April
2022

Country of Origin

Israel

Duet15 Prelude

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 D30Ref 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 +; DAC: Kinki Studio; Preamp/filter: icOn 4Pro + 4th-order/40Hz hi-low pass; Amplifier: Crayon CFA-1.2; Loudspeakers: sound|kaos Vox 3awf, Dynaudio S18 sub; 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: Audiobyte Hydra X+; Headamp: COS Engineering H1; Headphones: Final D-8000; Powered speakers: Fram Audio Midi 120
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: German Physiks HRS-120; Subwoofer: Zu Submission; Power delivery: Furutech eTP-8, Room: ~6x4m

Review component retail in EU: 4'153.10/pr to 6'533.10 contingent on TangBand or Voxativ driver

Ripol conversion therapy.
With Martin Gateley's sound|kaos DSUB 15, I'd undergone it and changed irrevocably. Inspired by Raal-Requisite's SR1a floating open-baffle ribbon headphones, I'd wanted equivalent speaker performance. That meant freedom from box talk, from room reactivity and its temporal blur caused by 360° reflective bass arriving late. Hifi lingo calls that room gain. Just like lumen gain from light reflecting in mirrors, room gain amplifies speaker output, albeit just in the long bass frequencies. While speaker designers can account for this extra output in the frequency response, they can't do anything about its textural discontinuity. That inserts itself between higher frequencies which arrive at our ears without or just with minimal reflections; and low frequencies which play room snookers in all directions.

There's no light switch to turn off room gain and remove its walls, floor and ceiling. Hence the vast listening majority has no actual means to identify its effect other than notice boom notes or zones caused by riding a room mode. They do recognize how the room causes spotty issues but otherwise remain oblivious to its wholesale smearing in the time domain. So fat ringy bass is endemic to all box speakers. Don't think so? No fish fully appreciates he's in water until he walks on dry land. How many millions of years of evolution will that take?

As it turns out, there is an off/off switch for room gain. One needs a dipole/Ripol/cardioid bass system which creates more directional bass from lateral even rear cancellation. In our main system, I run the big Ripol sub off a -6dB/80Hz 4th-order Linkwith-Riley analog filter. The mains see a mirror-imaged high pass. The sub's primary purpose is not extra bass. Our main speakers are -3dB @ 33Hz. They don't miss much. For full output to 20Hz, a 40Hz sub transition would suffice. But the Ripol's primary purpose is to bypass room gain in the time domain. Like a dipole, it creates cancellation on its sides. That attenuates the side walls as reflective surfaces. Over a dipole it then adds more attenuation of the front wall. That's why I've chosen my 80Hz transition. It cleans up time smear across the bottom two octaves. More makes merrier because those frequencies no longer behave omni. They've grown far more directional. Swapping between full-range speaker mode and hi/lo-pass mode is the otherwise elusive on/off room-gain switch. With it the fattening and blurring of omni bass is outed at once. Applauding ubiquitous box bass should be impossible thereafter. You can't unhear its effects.

Voilà, my pre(r)amble for today's assignment.

Thinking readers already made the connection. If Ripol as a specialized form of dipole bass is so special, why not make the remainder of the bandwidth radiate likewise? Full-range planarmagnetic and e-stat listeners already have done so. Ditto owners of dynamic open baffles from Diesis, Emerald Physics, Kyron, sound|kaos and Spatial. Now we add the Pure Audio Project brand to their roster. It debuted at High End Munich's 2013 Newcomer's exhibit. Owner Ze'ev Schlik holds a BSc in Electrical Science, is a hobbyist piano player and owns a small indie music label. He also ran a startup which enabled legal music downloads over cellular networks without DRM which had him work with a vast multitude of music labels. The company name's 'project' points at its modular concept whereby a given model uses a specific frame and baffle then provides options for different drivers and xover components. When DIYers contribute successful options like Leon Huijgen did with a series crossover for the Trio15, they are made available formally. For shipping each speaker disassembles. The recipient puts it back together with a hex key and screwdrivers.

8-inch Tang Band driver option.

Today is about their smallest, a 15-inch two-way with a choice of Tang Band W8-1808 or Voxativ AC-1.6 widebanders. Matte white, green, red, blue or black are the standard colors. 3-layer natural or caramelized bamboo adds €464.10. Custom matte colors add €345.10. Grills add €142.80. Shipping for EU customers is from Germany. When I contacted Ze'ev about a review opportunity, "6moons was one of the first magazines who covered our speakers at a Toronto show back in 2014. That was a serious kick forward for us. We'll be happy to supply you the Duet15 Prelude with Voxativ drivers. Actually, your timing is good as we have a demo set in the EU. There are two points I must highlight.

Custom 15" Eminence-sourced woofer whose suspension components of surround and spider are optimized for the loss of restorative force from compressed air trapped inside a box.

1/ the Prelude mentioned are green. You can see images on our web pages. Hope this works for you. If not, what finish would you like to have for the review?
2) There are a few shipping damages and the packaging is not in great shape. I'll try to get some photos. In case these blemishes will irritate, we'd be happy to ship to you the parts that need replacing. Regarding subs, the vast majority of our customers do not use them and those who do set them to 45Hz and lower mainly for home theatre. Like all our models, the Prelude are designed to perform to full satisfaction without subs."