"I done wrestled with an alligator, I done tussled with a whale, handcuffed lightning, thrown thunder in jail; only last week I murdered a rock, injured a stone, hospitalized a brick. I'm so mean, I make medicine sick."  - Muhammad Ali.
If you're a winner, some attitude is expected. If you're a loser, you just seem full of yourself and a sorry braggart. Here's what backs up Zu's attitude. Retro squared, future inside. First the retro. It weighs in on five fronts: paper membrane; midrange diameter; hard suspension; whizzer; and a cab wider than deep. In marketing, newer is always better. Paper diaphragms, yawn, are so last century. 21st century is beryllium, diamond, magnesium, carbon fibre; hard hi-tech membranes all. More marks of modernity go to narrow baffles, predominantly for cosmetic reasons. That means drivers of smaller Ø. Woofers either parallel up until their joint surface equals the desired displacement; or go bigger but to the side/s; or fire down inside the box. This coincides with the fact that at present, a diamond midrange of 5 inches might be achievable but not one at 10" like a Zu. One does see 10" pure bass units in aluminium but once diametres exceed 12 inches, the material of choice remains paper. Meanwhile metallic widebanders à la Mark Audio or Jordan tend to not exceed six inches. All the bigger widebanders are paper or wood veneer. That should make one pause and ask why. For today and simply to recapitulate, the Druid V is a retro champ because it uses paper up to 7kHz; runs a woofer-sized driver as a midrange; uses a hard-hung cloth not softly sprung rubber or foam suspension; adds a whizzer cone; and turns our narrow-front/greater-depth recipe around the lazy Susan by 90°. On most counts, specific models from Audio Note UK, DeVore Fidelity and Heco Direkt are partners in legacy crime. And of course the refrigerator-sized dual-concentric Tannoys so popular in Japan are the genre's still kicking grand daddy in many ways.

The not Intel but future inside thing comes from what Zu do to their paper. As a small underground contractor, fellow big-widebander fanatic Robert Bastanis customizes drivers beyond his own brand for Ichos Schallwandler and Zugspitz. He applies strategic damping dots to his cellulose membranes, then oven bakes them to cure four consecutive layers of different lacquers. Trenner & Friedl impregnate theirs with a "six-layered finish of Italian balsamic oil lacquer". Zu use nanotech compounds from cutting-edge materials science. That dopes their papery past in future fumes*. The rationale for why all of these makers monkey with their drivers in the first place is the same. It's to rigidify their cellulose cones without adding mass; then to mechanically iron out trouble spots which might appear when they ask big drivers to transcend pure bass duties and cover the entire vocal band up into the lower treble. Multi-ways exploit specialized drive units for limited frequency bands. Now it becomes a crossover's job to patch up division into unity. If needed, notch filters cut out narrow response irregularities. By self-imposed mandate, purist widebander guys may interfere only in the mechanical domain. The what and the how of it are closely guarded secrets like momma's hot sauce recipe.

Nanotech-engineered liquid solid ceramics, fibers and synthetic resins performed as promised for our paint finishes. It was during this process that we got to experiment with applications for loudspeaker cones and diaphragms. While we had extensively tested coatings, microspheres and binders on driver cones over the years, this new nano material presented a novel set of attributes and opportunities. Nanotech for cone materials, layups, binder additives and formulae, tubes, spheres, coatings, infusions etc. make for an exciting time to be a paper driver. Then we got sidetracked from the liquid solids and invested time in a whole new range of satellite-grade graphite matrixes. 
After a few years of on/off experiments with these exotic layups, we returned to nano materials and liquid solids to start treating the paper with various micro materials for even more vibrant and detailed tone. Today we impregnate the paper pulp post pressing with a liquid solid matrix utilizing several nano-processed materials. Some key components and compounds include nanosphere ceramic balloons, melamine, synthetic epoxy A/B, cristobalite, amorphous fumed silica and aircraft dope. Our apologies to DIYers, we cannot sell them this material due to the isocyanates. This can only be used in the industry and requires powered air-purifying respirators.

The widebander version of the original Druid with its then pointy phase plug, original tweeter below.
More retro versus contemporary shenanigans occur on bandwidth/excursion. With the right loading, many of today's premium 6-7" mid/woofers are capable of ~30Hz response. Vintage 10-12" mid/woofers might have barely made it to 40Hz, more commonly to just 55-60Hz. Modern drivers with underhung motors and big soft rubber roll surrounds are geared for large excursions. Zu's hard-hung driver will barely seem to move even during a big bass drum's lightning strike.

Add limited cubic air volume behind the driver. It should be obvious that the Druid V isn't groomed for subwoofer territory despite that diameter. On pure reach, a modern standmount could go lower in fact. With the Undertone and Submission as dedicated active subs in the same portfolio, that's only sensible. What drivers like Zu's are groomed for is meatiness and punch. A big midrange does something for tone density and chunkiness which 4" "ultra-tech" membranes in ceramic or diamond don't.

