The least "alive" Definition was the original Def2, before the 2010 HO drivers. And still, at modest levels it was comparatively excellent at representing full tonal body and presentation of graceful detail with dynamic contrast. Definition 4, and all the ZU speakers with the nano FRD generally, are as effective as you're likely to hear in being able to present aliveness at low SPLs.
The one caveat is -- *after reasonable break-in.* If you buy them new, especially during cold shipping months, they will not immediately bloom at low SPL, even if the apparent volume is there. But they limber up, and do what you want.
As for the resolution of Def4 compared to "conventional" speakers: I have in the past seen some reviewers compliment Zu speakers, with the one aside that in some words or others, Zu in general does not give you "ultimate resolution."
For older Druids and original Def2, there was some validity to that observation, though I argue reviewers who felt that way were mostly accustomed to intensely *over"-resolved loudspeakers, which is a common trait throughout high-end audio today and for much of the past decade. But in Def4, the combination of the nano-FRD and the Radian 850 supertweeter, I think Zu resolution is as high as you'd practically want, and I say this as a former electrostatic speaker listener, and my headphones are Stax.
A lot of what audiophiles hear as "resolution" is either rising top end, ringing and resonance, and crossover artifacts OR it's simply from recordings that are so inappropriately close-mic'd as to render the recording completely non-representative of how you'd hear the same music performed and heard from even the closest practical listening position.
I have no lingering resolution hunger in my mind's ear, when listening to Def4s with commensurately resolving amplification.
Phil
