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Reviewer: Srajan Ebaen
Source: Zanden Audio Model 2000P/5000S; Ancient Audio Lektor Prime; AMR CD-77 [on review]
Preamp/Integrated: Supratek Cabernet Dual; Melody HiFi I2A3; Eastern Electric M520

EQ: Rane PEQ55 active merely below 40Hz
Amp: 2 x Audiosector Patek SE; Bel Canto e.One S300; First Watt F3
Speakers: Zu Cable Definition Pro in custom lacquer; Anthony Gallo Acoustics Ref 3.1; Mark & Daniel Ruby; WLM Diva Monitor with Duo 12 passive subwoofer, Alto bass amp, Pre/Passive and Bass Controls

Cables: Crystal Cable Ultra loom; Zanden Audio proprietary I²S cable; Crystal Cable Reference power cords; 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
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
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: $3,100/pr

Sitting silently doing nothing, spring comes and the grass grows by itself. This Zen koan describes the gestation of today's assignment. "Hans here. As you probably already know, my interest in audio is inclined to the simple circuit and speaker solutions capable of optimum sonic pleasure. We have been working with Nelson Pass products since 1994 and continued with the evaluation of super symmetry and later his unusual transconductance amplifiers. The PHY-HP and Ocellia manufacturers Salabert and Furon have enhanced the feeling of correct orientation in the audio jungle of high-pitched saviors. Junji Kimura of 47lab too is part of the salvation from the ordinary and exchangeable conga line of me-to products.

"I have recently found much enjoyment with the works of Sakuji Fukuda in his thin-wall, solid wood and small wideband speaker. It's a monitor capable of surprisingly high performance, not in the same league as the aforementioned Ocellia or the Solovox but a speaker for smaller surroundings and as an alternative to the big rig. The Kotaro contains a small and unusual 'breathing type' super tweeter without beaming but extension beyond 100kHz. The crossover is at 15kHz.

"The speaker is built with mahogany and maple just as your vintage Gibson Les Paul - except for the older and selected woods of the Kotaro which are more than 100 years old. I am sending you some info and a picture of my friend Sakuji preparing for a new batch of Japanese art. If you find this of interest for yourself or maybe your reviewers Kari or Jeff, please let me know and I will send out a sample pair." [Hans I. Jonsson is the proprietor of Subas Audio, a Swedish importer of fine audio products in Örnsköldsvik who handles Pass Labs, Ocellia, 47labs, Murata, Almarro and Intermezzo Electric.]

Weighing a mere 2.5kg, with a 4" widebander spec'd to 70Hz, with an 86dB sensitivity and 4-ohm impedance, the Kotaro marries a small paper cone driver to a Murata super tweeter in a cabinet that is all of 163 x 247 x 192 millimeters WxHxD [or 6.42 x 9.7 x 7.6 inches]. This chassis is fabricated by Fujiken, a Japanese musical instrument maker. The company making and selling the final speaker is Micropure of Hino City, Tokyo. Vaccum Tube Valley imports this model formally called CZ302ES to America while Subas Audio handles EU distribution.

The concept of the speaker as musical instrument -- where the enclosure becomes an active contributor to the sound -- has its perhaps most famous precedent in England. Think loudspeaker stalwart Harbeth and its BBC collaboration which explored deliberately tuned thin-walled cabinets. The concept also is exploited by the above referenced French Ocellia brand, Auditorium 23 in Germany and one Onkyo model built in collaboration with famous guitar maker Takamine. This otherwise rarely applied notion is the polar opposite to the concrete bunker doctrine which is epitomized most famously by Wilson Audio with their super-dense X and M materials. To varying degrees, however, this ideal is pursued by the vast majority of speaker makers today. Their mantra is, kill the rear wave by absorption and deaden the cabinet - a double hit. What happens to internal pressures in a truly non-lossy speaker box? That's a good question. Added Hans: "These Micropure enclosures seem to manage the cold and hostile winter weather here up north so lets see about the more paradise-like climate in Cyprus. Sakuji San was a bit worried about Sweden at first since these speakers are more like musical instruments than the usual sturdy MDF/bitumen industrial assembly-line products.

