Power output (watts explained)
TL;DR
Amplifier power (in watts) determines maximum SPL from a given speaker. But specs vary widely by measurement condition (impedance, distortion %). "300W at 4Ω, 10% THD" is much less useful than "150W at 4Ω, 0.1% THD" - real music demands the second.
Amplifier power output is expressed in watts (W). But raw watts alone tells you nothing without knowing the measurement conditions.
Key spec parameters
- Impedance load – amps deliver more power into 4Ω than 8Ω
- Distortion percentage – “power at 1% THD” is usable; “power at 10% THD” is essentially clipping
- Continuous vs peak – continuous (RMS) is real; peak/dynamic is momentary burst
Marketing vs reality
Chinese Class-D amp marketing often quotes power at 10% THD – inflated numbers. The TPA3255 chip’s “300W per channel” spec is at 10% THD, 48V rail, 4Ω. Real clean output for music is more like 100-150W at 4Ω, 0.1% THD.
How much do you actually need?
- Efficient speakers (95+ dB) + small room = 20W is plenty
- Typical bookshelves (87 dB) + medium room = 50-100W ideal
- Low-sensitivity speakers (85 dB) or large room = 100W+ recommended
Ready to see this in action?
Browse honest, hands-on reviews of budget hi-fi gear that puts these concepts to the test.
