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Reviewer: Srajan Ebaen
Source: Zanden Audio Model 2000P/5000S; Raysonic CD168; Ancient Audio Lektor Prime; Abbingdon Music Research AM-77 [on loan]
Preamp/Integrated: ModWright SWL 9.0SE; ModWright LS-36.5; Music First Audio Passive Magnetic; Bel Canto Design PRe3; Wyetech Labs Jade; Supratek Cabernet Dual; Melody HiFi I2A3; Eastern Electric M520; Yamamoto HA-02; JAS Audio Bravo 2.3 [on review]; Trafomatic Audio Experience One [on loan]; Red Wine Audio Signature 30.2 [on loan]

Amp: 2 x Audiosector Patek SE; 2 x FirstWatt F4; Yamamoto A-08S; Bel Canto e.One S300; Fi 2A3 monos
Headphones: AKG K-1000 w. hardwired Stefan AudioArt harness; audio-technica W-1000
Speakers: Zu Cable Definition Pro in custom lacquer; Mark & Daniel Ruby and Maximus-Monitor with Omni-Harmonizer; WLM Grand Viola MkII Monitor with Duo 12 passive subwoofer, Duo amp and Sys VI active crossover; DeVore Fidelity Nines; Rethm Saadhana

Cables: Crystal Cable Ultra loom, Crystal Cable Reference power cords; Zanden Audio proprietary I²S cable; Zu Cable Varial, Gede, Libtech and Ibis; Stealth Audio Cable Indra, MetaCarbon & NanoFiber [on loan]; SilverFi interconnects; double cryo'd Acrolink with Furutech UK plug between wall and transformer
Stands: 2 x Grand Prix Audio Monaco Modular 4-tier
Powerline conditioning: 2 x Walker Audio Velocitor S fed from custom AudioSector 1.5KV Plitron step-down transformer with balanced power output option; Furutech RTP-6 on 240V line
Sundry accessories: GPA Formula Carbon/Kevlar shelf for transport; GPA Apex footers underneath stand, DAC and amp; Walker Audio Extreme SST on all connections; Walker Audio Vivid CD cleaner; Walker Audio Reference HDLs; Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; Acoustic System Acoustic Resonators
Room size: 16' w x 21' d x 9' h in short-wall setup, with openly adjoining 15' x 35' living room

Review Component Retail: €11,700/pr

Gdańsk -- or Danzig by its German name -- is Poland's sixth-largest city, principal seaport where the Motława River meets the Baltic Sea and, as Wikipedia calls it, "a conurbation with the spa town of Sopot, the city of Gdynia and suburban communities, which together form a metropolitan area called "greater Gdańsk" and the Tricity (Trójmiasto) with a population of over a million people... the city is famous worldwide as the birthplace of the Solidarity movement which, under the leadership of Lech Wałęsa, played a major role in bringing an end to communist rule in Poland."

Gdańsk also is home to Acuhorn whose upgraded Rosso Superiore 175 -- the figure equates to the centimeters of its profile -- seems keen on playing a role in bringing an end to certain assumptions about single-driver widebander speakers. This is partly tongue in cheek. The 175 uses two back-to-back widebanders after all. But the - um, other tongue is out of the cheek because Acuhorn relies not on Ciares, Jordans, Lowthers, PHYs, Supravoxes or Visatons but their very own clean-sheet driver. We've thus got a back-loaded 'dipole' fullranger with never-seen-before drive units, luxurious Siltech G6 silver/gold wiring and Polish origins. Never say never or else Bond, James Bond is your uncle.

Actually, the name is Unterschütz, Alicja Unterschütz. For years I'd been getting her e-mail press releases about Acuhorn's goings-on. So when the phone rang in Cyprus one late December afternoon and a lady announced herself as calling from Acuhorn, I said "hello Alicja" in my purriest of voices. She humored me with a giggle, then was all business about Acuhorn's new speaker models revised for 2007. The big thing was the latest generation TSR200 double Neodymium driver, giving today's four-chamber'd speaker model a system sensitivity of 99dB. Hello 45 triodes. Hello cheap but great amps. Trafomatic's 2A3-powered The Experience One integrated perhaps, nicknamed Theo in Cyprus? At least so I dreamed - prior to appreciating the likely consequences of the impedance plot subsequently supplied.

