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The Absolute Sound HP’s Workshop

The Wisdom Audio M-75:
Planar/Magnetic Hybrid System

|  Quick Jump

|  Introduction

|  Part One

|  Part Two

|  Part Three

|  Part Four

|  Inside the Brain


This review has turned out to be an investigation of the Wisdom Audio Model 75 speaker system. It was evident almost from the start that this hybrid moving-coil/planar-magnetic system was a chameleon. And the mystery that we had then to solve was this: The speaker is either far more neutral than anything is in our reviewing experience, or it could, in some way we could not divine (without measurements program), interact with the electronic components that precede it in the audio chain to highlight, even exaggerate the inherent characteristics of those other components. Complicating matters and causing us to go off the track and on intriguing side trips were so were some underlying issues that, until the last day of our listening sessions, made us fear that we had come up against one of audio’s most fundamental dichotomies: would we, as pursuers of the absolute, rather have an honest and uncolored speaker that tickled the intellect, or a more colored simulation of the real thing that moved the soul?

That question is one we have danced around without even reaching a resolution, because our unspoken assumption has always been that we couldn’t have both.

Speaker systems have, historically, always been the most highly colored players in audio’s chain of components. Each has its own quite distinctive personality- a concatenation of character “traits” that interact in surprising and quite often flattering ways with those parts of the chain that precede the speaker.

Let me come at this from another perspective: Consider the speaker as the narrator of the audio system. The teller of the tale. The question then becomes: How reliable is this Scheherazade? We have accepted, in principle, the notion that the narrator should tell the truth and nothing but, like the Fair Witness in Robert A. Heinlein’s Stranger in Strange Land. But do we ever know better: Speaker systems have been widely unreliable narrators since the dawn of recorded sound.

You might attribute their lack of reliability, analogistically, to each speaker’s individual biases, i.e., their own set of highly idiosyncratic “character” tics and traits, much like those that separate you from me, they from you, and each from the other. We might further analogize these as bendings of the truth, rather like the warps and weaves of perfect window glass, which we can make it sticky going when you’re trying to see clearly what the “characters” of the things on the other side of the window are really like. The inherent sounds of any other components in the system are thus subject to the speaker’s interpretations of the truths the other elements are trying to tell. (Imagine someone who doesn’t like you trying to write your biography, or someone who does like you smearing the preserves on thickly with a knife.)

The best designers in the field and their enviable brethren, the most commercially successful, have overtime devised narrators that tell a good story, not necessarily one that is true, but one that is emotionally and maybe aesthetically satisfying. These are the stories that all of us, as audiophiles, have grown up on and incorporated into are way of preceding, reproducing sound in the home. Thus, we have swallowed the hook with the fish. In other words, the speaker systems we cherish tell the most alluring lies. Or selected half-truths, as in, say a system like the early Quad electrostatic. Isn’t the Devil the master of the selectively told truth?

It took us a long while to rule out a serious interaction between the M-75 system and the amplifiers that drive this two-way system. And given that the system has an electronic “brain” filled with ICs (some are op-amps), we cannot be certain, beyond a reasonable doubt as they say in jurisprudence land, that there is not some potential for mischief here. But, as the Red Queen said verdict first, evidence later. The verdict: If there is a more neutral transducer ( top to bottom) commercially available in the marketplace, I haven’t heard it. And in all probability, this system could be made even better.

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Part One

The Adrenaline M-75 is one of three models manufactured by Wisdom Audio, a Carson City, Nevada, company. There is a smaller one-piece (per side) version of the speaker, the M-50, and a more upscale version called the “Adrenaline Rush” that has a much larger woofer array that the M-75, and an extensively handtweaked midrange/tweeter tower. The M-75 costs $38,000 in the lacquer finish we had for evaluation, which, considering that it is large, and imposingly well-built, sounds like something of a bargain in the High End sweepstakes. Depending of course, on how “good” it sounds.

Its main attraction is a 75-inch tall, 1.25-inch wide push-pull planar magnetic element housed in an infinite-baffle backward-sloping cabinet with a quite narrow footprint. No dipole this.

