A four-speaker surround sound system introduced in the 1970s that never caught on, primarily because of the recording technologies available at that time. Quadraphonic sound used two front and two rear speakers, and several formats were developed. Recordings on vinyl records could also be played on standard stereo turntables; however, one technique wore out the records too quickly while another did not provide sufficient channel separation. Quadraphonic open reel and 8-track cartridges were also available. Some of the quadraphonic content was later released in formats such as DVD-Audio, Dolby Digital and DTS. See
surround sound.