Ok I think I have this right so let me know if I go wrong. Lets say I have a pair of 250w speakers and I'm running a 250w amp to them. As I turn up the volume the watts double for every 3 db until I reach 250w which would be the point where the amp clips and another 3db of volume would push it to 500w or more blowing everything up. So then lets say I run a 500w amp to the same speakers once I reach the volume where it's putting out 250w I'm close to or at the point where the speaker clips. Another 3db of volume from that amp would probably blow up the speakers but that last 3db of clean power is reffered to as headspace. Therefore it's better and dare I say safer to have a bigger amp if your going to play your speakers at a volume close to there limits because a small amp quickly doubles watts when it starts to clip.