On gaps. "Yes, a user should experiment with placement, toe-in, cant and even height. Gap height is less sensitive with Soul VI than our previous designs and also varies with amps. Impedance plots are different again for different gaps. An owner's manual is currently being proofed. For a starter gap, the distance between hard floor and bottom of Soul VI is 3/8" [9.5mm]. Less, say ¼" [6.3mm], tightens up the bass a bit and even moves bandwidth down but at the expense of a touch of kick drum thwack. More gap like ½" [13mm] gives a bit looser bass. This all varies with amps, room, preference and program selection. When you cant back, the gap change is the average like a 1" [25mm] gap in the front and essentially none in the rear. Now Soul VI sees a ½" [13mm] gap. Some find that placing Soul VI on some form of plinth is a nice way to tailor the sound like butcher block, stone or a ceramic tile stack. This obviously changes the distance the driver sits from the floor and makes a sonic difference as it should. It also changes the interface of speaker and floor. Sometimes you want to couple to the floor with spikes, sometimes you want the speaker to float above it as decoupled as possible. There are many variables. I keep sheets and chunks of cork, hard rubber, soft rubber, aluminum and copper on hand for experiment as every floor and room seems to have its own needs, listeners too.
Nominal vs. actual impedance and the impact the size of the floor gap had on the saddle-response peaks of the MkII precursor.
On sonic references. "The short answer is yes, my sonic sensitivities today are very near those I remember as a youth. Getting there has been an interesting journey though. I certainly have favorite sounds, songs and methods of testing but I really try and turn off my brain when I listen, at least the frontal lobes. I like the primitive brain to take the lead and when things are more right than wrong, add dance to the response. I think learning about what each of us key into or choose to ignore is fascinating. What does it for me is near to what sparked my brain as a kid. I love being aware of feeling immersed. Music choice is a whole different set of reasons, preferences and moods. Specific to home audio playback, I do my best to recreate the dynamic realism of the experience. That's mostly the world around me with my ears and brain switched on. As heretical as it might sound, I really don't think that anyone needs to attend live events to be sufficiently tuned in to know what they like and hunt for. Lots of live music certainly helps to expand our experience and it did for me – classical big full-horn systems built out for tens of thousands of people for events surrounding the Unlimited Hydro races but also boats with thousands of horsepower, Unlimited and K-class boats up close and personal, hearing the sounds props made ripping water into massive plumes, to say nothing of those engines. Then there are all the sounds which are the Intermountain West or the isolation and solitude of solo winter backpacking.
"I love sound, how it feels, how I have to actively swim in it. The art that is sometimes brilliant in music and poetry is a whole different thing but just as magical. Combining the sounds of song, music and dance with nature is bliss. I think nearly all of us lean in this direction even if only subconsciously. What we might all do still better is realize that whatever the experience, it's in the past and was unique in our mind even if often there are big overlaps of shared experience. For me it's dynamic realism when sounds have seemingly infinite power and even the subtle and nuanced sounds effortless, full of grace and ease and slyly winks of its power. Impressions of sound and why they move us are really hard to express. I think Pete Townsend did a good job with these five lines:
One note sounds like a light ray
One note sounds like a new day
One note holds all the others
Millions of colors
So one note.
"As a kid I studied horns and was obsessed with 'theatrical perfection' and infinite impulse response. Then I spent 20 years in pursuit of flat magnitude response, keeping the time domain loosely in check. Since about 1995 the prime mover has been dynamic range, a kind of return to my impulsive roots but now with a clear view of bandwidth centered on the human voice. With huge dynamics in place, you can work and manage secondary aspects like bandwidth and linearity, even time. If you don't start with big dynamic potential, you will never have it regardless of how much you steal from another aspect. I love the hard hitting, deep and powerful. It's essential for a lot of music I love but I'm not a bass head. I love rich and vibrant guitar tone from all guitars but only players with tone and style. But I'm not a tone head. I love glitch, click, pop, static and feedback without end but I'm not a noise freak. I sadly spend way too much time listening in my own head as I escape the sounds of production, politics and the drone of forgettable repetition. We all need more time to listen, hear, feel, search for sincerity, the new and brilliant and maybe even meaning and our own unique voice. And I'm trying to contribute a bit of color where I can and some contrast.
