Light is kept in the "core" of the optical fiber by total internal reflection. This causes the fiber to act as a waveguid. Fibers which support many propagation paths or transverse modes are called mulitimode fibers(MMF). Fibers which support only a single mode are called singlemode fibers (SMF). Multimode fibers generally have a large-diameter core, and are used for short-distance communication links or for applications where high power must be transmitted. Singlemode fibers are used for most communication links longer than 200 meters.

Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together either mechanically or by fusing them together with an electric arc. Special connectors are used to make removable connections.

The Crown 180A, 280A, 1160A and 660A are high-value amplifiers for commercial and industrial audio. They provide 4-ohm and constant-voltage outputs (70V and 100V). The 660A, a six-channel amplifier, provides 4-ohm and constant-voltage outputs (70V and 100V) on channels 1 through 4, and 4-ohm outpus on channels 5 and 6. The amps are part of Crown’s Commercial Audio Series, which also includes mixers and mixer-amps. These low-cost units provide all necessary features in a simple building-block format. The sound system can be upgraded as a facility expands. For example, you can add more mixers for more inputs, or add more power amps (or mixer-amps) to handle more zones.