I’m not going to call this element a “ribbon” and neither should you, since it is similar, in operating design, to other planar units on the market and quite dissimilar from the trickier design of a true ribbon (for example, the tweeter element of the top-of-the-line Magnepan speakers). Earlier versions of this planar/magnetic unit were first manufactures in 1996 by Bohlender & Graebner, a separate company that preceded Wisdom and that sold- and still sells-custom made dipolar models to other manufactures (e.g. VMPS and Genesis). Tom Bohlender, the chief honcho, started Wisdom two years ago as the outlet for a speaker system of his own design.

The M-75 has two woofer cabinets, each containing two heavy-duty under-hung (short voice-coil/long magnetic gap) 12-inch drivers and a separate electronic “brain” of considerably complexity that allows him to personally tune both the woofer and planar sections for flattest performance in any room. And to make sure there are no mistakes, Bohlender himself comes with the system to do the tuning.

The system, as you may deduce, must be bi-amplified. Its sensitivity, says Bohlender, is 88 dB at 1 watt/1 meter and this means it “likes” power. Situated in Music Room 3 here in Sea Cliff, we found that 140 watts (tubed) was the minimum we could get away with, then not cleanly on the biggest orchestral peaks played fortissimo. We’re talking 140 watts on the midrange/tweeter planars. For the bass, we hooked up the mighty Krell FPB 600 STc, whose low-frequency performance is little short of stunning, and left it in place throughout the long and nearly always revelatory listening sessions. For purposes of our sanity (such as it is), we kept the cabling as a constant, and that means, throughout the days, weeks, and months of testing, we used Nordost Quattrofil (single-ended and balance) as interconnects, and David Blair’s Custom Power Cord Company Top Gun HCFi as the power cord for all the amps save the Krell, which comes with it’s own detachable AC cord. The only exceptions to the Nordost rule, otherwise, were a length of Siltech SQ-80 B/G3 XLR cable between the dialog-to-analog converter (the Burmester 969) and the line stage, along with a single-ended Forsell Air Reference digital cable between the Burmester 970 CD player and its decoder. Oops, almost forgot – we used the Nordost SPM Reference speaker cables between amplifiers and upper and lower sections of the system.

Scot Markwell oversaw Bohlender’s preliminary set-up. I took over the last hour and the fine-tuning. With one exception, the settings that yielded the flattest frequency response were those that sounded best to me. (One of the tricks we learned along the way was to keep the rotary controls on the “Brain” either below or at their “0” points, lest we invoke amplification from dreaded op-amps) According to Bohlender’s microphone/meter set-up, that response was flat (within one dB) way out past 20 kHz. However, when Bohlender set the system for the flattest frequency response at the other end of the spectrum, so response could be extended below circa 32 Hz, the bottom octave sounded overblown, wobbly, and “plummy” (as the British once were wont to say). To get the bass as taut and articulated as that I hear in the hall, we had to sacrifice flat response in the very bottom octave.

Well, not exactly sacrifice, since, as soon as Bohlender left the premises, we installed the Carver Sunfire Signature Cube (our old standby when we want those subterranean rumblings and organ pedal points), set to roll off above 30 Hz with a minimal phase angle. You laugh? Four 12-inch woofers equalized in two fairly substantial cabinets and we have to add a $1,995 sub-woofer? Right. At this point, we achieved, by slightly cheating, a truly full-range system, for about half the cost of several super systems we have auditioned of late.

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Part Two

Now we come to the tricky part. And I shall not, in the space available, be able to document the step-by-step progress of our adventures in trying to settle the conundrum this speaker set for us. Just keep in mind: If we had stopped the reviewing process at any point along the way, including our listenings on the last day before deadline, we would have been dead wrong about this speaker.

Our first impressions of the system were that it was a dramatically good reproducer, fully living up to the best advance word we had heard about it, and belying much of the bad stuff simultaneously circulating, some of which was centered on its earlier configurations.

Then as now, the Wisdom reproduced the stage upon which the orchestra players sit, and the dimensions of that stage, with a precision quite unknown to us. Oddly, the effect was mostly confined to the stage and it’s shell’s acoustic, not to the ambiance of the hall itself, where the Nearfield Acoustics’ PipeDreams reign supremely and seductively with an almost wrap-around, near-surrounded effect that is their chief calling card. By the way of contrast, the M-75s reproduced the depth and width of the stage with a precision that was uncanny, so much so that every other speaker system in my experience sounds as if it is adding fake or false depth, a simulation of layering, rather than distinct rows of players with clearly defined seats (or positions), with “air” and space to the front, side and rear of each. When other “good” speaker systems present layering, they do so amorphously, so that you think, “oh heavenly Hannah, that depth goes into the back yard,” but this is a further kind of depth instead of a farther kind, in other words, distance you can only guess at, rather than you feel the measure.

