Country of Origin


Gradient Box

Reviewer: Srajan Ebaen
Financial interests: click here
Main system: Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz, Tidal, Sonnet Pasithea, Soundaware D300Ref SD card transport & USB bridge; Preamp: icOn 4Pro S w. hi/lo-pass filter; Power amplifiers: Kinki Studio EX-B7 mono, Enleum AMP-23R; Headamp: Kinki Studio; Phones: HifiMan Susvara; Loudspeakers: Aurai Audio Lieutenant w. sound|kaos DSUB 15 on Carbide Audio footers, Audio Physic Codex, Cube Audio Nenuphar Cables: Complete loom of Allnic Audio ZL; Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps, Furutech DPS-4.1 between wall and conditioners; Equipment rack: Artesanía Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands; Sundry accessories: Acoustic System resonators, LessLoss Firewall for loudspeakers, Furutech NCF Signal Boosters; Room: 6 x 8m with open door behind listening seat
2nd system: Source: Soundaware D100Pro SD transport clock-slaved to Denafrips Terminator +; Preamp/filter: icOn 4Pro + 4th-order/40Hz hi-low pass; Amplifier: Goldmund Job 225; Loudspeakers: sound|kaos Vox 3awf, Dynaudio S18 sub on Divine Acoustics Kepler footers; Power delivery: Furutech GTO 2D NCF; Equipment rack: Hifistay Mythology Transform X-Frame [on extended loan]; Sundry accessories: Audioquest Fog Lifters; Furutech NFC Clear Lines; Room: ~3.5 x 8m
Desktop system: Source: HP Z230 work station Win10/64; USB bridge: Singxer SU-2; Headamp: iFi Pro iDSD Signature; Headphones: Final D-8000; Powered speakers: DMAX SC5
Upstairs headfi/speaker system: Source: smsl SD-9 transport; DAC: iFi Pro iDSD Signature; Integrated amplifier: Schiit Jotunheim R; Phones: Raal-Requisite SR1a
2-channel video system: Source: Oppo BDP-105; All-in-One: Simon Audio; Loudspeakers: Zu Soul VI; Subwoofer: Zu Submission; Power delivery: Furutech eTP-8, Room: ~6x4m

Review component retail: TBA

Sub sandwich perfected? "A submarine sandwich—also known as sub, hoagie, torpedo, hero, Italian or grinder—is a cold or hot sandwich made from a cylindrical bread roll split lengthwise then filled with meats, cheeses, vegetables and condiments." We're no foodie channel. Our sub sandwich involves a subwoofer. To perfect its integration with the main speakers, it too splits, just not a bread roll but frequencies. Those to the subwoofer filter via low pass (that which lets the lows pass). Those which hit the speakers filter out bass via inverse high pass. In the multi-channel space, pre/pros include all necessary bass management facilities. They may even include finely calibrated digital delay to compensate for a sub's time alignment if it doesn't sit equidistant with the speakers; or suffers DSP latency. Now one delays the signal to the mains to insure that their sound arrives at the ear simultaneously with the sub's. After all, late bass is slow bass. Nobody should want that. In the refined 2-channel space meanwhile, our preamps don't do any of it. At best they offer dual pre-outs. Those condemn us to augmentation or 'tack-on' mode. It's when both speakers and sub see the same full-range signal. That of the sub gets cut by the sub's built-in low pass often preceded by an A/D converter. It's usually adjustable between 40-120Hz but in certain cases could span 25Hz to 200Hz.

The intrepid user attempts to set this low pass so the sub rolls in where the speakers roll out. In dim man caves, there's much crossing of fingers, hoping for miracles and sweating proper phase to avoid a suck-out at the handover and achieve a seamless patch. In the worst case, it's like vintage hippie jeans lengthened at the hem with a flowery band. Colorful such upcycled pantalones always were been never of one piece. You can hear that the bass tacks on. It's not part of the original fabric. It's not fully integrated.

A better tailor filters the speakers in a mirror-image seam. He applies identical attenuation slopes at one frequency hinge so neither sub nor speakers see full-range signal. If done in the analog domain, this avoids digital latency from heavy DSP processing. Dual-filter mode is a compound win. We gain not just lower louder bass. We reduce bass stress on the main amp. Now that can be smaller/cheaper or better because we're not chasing max power. We reduce stress on the speakers whose excursions diminish for lower distortion. That creates less heat on their lower voice coils. Their impedance doesn't rise to become more resistant and choke dynamic range. Of this, the REL concept promoting a high-level connection knows nothing. It still runs unfiltered speakers. There nothing improves. It's just stereo 2.1. It doesn't convert a 2-way into a proper 3-way with active bass¹. Remember that in 2-ways, bass and midrange share one cone. It meets a 1" dome at usually ~2kHz. Relieving the bigger driver of low bass runs it at lower distortion with better dynamics. These gains extend across its entire bandwidth up to the tweeter. It's not just a marginal win. It goes well beyond more bass. Working smarter not harder, the work which the monitor's mid/woofers perform increases in quality. Who doesn't want better employees?

¹ Obviously if we start with a 3-way, we now convert it into a 4-way and so forth. Once speakers hit -3dB at 45Hz or lower, it becomes harder and harder to successfully tack on a subwoofer without unwanted overlap. The most common low-pass filter built into a subwoofer is a 4th-order Linkwitz-Riley. That defines by its -6dB point. If the lowest settable value is 40Hz or 50Hz, for such speakers that's already too high. 

Prototype motherboard without display.

If you now have an inverted When Harry met Sally moment—"I have what he's having"—you'll feel buggered. How to manage an active high pass when your purist high-end preamp plays snobbist to forget about subwoofers? We return to the generic sandwich popularized in 1762's England by one John Montagu, 4th Earl of Sandwich. Legend has it that our fellow suffered a substantial gambling problem to spend hours on end at the card table. When he began to order two slices of bread with a central slab of beef to munch on while gambling, his companions began asking for what Sandwich was having. The rest is his-tory. More than three centuries later, subwoofer fans not wishing to gamble on augmentation mode can once again count on Great Britain to lead the way. Here Hungarian expat Pál Nagy of icOn 4Pro fame designed more than mere condiment for our perfect sub sandwich. Somewhere in Manchester, he put together the whole stuffed shebang. Now you'll wonder what our audiophile version is of a hoagie's wet fill of roast beef, pickled onions, melted cheese and relish.