"As you will see, the product line is big, including a speaker for bass players. Most interesting is the way they tame the enclosed air inside the speakers. Most constructors worry about the rigidity of the cabinet walls but care less for the enclosed air pressure releasing through the thin driver membranes. Well, the Kotaro will demonstrate what can you expect from a company that calls itself Pastoral Symphony and its approach Sound Healing Technology!"

The Micropure website shows three impulse response measurements taken in the anechoic chamber of Nihon University, Faculty of Production Engineering. They exhibit the difference of settle times between Micropure's decoupled and air-gapped driver mount technology and a conventional bass reflex cabinet against the original signal. In these measurements, the vented box suffers delayed settle times at higher amplitudes which the designers blame on sound leakage through the diaphragm and surround. Micropure claims that its enclosure technique minimizes pressure differentials inside the box via a small slit around the driver, the tweeter in the Kotaro's case. This pressure equalization is said to make for superior settling times of the driver and does not model like a conventionally ported alignment. Furthermore, Micropure claims that its mechanical solution allows for a lower F3 from a given size chassis independent of the chosen driver.
User endorsements on the Japanese home site include broadcasting stations, studios and churches where Micropure public address and studio monitors are installed.

At 86dB, the Kotaro clearly is not suited for the usual micro-power SETs often associated with wideband single-driver boxes. Remember that what looks like a tweeter here is really "just" a super tweeter. It's active above 15kHz only. For all intents and purposes, the Kotaro remains a single-driver design
. Which now gets us to exactly what little I knew -- and how much I didn't -- when I accepted this assignment. My motion was purely based on this Swedish reader. I sensed that his listening priorities and sensibilities were akin to mine. Hans has additionally committed his tastes to business. To me, this lent extra credence. Enthusiasts like Hans can only sell what honestly excites them. Based on what else Hans sells, his standards of excitement were just fine by me.

Getting hooked up with the Kotaro was all about the Global Village concept: Internet connectivity plus audio community plus a portal to interface the two. Let's see where this encounter shall lead. At its specified 70Hz extension, I'd run my WLM Duo 12 subwoofer below 80Hz for a true full-range showing of this Japanese mini. At $3,100/pr, it does seem expensive only until you remember that a pair of add-on Murata super tweeters range from $1,950 to $2,950 on their own. That puts the Kotaro's sticker squarely into perspective. It's right where it belongs and checks out just fine. On paper.

As the CD shows for size reference, it's only after you've unpacked the Kotaros that you realize these are some really tiny fockers (compliments to Ben Stiller and Robert DeNiro in The Fockers II hilarity where the cute signing twin babies act as stunt doubles for each other). And, these fockers are incredibly light. Forget python speaker cables unless you mean to capsize 'em. To insure that the cabinets would activate properly, Hans had included six Cocobolo wood blocks with BluTak on one side, a tiny felt pad on the other. This would create minimum contact on the bottom and maximum freedom to breathe once parked atop the stands.

While on breathing, I was fortunate that shipping had displaced one of the plastic grills over one of the OEM'd Murata EST-02Y "breathing" tweeters (I'd otherwise not attempted to pry one cover loose). When the Japanese describe their tweeter's profile as spherical, they're factual. It's a perfectly golden dome. This 8-ohm 90dB efficient piezoelectric ceramic diaphragm has its first breakup mode at 103kHz and short-term power handling of 300 watts. That seems very tenacious for its pinky tip size - tinaceous.

The binding posts have separate provisions for 1/4" and 5/16" spades, the former underneath, the latter above the non-removable collar.

The wood work is of very fine quality. It received instant thumbs up from my interior decorator and better half. Not a peep over lacking grills neither which is rather unusual for her. Must be the gorgeously wavy grain pattern of the front panel here. While I would usually grab a screw driver and unseat a novel custom fullrange driver for closer inspection, Hans, with keen foresight and in writing, had warned me explicitly not to. Apparently Micropure applies precise torque on the fasteners to tune the driver/cabinet assembly, meaning I'd screw up proper tuning when reseating the driver.

With my WLM Diva Monitors vacating their customary perches, the Kotaros took their place and were duly dwarfed by the stands' top plates. The Kotaro is barely wider than a jewel case and barely an extra inch deeper. For amplification, I started with the 10wpc FirstWatt F3 ahead of which sat the two WLM control boxes to split the signal actively above and below 80Hz, ahead of that my customary ultra hi-gain Supratek Cabernet Dual 6SN7/101D preamp and ahead of that the AMR CD-77.