What am I saying here? Something like this: The M-75 captures the “volume” of the stage itself (not the volume of space of the hall in front of the players, which is only ordinarily in evidence, compared with the PipeDreams) that is the essence of continuousness. By contrast, when other speaker systems reproduce the soundstage in front of the mikes, they impressionistically create strands of depth, layered, but somehow separated (as in strands) as opposed to being part of a continuous texture, not only folded, but wrinkled in time/space. (Watch out, here comes another analogy: Suppose you imagine the players on a rubbery stretchable material, like a balloon’s surface, versus the players in fixed positions on a genuine wooded floor of mixed dimensions.)

One startling consequence of this fixity of staging and imaging is that orchestral instruments, given a minimally miked recording, stay the same size and are not subjected to the yo-yo dieting effect that seems to occur in the interface between other speaker/amplifier combinations. What this means is that when played loud, the instrument doesn’t get bigger- but its soundfield does. Given that, a recording, like Dave Wilson’s of Debussy Sonata for Violin and Piano (played here on cello), gains realism from the focused and consistent size of both instruments. And when the cellist rocks around sideways, you hear this instead of a bulging too-close-to-the-mike effect. [Wilson W-8722. Find it; it’s worth the search.] More fascinating yet, the piano, such as a living bitch to record, is so exactly positioned that you can tell, even without reference to Wilson’s noted, which way it is oriented. (Hyperion Knight, in his electrifying reading of Stravinsky’s Petouchka for solo piano, also on Wilson [8313], has, until now, sounded a bit indefinitely positioned, when it comes to the spatial deployment of the keyboard. No more. Another recording worth the search.) Even on certain kinds of popular dance music (“Don’t You Want Me, Baby”) [Virgin 466-12B, a 45 rpm single] or Propaganda’s Machinery [Virgin/ZTT 12-ZTAS 12]), there is clear pleasure to be taken in the prices construction of the sonic soundfield, where the dimensions of depth, width, and placement are manipulated for maximum emotional effect. Maybe not absolute, but oh-so-spectacular in that pancreatic way.

Another aspect of the speaker’s performance independent of any of the associated equipment with which you use it is the fine-tuned balance between the woofer and the planar units, centered in the 150 Hz range. I have no idea what kind of jiggerypook Bohlender hath wrought here; the crossover point is sonically seamless, although the “character” of the woofer isn’t quite. But this is no case of a troubling discontinuity. The woofers complement, in a way that interlocks convincingly, the planar/magnetic panels. In listening, one accepts a certain amount of difference between the two sections – and not because they sound exactly alike, but rather because each enhances the sound of the other.* For those who think in conventional design terms, the satisfying blend I observe here is puzzling, given the proximity of the crossover point to the middle frequencies (that 150 Hz range) and the difference in the material used in the drivers’ construction. Could it be, I have come to wonder, that Robert E. Greene in his lust for flat frequency response uber alles has a genuine point to make? Unlike him, I do not have perfect pitch and so small frequency deviations, taken as part of a bigger picture that includes dynamic contrasts, frequency extension, continuousness, et al., have never bothered me as much as they do him.

From the start, it wasn’t a question of whether the M-75s were neutral – they are startlingly so. What we had to determine was just how neutral.

* Such is an example of one of those byways, about which you may wish to speculate. Is there perhaps some merit to the idea of not matching woofers and the upper range in a hybrid system, but rather aiming for a kind of complementary set of colorations that lock together so well that they synergistically make the more convincing whole?

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Part Three

At the outset of testing, the system consisted of the Audio Research Reference Two line stage, and early version of the Plinus SA-250 Mk IV amplifier, and the Burmester CD player and its digital decoder.

After we had recovered from the first rush of excitement (that is, hearing the system’s strengths), we began to hear little “peculiarities” and worse, began to find the sound a bit monotonous in its bland sameness. To add to it, I had received (at my own asking) a long detailed letter from a reader of startling perceptivity who had given up on the speakers because, he thought, after all was said and done they just didn’t sound like live music.

