Zu def 4 are they the best speaker made?

Unless you are playing them outside, the room has the most impact on how a system will perform. That's the bottom line.

maybe these speakers just work with the op's set up.  I've had a few speakers in my systems over the last 30+ years.

I currently run a fully modified and upgraded pair of SoundLab A1's augmented with a pair of Sunfire Subrosa subs.

so far, that's been "the best" speaker set up I've had. Before that it was a pair of Carver Amazings... so as someone else pointed out.. it is all about room interaction and context, plus your personal preferences..

Love the Zu guys.
Something very appealing about the "live" quality of their high sensitivity speakers. I have had Druid in and out of my setup several times. But they are currently sitting disconnected in the hallway. Because for me tonal balance is a priority. Check the response curve:
http://www.soundstage.com/measurements/zucable_druid/
They are very fun listening, but not an everyday solution according to my preferences.
PS. That curve is for an older version. I hope someone can post a link to measurements for a more current model. It probably looks a lot better. Of course measurements aren’t everything.

Best speaker ever made? You gotta be kidding... If anything, it's one of the worst, and for the money, definitely not worth it.

Bad bass, horrible blurry mids, crappy extension, and for all their high efficiency, not even that dynamic or lively even.

The damn things sell for $16900. There's like a million better products out there for HALF this money, let alone at this price.

I definitely don't get it.

I think I saw Zu speakers at an audio show only once. They kept me less than 30 seconds in the room. Don't remember the model or any details, just the brand.

Also, I remember reading this comment about some Zu speakers (yes, it was for a cheaper model):

**** Munich High-End 2016 ****
"Right: Zu loudspeaker from whizzer cone driver and compression driver fitted with waveguide. The speaker sounded plain awful. Close to worst sound on show." 
http://www.troelsgravesen.dk/MUNICH-2016.htm

Nice ad, though. 

I don't know why there is always so much debate on speakers and electronics. Doesn't it stand to reason that in taking account of room acoustics, individuality in people's hearing with regard to even hearing all the frequency spectrum, and the wide range of electronics, electric cords, conditioners, wire connectors, etc. . . . not to mention the constant “improvements” that never quite get to the perfecting of sound reproduction . . . that there is a lot of spoof in advertising -- not to mention brainwashing with regard to all of this?

I grant you that there are improvements in equipment . . . but these breakthroughs, I feel, will ALWAYS be there, as it is the lifeblood of the industry. It is like medicine . . . always finding ways to mask symptoms and always coming up with medical breakthroughs -- but RARELY, if ever, a CURE.

Half the fun, I am convinced, is the man child comparing how much he paid for his equipment and then debating just how much better it is than his neighbor's setup . . . not to mention how everyone seems to have those “golden ears” that set them above everyone else in telling them what to buy, which is the newest BEST . . . that is, until it becomes last months old news. Hey, it is the proverbial carrot that is being dangled in front of a hungry man's face that keep the cash flow going and opens up a man's wallet to spend how many hundreds of thousands of dollars by the public -- knowing full well that this stuff is marked-up two-thirds over the value and the cost of making the product in the first place.

As I recall, we all just salivated just seeing the latest and greatest when going into the stereo stores . . . let alone everyone just mesmerized as the sales person told us what we are hearing -- and believed it.

It is a grand hobby -- always will be; however, doesn't commonsense dictate that somewhere along the line that “carrot” will be always hanging just slightly out of reach of music narvana?