Amp Power vs Impedance
See how much power an amplifier makes at different impedances and how well it matches your subwoofer's RMS rating.
Inputs
Continuous power handling from the driver’s spec sheet.
Power at different loads (ideal)
How it works
An amplifier is (roughly) a constant-voltage source: it can swing a fixed maximum voltage, and the load impedance decides how much current, and therefore power, it delivers. Halve the impedance and the current doubles, so ideal power doubles too.
P = V² / Z = I² · Z V = √(P · Z) I = √(P / Z) P₂ = P₁ · (Z₁ / Z₂) (ideal, voltage-limited)
In real life, small power supplies, thermal limits and current limits stop amplifiers from exactly doubling at each step, many get 1.5–1.8× going from 4 Ω to 2 Ω, and 1 Ω rated amps often use dedicated output stages. Treat the numbers as the best case, and use the amp’s spec sheet where it lists specific loads.
Matching amp to sub: the sweet spot is an amp delivering between about 75% and 150% of the sub’s RMS rating. A little more power than the sub can handle is okay for dynamic music if you set gain carefully, but a clipping amp (square-wave distortion) kills voice coils faster than a large clean amp ever will.
The decibel difference tells you how far the amp is from the sub’s limit: +3 dB is double the power; ±1 dB is barely audible.