Specifying and Powering a Live PA System

The whole task here is the one every live-coding act eventually faces when the laptop leaves the bedroom: a 150-cap bar gig where you must promise a booker that your bass-heavy electronic set will hit level without frying the rented tops. That means working backward from program material — dance music demands far more low end and headroom than a poetry night — to amplifier watts, loudspeaker sensitivity, cable gauge, and a rig you can commission without hum or smoke.

The arc starts supported: given a fixed speaker and amp, drill the sensitivity-plus-power-ratio arithmetic (see “Loudspeaker sensitivity plus power ratio in dB gives maximum SPL at 1m”) until converting watts to dB is reflexive, checking answers against the speech-versus-music SPL targets. Next exercises open one decision at a time — pick a wire gauge for a long run, decide when bridging an amp into a sub makes sense, argue active versus passive crossover for a biamped rig. A troubleshooting pass then rehearses the failure modes: why a clipped amplifier delivers roughly double its rated power into vulnerable compression drivers, how duplicate ground paths become a hum antenna, and why a polarity-flipped woofer is not merely “out of phase.” The unsupported capstone assembles all of it into a written spec and commissioning checklist for a stated venue.

Every required atom is a gate: the capstone’s SPL math, gauge choice, crossover and distribution decisions, and its clipping/ground-loop/polarity checklist items each fail without the corresponding atom. The supporting atoms — decibel definitions and phase-interference basics — are refreshers from earlier work that make the required material faster to absorb, not new gates.