I concluded that I was hearing inherent colorations in the planar/magnetics, colorations not uncommonly found in quasi-ribbon designs like this: a fine-grained sandy texture in the upper midrange; a resonant, broadband frequency emphasis there that sounded somewhat glazed in texture, with a midbass I decided was not as complementary as I had at first thought, one that sounded slightly “fat” in the way that so many woofer designs of years past had (particularly notable in early Infinity “big” speakers).

At this time, one of our reviewers (Mike Silverton), had begun hounding me to see what I thought of his latest “protégé,” the Quantum Symphony Pro, a kind of metaphysical and upscale system “conditioner” whose effects on his Wilson Watt/Puppy Sixes (with Levinson electronics) was subtle and, as he heard it, a worthy enhancement of the musical experience. We had the unit in the house, so I decided to take a listen, little realizing that the Quantum was already in the system and that the adventure would be taking it out.

In the next listening session, I played a few bars of the new Classic Records issues of the Saint-Saens “Organ” Symphony (the justly famous Munch/BSO recording), then asked Markwell to take the Quantum out. And put it back in. And take it out. Not that the repetition was necessary; without the Quantum, the most flagrant colorations simply disappeared. What I had thought to be planar/magnetic colorations, the pseudo-ribbon “sound,” was mostly gone, and the midbass was appreciably tightened.

I am not talking subtleties here. The differences were plainly dramatically evident. I had been expecting “subtlety.” Zip that.

I still thought the reissue left something to be desired, for, among other things, the highs weren’t quite as I remembered, being a bit hot and solid-strately on the strings and high percussion, with the tight cymbal crashes, in particular, spraying instead of sounding almost “cupped,” with little or no decay tail. The player can make them “spray” by hitting them off each other, or by hitting them softly and head on, he can give them fireworks-like cupping sound. (Imagine, if you will, clapping your hands when they are cupped, as opposed to smacking them past each other, palms flat.) As I had before I waslaying the blame on the speaker. It was clear there was a narrow spike of some kind involved and I thought it was occurring at the point where the high frequencies (not around 5 kHz as I surmised, but close to 7 kHz0 came in. * By chance, we had just became temporary heirs of a $2,500 all-tube line stage from Deutschland, the Audiovalve Eklipse, which, for that cat’s curiosity’s sake, we decided to substitute for the Audio Research.

* There are six aluminum wires running much of the length of the panels, two of them dedicated, via a shunt, to the two octaves.

Pause for reflection: We in the business of writing reviews often find ourselves hung out to dry by the very phrases and clichés we use almost without thinking. You know the sort I’m talking about: “I never knew the record could sound like this, all the detail, all those inner voices”), or “I stayed up all night listening to my Bose speakers,” or “it brought me closer to music itself,” or “it was like a window through which I could listen back to the original.” That these phrases, the Bose excluded (substitute something more likely), describe real listening experiences isn’t what I find annoying. It’s the fact that we have all used such clichés to excess, leaving us without an original turn of phrase when the experiences described in such clichés take on a new impact and intensity. To borrow a visual analogy, the difference was like that between standard television and widescreen High Definition Television. That obvious, yes. And not completely flattering to the Audiovalve. The differences were as distinctive and easily distinguishable as the sound of the voices of people close to us. Distinctive, and as if highlighted, as in the sky written. In Issue 123, Jonathan Valin (p. 83) had, after some listening, nailed the sound the Wisdoms revealed instantly. He wrote: “With the exception of a bit of reticence in the very top treble and just a slight bit of added energy (typical for ARC) in the upper midband…this is the most dynamically neutral preamp ARC has made in many a moon” and “only in the very deep bass…does the Ref 2 sound a bit out of whack, a bit overgenerous and undefined” which he describes as a “ slightly biggish deep bass.” (Not that I remembered his exact words; truth to tell, I had forgotten them until we compared notes.)

When I made the switch with the Audiovalve, I heard instantly what JV had been talking about. Those cymbals (near the beginning of Side Two of the Munch/BSO disc) weren’t tightly “cupped” but sprayed, evidence of that narrow spike, one that added glamour to the sound and a bit of extra dynamic “snap,” but also obscured the slight roll-off in the top-most highs he describes. Ditto for the bottom bass (say below 50 Hz to about 30), which is bigger than life, and acts as a disguise for a loss of energy in the bottom octave, also making the 30 to 50 Hz range sound less than finely articulated.

