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Yes, not unlike your author, the Adagios feature underhung drivers. Cough. Go on now, we have already anticipated your mental flights of fancy and to that end built in any number of snickering whimsical allusions, metaphors and Blazing Saddles references. To paraphrase Robert Lee from our interview: What's the point of reducing amplifier distortion to subatomic level if the transducers in your loudspeaker system are putting out levels of distortion peaking anywhere from 5 to 20%? Lee's use of underhung drivers is based on solid theoretical principles and offers a palpable musical upside. Yet you would be hard pressed to find underhung drivers and a ribbon tweeter employed together in any but the most advanced, expensive designs.

No less a loudspeaker legend than Jim Thiel employs underhung drivers in his own critically acclaimed loudspeakers - though it would seem that the notion of referring to them as underhung makes an old school engineer blush. In his own literature, Thiel references their deployment as short-coil/long gap technology. Fair enough. (In the interest of completeness, I should point out that Thiel markets a very well-received 3-way, the Thiel CS2.4, which features an eight-inch underhung driver with a metal cone coupled to a passive radiator and a coincident tweeter/midrange driver array that retails for $4200/pr and is definitely worth an audition.)

Meanwhile the folks at Wisdom Audio, who produce some remarkable high-end loudspeakers of their own, have no such compunction. A round of underhung drivers for the house, barkeep.

In perusing both their websites, I found some technical explanations of this technology that articulate the advantages far better than I ever could. I've taken the liberty of quoting from both the Thiel Audio and Wisdom Audio websites as follows.

First, from the Wisdom Audio web site:
The underhung driver allows the amplifier to see a constant impedance load instead of a constantly changing impedance load associated with overhung drivers. Distortion is lowered tremendously and a tight, visceral response occurs simultaneously along with less effort for the lower frequency demands placed upon the driver. Piston extension and travel capabilities are increased dramatically while increasing control. The cone weight can be increased allowing the use of stiffer composites...


Since the magnetic force on the coil is constant and completely symmetrical... there is a constant relationship between applied coil current and generated force...because the voice coil is always surrounded by the same amount of metal and magnetic flux density, the electrical impedance is also independent of position and cannot produce distortions by this mechanism. Very good thermal coupling of the voice coil to the top plate, which always surrounds it, contributes to high power handling and low compression.

Finally, from an article by Kathy Gornik on the Thiel website:
The driver's voice coil, which is attached to the diaphragm, is positioned inside a magnetic airspace (called a gap) created by the fixed structure of the driver's motor system. This fixed structure, comprised of a magnet, steel top and back plates, and a center pole piece, creates a magnetic field around the voice coil. When power from an amplifier is applied to the voice coil, motion of the diaphragm/voice coil assembly is generated due to the interaction of the voice coil's electrical current with the magnetic field. This motion of the driver's moving system is what creates the sound we hear.

A typical driver will have a magnetic airspace for the coil that is somewhat shorter than the voice coil itself (a short gap). By allowing a longer voice coil to overhang a magnetic airspace that is shorter than the voice coil, the voice coil can move a given distance and still have some portion of itself inside the magnetic airspace. This avoids excessive distortion while the coil is moving; however the results are not fully satisfactory because magnetic leakage exists both in front of and behind the magnetic airspace. Depending upon the position of the coil within the air space as it moves, interaction with this magnetic field leakage produces significant distortion (usually up to about 20% before the coil leaves the air space).

Jim Thiel's solution has been to develop the short coil/long gap technology. In this system, the thick, multi-layered voice coil is as short as it can possibly be in length. The magnetic air space of the gap is made much longer than the coil. When demanding high power conditions are applied to the voice coil, it is able to move very far in either direction without any of the coil ever leaving the full strength of the magnetic air space or interacting with the magnetic leakage.

This approach requires magnets and magnet-system parts that are several times as large and expensive as those found in conventional driver systems, but the startling results are a ten times (order of magnitude) reduction in driver distortion, even under the most demanding of conditions. Thiel's short coil/long gap driver technology is heard by the listener as cleaner, clearer sound reproduction that does not disappoint for ease, naturalness and effortlessness.
Interview with Robert Lee - continued
Tell me about the transmission line.

The use of a transmission line greatly increases low-frequency extension and minimizes the impedance peaks we see in ported alignments.

Why only one set of speaker terminals?

I am using our Acoustic Zen Satori speaker cabling for hookup wire which is 10 AWG/6N zero crystal copper. That is far better cabling than most people have going from their amplifier to their speaker. I really do not want for people to alter these relationships. I have already fine-tuned the frequency response and tweaked all phase adjustments. If somebody employs a bi-wire setup, it could alter the overall balance so I prefer a very simple, direct connection.

