Audio/Video, Communications, and Control Systems
This domain covers distributed audio, video distribution, intercom, and building control. Understand signal types-analog line level versus digital-and the cabling each expects: balanced audio, coax for legacy video, HDMI and HDBaseT for modern distribution, and twisted pair for control buses. Know impedance matching for speaker loads, the difference between 70 V distributed systems and low-impedance systems, and how to calculate amplifier power when paralleling speakers. For control systems, understand bus topology, termination, addressing, and the difference between a star and a daisy-chain network.
Traps: paralleling too many 8-ohm speakers and dropping below the amplifier's minimum impedance, exceeding HDBaseT distance, and mixing control-bus protocols on one segment. Also watch for grounding loops that cause hum, and for assuming a wireless control link is reliable in a metal enclosure.
Rule of thumb: for low-impedance systems, the parallel impedance must never fall below the amplifier rating; for 70 V systems, sum the tap wattages and keep them under the amplifier rating.
Worked example: four 8-ohm speakers in parallel equals 2 ohms; if the amplifier is rated to 4 ohms, use series-parallel pairs to restore 8 ohms or switch to a 70 V system with taps.