November
2019

Country of Origin

Italy

Aura

Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz Hifi, Tidal Hifi, COS Engineering D1, Denafrips Terminator, Soundaware D300Ref as USB bridge/SD transport, Jay's Audio CDT2 MkII & DAC2-SE
Preamplifier: Vinnie Rossi L2 Signature Preamplifier, Nagra Classic, Wyred4Sound STP-SE Stage II, COS Engineering D1, Vinnie Rossi LIO (AVT module)
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1 monos, SIT3. F5, F6, F7; Goldmund/Job 225; Wyred4Sound mINT; Nord Acoustics NC500 monos; LinnenberG Audio Liszt monos, Bakoon AMP-13R
Loudspeakers: Audio Physic Codex; Cube Audio Nenuphar; Kroma Audio Mimí; EnigmAcoustics M1; Albedo Audio Aptica; EnigmAcoustics Mythology 1; Boenicke Audio W5se; Zu Audio Druid V, VI & Submission; German Physiks HRS-120; Eversound Essence; Fram Midi 150 & 120; Acelec Model One
Cables: Complete loom of Allnic Audio ZL 3000; Zu Event; KingRex uArt double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo; Ocellia OCC Silver
Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps/sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands
Sundry accessories: Acoustic System resonators
Room: 4 x 6m with high gabled beam ceiling opening into 4 x 8m kitchen and 5 x 8m living room, hence no wall behind the listening chairs
Review component retail: €23'000/pr

NSB. Hifi has its share of acronyms. NFB abbreviates negative feedback. NOS stands for either new-old stock or non-oversampling. The former applies itself mostly to vacuum tubes but could equally pin to unused out-of-production parts like transistors or capacitors. No oversampling refers to D/A converters. To coin a third three-letter creature, let's have NSB mean no stupid boxes. It arrives us at open baffles which mount drive units to open-backed planks. Brands promoting them include Decware, Emerald Physic, Kyron, sound|kaos, Spatial and today's Diesis. In one fell stroke, NSB eliminates time-delayed reflections through driver diaphragms; internal resonances aka box talk; heroic attempts to absorb/damp/kill half the generated acoustic energy inside an enclosure; plus the rising costs of making ever larger heavier boxes ever more inert whilst finishing them off to luxury standards in shiny lacquers, leather, veneer or anodized aluminium.

Free lunch is mostly a myth so open baffles extract their own pay. Driver front/rear waves are free to wrap around the baffle edges, have in-phase/counter-phase signal meet and cancel out. This creates far fewer sidewall reflections and becomes a major bonus of integral room treatment. It also means far less efficient conversion of raw woofer diameter to bass power and extension. Where a compact ported monitor might do a pert 35Hz from a top-quality modern 5½" mid/woofer whilst giving up much sensitivity in trade, an open baffle with dual 10-inchers could peter out at 55Hz. To compete on LF bandwidth, dipole woofers routinely double up and quickly grow to 15" even 18" across. Wherever narrow means chic, broadly baffled speakers appear more agricultural. Dipoles also eliminate the usual underwear which hides from our view hookup wiring, driver magnets and filter parts. Their private bits are on open display like a sky-clad Mahavira follower unless an acoustically transparent rear grill conceals them.

Finally, the shove, crack and pop of familiar sealed and ported bass doesn't fully translate to open-baffle bass. Its woofers aren't back-loaded by air that's trapped or at least compressed inside a box. They see the entirety of your room's volume. Hence dipole drivers compensate for their weaker back loading with stiffer suspensions. From all that we expect dipoles to not just look different than box speakers but to sound different and to behave different within our own four walls. We expect far more air displacement from seriously increased cone surface, so dynamic advantages. Like omnis, dipole radiation well into the presence region predicts richer tone from deliberately playing the room's ambient field. What exactly absence of box effects sounds like remains an open-backed question to all who've only ever heard box speakers. For that aspect, they have zero precedent.

The Diesis Audio Aura is the company's next offer beyond their entry-level version. So it scales up the previously reviewed €16'900/pr Ludos by growing its bottom woofer below 200Hz to 12". The upper unit meeting the compression tweeter at 1'800Hz remains at 10". It runs wide open at the bottom. That eliminates a high-pass filter to work as a mid/woofer. Such geometry is usually referred to as a 2.5-way. The spherical tweeter horn of Ludos becomes an exponential sort for Aura, with a rectangular mouth in fiberglass/ABS. Despite combining the frontal radiation surface of a 15.6" single woofer, out-of-phase cancellation renders bandwidth just 42Hz to 23'000Hz ±3dB. On raw energy, dipole radiation equals that of a box-loaded 22" woofer. That's vastly more air motion than our 6.5" ported Kroma Audio Mimí of the same bass extension displace. For depth mining beyond Aura, Diesis offer their dipole Bonham Tribute, a 21-inch circular passive subwoofer whose outboard crossover features an active low-pass filter adjustable from 25Hz ro 55Hz in 5Hz increments.

System efficiency for Aura is 93dB/2.83V, nominal impedance 6Ω. The baffle material beneath the thick wood or white Corian dress plates is Clad58, a composite of marble and cement particles suspended in resin. The dress plates and horns are interchangeable. This allows for after-sale changes to live through decor alterations. Aura measures 30 x 41 x 114 WxDxH, weighs 47kg and ships in a wooden crate, one per unit. The rear baffle of stretched cloth over a metal frame removes easily. This allows access to the crossover at the bottom where one capacitor mounted to a terminal strip can be easy swapped for two other values to adjust the tonal balance to room and taste. Incidentally, the Diesis portfolio goes beyond loudspeakers with the models Neptune and Evento 20-11. The former is an ambitious network player with display, the latter a hybrid 105wpc integrated with E88CC preamp stage and optional phono or DAC card. It's thus possible to assemble a nearly complete Diesis Audio system.

 … to be continued…