By contrast, the Audiovalve was flat down into the very bottom octave, with considerable definition and articulation (listen to the massed strings at the beginning of Mehta’s traversal of Holst’s “Saturn” from The Planets, Decca SXL 6529) and it got the fast transient cymbal attacks just right on the Saint-Saens, allowing its top end, which I found just slightly dark and closed in, to be heard. The Eklipse maintained tight control over the decay tail of those transients. Alas, the Audiovalve was audibly shy of the kind of dynamic blossoming and impact of the ARC, sounding restrained in a way that made you want to turn the thing up to get more “impact.”

One more small substitution that afternoon began to convince me that the M-75s were so decidedly neutral that hey allowed each proceeding part of the system to speak at full voice. The Eklipse came with brass feet and padded on the bottom with soft felt. We put the Nordost Pulsar Point isolation devices (the titanium version) under the chassis and, behold, the dynamic footprint of the tubed line stage sharply improved.

And if that comparison was a shock, the later insertion of the Plinius M-16 line stage provided a bigger one: We went from the dark to light and neutral, from the dynamically somewhat compressed dynamics with the swagger and vigorousness of the real thing. The Plinius had a low frequency aliveness and “authority” alien to the Audiovalve and the Ref Two. The M-16, like all Plinius products we had previously auditioned, wasn’t entirely “cooked” when we substituted it into the system, so a top-octave softness and fine grain were there. And heard, need I add, with perfect clarity and zero ambiguity. (Such, I have both been told by those veterans of he Plinius warm-up wars and learned for myself with other Plinius components, would disappear in due course.) Even the difference between Nordost aluminum Pulsars and their titanium ones took me by surprise, and hardly had I recovered from that than Charles Hansen of Ayre Acoustics showed up with small isolation blocks made of wood, which sounded yet again different and distinctively so through the Wisdom system.

It took us awhile to get our collective feet on the ground where the amplification was concerned. And we were tempted to tear down the road toward a more critical and general assessment of the interface problems that characterize the mating of amplifiers and speaker systems-but that was, as a prof used to say to me in college, “Not within the scope of this course, Mr. Pearson.” Um-huh.

During the set-up procedure, Scot Markwell, who had intended to use the high-powered Atma-Sphere MA 2 Mk II O(utput) T(ransformer) L(ess) amps, found an incompatibility that had us looking for possible reactance problems with the towers. After some littler research, we found that the impedance of our particular pair of towers ran at 4.8 ohms, with a .5 to. 8-ohm dip at the 7 –kHz transition to the top octaves. (For the resolution of this, see Markwell’s sidebar to this essay.)

I am leaving out, as I said I would at the outset, many of the interim steps as we tried component after another to see if we could determine the degree of neutrality of the system. And we worked with the six high-powered amplifiers we had on hand.

If you didn’t push it, the Innersound ESL amp, designed to work with electrostatic speakers, sounded unusually pure and sweet (thus, quite, quite music-like) and had it had a power supply large enough to accommodate the intense demands we made upon its output, it might well have ranked at or close to the top of the list. But push it we did, and toward or into clipping, it fell apart, seemingly transposing the entire weight of the frequency range upward and into hard clipping (like jangling, icecoated piano waves). Hansen’s Ayre Electronics V-1x amplifier drove the speaker beautifully, but sounded, to these ears, a bit opaque in the upper middle frequencies. Listening with us, Hansen heard a grain structure in the system that we were hard-pressed to detect, until we realized the contact points through the entire assemblage of components hadn’t been cleaned. As soon as it was done (after Hansen went back to Colorado), that “grain” was entirely gone. Zero problems with another Audiovalve, the Baldur 140 wpc, class-A monoblock tube amps, save for the need for slightly more (3 dB?) output to accommodate the murderous HP power-music tests. Two amps performed flawlessly on the system: the Plinius SA-250 IV (which we did not test at length, preferring to await the arrival of a current production model) and the new Edge NL-10 amplifier, which sounded like, but better than, the best Goldmund electronics I’ve heard (none, I must add, of recent vintage) and also like the Spectral M-360, which I wish I had been able to keep on hand as a reference, so pure was its sound.

