Wattage is the number most buyers look at first when evaluating an amplifier. It is also the number most susceptible to manipulation, selective measurement, and outright misrepresentation. Understanding how power ratings are derived — and under what conditions — is essential before placing any weight on the figure printed on a specification sheet.
Amplifier power output is typically measured at a single frequency, most commonly 1 kHz, into a resistive load — usually 8 ohms — held for a brief duration. This is not how music works. Music is a complex, broadband signal with rapid transients and continuous variation in frequency content. The amplifier must deliver current across the full audio band simultaneously, into a loudspeaker load that varies with frequency and is not resistive. Measuring into a static resistive load at a single frequency tells you very little about how the amplifier performs under these real conditions.
The measurement conditions also vary enormously between manufacturers. Some specify power at 0.1% THD — a demanding standard that reflects clean, undistorted output. Others specify it at 1% or even 10% THD, where the amplifier is already well into audible distortion. An amplifier rated at 100 watts at 10% THD and one rated at 100 watts at 0.1% THD are not delivering equivalent performance at that power level — but both can claim 100 watts on the box.
Bridged mono configurations, in which two amplifier channels are combined to drive a single speaker, are another source of inflated figures. A stereo amplifier rated at 100 watts per channel may be specified as 400 watts in bridged mode. What this conceals is that the bridged configuration typically doubles the effective load impedance seen by each amplifier channel and reduces current delivery capability — making the higher power figure meaningful only into specific, often undemanding loads.
The watt figure on an amplifier is a starting point for evaluation, not a conclusion. Always ask: at what distortion level, into what load, at what frequency, and under what conditions?