Quadraphonic open reel tape

Quadraphonic open reel tape or Q4 was the first medium for quadraphonic sound recording and playback, introduced to the American market by the Vanguard Recording Society in June 1969.
History.
It was based on reel-to-reel tape, and was first used in European electronic-music studios by 1954.
Like other quadraphonic formats it was unsuccessful and disappeared by the late 1970s.
Operation.
All available four tracks were used in one direction on the ¼-inch tape, playing at a speed of 7½ inches per second (twice the speed of the regular 4-Track reel to reel tapes).
The four fully discrete tracks had full-bandwidth (unlike Q8 cartridges which had limited dynamic range).