Speaker
Power / headroom
Can the amp hit your peak SPL at your seat, with margin to spare?
Simple
Can the amplifier get your speakers loud enough — including the brief loud peaks — from where you sit? The answer depends on the speaker's efficiency, your distance, and how much spare power the amp has. Comfortable headroom means clean peaks; no headroom means the sound distorts when the music gets dynamic.
The theory
The engine chains several relationships: it converts the speaker's 2.83 V/1 m sensitivity to a 1-watt reference, subtracts inverse-square distance loss, adds room gain to get effective sensitivity at your seat, then computes the watts needed for your peak SPL and compares to the amp's actual power into that impedance. The result is headroom in dB: 10·log₁₀(ampPower / powerNeeded). Below 0 you clip before reaching target; 0–3 dB is marginal; 3–12 dB is the sweet spot.
For experts
Two nerd details the model bakes in. First, 2.83 V is only 1 watt into 8 Ω — into a 4 Ω speaker it's 2 watts, so the headline sensitivity number flatters low-impedance speakers by ~3 dB until you normalize to a true power reference, which the engine does (−10·log₁₀(8/Z)). Second, the engine caps "good" headroom at 12 dB and labels more as merely unnecessary, not better — but the real argument for big headroom is that clipping, not power, kills tweeters: a clipped waveform from an undersized amp dumps high-frequency harmonic energy into the tweeter that clean high power never would. So the counterintuitive truth is that a 200 W amp is often safer for your speakers than a 50 W one, provided you don't abuse it. The 3 dB minimum exists because music peaks are exactly the moments you can't afford to run out of runway.
Normalizing 2.83 V sensitivity to a true 1-watt reference.
Required watts from the SPL gap at your seat, and the headroom between available and required power.