Little of newsworthiness tends to occur in the niche sector of high-eff speakers without adding acoustic gain from the spherical, hyper exponential, Tractrix or related frontal wave guides called horns. To approach 100dB/1w/1m with a nude driver is a different kettle of fish. By mentioning her new transducer, Alicja sure knew how to get my attention. This driver is built up between two anodized aluminum plates of 1.6kg mass that are an integral part of the structure in lieu of the traditional basket. A high-density high BL parameter* Neodymium motor is said to exhibit minimal losses. This focuses the magnetic field into a 0.9mm air gap** for maximum flux density and high voltage sensitivity and drives a 4-gram pure paper membrane with whizzer cone through microscopically thin 180 micron voice coil wire in the review model (150 microns in the 155 top model).

Beyond enhanced stage depth from near omni dispersion and the doubling of cone surface particularly welcome in the bass, the back-to-back mounting of drivers, magnet to magnet, can also invoke the principle of cancellation of equal but opposing forces. Horizontally opposed identical drivers fed with identical signal will, just like BMW's horizontally opposed V-Twin Boxer engine, transfer the least amount of vibration to the enclosure. This benefits signal clarity especially in the micro range of dynamics and details. Alas, it certainly relies on
in-phase bipolar dispersion for the 'equal but opposed' bit. As it turns out, Acuhorn uses the term 'dipole' to designate their use of horizontally opposed drivers, not to differentiate between their relative polarity. The 175 is connected in phase, thus a bipole. The top model Grand Biancore 155 is an anti-phase dipole just like traditional panel speakers, i.e. electrostatics, planar magnetics and open-baffle dynamics (unless their rear radiation is deliberately blocked and absorbed). All full-range dipoles fight out-of-phase low-frequency cancellation where radiation turns 4pi. Not building open-baffle panel speakers, Acuhorn isn't forced to contend with dipole acoustic cancellation effects. With the 175, they
embrace the two freebies of mechanical vibration attenuation and bass gain. With the 155, they deliberately reject them. Regardless, dipole and bipole radiation in a commercial full-range widebander is arguably a first in the market.


* BL factor (drive factor), given in Tm (tesla metres), describes the strength of the motor structure applied to the voice coil. A high drive factor is a precondition for high sensitivity. It also damps the driver's self-resonance. If the BL factor is too high, bass reproduction is compromised. For context, Beyma's 98dB 12KX runs 14.5 BL to a dual-concentric 12-er. A superior but more traditional 6-incher like Audio Technology's SD Flexunit runs a BL of 7.35. Aurasound's 1808 monster 18-incher explores the outer force factor limits, achieving 98dB with a gargantuan BL rating of 24.5.

** The voice coil moves within the air gap and provides the required magnetic field. The air gap should be as tight as possible to increase magnetic induction and efficiency. The production requirements of smaller air gaps become more demanding because of the closer tolerances involved. Lowthers use a 1mm air gap width. At 0.9mm, Acuhorn's is just a tad narrower still.

Looking at Acuhorn's lineup for a quick overview, we find four models whose numbering system designates height in centimeters. Two are the already mentioned 'dipoles' (the Grand Biancore 155 at €14,400/pr and today's review subject, the Rosso Superiore 175 at €11,700/pr), two are monopoles (the Nero 125 at €7,800/pr and Secco 145 at €8,800/pr). The 175's black-anodized aluminium plinth measures 29 x 43.6 cm and sports M8 threads for spikes as well as holes spaced 27 x 39.2cm to permanently bolt the speakers to the floor.

