Amplifer Wattage Question

Russb - try this formula L = P^(1/3.5) where P is a ratio of power and L is a ratio of loudness. In your case L=(250/10)^(1/3.5)=2.508

Magfan - It cannot be done since woofer midrange and tweeter have completely different power ratings. Applying full power at midrange frequency will most likely damage midrange speaker and doing the same at high frequency will definitely take out the tweeter. It is difficult to estimate proportions between lows, mids and highs since it is recording dependent. Music power delivered to speakers is only a few percent of peak power so measuring speakers' max RMS power is not the answer.

Russ - You have to remember that listening is logarithmic so power has to increase/decrease ex-potentially. Half as loud means 1/10 of the output power. If you add to it silence in the music it will become obvious why average music power delivered is only few percent of peaks. Measuring amp with sine waves (test tones) on a dummy load won't tell the story either since speaker impedance is complex. In addition 100W rated amp might put much higher momentary peak power - design dependant. IMHO measuring doesn't make much sense. I would be the most afraid of under-sizing amp since it will lead to clipping = high frequency energy delivered to tweeter = overheating. If your amp is strong you should be able to hear when your speakers distort.

Magfan - I don't listen to sinewaves either, I find it a little boring.
If the goal is to measure RMS power delivered than standard RMS meters will be probably useless. They don't measure well at high frequencies and they have limited crest factor. Since RMS is defined as DC that produce equivalent heat perhaps measuring temperature will be more accurate (resistor in series?). I wonder myself if there are any professional power meters that measure music power accurately. I'm not sure how important it is.

As for Zobel in D-class - many people complain about it. Yes it will be damaged with prolonged exposure above certain frequency but it will never happen in real live.
I would say that average power that amp can deliver is not of use. I want to know how much peak power (or peak current) amp can deliver. 80V supplied 1kW Icepower (1000ASP) can deliver about 40A on 2 ohm load for about a second and that is very impressive (3.2kW). At 10kHz its output power is limited to 200W but this would make person deaf and I don't know of any tweeter that can take continuous 200W (more like 20W max). In real life average music power that tweeter receives is a fraction of a Watt. The most important is match, that you mentioned. My experience is limited, but from what I'm reading certain amps just "like" certain speakers more than others.

Russb - 100W is 2x louder than 10W. 200W is 1.23x louder than 100W and 250W is practically the same as 200W. So in total 250W is about 2.5x louder than 10W.