This review page is supported in part by the sponsors whose ad banners are displayed below

When Sean forwarded tracking data for the Submission, he took the opportunity to comment on what I'd penned by then. Agree with all nearly in full. I too am in love with Druid V + SIT-1 with Allnic L-5000 DHT preamp but having more of the same power would be sweet. With the SIT-1 you're only getting roughly half the rated power. Into the 8Ω Definition Mk.IV you'd get about 3dB more SPL (weighted so its active sub is not included). I should also outline how I arrived at our driver design. It's not simply a rebuilt Eminence. We actually spec what they make/use/layup for us. They are the main parts and labor outside of Zu. Their contributions to our driver build factor at about 40% of its raw cost. The engineering is largely Harry Olson's going all the way back to the 1930s and his first job at RCA. The 10" frame is because that's about the size of a human head. I love working with Eminence. They are more vertically integrated than any driver manufacturer I've ever seen. Besides their own Eminence-branded products they offer roughly 20.000 other driver models for currently active OEMs. Of those, three models are specific to us. Granted the vast majority of those 20.000 parts are pro and guitar but there are a handful of us in hifi who lean on their manufacturing technologies and production efficiencies too.

The 30Ω+ magnitude of impedance fluctuations below 150Hz looks similar to the saddle response that's typical for a ported alignment. It suggests—and listening with the 8wpc Yamamoto 300B bore it out—that low-power low-current zero-feedback SETs might not be the most ideal amps to get the best from Druid V's bass despite producing plenty of loudness.

With Yamamoto A-014 (Takatsuki 300B or EML 300BXLS)

There are two other small points. Your comments about the Druid's lower presence region are spot on. This helps differentiate us from nearly everyone else. Hifi resolution heads will read what they want, tone junkies will get theirs. It's always easier to get 1–3kHz resolution from a small 3, 4 or 5-inch driver because a ¼-length 1kHz wave is right about three inches. When you build for a narrow power band, that's easy to dial in. Two, surface area is just one variable and data point in a pretty complex relationship where membrane density, density gradients, dynamic propagation velocity, dynamic behavior and phase gradients all factor along with wave-front source, wave-front propagation and observation. If we could take the efficiency from 100dB to 110dB within the same 10" frame across similar bandwidth and timing, how would that impact the primal sense audiophiles loosely ascribe to surface area?

You wrote, "...hazarding a guess, it's this particular quality I assume the Definition IV elaborates on further simply as a function of twice its air-moving cone surface. That's what this game is all about after all: getting air to move around our ears."  Yet there's more to wrap our minds around. The Def IV certainly has more presence and clarity in the presence region yet there's also more mutual interference because of the twin widebanders. At the seating position the main thing that explains the perceived and measured improvements of this bandwidth's performance is destructive interference. This was a new idea to me which I only stumbled upon through the R&D efforts we put into the Definition at the turn of this century. It's tough to talk to audiophiles about destructive interference being a good thing though it gets easier once realization sets in that anytime there's any transduction of power and signal, there's also going to be distortion. It's all about harnessing this distortion by properly managing it. This improvement through interference wasn't new but using twin full-range drivers like this was not anything I'd seen or read about. Despite a similar arrangement, it's a long way from what Joseph D'Appolito outlined for M-T-M alignments.

Again and clearly by design, the Druid's particular voicing relative to its darker heavier lower presence region—1kHz to 3kHz—is a direct and unavoidable function of a 10.3-inch driver covering this bandwidth. Because that driver avoids a low-pass filter, Zu's auxiliary tweeter can't roll in before 8kHz. This means that the region where human hearing is most sensitive remains handled by what essentially is a big woofer. That's key to Zu's house sound. It also explains why the company must use it across all models from most affordable to most exclusive. Anything else and that very recognizable very specific Zu quality would be—poof—gone. Don't see eye to eye with this choice? Look elsewhere. Nothing you could possibly do with electronics and cabling can 'operate' this signature out.

Like the Definition IV's built-in amp, the Submission's is an OEM Hypex UcD 400 V5* affair with beefy linear power supply and integrated capactive storage/voltage regulation all encased in very solid 6.3mm aluminum stock [at right is the Undertone's plate version]. Functionality includes stereo line-level inputs (from a preamp or integrated's pre-out); a mono line-level input (from a pre/pro's or home-theater receiver's 0.1 sub out); and 500Ω speaker-level inputs.

The latter clearly share their ground as indicated by the presence of just a single negative terminal. Should your main amp be of the bridged variety, it would see a short when connected. Hence the option to insert the Lundahl transformer box in such scenarios.

For adjustments there's the customary attenuator from -110dB to 0 and a variable low-pass filter across 10-110Hz. The phase control couples a 0/180° coarse adjustment to very fine adjustments. The 115/230V power mains selector wants to see a 10A/8A fuse respectively. There's also a built-in non-defeatable 12Hz/4th-order Butterworth infrasonic filter.

* I don't think there's any Ncore trickle-down in these very dense reliable packages. They are however a really excellent match up with the Eminence LAB-12 subwoofer driver.

Finally there are two controls dubbed PEQ gain dB and PEQ frequency. The former is an LF boost with max +6dB of added gain across a narrow 1/2-octave bandwidth. The latter sets the EQ corner frequency between 20-50Hz.

Whilst the Submission's main enclosure might look just like a Definition IV, its internal structure and braces are obviously optimized for dedicated subwoofer use. This includes an 'inverted' or upside-down Griewe cartridge which in this sealed alignment works differently than in the Druid V.

As used in the Submission the UcD amp gives you a very solid 400Wrms across its bandwidth. Shorting protection is integrated into the main board. Besides the casework and layout there are a few other interesting details. Power consumption when idle is very low and less than 6 watts. The power switch disconnects the transformer so there is no power consumed when switched off. The amplifier assembly is fully grounded and shielded whilst the casework is vent free. Paying attention to the assembly's thermal design, the majority of heat dissipated under power is radiated into the room via the faceplate and not into the cabinet. If you are driving it hard the faceplate will become warm to the touch but even under severe demands the power transduction efficiency is over 70%. Interconnections between filter and amp are all solderless insulation displacement connections using 3M adhesive encapsulating IDCs and the wire used for these are the same we spec and use for Mission interconnects. All power supply connections are solderless and feature premium Panduit disconnects. The Amp to speaker bulkhead pass-through and interconnection is handled via speakON 8-pole connections terminated per ZuB3 convention (same as in Definition IV). While this amplifier assembly has been five years in testing and proofing and is very robust, things can still go sideways. Learning our lesson with the nearly impossible to field service Definition I and II, the Submission amplifier is easily field replaceable and only requires the removal of 6 x #2 Philips screws and the disconnection of the backside ZuB3. The amplifier is completely rebuildable with little labor cost and no special tools (though factory service would be highly recommended).