At 50kg (110lb) with 20 x 40 x 175cm (7.8 x 15.75 x 69 inches) dimensions, the 175 clearly hides internal bracing, its Plywood core lighter than equivalent MDF and some weight taken up by the aluminum plinth. This invites speculation. How simple or complex might the innards be? They vent into the room via a single large slanted mouth below the rear-firing TSR 200, equivalent to how the 145 above does it atop its driver facing forward. The 175's quite insignificant depth affords little room for repeat bends. In the Acuhorn, there is no traveling up, down, back up and then out of rear emissions as would be in a folded horn like the simpler single-fold Hedlund to the left. There are four internal chambers of different sizes working towards a common big mouth on the back. Two smaller chambers adjust a frequency response plot in the midrange and two big chambers operate at bass frequencies. Given the 1.75 meter height, the rear wave does propagate for some meters inside the enclosure before exiting. Regardless, even imaginatively convoluted internalists will regard the final pricing as ultra-steep. After all, this remains a rectangular box with two drivers and no crossover. However, some of the more expensive 160mm widebanders that would fit inside the 175's baffle are the Lowther A55 (€ 809) and Supravox HP 165-2000 (€ 525). At 200mm, Lowther's PM4A demands € 1,239, the new Feastrex units more yet. Seeing how today's speaker requires four drive units, one could spend nearly 5,000 euros on Lowthers alone.

The awards above are from High Fidelity Online by the way, Poland's audio e-zine. Its Wojciech Pacula twice awarded Acuhorn Product of the Year over a
three-year period while noting that this year's 175 was a significantly more refined and accomplished performer than the earlier 125 which he found to be distinctive but not without flaws. To read up on single-driver speakers and their various loading schemes for a general overview with select examples, James Melhuish's forum is one informal resource.

Nextgen WBT-0710 Ag silver single-wire posts on aluminum plinth, engraved model name facing up
Back to pricing. The general perception (which doesn't account for dealer and distributor margins nor the raw costs of low-volume custom parts) will be that the Rosso Superiore is priced on performance, not bill of materials and labor. Or perhaps to offset soft sales in the small specialty sector it serves. Or as a hand-crafted object d'art. All of it tends to be operative in high-end
audio. It makes it doubly gratifying to identify the occasional component that defies this ubiquitous pricing scheme. The 175 seems not to, rather pushing in the opposite direction. With two drivers and in push pull. At least conceptually then, it promises that while one is pushed away from a high-value proposition, one is also -- with monster magnets no less -- pulled irresistibly close for a most impressive performance. Hopefully.

To put the TSR200's earlier specs in context, the ARZ 6608 also made by TVM Acoustics for general consumption is as good a comparator as any: Fs of 75Hz, possible frequency response of 60 - 20,000Hz, sensitivity of 91dB, BL factor of 5.2Tm. Compare that to Acuhorn's modified Tesla - less moving mass, higher BL factor. As a result, we arrive at the highly desirable 96dB driver sensitivity for the 175 model, creating a colossal bipole sensitivity of 99dB without horn-loading. This clearly requires a rather more powerful motor; a more sophisticated cone structure to retain the necessary stiffness while shedding weight to reach the specified 4 grams; and a superior lighter voice coil. In short, it requires an altogether different driver. It really shares little with its preexisting platform except for basic paper membrane know-how, akin to the well-known Zu/Eminence collaboration.

Acuhorn," Alicja reported, "is a joint venture between my husband Wojtek and me. Our last name is Austrian, from Wojtek's ancestry. Wojtek ran a very large antique restoration business where he eventually became involved with vintage paper-membrane drivers. Initially this was just a hobby but four years ago, we turned it into our Acuhorn business. We worked with Czech firm TVM Acoustics from the very beginning because due to our investigation into superior vintage drive units, we were very impressed with the quality of their paper membranes. TVM is part of the former Tesla conglomerate. Today for example TVM furnishes Volkswagen with various audio-related parts. They're a large enterprise. However, our proprietary driver codeveloped with them -- we use the same driver across our line but with slight modifications to suit each model's specific purpose -- is quite different from their other commercial loudspeaker units. Ours is highly specialized to suit our goals. For example, we specified N50* neodymium for the motor, the very highest and most expensive grade. We demanded particular voice coil wiring. We eliminated the traditional basket to optimize airflow for best thermal conditions and superior dynamic range. We specified twisted 21 x 0.1mm Siltech G6 silver/gold alloy voice coil lead-outs which continue on as hookup wire to the loudspeaker terminals. And so on."