Though it seems a counter intuitive amp/speaker pairing, with gain padded by the preamp, it worked splendidly. On first encounter, the treble quality stood out instantly as being of rare beauty - refined, effortless and dare I say it, breathing. There's no grain, no harshness. Nor is there any forwardness or emphasis. Last time I checked, my hearing hit the brickwall at exactly 17kHz. Stuff at 25kHz, with gain cranked way up high, was eventually felt in the bones of my skull, not at all as sound but as a weird pressure sensation.

Suffice to say, I'm deaf and oblivious to regular amplitude sounds above 17kHz. Likewise, CD dies a sudden death at 22.1kHz. Theoretically, the Murata super tweeter should see action over only a very narrow band, far less than an octave. While tests have shown that some musical instruments do produce harmonics above 40kHz even, RedBook software can't capture that data and hence won't pass it on to this tweeter.

Regardless, Elly Ameling's soprano on Hector Berlioz' "Le spectre de la rose" from Les Nuits d'été, Op. 7, wasn't just serene purity personified but fleshy - not mere energy and vibrato but tone color, the antithesis of the glass-breaking white shrill. I'm not a fancier of classical Western operatic soprano precisely because to my ears, these voices don't sound entirely natural. They break records but, in general, go rather seriously on my nerves.

The Kotaro suggested this old dog could learn a new trick and change religion. To stress this point, the Kotaro behaved very differently than the just-reviewed Esoteric AZ-1 "digital" integrated amplifier whose treble performance was unusually incisive and whose general portrayal very transient-led to make for an overabundance of ultra-obvious, nearly relentless and sharp, pungent detail. The Kotaro's treble, on that old stumbling block called massed strings such as you'd find in the "Adagio" of Bruckner's Eight Symphony, was sweet, suave and elegant. Think about glockenspiels, triangles, cymbals, solo violin, all with endless decays and a lot of inner life rather than mere tizz or fiery brilliance. Instead of brighter and whiter, the treble gets sweeter and more golden. Inherently nasal instruments such as oboes, bassoons, the upper registers of the bass clarinet and Jan Garbarek's soprano saxophone build out their true timbres as well. This kind of detail is more than just musically benign. It's addictive and counters the hyper-realistic trend of typical Class D amp behavior. There's nothing dry or pushy here. Bowed instruments of all persuasions -- say the viola on Garbarek's elegiac In Praise of Dreams -- are particularly well-served by the Kotaro magic.

This treble and its associated detail behave like superior European sweets. Unlike their American counterparts, they use a minimum of sugar. Their fine flavors linger. They don't attack by being blunt and painful to your teeth. That's the Murata in the Kotaro. Apparently. Why 100kHz extension would matter in the first place, despite various theories offered up on the subject, is ultimately still an unanswered riddle. Where does the Murata get its ultrasonic signal from? What's beyond question is the utter classiness and refinement of the Kotaro's top end. I do doubt that this speaker is listenable without a subwoofer however. On the aforementioned Garbarek release, there are synth and drum-generated heart beats completely outside the purview of these mini speakers and the music simply doesn't sound the same without those anchors. Ditto for subtle ambient data embedded in the bass. Once you know what should be there, you can't live without it. Okay, I couldn't, wouldn't. But, 70Hz reach
with a skosh of boost from the WLM's active box massaged in below 150Hz (2dB seems about right), then handed over to the Duo 12 subwoofer at 80Hz - now that's a very serious recipe for complete satisfaction. In which case, anything lower from the micro mains would be throwaway data so it might as well not be there in the first place. And yes, this speaker cabinet is active. It resonates very finely just like a guitar body does. Even so -- or more likely, because of it -- notes let go incredibly quick. There's no audible blurring, quite the contrary. Yet nothing is etched or stark at all. Rather, instruments sing, their notes ring out to where everything appears very open-throated. Without mechanical blocks. Freely gushing.

