How much amplifier power do you really need?

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Interesting post, @Confused.  It agrees nicely with what Roger Sanders says in his white paper (which I know I've linked to before).  To pick some salient points:

You will find that conventional, direct-radiator (not horn-loaded), magnetic speaker systems of around 90 dB sensitivity, require around 500 watts/channel to avoid clipping.  More power is needed in larger rooms or if you like to play your music more loudly than most.

The key point I'm trying to make is that audiophiles usually are using underpowered amplifiers and are therefore listening to clipping amplifiers most of the time.  When an amplifier is clipping, it is behaving (and sounding) grossly differently than its measured performance would suggest. This is because we always measure amplifiers when they are operating within their design parameters -- never when clipping.  A clipping amp has horrible performance, so attempting to measure it is a waste of time.

In other words, we usually listen to an amplifier when it is clipping and we measure it when it is not.  This is why amplifiers sound so different than their measurements would imply.  It is not that measurements are wrong, it is simply that we are listening and measuring different conditions.

It should now be obvious why objective measurements don't seem to give much insight into the performance of amplifiers.  It is not that objective measurements aren't accurate (they are superb), but simply that we don't usually operate amplifiers within their design parameters.  So we aren't listening to them at the power levels where they operate properly and where their measurements are meaningful.

To have a truly high-fidelity music system therefore requires very powerful amplifiers.  Amplifier power is the single most important factor in choosing an amp.  Without adequate power, all amplifiers sound badly.  You can pick a clipping amplifier based on it not sounding as badly as another amplifier (tubes usually preferred over transistors), but if you really want clean, dynamic, effortless, and smooth sound, you simply must use adequate amplifier power.