One of the jerkazoid things I did during the testing was to abandon my reference (full-featured) preamplifier, the Burnester 808 Mk V, which, inserted into the system during final days of testing, popped the competition in virtually every respect. I came away with the new respect for its performance and it allowed me to hear into the Edge in a way that was revelatory (but don’t think I’m giving away all my findings just yet). Along the way, we increasingly listened to LPs on the Clearaudio Master Reference turntable with the Lyra Helikon MC cartridge and ran through a number of phono stages, starting with the Aesthetix, Io, which has served as a reference for some time, moving to a British-made solid-state unit, The Groove (at $2,400 a steal, but one that could be bettered with a 47 k/ohm load for moving-coil cartridges, instead of the 1 k/ohm load supplied with the unit). You moving-coil folks will know what loading down a great cartridge will do – and these listening tests proved the Helikon is more than a match for its younger sister, the limited-edition Evolve 99 reviewed in these pages some time back – and that is shear off the high-end air and bloom, which can leave the Wisdoms sounding bland and boring. Finally, we moved back to the Io, and then, just for kicks, the moving-coil stage in the Burnester. Another revelation. By contrast, the Io introduced what sounded like a mist into all the spaces of the soundstage – which made something approaching a muddle of the quartet and choral group on the Pergolesi Magnificat [Argo ZRG 505], a recording that, reproduced well, is one of the most thrilling to hear (but difficult to play back cleanly with correct timbral differentiations of each section of the choir). With the Burmester back in the system, the vocal quartet stood out against the choir, as it hadn’t with the Io, and the boy sopranos acquired that unique timbre that can give you the shivers when they are singing away up high and above a mezzoforte.

The Burmester/Edge combination, on this speaker, brought the system to life. Some component combinations, played back through the M-75, made it sound not only lifeless, but far removed from sonic reality, as a run-through of Brad Miller’s thunder and lightning storm [on The Power and the Majesty, Mobile Fidelity MFSL 004] had depressingly demonstrated.

I decided that the system was a wonderful reviewer’s tool, but it didn’t make me want to listen to music. And on that note, this review, in its first draft, would have originally ended, with me waffling because I knew I should have more than just respect for it if it were the reliable narrator I had found it to be.

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Part Four

During these extended listening sessions, I had, at one point, substituted the Danish Gamut amplifier (as close to a single-ended solid-state device as you can get, with its single MosFET output per channel). Before the Wisdom system had arrived, I had done enough listening to this amplifier to recognize it as one of the great ones, with an unheard-of fidelity to the contours of a music event. To me, it took solid-state design to a new level of achievement. But when I first inserted it into the system, I didn’t take care to adjust the output of the tweeters to match the sensitivity of the amp and thus had a mismatch that sounded unpleasant enough to cause us to dwell on the amp/speaker mismatch problem, which, thanks to episodes like this (during the early sessions), we thought more important than it later turned out to be.

I am not suggesting that finding an amplifier that allows the speaker to show its stuff isn’t important. It is critical. The Wisdom speakers, in most showrooms and demo set-ups, are going to sound disappointing, possibly even atrocious, with the wrong gear further up the audio chain. And the speakers will be blamed.

At the end of the tests, we gave the Gamut another whirl, this time, taking care to match the planar units’ output to the amps’ output. I dug deep into my record collection (the last several weeks of the listening were done exclusively with LPs) to find old favorites, long unplayed, including the magnificent Argo recording of Pergolesi’s Magnificat (the perfect test of how the electronics will decode both solo and massed voices, from baritones up to boy sopranos) and the wondrous Three Worlds of Gulliver from The Fantasy Film World of Bernard Hermann [Decca PFS 4309]. (The Burmester 808 was on the front end, being fed by the Clearaudio Reference arm/table, set up with the Helikon cartridge.)

And the speaker not only came exploding (okay, overstatement, but that was the subjective effect) to life, but the veil that had seemed to be there during the early weeks of testing was nowhere in evidence, and the entire instrumental and vocal ensembles had that quality of “thereness” rare in any audio experience. The Gamut actually reminded Markwell of the best in triode amplification, while to me it did all the things that tubes do, without any evident tube-like footprint, and had the clarity and transparency of the best solid-state. Indeed, this was the first time the system exhibited real transparency, knocking me off the fence and making me want to spend time just listening to music for the fun of it.

This said, I am still troubled by the complexity of the “Brain” and by its reliance on devices that are thought to be, by general consensus, inherently less than state-of-the-art. Which occasions the thought that the Wisdom Audio system might be significantly improved upon. And in its “Adrenaline Rush” model, the “Brain” is considerably more complex and sophisticated in its design.