In many ways, the Kotaro reminds me of the Audio Physic Spark, another upscale, not inexpensive micro speaker which, without a subwoofer -- but Audio Physic had their Luna to remedy that -- was really just half a speaker for most serious applications. In our very modest foot-of-the-bed mini rig usually fitted with Gallo's A'Diva Tis, the Kotaro made more bass, additionally benefitting from just a bit of reinforcement from the table. Its bel canto quality remained apparent even here though the lack of source refinement -- a good USB DAC would have come in handy to upgrade the Sony Vaio's sound card -- was also more obvious than usual. Most of the special qualities abundantly tacit in the big rig were a mere memory here, suggesting that unless fed a premium diet, the Kotaro's talents will be mostly wasted. Don't mistake this for finicky. It's not. It's simply capable of far more which you won't hear unless the remainder of your kit is up to snuff. Here the Melody/Onix SP3 certainly filled the slot but the source was massively outclassed.

Enter my wife's mini rig with April Music Aura Note, Zu Audio Libtec cabling and Zu Audio Druid Credenzas. Slipping in for the latter and playing one of her favorites -- Barber's Adagio for Strings Op.11 [Chandos 8593, Israel Chamber Orchestra under Yoav Talmi, with Bloch, Grieg and Puccini completing the programme] -- the minis from Japan showed off their mettle again. The waft'n'wane factor of massed strings calls for maximum cantabile and the Kotaros did this better than the Druids, with more expansive harmonics and more inner life. This particular composition (which reportedly was played during JFK's funeral) lacks low bass and thus didn't really show up the Kotaros too short. Cueing up Mercan Dede's Su [Escondia 6510-2] for a round with the stupendous vocals of Dhafer Youssef on "Ab-i Hazan" gave the lead to the Kotaros in maximum vocal expressiveness again. Yet by lacking to flesh out the bass beat which isn't even subterranean here, the Zus beat 'em in spatial realism and scale which simply was grander. Ditto for my wife's beloved piano music. The necessary warmth from the lower octaves, the rumbling, the foundation of what makes a concert grand a concert grand and not a Casio, was beyond the grasp of the Kotaros even with close boundary reinforcement.

That's really their Achilles heel. Truly exceptional in the range they do cover, this very excellence makes the lack of completeness of this excellence painfully unsatisfactory without a quality 'after-market' bass system. You're only getting two thirds of the goods, albeit top-shelf two thirds. A smaller REL or equivalent sub would certainly be up to the task. Including the necessary stands for the minis though, this will add somewhere between $1,500 to $2,000 before the Kotaro proposition can be considered final. Once you embrace the reality of a $5K three-piece system with all the placement and tuning flexibility this entails, you've arrived at what ultimate ownership of the Kotaro will have to entail.

Running them either full-range or filtered with the Duo 12 sub (acoustically a negligible difference between an F3 of 70Hz in the first scenario, a 4th-order high-pass at 80Hz in the second) showed the latter to be preferable by being tauter and more controlled. While the extension from the box size is rather impressive, it comes at the expense of some looseness in the upper bass. Filter mode puts the burden on the quality of the filter, mostly an issue even with superior active subwoofers where keen ears will detect how they veil the satellites. WLM's active outboard solution completely sidesteps this problem and demonstrates, at least for me, a truly ideal system scenario for the Kotaro. Of course that's about $5,000 just for the bass system. But make no mistake, the Kotaros are worth it and every bit the equal to this expenditure in the range assigned to them. We're simply playing in a rather different league now than proposed on paper by the Kotaro's asking price. Yes, you could set them on a credenza, avoid the stand, forget the sub and call it quits. However, I'd call that a significant compromise and underselling the Kotaro's potential if you listen to more than breathy female vocals.

In the above setup, the puny 'uns played very loud without any compression from my 18wpc Melody I2A3 with JJ output glass. The moment I switched the Kotaros to full-range mode however, excursions increased visibly without really adding any useful extension. This could be easily checked by muting the subwoofer. The increased excursions sans filtering and on the bass-heavy music I enjoy now became a bottleneck for achievable SPLs without distortion or compression. Upping driving power to 50 watts of gain clone muscle with an AudioSector Patek SE delayed the bottleneck but didn't cure it. The solution is to high-pass these minis at 80Hz. Then let 'er rip without Physics limitations.