Alicja also related how their time in business since 2004 constituted an expansive wood shack period for ongoing developments of sorts. Repeat trade shows like Munich and Warsaw became opportunities to evaluate their progress against the wider market and expert feedback. Hard work over the last four years has now culminated in the "improved audio 2007" maturity of their proprietary driver platform. In tightly modified iterations, this platform is adapted to four different but always carefully matched loudspeaker enclosures of undisclosed internal geometries. Now Acuhorn feels

ready to bang the big drum and enter the global market. Alicja is confident that they have created something very unique, refined and compelling to contribute. Hence her review solicitation at the close of 2007. "The time is ripe."


* Neodymium magnets are a composition of mostly Neodymium, Iron and Boron. As a general rule, the higher the grade (the number following the 'N'), the stronger the magnet. The highest grade currently available is N50. A small Neodymium N50 magnet the size of a 50-cent coin will take 27 lbs of force to pry off a refrigerator door. Besides magnetic strength, magnets also feature thermal ratings which indicate at what temperature first demagnetization losses occur. Higher ratings imply higher temperature resilience.

Alicja continued:
"Our offering separates out into the Classic line with the models 145 and 155 and the Modern line with the models 125 and 175. Thus there is a monopole and dipole in each group. These two product lines are voiced differently to appeal to different audiences. Standard finishes for the Classic models are Walnut and Maple, for the Modern models Bamboo and Wenge. Custom finishes are available for a surcharge.

"We craft our cabinets from our own wood panels. Those are high-pressure laminates of nine 2.5mm cross-cut wooden layers (standard Ply layers are peeled off a tree trunk to be far softer than what we use while suffering crushed grain structures).

"Because of the CNC-machined precision tolerances of our motor assemblies, their highly polished surfaces and ultra-thin voice coil wiring, we do not suffer VC alignment issues in transit despite our narrow 0.9mm gap. Incidentally, driver Xmax is 1mm.

"We spent much ongoing research and development on this driver. And yes, I am well aware of claims in the DIY communities pretending to have cloned our speakers with commercial drive units." Though I couldn't, I did see Alicja's eyebrows raise over the telephone line. Being a lady, no further comments were necessary. Quiet amusement sufficed.

"In-room response of the 175 is 30 to 20,000Hz. As the frequency vs. impedance plot shows, amplifiers stable into 2 ohms are required. While we have shown with KR Audio at the Munich shows and enjoy tubes, the modern models work exceptionally well with transistors." This was a breath of fresh air in a myth-laden sector where hi-eff widebanders are automatically assumed to require valves.

The impedance plot does show how the meat of the range hovers between 2 and 3 ohms, with a strong saddle response between 25 and 80Hz that recalls ported alignments. 40Hz dips just below 2 ohms for a stretch. Your average tube amp might well prefer Paul Speltz's clever in-line impedance converters.

Fortunately for my low-power tube amps, Paul had insisted I hang on to his Zero Boxes post review for future assignment where they "might come in very handy". He must have intuited the arrival of the 175s. But first,
designer Wojtek Unterschütz's rationale for going 'dipole'; and what compelled him to designate certain models 'classic' and 'modern' in terms of voicing, design parameters and what type of music he anticipates these two discrete target audiences listen to the most:

"For the classic models, certain parameters of our TSR200 platform were adjusted for conventional 8-ohm impedance and the speakers were voiced to complement the vinyl/triode-type listener of classical music who is willing to spend a great deal of time on the proper setup of his or her system. The timbral beauty of violin and voice will be of foremost importance to this listener. That's who the Secco 145 and Grand Biancore 155 were optimized for. The modern 4-ohm models of Nero 125 and Rosso Superiore 175 build on a solid bass foundation which is vital for lovers of modern music with its infrasonics. This listener will often be a set-and-forget type with transistor amplification such as Spectral DMA-160S, Mark Levinson No. 434, Nagra PMA or other fine solid-state amps who expects superior results with very little audiophile fuss. It's important to stress that these somewhat artificial distinctions are quite fluid. It's not that our classic models require tubes and classical music, our modern models transistors and modern music. Talking in such terms quickly becomes a straight jacket. Suffice to say that we perceive a basic polarity of listening priorities and address them with two different lines, one that begins with the midrange, the other in the bass.

