Zanon,
The actionable part of Atkinson's empirical evaluation of Essence was this:
"In many ways, the Zu Essence is an underachiever, measurement-wise. But the surprise for me, when I auditioned it in AD's room, was how much of its measured misbehavior was not too audible, other than the rolled-off highs and the lack of impact in the lower midrange. I suspect that Zu's designer has carefully balanced the individual aspects of the Essence's design so that the musical result is greater than the sum of its often disappointingly-measuring parts.John Atkinson"
I don't have a 150Hz problem in my installation. "Lack of impact in the lower midrange" disappeared after months of use. The Zu FRD does need to be USED to fully realize its potential. I had a 60Hz anomaly -- what you call "freakiness," a term I expect to see Atkinson adopt in his empirical counterpoints -- that took awhile to learn how to tune out to the point of irrelevance. My Druids were early versions with the pleated-paper cone. I could hear meaningful changes in bass to mid-range performance in gap-height changes of less than 1/16" inch. Essentially the Druid's partial Griewe implementation delegated to the floor and the floor-plinth gap some of what functionally is fully handled in the enclosure and at the finger vent in Soul's full Griewe model.
On Druid, that floor-plinth gap forces trade-offs. Too high and the deeper bass you dialed in is euphonically fat. Too low and that definition and tautness you dialed in gives up some bass extension. The original pleated cone FRD was more Draconian in these trade-offs than the roll-edge cone of later versions. The 4-08 upgrade gave me more tunability, but in less space. The Zu-spec for floor gap on the older pleated cone was 2 CD jewel cases. For the newer roll-edge cone, it was 1. The increments for sound changes became minute, while the trade-offs were more elastic.
I never understood the claim that Druids have "no bass." My Druids system is on the narrow wall of a 21' x 12' space in an open plan house. The "back" of the space flows into the kitchen. A 38 Hz wave is just shy of 30 feet long. That sounds about right when I stand in my kitchen.
Last fall when Sean Casey visited for a Zu house party I hosted, he was listening to my Druids system and suddenly started rifling through a stack of magazines by the couch. He pulled out two identically thin issues of "American Photographer" and slid them under the center of the plinth, further modifying the gap after I had cranked the plinth studs all the way in. Magazines under, perfect. My 60Hz problem was for practical purposes gone, at least in my room, and I got more extension and definition in the bass region.
The Zu boys are very practical about finding the sweet spot in inevitable trade-offs between sound, target customer environments, manufacturability, economics. They know what sounds good in real world residential rooms and have delivered something that works well in the widest range of room, construction and system types of any speaker family I've used or had experience with in 40 years of spending my own money on audio. Few loudspeakers in home audio are universal but a Zu speaker, the BBC LS3/5a, and the original Quad electrostatic come far closer than most.
Phil
