The Cantata 700 is a commercial background music system and corresponding cartridge format developed by 3M that was in use from 1965 and until the 1990s.
Cantata 700 Wikipedia
The nearly square shaped cartridges are among the largest ever built. More than 24 hours of playback fits on a single cartridge. The music distributed by 3M consisted exclusively of mono recordings by company's own "3M Orchestra".
The cartridge consists of a reel-to-reel mechanism intended for playback only. Internally, there are two counter-rotating 8⅜ inch tape reels, tape guides, deflection rollers for the magnetic tape, and a reel brake. The reel brake engages when removed from the machine and released by a pin in the drive. The opening is on the front side between the deflection rollers to allow the drive access the tape and engage pins, capstan and mandrel for tape traction, rolls and release the reel brake. A mark at the end of the tape triggers the tape to reverse.
All offered machines were playback only. The first models 94BG and 94BZ were offered in 1965 and bundled with two cartridges of the customer's choice for $429.00 USD (with inflation in today's value: $3260 USD).
The player dimensions are not much more than the cartridge itself. The machines are equipped with a speaker jack for 6 W and 8 Ω, and a microphone jack for announcements. Inserting the cartridge consists of manually fitting it into pins and mandrel. The lid is only a cover. A fan wheel is located the bottom end of the motor drive shaft and its top end and presses against a rubber wheel which couples the drive mechanism to the motor. The machine has no belts.
The tape passes the capstan before and behind the deflection roller. Before the tape ends, it triggers the reverse mechanism which changes the drive to the other reel in the cartridge. The other pinch roller shifts to the capstan drive shaft and the tape head also shifts on the level of the other reel; adjusting to the height of the tape. This design does not require the head to turn over over, instead, the ¼ inch wide magnetic tape turns over by the deflection roller. Tape speed is 1⅞ Inch per second; which is same as the Compact Cassette.
In 1970 3M introduced a new model where the cartridge was located in a drawer tray, offered for rent only. Sound and tape speed control quality were of nominal quality for the time period, yet considered acceptable for its usage as background music.Variety Library V 168
Rhythmin Library 165
Melodie Library 165
Rhythmin Library Series II 266