K231

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, Denafrips Terminator+ clock-synced to Gaia reclocker, Avatar CD transport, Soundaware D100Pro SD card transport; Preamp: icOn 4Pro SE; Power amplifiers: Kinki Studio EX-B7 monos; Headamp: Kinki Studio; Phones: HifiMan Susvara; Loudspeakers: Aurai Audio Lieutenant, 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 D300Ref SD transport; DAC: Denafrips Terminator; Preamp/filter: icOn 4Pro + 4th-order/80Hz hi-low pass; Amplifier: Crayon CFA-1.2; Loudspeakers: sound|kaos Vox 3awf, Zu Submission; 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 Win7/64; USB bridge: Audiobyte Hydra X+; Headamp: COS Engineering H1; Headphones: Final D-8000; Powered speakers: Fram Audio Midi 150
Upstairs headfi/speaker system: Source: Soundaware A280 SD transport; Integrated amplifiers: Schiit Jotunheim R, Bakoon AMP-13R; Phones: Raal-Requisite SR1a; Loudspeakers: Acelec Model 1, Power delivery: Furutech GTO 2D NCF
2-channel video system: Source: Oppo BDP-105; DAC: Kinki Studio; Preamp: Vinnie Rossi L2; Power amp: Pass Labs XA-30.8; Loudspeakers: German Physiks HRS-120; Power delivery: Furutech eTP-8, Room: ~6x4m
Review component retail: $499, add $12 for extra filter cards

Sublime? I've been harping on about a sub/sat division of labor for a few moons just not in tack-on mode as proposed by REL. I prefer proper hi/lo-pass filtering. That doesn't just add bass but restricts the bandwidth of the mains, minimizes their distortion (no more big excursions from low-bass attacks) and maximizes their dynamic range (less heat on the voice coils, again from no longer seeing demanding LF). In two not multi-channel preamp practice, the necessary functionality of a high-pass filter for the mains tends to simply be amiss. If you don't have a sub with high-pass outputs or want to improve over them, you're stuck with €3K+ analog filters from JL Audio, spl and Wilson; digital filters embedded in Bel Canto, Linn and TotalDAC kit; or cheap pro-level digital xovers like Behringer's. It's why I commissioned Pál Nagy to embed a fixed 40Hz hi/lo-pass filter in my icOn 4Pro SE passive magnetic preamp. That functionality proved popular enough to soon scale up to his fully variable remote-controlled Gradient Box pure analog smart crossover.

If you're the impatient sort or a reviewer with certain assignments to handle now, there's also Mark Longley's SublimeAcoustic K231. That can be used as a 1-, 2- or 3-way filter via plug'n'play modules. I bought it with 40Hz, 60Hz and 80Hz cards all with 24dB/oct. Linkwitz-Riley attenuation. Two cards are standard, each extra one adds just $12. 2nd-order slopes are available by request and filter hinges in 10Hz increments cover 40-200Hz so nearly all conceivable applications.

The box itself sets you back $499.95, delivery from the US to Eire added $71.66 with DHL. Considering analog options elsewhere, that was Irish baby potatoes or small fry on the main land.

A bay on the belly secured by four screws accesses the filter card headers for easy swaps. Going with one not two filters, I'd only use one header. The back sports ¼" TRS-style balanced i/o (one in, three out) and matching RCA. The front runs sun-dial marked metal-film pots for the three ways—I'd only use two—plus a baffle-step compensation control for DIY speaker builders which I'd bypass. Refer to this manual for all specifics. With Grimm Audio SB1 subs in for review, I wanted to explore different bandwidths and Mark's solution now gave me the three filter frequencies I reckoned were most appropriate.

As to harping on about the subject, you may think of harps as celestral muzak pluckers but any listen to Deborah Henson-Conant adds real jive. Andreas Vollenweider's amplified instrument then corrects the record on low very powerful bass. Now we'll segue into the subject of this review: the optimizing of LF reach, control and timing over entrusting bass to the usual passive loudspeakers. But what if the passives are a bit unusual?