Audio, Video, and Home Theater Systems
Audio, Video, and Home Theater Systems tests signal flow, impedance, amplifier loading, display interfaces, distance limits, and calibration. Expect questions on 70 V distributed audio, speaker taps, HDMI and HDBaseT, EDID, HDCP, aspect ratio, and room acoustics.
Core rules
- A 70 V distributed system uses transformer taps on each speaker. Add the tap wattages; the total must not exceed the amplifier's rated 70 V output, and good design leaves headroom.
- Match speaker impedance to the amplifier only when using a direct low-impedance system. Do not mix 8 ohm speakers and 70 V taps on the same output without a proper interface.
- HDMI has distance limits that depend on cable and resolution. HDBaseT extends HDMI over twisted pair but still needs compliant cable, power, and endpoint support.
- EDID tells the source what display formats are supported. HDCP is content protection; a failure can show a black screen even when the cable tests good.
- Calibrate display brightness, contrast, and audio delay. Treat first reflections and bass modes with placement and acoustic treatment before equalization.
Worked example
A 70 V amplifier is rated 120 W. Ten ceiling speakers are set to 7.5 W taps, so total load is 75 W. At 80 percent usable output, the amplifier can support 96 W, so 75 W is acceptable. If the design added five more 7.5 W speakers, the load would be 112.5 W, leaving too little margin and risking overload on peaks.
Traps
Adding tap wattages incorrectly; mixing 70 V and low-impedance loads; using a passive HDMI cable beyond reliable distance; ignoring HDCP and EDID; and fixing room acoustics only with equalizer settings.