"The in-phase orientation of the modern dual-drive model increases bass amplitude and punch from greater cone surface and displacement, then adds the acoustic gain of the rear drivers' coupling with the front wall. The anti-phase orientation of the classic model generates less bass but emphasizes the spacious farfield effects which are popular with concertgoers of classical music. The above graph represents the load presented to the amplifier, with the frequency response measured in the traditional mixed-field mode. With regard to the various internal chambers which differ from model to model, I'm only prepared to say that they combine elements of TLs, rear horns and compound chamber loading which, in combination, don't conform to any one given approach. From an aesthetic perspective, we wanted clean modern lines, top finishing, bespoke details and a slender profile with realistic footprints that would make our loudspeakers unobtrusive complements to cared-for living environments. When it comes to parts, we rely on only the very best, from Siltech's G6 wiring (four times as expensive as the G5 we used before but well worth the difference) to our custom wood laminations not available stock anywhere to of course our unique driver, the aluminum engravings, top-line WBT posts and overall fabrication excellence.

Rosso Superiore 175 concept
"Finally, our reliance on super-powerful Neodymium motors with extreme flux density is not for maximum sensitivity. It is for maximum signal transfer to the voice coil wire, just as an MC cartridge reads the needle movement in a groove with only a few coil windings in the cartridge. This requires higher-quality phono stages and amplifiers but the results speak for themselves. In a similar way, the profile of our motor was optimized to allow for the fewest turns of our narrow voice coil. The objective was to focus the transfer of magnetic impulses and minimize dispersion losses in the air gap. The entire project was based on our 4-gram paper membrane whose upper suspension is a continuation of the same material as the diaphragm itself. We defined all the electromechanical Thiele/Small parameters. We carefully selected all parts of the driver's mobile equipment (cone, upper and lower suspension, voice coil and voice coil leads) to achieve the lowest possible mass for the most highly resolved music playback that honors even the tiniest signal fluctuation. Depending on the speaker model, these T/S parameters are adjusted. This includes the voice coil and sensitivity specs. With two drivers, the Grand Biancore 155 achieves 101dB, the Rosso Superiore 175 'only' 99dB."

I own the Indian Rethm Saadhana, a modern example of the high-sensitivity widebander speaker art. I secretly belabor the fact that Lowther continues to get away with selling their flawed DX55 unchanged and for serious coin, leaving it to the loudspeaker manufacturers to devise extensive modifications to overcome the Lowthers' well-known shortcomings. In this light and prior to even hearing it, Acuhorn's project of developing a from-the-ground-up new fullrange drive unit in conjunction with an expert Czech transducer manufacturer is big news and most welcome. That such news would issue forth from Poland and a mostly unknown small firm rather than a big, entrenched speaker design house is doubly surprising but perhaps not. After all, none of the majors*, on either side of the consumer audio fence (drive units and finished loudspeakers), bother with the genre. It is left to the small, enterprising outside companies to pursue ongoing innovation and relevance in this sector.


*With the 12/14/07 announcement of the 96dB X1-04 F8 in Seas' new Exotic line, this statement must now be modified to "except for Seas". Kudos to the Norwegians!