Ear right up to the Murata, it might as well not be there. That's how non-existent its output appears to me. Yet there's no doubt in my mind that the open-throated bel canto quality and filigreed, glistening golden treble of the speaker hinge on its presence. The cabinet is uniformly lively as soon as it's activated by signal yet there is categorically no smearing, ringing or hollowness, i.e. none of the artifacts popular opinion groups under cabinet talk. Somehow I suspect that the success of this thin-wall recipe depends on the limited bandwidth. If this cabinet was larger and contained a 7" mid/woofer, I'd expect a compromised midrange, never mind ringy bass. In its actual incarnation, it must be the uniformity of fine vibrations in the solid wood walls which contribute to the speaker's uncanny ability to let go of the notes such that they decay properly instead of being killed off from overdamping. This on-the-breath sensation of unclipped fades evaporating naturally on the air is the essence of song -- vocal and instrumental -- and the opposite of mechanicalness whereby synthesizers always betray they're fake. When tones ring out, they seem organic, not canned. That's the Kotaro. Entirely non-metallic, fluid and most graceful. And reliant on high-class ancillaries to paint the full picture.

Because our perception of directionality and focus is wedded to the presence band and treble, any transducer excelling there will create more acute presence and a more unequivocal localization in space. Needless to say, the Kotaro owns these categories. It's softer though and not quite as holographic as Anthony Gallo's CDTII whose treble transients are sharper and whose off-axis response is more omni in nature. While very nimble, the Kotaro can't dynamically compete with my Zus and WLMs. Their far larger cone areas displace more air and also make for greater tone density. That's more wallop. The Kotaro's success is that it achieves its airy, spacious and fast sound without bleaching or etching. Yes, the overall presentation distinctly lacks bass but if you listen just for the vocal band, there's nothing lean about it.

Unlike most all competitors in the 4-inch-as-full-range category, the Kotaro is so beyond peakiness as to render even the faintest notion as potential thereof or even a rather common issue mute. However, it does warrant mention if only to differentiate and distinguish it from that competition. On this particular count, the Kotaro behaves as normal as any superior 2-way crossed over at 2kHz would. That it manages that with a 4-incher going up to 15kHz is very abnormal and quite the engineering triumph.

If you're looking for subjectively full-range sound from the smallest possible speaker, the Kotaro ain't it. For that stunt, think Mark & Daniel Ruby, Topaz or Sapphire - three equal-sized
models which reach 45Hz with 100 watts in different trim levels of parts quality and even in the most costly makeup, are still nearly $1000 less than the Micropure. If you fancy a less muscular sound however that's more about song and poetry; if you can justify the extra expense for less bass plus the extra expense to add the missing bass... then the Kotaro makes an unusual proposition. I think of it as two thirds of a world-class loudspeaker system that will eventually or right away mandate a superior subwoofer - unless you're talking a secondary, less serious setup in a small space where you might consider the Kotaro a rather expensive proposition. In a take-no-prisoners setup and suitably hi-passed, 15-20wpc of premium power will be sufficient. Particularly tubes of course will really sing on what, in essence, is a crossover-less single-driver miniature speaker. Not cheap, clearly limited in bandwidth and thus only for the discerning, Micropure's Kotaro is an unusually accomplished, counter-intuitively linear and truly magical device in its niche category. I was thrilled to make its acquaintance. When wedded to my WLM sub with active divider network, I considered it something I'd live with in a heartbeat. It would outperform most conventional "full-range" tower speakers at $10,000. That's really how good the Kotaro is at its gig and the WLM Duo 12 sub with outboard active crossover and outboard bass amp at its part.

That's when and where the Kotaros really make sense. And just as my Yamamoto A-08S 45 SET with Emission Labs solid plates produces my favorite treble of any amp I've owned yet, so the Kotaro for now occupies the equivalent place amongst my speaker acquaintances of treble babes - the one. The treble here is extended yet sweet, detailed yet golden, easeful, spacious and completely non-fatiguing. And those effects spill over heavily into the vocal range for the same kind of aroma. If that's the Murata's doing and signature, it's really quite the John Hancock from a very special transducer. And let's not sell short the widebander. After all, it's really doing most -- or, if you rely on the apparent nothing emanating from the gold dome -- all of the job here. How this ultrasonic concept works is a mystery to me. That it does is loud and clear. Actually, soft and sweetly...
Manufacturer's website