Audio Tape Specifications - Compact Audio Cassettes

Compact Audio Cassettes

The tape in a compact audio cassette is nominally ⅛ inch but actually slightly wider (3.81 mm). The small mass of the spools and mechanism generally allows thinner tape to be used than is practical with reel-to-reel.

The thickest tape normally used in cassettes is about 16 µm in thickness, and is used in C60 cassettes and in shorter lengths such as the C46. As the standard tape speed for a compact cassette is 1⅞ ips and a C60 cassette records 30 minutes per side, a C60 cassette in theory holds 281¼' (85.73 m) of tape. In practice there is some variation, for example Maxell quote their C60s as being 90 m (295') in length.

Tape about 11.2 µm in thickness is used in C90 cassettes, and also for those intermediate between a C60 and a C90, for example the C74 produced specifically for recording a standard length CD. Most equipment manufacturers optimize their equipment for C90 cassettes but fully support shorter cassettes using either 11.2 µm or 16 µm tape.

A cassette longer than a C90, such as a C120, must use even thinner tape. Most equipment manufacturers discourage the use of these longer cassettes, partly because the tape is so fragile, and also because of the difficulty of providing optimum recording over an extended range of tape thicknesses (thinner tape is more prone to "print through" echo). However C180 and even C240 cassettes have been produced both for the consumer market and for specialised applications such as call logging.

Rumours have sometimes associated C120 and longer cassettes with double or triple play reel-to-reel tape, but in fact even C60 cassettes use tape thinner than double play and little thicker than triple play. The main thing that the longer cassettes have in common with double and triple play reel-to-reel tapes is that they are pushing similar limits of technology, and as a consequence suffer similar problems.