After confirming that the review pair was delivered fully broken in, it became clear very quickly that the supplied frequency response chart did indeed translate accordingly and that I would not be able to "get" the design goals involved. Regardless of amplifiers employed -- Red Wine Audio Signature 30.2, bridged Audio Sector Patek SEs, bridged First Watt F4s, Bel Canto Design e.One S300 -- the lack of treble extension meant insufficient harmonic development while the absence of impact and punch in the 100 - 300Hz power zone from lacking air displacement parlayed as somewhat listless. The active rear radiation at first caused undue swimminess and blur but installing Franck Tchang's ultra-affordable "sugar cube" diffusers in a grid of 16 ($200 for the set) on the front wall between the speakers ameliorated that.

In-room bass extension went surprisingly low but even after acoustically damping the deliberately strong early reflections, some narrow-band ringiness remained to suggest possible organ-pipe resonances in the internal line. A strong point of the Rosso Superiore 175 was surely the amazing soundstage depth thrown by the opposed drivers. Where I couldn't get it to sing was with immediacy, jump factor, tone luster, dynamic reflexes and an appealing tonal balance. Reflecting on the asking price and what other speakers in my arsenal offer by comparison, I suffered severe disconnect. As an honest appreciator of the widebander genre, high speaker sensitivities in general and highly satisfied owner of the Rethm Saadhana, Zu Definition Pro and WLM Grand Viola Monitor, I went into this assignment expecting a variation on familiar virtues. What I met instead was something I responded to as "all wrong".

Shelley Katz' Podium Sound speakers too are of the sort to engender violently opposed reactions by relying on diffusive rather than direct sound. As Ralph Werner said so poignantly in our translation of his Model 0.5 Podium Sound review for, "...those who are spoon-fed on conventional dynamic transducers and thus already immune to the charms of regular panel speakers will likely find the Podium speakers "completely wrong". The sonic picture occurs far in the distance without dynamic low-frequency kicks and while the high end is clear and precise, the Podium 0.5 is far from being an atomic microscope. This could be an area even panel aficionados will fault since the casual eye will see a panel and assume that it should resolve the smallest of dust motes or otherwise be disappointing..."

Having heard the Podiums, I concur with Ralph's description wholeheartedly. Yet it has to be said that after a 10-minute exposure, my brain, as did his after a while longer, spontaneously switched. We both came to terms with the presentation on its own merit and "got" it. Yes it is profoundly different and yes, it does mimic the diffuse far-field sound in a concert hall to an unprecedented degree. Marja & Henk on staff formally reviewed the larger Podium Sound Model 1s and believe their technology to be of break-thru status in what it achieves.

With the Acuhorns and despite Alicja's suggestion that my initial reaction was quite common and to simply give it some time, my brain refused to switch because of the tonal balance, hooded top and soft attacks. I simply could not conceive how extended exposure would overcome my initial reaction. I thus did something highly unusual. I packed up the 175s within one week of their arrival and after playing them extensively during that time with all the possible component swapping I could. After duly but with a heavy heart penning a lengthy description of this frustrating experience, I then reflected on the situation. With a few days of distance, I elected to paraphrase the gist of that second page in these last few paragraphs. The message is identical but the sheer fact that Acuhorn does enjoy distribution, satisfied owners and two "Product of the Year" awards also proves that my take is far from universal. An undue quantity of counter arguments is unnecessary. While I personally don't feel the speaker to be ready for prime time, others have spent serious money on them and are reportedly perfectly pleased. It would be hubris on my part to insist that they -- or future owners -- share in my reaction. What more needs to be said?

Quality of packing: Double card board with 2-inch thick cardboard liners and seran-wrap final protection.
Reusability of packing: Once. Outer carton showed shipping scars including deep gauges but the inner protection kept the goods safe.
Quality of owner's manual: None provided, none necessary.
Condition of component received: Flawless.
Completeness of delivery: Perfect.
Website comments: Stylish but not completely informative.
Human interactions: Professional, helpful and friendly via phone and e-mail.
Pricing: Very expensive for the concept.
Final comments & suggestions: Non-linear tonal balance with deliberate treble depression. Speakers create more than usual interaction with front-wall due to rear-firing driver and 'horn' mouth. Maker recommends perfectly parallel setup with zero toe-in and solid-state amps due to 2-ohm impedance.
Acuhorn website