With 200-watt LinnenberG Liszt and 10-watt FirstWatt SIT1 monos at Capital Audio Fest 2017. Photo by reader JL.

RMAF 2017. "In 2001 the first Druid dropped and for the launch of 2017's MkVI, we decided to take it back to 2001. To showcase our next big step, the decorations were in homage to Stanley Kubrick's 2001: A Space Odyssey. We showed the new Druid ($10'000/pr) on a Peachtree Nova 300 ($2'500) cabled with Zu Event ($3'000). Supporting the very bottom octave were a pair of our Undertone subs ($2'500/ea.) set to a 28Hz 3rd-order low-pass to even out the room's bass response and give listeners the needed infrasonic energy and life that doom soup, black metal, big orchestra and big pipes require."


The key bit in this quote was the Peachtree integrated, a 300wpc ICEpower-based class D amplifier. To many more traditional widebanders like Rethm and Voxativ, such a mention—much less their makers' actual use of a class D denizen during a show demo—would be anathema.


That's because anecdotal evidence shows that their high-efficiency designs work best with tubes, often in fact the low-power SET types. Zu too have championed Audion and Melody valve amps but they don't limit themselves to valves or low power.

One underlying reason is power handling. Zu speakers can famously dish it at club levels. It's something our household and our music don't exploit. Here our Druid V are a V12 truck which we never drive in more than 2nd gear and then really only on perfectly smooth black top.

The fact that we do so happily tells you that these needn't be driven hard to sound good. It's simply something one can do when the mood strikes; which apparently struck team Zu during their Saturday night party at the Denver show even if we're told that the crowd didn't quite get down to actual dancing. Audiophiles. What to do? Bang the jungle drums louder?

During RMAF's seminar of "Young Guns of Hifi".

Bringing it home, demoing $10'000/pr flagship 1.5-ways with a $2'500 all-in-one super integrated to collect plenty of very favourable press mentions for sound quality goes a way toward softening the blow that the hi-zoot VI asks nearly double that of the V. But then, the latter remains with the program. No Druid gets left behind.


On November 13th, new stronger packaging was sorted and my shipment just one week out. "Would you like a top-side through-plinth key way to allow for easy footer adjustment? This is something we will offer. It makes leveling and adjustment very easy but the price to pay are small holes in the plinth, one directly above each of the spike/footer threads. Initially I didn't want to offer this because I like the clean hole-less look; and with most of the speakers we have prototyped and all that we've taken to market, performance was best with a rigid floor connection.


"But Druid VI behaves differently and doesn't really seem to benefit from coupling to the mass of the floor. I am still collecting data from placing it in various rooms with various floors. Since already footers seem to work just fine and as this option can be ordered as an easy inline operation, we are offering it up. While there are lots of variables with footers and spikes and flooring, I have found a pretty cool leveling footer that performs properly and remains easy to use.


"It has a precision 'sloppy' swivel interface between pad-cone and shaft. The 18mm ball bearing is spherical, the mating bearing surface oversized, slightly parabolic and directly machined into the steel footer cone. The assembly is captured via press operation so no pain-in-the-arse ball bearings that rest freely in cups. The footer is also padded with a 2mm mid-durometer rubber bottom which your floor will love. The rubber pads are countersunk into the cones and adhesively potted so their sheer strength is super high. These pads won't peel off when sliding things around. Because these footers can be used regardless of the key way option, we'll include a set."


As you'd expect for a mechanically revisited design, the important floor interface didn't escape Zu's prying eyes. That the final solution would be efficacious and easy to use is an added bonus. No worries here over misaligning a ball bearing which as a result binds up to no longer work as intended; or unintentionally marring parquet floors with pointy spikes during a driveby bump - though those may be used as well as shown next. To appreciate this speaker's technical roots, watch this 20-min. YouTube video wherein Sean Casey answers Stereophile editor John Atkinson's questions on his unconventional design choices and what they're really in service of. For a factory tour, watch Berlin contributor John Darko's 2016 Vimeo video.


On Zu's so-called Griewe loading relative to these two large-diameter pipe openings, "the original concept came from the mind of Ron 'Ogre' Griewe, a motorcycle freak globally known for his two-decades plus contributions to Cycle World magazine. Ron loved to go fast on bikes and making them go faster. Stuck in Los Angeles traffic one day, thinking about ways to get more power from the less-than-ideal bent twisted exhaust pipe and muffler of a motorcycle, he came up with a set of interesting precepts to better manage power-robbing turbulence and general particle behaviour. His biggest trick was to improve power conversion whilst making the system quieter when engine noise is both annoying and also can cost power. These ideas were not completely new. By the end of the 60s, smart aerospace guys had already fleshed out, modeled and proofed a partial fluid/thermal view of sound. Yet outside their realm and the theatrical perfection* of a textbook, there was virtually no application for it in the canon of the internal combustion engine art. Ron was the first I know of to apply particle behaviour models to the motorcycle. Regardless of other tuning solutions, Ron's exhaust designs all had one thing in common: the final segments and exit placed the sound-absorbing materials in the region of highest particle velocity, not in the area of highest particle pressure. There are other more esoteric elements to it but the inside-out muffler is easiest to visualize. [This link shows certain aspects of an advanced muffler design. - Ed.]
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* This is an old audio term from the days when the playback and sound reinforcement arts were maturing. Theaters were big and generally of high import. Sound system installations were permanent, there was a greater percentage of smart guys in audio and healthy research, development and fabrication budgets were common. What an audio team was able to create when space constraints were generally matched to wave size; when power transfer efficiency was a priority; when a building's acoustics were fundamentally considered and the sound system didn't need to be moved; when optics were a near non-priority—that was theatrical perfection.