If you have unlimited funds and unlimited size, you can make your loudspeaker do anything you want. Then you can end up with a Wilson Audio Alexandria, which was pretty bloody awe-inspiring when I heard it in a tuned room at Innovative Audio in New York. But why the hell shouldn't it be? It costs $125,000/pr, weighs several hundred pounds and is taller than Wilt Chamberlain. There are no practical limitations. I found that your speaker had some of the best attributes of a good two-way and a floorstander. Still, at its $4,300 price, there have to be some compromises. What were the relative trade-offs you had to address? The Adagio does more things well than most speakers I've heard at its price yet naturally, it won't have the frequency extension of a Vandersteen Quattro with its built-in subwoofer. Nor does it have the immense soundstage and ambience retrieval of the Dynaudio Confidence C1. However, both are more specialized speakers and both are significantly more expensive.

That is a good point and I would like to say this. There are thousands of speaker manufacturers worldwide but so far I have identified less that ten who employ underhung drivers. I think that underhung drivers are the best solution to reduce harmonic distortion in the bass. No one ever talks about the huge amounts of THD in the low frequencies, especially when you are playing things loud. Most drivers create from 10-12% THD when you listen at over 10 watts. If you are listening to 10 watts through your speaker system, you get 5% harmonic distortion. So what are you listening to? When people design amplifiers, they rate them at 0.05% harmonic distortion. Meanwhile even at modest volume levels, your low-frequency drivers put out 5% or greater harmonic distortion so nobody can listen at even low levels and achieve true purity with low distortion, never mind concert levels.

That's why I selected to use both the underhung driver and a ribbon tweeter of my own design. The advantage of ribbon tweeters is their low distortion. The drivers in the Adagios result in what I believe to be the lowest distortion loudspeaker system in the world - at any price. People are so concerned over distortion figures in their amplifiers and CD players and would never dream of accepting the levels of distortion their speakers routinely put out. Most audiophiles remain unaware of this simple truth.

Even when speaker makers achieve good phase coherence, they are still using high distortion drivers for low frequencies that impact the quality of the signal. When listeners hear the resolution and low distortion achievable by underhung drivers, I predict many other manufacturers will follow suit and employ them. It's like the use of single crystal copper which Acoustic Zen helped popularize in cables. Now many manufacturers employ single crystal copper and silver.

The only company doing something like I am doing now (using ribbon tweeters and underhung drivers) is Wisdom Audio. And their top-line speakers are far more expensive. Thiel has been at the forefront in this arena but they feature a different style of tweeter/midrange. So the Adagio is really a very unique loudspeaker product. At only four feet high, it is a very good speaker for the average rooms most people actually have. Unless you use a very, very large room, the Adagio should be just right for most real-world listening environments. People have been taught that they should get a really large speaker that has the potential to excite plenty of reflections from wall to wall; to excite bass frequencies and room nodes; to produce all manner of colorations and frequency cancellations. Not the Adagio. It is perfect for 15-20 foot rooms.

Without neighbors getting most of the bass [laughter]. Obviously, there are speakers that will do certain things better, yes?

I am already working on a subwoofer that will match the Adagios perfectly, handle all frequencies below 60Hz and go down cleanly to 18Hz. I think the only thing the Adagios cannot do is give you that punch and pressure and power below 30Hz. Yet you can still hear the bass clearly all the way to the bottom of the piano and when the low frequencies stop, the drivers stop instantaneously. There is a minimum of uncontrolled motion and overhang. That is another advantage of underhung woofers.

Your bass drivers do stop on a dime, with no discernible overhang. And the tweeter is not bright at all.

Other things that are very important to me as a designer are the phase and impedance curves. I think those are far more important than ultimate SPLs. You want those curves to be as flat as possible so you don't place a terrible strain on the amplifier. My phase curve is essentially flat from 10Hz to 40kHz. And the nominal impedance of the Adagios is 5 ohms. It is most flat from 100Hz to 10kHz, almost a straight line keeping within that 5 ohm impedance. You don't have different frequencies displaying wildly fluctuating impedances. Impedance is like resistance. So if different frequencies display different levels of resistance, the amplifier reacts and distortion is the result. As audio designers, we must reduce distortions wherever we find it to make the experience of listening to music more involving. That is the ultimate goal.
Robert Lee and Chip Stern

So there you have it from multiple credible sources: significantly lower distortion, a constant impedance, greater driver excursion potential and control, increased low frequency extension and the option of employing denser cone materials. The musical payoff should thus be a cleaner, less fatiguing, more natural sound; less strain on your amplifier; a decrease in cone anomalies; enhanced driver excursion with a more instantaneous response to transients; the ability to employ stiffer cone materials such as the Adagio's dense ceramic-impregnated fabric cone that make for a quicker, more nimble driver low in colorations and distortions that can react quickly and stop on a dime to minimize bass overhang.

