I had an extended comparative listen to Essence and my Druid Mk4-08, as well as my Definition 2s, in my home.
As background pertinent to this particular question of whether a Druid 4-08 owner should upgrade to Essence, I'll add that I started in Zu with a used pair of Druids five years ago that were, as Sean Casey then noted, "...somewhere around Druid 2-1/2." A later change took them to "...about 3-1/2..." And then they were upgraded to Mk 4-08 shortly after that option became available.
I agree with facets of everyone's observations about Essence vs. Druid 4-08. Both Bonesetter and Audiofeil, for example, are correct. Druid and Essence do have distinctly different sounds, and yet compared to most speakers they have more in common than in difference, due to the prevalent character of the Zu FRD.
So, I'll first answer the question posed, then explain. My advice to anyone who already owns and loves Druid Mk 4-08s is to forego Essence and stay with Druids until you can afford or are inclined to make a bigger jump up the Zu line. That said, anyone not already in possession of Druid 4-08 and new to Zu will likely be deeply impressed by the speaker, for all the reasons Zu owners trumpet, and that Art Dudley noted in his Stereophile review.
No doubt, Essence sounds more like most people expect a quality loudspeaker to sound, than does Druid. Essence has just enough greater low-end extension to impress the listener as "full range" and not in need of a sub-woofer. The actual response difference before roll-off is only about 8 Hz (advantage Essence), but the presence of bass more fully underpins the music in all respects. This is directly a function of the larger cabinet loaded with a full Griewe cartridge and that works just great. Top end isn't actually as much more extended on the Essence as it sounds, but here the difference in presentation is divergent. Druid has a reserved teble character while Essence puts the entire high-frequency content of whatever you're listening to right up front. You've moved much closer to the performance. This is almost entirely due to the switch to a ribbon supertweeter in Essence. The sparkle factor common to hi-fi is fully accounted for, clean and incisive without ringing. But the ribbon is bit of a trick way to get more of the resolution and frequency extension of Definition without the more costly (and correct) high frequency output management possible from its two FRD + supertweeter configuration. Together, Essence's bass and high treble presence yield a speaker that delivers the essential character of Zu FRD crossoverless sound in a speaker that emulates commonly-available good hi-fi speakers.
There's also a difference in dispersion and soundstaging. The Essence FRD is unique to Essence in Zu's line -- you will notice a small difference in its whizzer cone as well as a large difference in phase plugs. Essence will spray sound over a broader area, getting from the single FRD configuration more of the dispersion delivered by the two FRD Definition. So Essence scales spatially better than Druid with a much larger sweet spot, and in particular would be a more successful HT / music double-duty speaker. Essence is and will be a successful speaker for Zu because it meets mainstream expectations for how loudspeakers sound. Essence could be successfully sold in a Magnolia store alongside Sonus Faber and Vienna, while Druid probably could not irrespective of its quality.
But if you own Druids and appreciate that speaker's magic for what it is, then Essence takes some of that away. This is the cost of incorporating the ribbon tweeter in Essence. Notice the specs: Essence has an efficiency rating of 97 db/w/m whereas Druid was 101 db/w/m. The FRD in Essence is dialed back a bit to match the lower efficiency of the speaker's ribbon supertweeter. Now, if you are new to very high efficiency crossoverless speakers that also handle gobs of power, that 97db/w/m will seem revelatory. But if you're already accustomed to 101db/w/m, that 4db loss in jump factor and tonal density is audible, and missed.
To be clear: I have two systems and one of them has Definition 2s, so I have subterranean bass available in the next room. Still, for me Druid is not a bass-shy speaker and I listen to them as much as my Definitions. Good to 38Hz is fine with me, especially when the bass coming from the speaker is as natural and defined as it is from a Druid 4-08. Likewise, Druid 4-08 does not lack high frequency response -- it is simply a more distant perspective. So I don't value the differences here in the top and bottom extensions as much as many (maybe most) speaker buyers do. What I do know for certain *for me* is that the small-but-noticeable reduction in midrange tonal density and dynamic life forced upon Essence by adoption of the ribbon tweeter is not worth any changes to the extremes, given that I already have Druid 4-08s. Many people will emphatically disagree.
I auditioned Essence expecting I'd want to upgrade, though when I heard that Zu had chosen to incorporate a ribbon tweeter, I was skeptical of the decision. Hearing the two, I elected not to change, for reasons noted.
Druids were a polarizing proposition, which in some respects helps a young company get off the ground. Hi-Fi mavens tended to either love them quickly for all the right reasons, or question whether the owner knew anything about high-fidelity audio at all. Non-audiphile music lovers tended to embrace them. I am also pretty sure that WAF generally favors the slender depth profile of Druid over the bulkier-but-same-footprint Essence. However, no doubt Essence is more of an 85/15 proposition in favor on sound. It has a crossoverless mid-range correctness most people rarely hear, dynamic life completely alien to the majority of attainable hi-fi, but with top and bottom extension that cues high-end audio respect.
The differences I am citing are likely too fine for anyone but an existing Zu Druid 4-08 owner (or a sufficiently-interested audio geek willing to spend the time comparing) to appreciate or care about. But I do think that most Druid 4-08 owners will hear those differences as larger and prefer to keep their speakers, skipping Essence in favor of stretching to Definitions or jawboning Sean to build a pair of Presence. Or just enjoy what they have and see how the Zu line evolves.
But that's just me.
Phil