"The Druid VI's changes to our Griewe implementation seen within the cabinet's long chambers is a big difference over anything we did before. Its twin pi-driven chambers and their profiles both internal and external better reduce turbulence for lower noise. R&D was by trial and error but within the realm of fluid dynamics modeling, it helped us cut standing wave ratios by more than half over the Druid V and created increased opportunity for broader and deeper tuning to damp out frequencies that need a bit of handling. It resulted in less noise, better amplitude response, better time-domain accuracy, a cleaner electrical impedance curve and a slight bump in net efficiency. Where did these researched refinements come from? A pretty healthy chunk was lifted from a currently secret project and its modeling: the Zu Bubble Horn or Zu's Horny Bubble depending on day and company. Still, it doesn't say all that much about what the Zu Griewe model is. It still operates outside the tried 'n' true Thiele/Small parameter-based speaker/box models which are quite good at at predicting performance within the longer bass wavelengths. It's once we start looking at shorter wavelengths, particle behaviour and start adding diffusers, nozzles and more complex wave functions as done within the Druid VI that explanations become quite difficult.


"Zu Griewe designs can feature ports, ducts, nozzles and diffusers but usually not all at once. But they do not behave like bass-reflex ported designs, tuned pipes or horns though certainly there is overlap as they are all based on wave and power transfer functions. Griewe does not need to be a specific physical appliance or device though many of our speakers do use something called a Griewe cartridge. The main drawback to Zu Griewe designs is the complexity of modeling and precision of fabrication. And yes, I used the word 'port'. A port is any opening which enables air passage. Most though not all Zu Griewe designs employ ports but are not conventionally ported speakers which operate as tuned Helmholtz resonators. Still, within all of our current loudspeakers reactivity does modify the electrical impedance curve. This is one reason why adjusting the floor gap changes the sound and relationship with the amplifier. If budget and space allow, Zu Griewe modeling and implementation can improve traditional bass reflex designs in better or equal net efficiency while being equal in realizable SPL; superior S/NR; superior bandwidth; and physical size smaller than or equal for similar sound pressure levels with less distortion.


"In a typical ported loudspeaker, the bass reflex is a usually highly reactive system which increases sound pressure levels for a tuned octave at the expense of bandwidth elsewhere. But the appearance of ports isn't equal to bass reflex loading [the reader may recall Frank Tchang's 'breathing bores' which acted as decompression exits not ports - Ed.]. Being that most of our ports are long and skinny and function more like the transfer ports on a modern two-stroke internal combustion engine, we call them finger ports. Any reactive system impacts impedances to improve perceived bass performance. The resonant tuning draws more power from solid-state amplifiers of which the vast majority function as a voltage source. One question is, at what expense to the amp's performance, loudspeaker matching and overall playback fidelity? I hear it as forgettable tone, reduced resolution and lower realism. Technically it's increased noise, expanded group delay, distorted bass, reduced response below the tuned bandwidth and increased harmonic distortion. That said, there are some really great-sounding bass reflex designs but those which I find satisfying leverage a lot of cabinet size (large spring forces), large port areas approaching the operational area of the diaphragm and limited port length. All of it contributes to better timing and reduced noise but with radically increased cabinet complexity and cost.

"What a typical ported loudspeaker doesn't account for are broadband quality functions or adequate control of broadband low turbulence within the fluid dynamics/particle-based models. Sure, loudspeaker designers have added flared port profiles, even taking them to nozzle-level of refinement and adding laminar-enhancing devices—my contribution to the original Talon Audio loudspeaker back in 1999—but that is still far short of what goes on within the Druid."


Druid VI dominance? After the Capital Audio Fest, reader and Zu owner JL accompanied Sean to the personal system of a Zu Dominance owner in Delaware where JL had opportunity to compare the two [see left]. "At the show, the VI looked and sounded incredible. I hung out with the Zu guys afterward and got a chance to hear the Dominance. Those were pretty far out. The guy who owns them has a ton of custom Zu stuff. It was pretty special to hear and see something that was an earlier all-out assault of Zu tech and yet was eclipsed in key areas by the new Druid. To observe in person that simpler can be better made me feel good because while maybe someday I could afford to own the Druid VI, I could never afford anything like the Dominance.


"And the photos really don't do these justice. The matte white finish of the Druids was stunning. And there I've never before liked white speakers. Years ago, the whole old iPod and iMac craze made me dislike white electronics in general. And yes, the Dominance is discontinued for now. Sean wants to eventually make a new version but it's a super costly proposition. For now they are working on smaller prototypes but those won't be called Dominance but possibly Presence and Experience."
... to be continued...

Zu Audio website