We are not able, at this point, to speculate about the true potential of this system, or the sound of its bigger and much more expensive brother. On the face of it, there would seem to be room for growth. But, one may ask, exactly how much of its present “character” is the fault of the speaker itself and how much the fault of the gear in front of it? The Burmester/Gamut combination shows the speaker at its very best, but how many such combinations are we – or more specifically, you- going to find that will bring out that best?

The M-75 has to be turned up (unlike some of the electrostatics we’ve tested, notably the Beveridge of yore and the modified Quad ESL-63s) to create its full effect. Its resolution does not, like so many of the early Magneplanar units, extend deeply into the pianissimos of the sound, though with Gamut (particularly on the Herrmann and on the RCA/BMG “hp” CD of Mahler’s Third with Leinsdorf and the BSO), it goes further into the pianissimos than I had thought possible. If I had to call a shot on an overall coloration, particularly of the planar unit, I’d say it slightly to the tan side of neutral and of this I’m fairly certain. There is a kind of very low-level texture hard to hear and harder yet to describe that may well originate in the Brain and may slightly “veil” the lowest level information, unless you crank it.

I believe the Wisdom M-75 to be perhaps, metaphorically speaking, an order of magnitude lower in overall coloration than virtually any other speaker. Simultaneously, I believe, on the basis of purely observational listening, that it also is, in part, an unreliable narrator in somewhat compressing low-level dynamics and in its hard-to-describe “character.” (I have no idea how one would “measure” such degrees of coloration, hence, the word metaphorically.)

Given the “right” amplifier, this can be a dream speaker, as our late listening finally demonstrated. And the price is right. Up until the tail-end of listening. I thought the choice here for those interested in the M-75 would be between a colorful simulation of the real thing from a less truthful speaker or a more neutral, if somewhat unlifelike, approach to the absolute. But in fact, if you are willing to bear with it and search out the components that give you what you conceive as the closest replica of what we call the absolute, then this is one of the few systems thatjust may, like Scheherazade, thrill you for a thousand and one nights.

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Inside the Brain

Tom Bohlender of Wisdom Audio borders on vehemence about the “Active Brain,” the crossover unit that is in the heart of all three speakers in his line-up: The (mandatory) bi-amped systems cannot be correctly run without it.

The Brain is an almost infinitely adjustable active device. He says that only an active unit is capable of making the speakers “right” in terms of spectral balance and the ability to easily absorb large power inputs. He believes a passive crossover network would entail component saturation and distortion, resulting in compromised performance.

“The Adrenaline Active Brain,” says his literature, “is a fourth-order constant-voltage crossover that provides both low-pass and high-pass outputs. The crossover network is implemented as a fourth-order state-variable filter. The slope of each output is 24 db/octave and, because of the fourth order design, the high-pass and low-pass outputs are always in phase with each other…All…crossover work is done at the low end (sic) preamp level and then distributed to the designated amplifier, which allows for better amp load preference.”

On the surface, the Brain is similar to the device used in the Nearfield PipeDreams speaker system, but the M-75 Adrenaline unit is more complex and adjustable, able to fine-tune the frequency response of the system to individual room acoustics and the sonic preference of the owner.

Inside the chassis, one finds bank after bank of dipswitches used to effect the changes needed for the set up of the Adrenaline M-75s. These control the integrated circuits (which are basically just resistor-capacitor arrays) that make up most of the active part of the Brain. Bohlender says that, for the planar portion, there are three banks of adjustment per channel, with 12 switches per bank. For the bass region, there are six banks per channel, each with 12 switches. For fine-tuning of the crossover region, there are another two banks of 12 per channel.

Bohlender gave me a simplified explanation of how this tuning circuit works: Each dispatch turns a resistor in the ICs on or off. Most of the time, the majority of the switches are off. When one is activated, it causes a resistor on the shunt side of the circuit to “pull” on a capacitor via a predetermined voltage drop to effectively cause the cap to change value, thus altering the frequency response in the discrete band of that switch’s domain. The signal, meanwhile, does not have to travel through any extra parts to “feel” this tuning; the altering of the cap’s value by shunting it to a resistor effects the slight equalization needed.

