Quadraphonic open reel tape (Q4) was first introduced by Vanguard Records in 1969, and was only ever available in the US market.
It used ¼-inch tape, playing at a speed of 7½ inches per second, and had 4 fully discrete tracks with full-bandwidth (unlike Q8 cartridges which had limited dynamic range).
Like other quadraphonic formats, it was unsuccessful and had disappeared by the late 1970s.
Sources / Resources
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