"One last thought, we're now pushing minimum burn-in from 2 weeks to 3, maybe even 4. Generally I don't listen to anything without a month of 24/7 burn. The logistics/exposure of increased burn-in is complicated but these do need it. The feedback from a few dozen customers has been very positive but a few, including a few of us here at the shop, are finding that two weeks aren't enough to put the cone into its target stiffness-to-damping profile. Asking customers to complete mechanical burn-in on their end is really not acceptable. More time is also really good for the Jupiter cap and the teflon in the cable assembly. So I think we should cook your set for four weeks, too."
On Zu/Griewe loading, "it's a multi-octave impedance-modifying model. The original concept is Ron Griewe's, a motorcycle legend. A bass reflex speaker uses a simple Helmholtz resonator to augment lower frequencies. A Helmholtz resonator consists of a rigid-walled cavity with a neck (port) of a specific area and length. The fluid/air moves as a unit within the port tube to provide the mass element and the acoustic pressure within the loudspeaker box provides the stiffness or spring element. The resistive element is provided by the opening that radiates the simple source sound. Zu/Griewe tech is fundamentally a waveguide of expanding acoustic cross section terminated and driven at one end. Propagation within the loudspeaker is mostly planar and standing waves don't get as stimulated. The basic idea is acoustic matching of the high Ω of the cone to the low acoustic Ω of the room; the reduction of non-planar propagation in more than just a single octave; and the reduction of internal standing waves."
Disclaimer: many Zu owners love tubes. I no longer do especially in power amps so divested myself of all such specimens. My review will thus focus exclusively on transistors, from FirstWatt's SIT-1/SIT-3 amps to Enleum's AMP-23R to Crayon's CFA-1.2 to Kinki Studio's EX-B7 so from 10wpc to 250wpc with a few pit stops in-between. If you were hoping for 300B or 845 triodes, you've come to the wrong place. Likewise for grunge, glitch, metal, screechy overdrive and club SPL. Those I don't do either. Given the intro pages, we expect Soul VI to be very strong in these areas. How would it fare with more artsy fare, even classical chamber music? Can a speaker with personality—and Zu speakers do have theirs—do justice to all kinds of music? Or does personality play favorites instead?
For the 'B' side of my review, here's Steve Guttenberg's take which also includes Soul Supreme comparative comments from a long-time owner. For an inclusion in a very short list of 'Best of 2021' finds, there's John Darko's video and his parallel mention/reco of KEF's KC62 micro sub should we wish to bolt onto this speaker 20-40Hz reach. Interestingly, there's also a surprising comment on the Soul's detail retrieval relative to his pair of Wilson Audio Tune Tot.
To kick off my own comments, we'll head upstairs. There the Soul VI would see optional companionship of Dynaudio's dual 9.5" sub. Traffic cop for stereo 2.1 would be a custom 40Hz/-6dB 4th-order Linkwitz-Riley hi-lo-pass filter. That's executed purely analog in an external box following my icOn 4Pro autoformer passive. Without sub, the latter would run straight into a Job 225. That happened to hog the amp shelf just then. Here the digital front end is a Soundaware D100Pro SD card transport feeding AES/EBU into a Denafrips Terminator DAC. On international border-crossing hustle, my pair had departed Zu's Ogden/Utah FedEx facility at 18:30 on a Thursday, hit Memphis and Indianapolis then Paris and the UK's Stansted to arrive in Dublin with a 'ready for clearance' notice by 12:07 three days later so Sunday. Had that and the next day been working days, door-to-door delivery would have cut 4-week break-in down to 4 days. That reflected higher conversion efficiency in the shipping domain.