This ties up our chapter on attitude. It's been Zu's contention from the very beginning. Modern sound has lost the plot by prioritizing micro detail and precision over real substance and shove. Their forward-into-the-past recipe does things the way they used to be done. But because even Zu live in 2016, they have, over the years, spit polished their recipe to maximize what resolution and micro detail may be mined from their unwavering foundation of retro values. As owner JL confirmed, the Druid V's quieter box goes beyond its earlier incarnations including the Soul Supreme as a more extreme expression of purely mechanical optimization.

In Albedo Audio's Aptica, I own a premium example of ceramic drivers done right. It's my resident reminder of modern resolution. How far up that imaginary ladder could the Druid V push itself by comparison; and where/how would it diverge by adding qualities the other simply has to go lighter on or miss altogether to retain its particular focus?

Before we go there, no Druid V comments would be complete without mention of the pyramid. Did the druids build the pyramids? Wasn't that the Egyptians? To actually see what's inside today's Druid box, click on the image of the Essence foam cartridge. That'll bring up a drawing of the inner V. From Stereophile's Soul Supreme review, we learn that "....though Zu takes pains to explain that the Soul Supreme's downward-firing, finger-shaped ports do not behave as they would in a typical reflex-loaded speaker, the impedance-magnitude trace does have the double-humped shape in the bass that indicates some sort of reflex design. The saddle in the trace centered on 45Hz implies that this is the ports' tuning frequency."

Over the years, Zu have refined what they call Griewe loading. This is named after Ron Griewe, late Cycle World editor and contributing engineer to numerous motorcycle firms on exhaust tech. Without radiation resistance from a partially sealed bottom facing your floor at a predetermined distance, most Zu speakers would be open pipes, with the driver/s on the upper sealed end and an open hole at the floor for no bass to speak of. But they're not sealed either. There is some air exchange, albeit without the tuned pipes of conventional ports. The Druid V's massive billet plinth terminates the cab to the floor and not only sports lateral 'air escape' grooves but spike inserts to create an actual gap above the floor. The more you screw out the spikes (or set them on spike shoes to increase height), the taller the gap. This lowers the radiation resistance seen by the widebander's back to alter its tuning. Where the square footprint models like the Soul include a foam pyramid to take up most the interior space, the V's "half square" cross section and internal liners leave no room for a full cartridge (the insert below shows inner-wall treatment). But something working in similar fashion is still in there. At what exact intersection of possibilities—port, rear horn, transmission line—the Druid V operates is simply a bit opaque. Suffice to say that a variable floor gap affords the user some fine tuning; and that according to John Atkinson's measurements of at least the related Soul Supreme, this tuning behaves not unlike ports in the saddle shape of the impedance curve. And those steep changes of impedance magnitude might explain why finding the perfectly matching Druid amp isn't as basic as saying "make it a SET and all will be well". Hence my review's focus on heavy amp swapping to report on various results.

To wrap up the mystery of the pyramids, the Aptica speaker too is an open downward narrowing pipe of sorts, albeit one modeled as a transmission line which adds two integral Helmholtz resonators to attenuate its primary organ pipe resonances. And our Swiss soundkaos Wave 40 widebanders sport a 'scoop' loading which combines certain attributes of ports and short rear horns. In short, any number of designers operate between the lines as it were; and most who use widebanders mate them to some form of rear horn to augment LF output. Because horns expand but nothing in the Druid V's cab does, it's not a horn. In fact, the Soul's version of the pyramid cartridge creates clearly narrowing air space toward the exit. That and the fact that foam isn't a solid but acoustically semi transparent though also absorptive probably makes it closer to a quasi transmission line. How all of it applies to the Druid is far from crystal but in this 5th incarnation, we know that much thought has gone into how best to manipulate internal air flow and pressurization on the membrane's back side. Anyone who needs to know more must buy a pair, saw it open and then get busy modeling dimensions, geometry and materials in Comsol. We give up and let our ears be the judge.

More from Sean Casey. "Rock'n'Roll loudspeakers these are. That's pretty close to what you actually want for big orchestral stuff, be it Gustav Mahler, Richard Wagner (yesteryear's German Krautrock) or current Krautrock, metal, doom, noise, dance in all of its forms, deep ambient, found sounds, glitch and even "robotic" music as you've been known to call some soulless and occasionally interesting programmed music. Druid is better than Soul Supreme for nine out of ten okay with the fact that size and height matter. Those who say otherwise can and should consider the various reasons why expressions to the contrary exist. Size of room sure comes into play but with the Druid, mostly in Manhattan and Tokyo. They really aren't that big, they just have a very healthy dose of ego. A word on wood as that seems to be a theme; and drivers as the rapidly vibrating things they are - nothing save smart carbon-based composites have the combination of very high strength to weight and the fatigue properties of wood which is the only stuff that can really best it. Paper cones work, paper and nano-level augmentation work even better. Power transfer is a core ingredient of the magic sauce. Cone motion is a highly visible metric of inefficiency and also a measure of distortion. You don't want your woofers moving when you are playing back Live at Leads at concert level (oh wait, hifi speakers can't do that—not well anyway—but they should if you like more than simple and soft). The perfect loudspeaker would have nearly 100% power transduction: one electrical watt in, one acoustic watt out. And your woofer, you wouldn't see it move even with Keith Moon and John Bonham inspired live-level replay of massively large bass drums being beaten into submission."