Higher sensitivity - more dynamic sound?

Thanks Duke, that might explain why I really like tube amps feeding high efficiency speakers.  Most of the tube types I like don’t put out much power.  I like 45 and 2a3 in SET amps and 6L6 and KT 66 for push pull amps.  In my own amp that is currently in my system, I run 349s—two per channel for about 5 watts.

Good dynamics is not just about the range of capability.  It is more about whether, when the signal goes up, there is a corresponding increase in the output of the speaker (i.e., no compression).  This is less the case with low efficiency speakers because, more watts have to be delivered for any given volume level, and a bigger proportion of those watts are being dissipated as heat.  The problem with this heat is that heating of components increases resistance which reduces the flow of current/power.  In other words, there is not a proportional increase in driver output to the power being delivered to the speaker because of such heating.  This is thermal compression and it is a bigger issue with low efficiency drivers which, dissipate more of the power being sent through the driver as heat than is the case with high efficiency drivers.