Yes, Glory has it right. I've been too busy listening to my Def4s to take time to write about them. I bought about 50 more CDs and vinyl discs since they were delivered, and I'm plowing through my thousands of existing discs. It's cutting into my work productivity!
Here are the short strokes, while I get my full narrative together:
To understand Def 4 you have to know Def 1 and 2. I'll write about this later. The basics however are apparent regardless of your historical exposure to Zu.
1/ Top to bottom, Def 4 is for the first time a Definition-archtecture speaker that has the holistic charcter of Druid, with Definition's accuracy and scale. Its tone, speed and dynamic characteristics are now fully uniform top to bottom. In prior versions, the dual FRDs, super tweeter and the sub-bass array left traces of their independence. No more.
2/ Def4 soundstage is as wide and deep as your room allows, and will go beyond to serve the dimensional characteristics of the music performance recorded. For anything from a Blu-ray movie soundtrack to a full orchestra to a trio or solo performer in an intimate space, spatial representations are closer to the perception of live performance than in any Zu speaker to-date (though I haven't yet heard Dominance).
3/ Even in a tricky room, the new 12" cast-basket down-firing sub-bass driver and its driving amplifier more evenly loads a room with bass, with fewer resonance, bass-piling and reflective problems than the older and once-excellent 4x10" back-firing sub-bass line array on Def 1&2. Most of the bass resonance problems that I've in the past just had to listen through in my main room, are mitigated to the point of irrelevance. Bass is prodigious when the recording calls for it, but in all cases is reproduced with higher definition and charcter unique to the given bass instrument and the player's style, than in prior versions.
4/ Top to bottom transient uniformity is unprecedented for a dynamic speaker. Def4 has electrostatic-like speed and uniformity, while retaining the punchy heft of a responsive magnet-motor cone speaker.
5/ The inclusion of the Radian compression supertweeter is a very large advance over prior Definitions, if your high frequency hearing is still intact. It is extended, liquid-smooth, fast and not beamy. It is what Definition needed from Day 1. Similarly, the nano-treated main drivers are responsive and transparent to a new level of revelation because even further stiffness has been achieved in the cones, with only a fraction of the added mass of prior treatments. As I understand it, only around a gram or less of treatment compound is used now per driver. You hear it, in speed, attack, articulation and tone.
6/ As I'll elaborate in a more complete assessment, cabinet talk is suppressed yet again over the prior version, sharply reducing the tonal artifacts introduced by high SPLs in prior Definitions.
7/ An unexpected consequence of all this attention to advancement: somehow and counterintuitive to landing a more revealing speaker, regular Redbook CDs are more listenable and satisfying than ever before, without any change to my sources. I expected a more transparent transducer to render older, or more compressed or generally poor CDs to challenge my tolerance for listening to them. But the reverse is true. These speakers have me mining deeper into my CD collection than in quite awhile. Vinyl gets its due but I have a lot of music unavailable on vinyl, and I'm enjoying all of it more.
8/ Tonal integrity and holistic realism remain evident in the bursty, one-voice Zu way, but beyond what anyone has experienced who hasn't heard Dominance or Def4. This is not an incremental iteration of Defintion.
I''ll get more tapped into text tomorrow or Monday.
Phil
