80s and 90s, which had a surround speaker that was frequency limited from 100Hz to 7,000Hz. In addition to the full-range Quadrophonic rear speakers, the rear speakers were also stereo, something that would not be easily achieved in motion picture sound until the early 1990s, when a variety of 5.1 channel surround stereo systems emerged (SR-D, DTS, SDDS).
There were two methods to present Quadrophonic stereo, either discrete on 1/2" and 1/4" audio tape or compatible, which employed one of the first matrix technologies for presenting stereo sound. The compatible method relied upon a matrix algorithm that would allow the four channels of sound to be carried on just two channels. This meant that conventional stereo records could play back either the Quadrophonic matrixed track or a conventional stereo track on a standard 33 1/3rpm long playing record. This was a key component to its limited success in the record industry. Over 1,000 albums were produced with Quadrophonic sound technology. The last Quadrophonic albums were made in 1978.
The discrete method for Quadraphonic sound allowed for the four separate channels to be played individually from four channels recorded on an audio tape. For a short time Quadrophonic sound was recorded onto 8-track audio tape cartridges, called Quad-8. In the broadcast domain, some FM stations actually partnered with another FM station; one station would broadcast the front channels on its signal and the other station would broadcast the rear channels. Stations could also broadcast the matrixed signal, requiring a single station. This signal could be decoded on home receivers that were also used for the compatible records.
Quadrophonic stereo was adopted for the motion picture industry on the rock opera film Tommy (1975) and re-branded Quintaphonic Stereo. Tommy has the distinction of being the only film to have been released in Quintaphonic stereo.
The Quadrophonic speaker placement is frontLeft, frontRight, rearLeft, and rearRight (fL,fR,rL,rR), with the listener sitting equidistant from all speakers for the optimum Quadrophonic experience.