Audio Systems, Microphones, Loudspeakers and Amplifiers
What this domain tests
Audio Systems, Microphones, Loudspeakers and Amplifiers tests microphone types and polar patterns, impedance and sensitivity, speaker systems and crossovers, amplifier classes, gain, distortion, feedback, and matching.
Core rules
- Dynamic microphone: rugged, no phantom power, low output. Condenser: high sensitivity, needs phantom power, typically 48 V, and an FET impedance converter.
- Polar patterns: omnidirectional, cardioid, figure-of-eight; proximity effect boosts bass close-up.
- Speaker impedance is nominal; multiple speakers in parallel lower impedance and increase current demand.
- Amplifier power: P=Vrms²/R; music-power ratings are not continuous RMS ratings.
- Class A conducts 360°, AB about 180–360°, B 180°, D is switching; class D efficiency is high but needs filtering.
- Negative feedback reduces distortion and widens bandwidth at the cost of gain.
Worked example
An amplifier is rated 20 W continuous into 8 Ω. Vrms=√(P×R)=√160=12.65 V; Vpeak=17.9 V; peak current=17.9/8=2.24 A. If the same 12.65 Vrms is applied to a 4 Ω load, power becomes 12.65²/4=40 W and current doubles, so a 4 Ω speaker may overload an amplifier rated only for 8 Ω.
Traps
Connecting 4 Ω speakers to an 8 Ω-only amplifier can overheat the output stage. Phantom power can damage some ribbon microphones. Peak or music-power figures are not continuous power. An open speaker line gives no load, but a shorted line can damage the amplifier. Do not confuse sensitivity with maximum power handling.