Fascinating discussion going on about the nature of 'dynamics' over on this thread : http://www.diyaudio.com/forums/multi...nger-what.html
Pano writes (post 1174):
There is a consistency across several decades and cultures that high efficiency speakers sound more dynamic than low efficiency. That's a common subjective assessment, so we might ask "why?"
I'm not going to chip in on that thread because I have bigger fish to fry, but ISTM they're all barking up the wrong tree. That's because the question itself isn't quite posed correctly even though its a great start. Nobody listens to speakers alone, they're always powered by amplifiers. The answer to dynamics lies in amplifiers, not speakers. Put another way 'Its the electronics, stupid!'.
Higher efficiency speakers tax amplifiers (here meaning their power supplies in the main) much less - so there's no way to do an apples-apples comparison...