In toto, there are almost 10,000 possible settings, but Bohlender says he rarely uses more than 200-300. Still, this is more than a handful for most of us, and is why Bohlender sets up every system he sells. I watched him do this at HPs with a microphone and a pink-noise generator-equipped real-time analyzer for almost eight hours. He had to repeatedly refer to a thick sheaf of papers to make sure that he was hitting the right switches for the changes he wished to effect.

Clearly this is not a system that can be set up by an average owner. Bohlender has begun to train dealers in this procedure, but for the moment he is the Lone Ranger for this critical portion of the installation.

According to literature, the set-up and adjustment of the Brain involves several steps. First, both channels’ controls must be set to their initial starting points. There are four adjustments for each channel; The damping control raises and lowers the volume of the Planar driver and the LFR (Low Frequency Regenerator) in the vicinity of the crossover point, normally around 125-250 Hz 9this effectively adds or subtracts vocal chestiness and perceived “roundness” of instrumental sounds), and is set to 0 dB; the Qb control knob, which affects how tight or loose and how deep and visceral the bass response from the LFRs will be and allows a bit of adjustment to rooms and conditions, is initially set to a value of .55; the Planar and LFR knobs control the amount of gain/ output levels of the planar magnetic driver and the low-frequency units, respectively, and are set to “Zero” to start. At their 0 positions or below, the Planar and LFR controls do not add gain to the system and are totally passive. Bohlender advocates never raising the level of either past 0 unless the amplifiers in use are so mismatched in sensitivity or power rating that adding active gain is necessary to bring the system into proper balance. Op amps in the crossover are used to add this gain. If needed, but the cleanest signal path is maintained if they are not invoked.

Next, Bohlender begins to examine the in-room response at the listening position. As he looks at the pink noise trace on the RTA, he uses the adjustable settings to achieve his desired in-room response. Generally he likes to set the system up so that the response at the listening position is slightly rising from 30 to 15 Hz (for best low-end impact), then as flat as possible from 30 Hz out to about 5 kHz. At this point, he likes to shelve down the response 1-2 dB and maintain flat response out to 20 kHz. Here the banks of dipswitches come into play, and are activated as needed to smooth the response of the system. Bohlender also includes a 3-position toggle switch on the rear of each tower that may be used, once system setup has been finalized, to alter the output of the speakers between 10 kHz and 20 kHz; the center position is deemed to be “normal” with neither boost nor cut; the “up” position adds a 2 dB boost, and the “down” position makes a 2 dB cut. This allows some mild tailoring of the highs without futzing around inside the Brain.

When the results are properly achieved, one can then substitute amplifiers for either the low- or high- frequency sections with only minor alterations to the Brain’s level controls, which we did throughout the review period (actually we used the Krell FPB 600 STc amp for the bass throughout the testing and tried a number of other amps, both tubed and solid-state, for the planar magnetic panels.)

Bohlender says that the M-75 system exhibits a particularly benign, purely resistive load of about 4.8 ohms to the amp driving the planar portion and either 3 or 12 ohms to that driving the bass, depending on whether the woofers are wired in parallel or series. This implies that the system should be adaptable to a fairly wide range of amplifiers, depending on one’s sonic preferences, and indeed this seems to be so.

The one exception we observed in Sea Cliff is that if we try to use the tubed Atma-Sphere MA 2 Mk ll OTLs, the treble energy above 7 kHz is shelved down several dB relative to the rest of the spectrum.* To use the Atma-Spheres, the Brain would have to be re-set in somewhat different pattern than for most solid-state and transformer-coupled tube amps. If dialed-in for the Atma-Sheres (and probably other OTLs as well), we could not use non-OTL amps without resetting the Brain’s dipswitches (a major undertaking), but at least the flexibility is there.

* There is a slight wrinkle in the main driver’s portion of the impedance “curve,” in that each set of planar magnetic drivers that Bohlender assembles into each system are individually adjusted to achieve the proper balance between the main portion of the drive element (which uses 2 traces; Bohlender refers to this area as the “Smart” portion of the driver, meaning that he manages to make it behave as if they were dedicated, separate element, when it is, in fact, physically part of the same driver). At 7000 Hz, where the “Smart” portion takes over, the impedance of the driver can (depending on the individual drivers’ manufacturing tolerances) drop just a little (.5-.8 ohms between 7 kHz and 8 kHz), thus causing an OTL design such as the Atma-Sphere to have a slight power response droop, causing the shelving down of apparent response referred to above.

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