640-Audio Signal Processing, Amplification,and Reproduction Equipment
I. General
640.1 Scope. This article covers equipment and wiring for audio signal generation, recording, processing, amplification and reproduction; distribution of sound; public address; speech input systems; temporary audio system installations; and electronic organs or other electronic musical instruments. This also includes audio systems subject to Article 517, Part VI, and Articles 518,
520, 525, and 530.