[quote user="al7478"]Highly relevant and insightful closing paragraph there. Ahem. Anyway, does that mean that more watts can equal better performance even at low volumes...?[/quote]
Here's what I think..
Yes, higher wattage helps at lower volumes.
But higher wattage drives up the price of the amplifier, so by adding extra watts (and keeping the price the same) to give you more dynamics you might be making unwanted sacrifices to other areas of your sound.. as the other guy mentioned, signal to noise ratio (SnR) and total harmonic distortion (THD).
The sweet spot? that depends on way too much to be able to give a good figure, but your speakers will have a recommended amplifier power to be used with them. I would suggest aiming for the upper end if you are particularly interested in the dynamics of it, what might be a problem for you though is setting your volume - you don't want to end up with the situation where your comfortable listening zone (out of ten) is somewhere between 1 and 1.0001. (I'll admit a slight exhaggeration there to make the point)
Right, the more complicated question... sadly deems a more complicated answer
Yes low volumes can have sudden moments of higher power requirements, if you think about the audio signal, time vs amplitude, it is moments of higher slew rate
that require more power. Easiest way to think of it is this, perhaps. Take a perfect square wave at 100% amplitude, using the full range of the speaker. When you go from -100% to +100% your speaker cone has to, technically, move at infinite speed. this is impossible. The amplifier has to accelerate that speaker cone really really fast, this requires power. Its this kind of power requirement that is referred to as the 'peak output power' which is often also quoted with speakers.
Another thing relevant. make that square wave almost
perfect. So it is basically a clipped sine wave of massive amplitude (lets say 10x the amplitude of the left over imperfect square wave). The power dropped across the speaker when reproducing this square wave is the same as the power required to produce the 10x as loud sine wave. Bye Bye crossover. So in essence, you are more likely to kill your speakers with an amplifier driven outside its power range than you are using an amplifier with too much power for the speakers at too higher volume.
It goes against what you would think, because you'd think that throwing the bass cone out way too far will damage the mechanics of the speaker. Yes it will, but as it gets further and further out, beyond its rated distance the response of the voice coil becomes non-linear. So you double the input and you no longer double the displacement of the speaker cone. It will, however, sound awfully distorted and it will be clear you are overdriving the speakers. overdriving the amplifier could be mistaken for overdriving the speakers too though and in reality it is more likely to cause damage.
Hope that answered your question. I never know how far I can go into technical terms when people ask things like that though so if you don't understand anything I'd be happy to clarify... or if you're up on that kind of thing I can keep the response a lot more brief in future