Likewise for the rationale behind Lee's circular ribbon tweeter. He deploys a nearly weightless transducer that is exceptionally smooth, fast and clean, richly detailed and not at all bright. Given the 3000Hz crossover point (representing the very upper reaches of the piano's upper register), the Adagio's tweeter is not so much dealing with the fundamental frequencies or the leading edge of transients but is more fully occupied with the accurate reproduction of complex harmonics and the overtone content of music (which nevertheless can have a profound impact on the subjective performance of the low-frequency drivers). Thus we can discern the reasoning behind Lee's use of a steeper 18db/octave crossover wherein he endeavors to tweak the phase to make things as flat as possible. Anyway, that's more or less how I understand it.

I have already communicated my rapt enthusiasm for these loudspeakers. Let me detour into the nature of the current reference system to make my following sonic observations on the Adagios more relevant. For the past year and a half, I have done without my customary muscle amps. After an extended conjugal visit, I returned the 500-watt McCormack DNA-500 with more than a tinge of regret. For a while, I had a bridged pair of Butler Audio TDB-2250 in house, which were then needed at the NYC show and never returned.

Since last summer, my primary reference amps were more modestly endowed integrateds: a 70wpc transistor Simaudio i-5 and a 28wpc tubed Mesa Tigris. The i-5 has been superseded by a Simaudio i-5.3 and thus went back before the Adagios arrived. Nevertheless, the Adagio proved to be very efficient and an easy load for the Tigris integrated configured in 2/3 pentode mode (featuring two 6V6 running in pentode and four EL-84 running in triode through a common output transformer) with 4dB of NFB. The majority of my speaker break-in time and formative listening with the Adagios were taken with the Tigris. With more modestly endowed speakers such as the Epos ELS3, Alon Lil' Rascals, Meadowlark Swallow, Linn Tukan and Joseph RM7si Signature MKII, the Tigris worked like a charm. While the Adagios proved a fine match at moderate to slightly pushed levels, at the dynamic volumes I'm accustomed to listening to music and driving my system, it couldn't quite handle some of the more extreme audio gauntlets I made it walk. Thus the leading edge of some transients didn't quite come off all that cleanly and while the amp strained to control the bass, the top end could at times get a little grainy. So the Tigris was the weak link in this particular signal chain. But in a smaller room and listened to at something other than the full-throttle Vlad the Impaler concert levels I often favor, the Tigris would prove a more than adequate amp for the Adagios. Designer Randall Smith has his Tigris teamed with a pair of Meadowlark Kestrels - easy to drive, full of flava.

It was when the Rogue M150 monoblocks arrived for an upcoming PFO review that I finally felt like I could bet the ranch on what I was hearing from the Adagios. These monoblocks -- which derive more from the circuit topology and technical advances of the imposing 200 lbs Rogue Zeus than from the M120 monoblocks which they supersede -- are KT88-based tube amps with an uncommon amount of elegance and sheer drive, putting out an honest 100 watts (and then some) in triode and 150 watts in Ultralinear. Without jumping the gun too much, let's just say -- in NYC's finest cabbie speak no less -- that these amps are an eight-balled motherfucker and that running them even in triode mode was more than adequate to help the Adagios reach their full sonic potential tonally, spectrally and viscerally.

While the Adagios were most assuredly not designed to give you a lap dance (the transition from the upper bass to the lower midrange is about as smooth and seamless as you are likely to hear); and while there are certainly more punchy speakers out there - when I got the Rogue M150s into my system, I was disabused of any notions that the Adagios were somehow light in the loafers in terms of sheer low-end wallop. Team the Adagios with an amp that has some balls (in this case, eight), and you should be able to drive these speakers as hard as you want without inducing grain, audible distortions or enervating fatigue. I cannot recall experiencing that with any other amp/loudspeaker combos I ever had in my listening room (although I can
recall coming pretty close with the Rogue Magnum 99, the McCormack DNA500 and a pair of Joseph RM25si MKIIs). This speaks not only to the unimpeachable quality of the Rogue M150 as reference amps but also to Robert Lee's stated goals of minimizing driver distortions. These babies are about as clean as you can get.

At the heart of my system sits the VTL 5.5 linestage preamplifier. It's my old standby (I also employ a Rogue Audio Magnum 99 which is excellent too in its own way). While the 5.5 doesn't wear its tubiness on its sleeve, it offers all of the detail, harmonic richness, depth of field and midrange layering one would expect from a great tube preamp but does so without the sappy bloom or muted top end that makes some suck preamps sound more MyFi than HiFi. Having lent this preamp out to some better-heeled audiophiles than myself, I can report back that it took on preamps costing five times as much without breaking a sweat.

Which brings us to the centerpiece of my signal chain and one of the greatest audio achievements of the past 25 years - the Linn Unidisk 1.1 universal player. It represents an absolute standard of front end resolution, a component that's reliably awe-inspiring yet supremely musical in a manner that never calls attention to itself. So exalted in fact is the Linn1.1's playback that I found myself turning to other digital and analog sources during the audition process just to discount its overwhelming, indisputable authority. These included the tubed Njoe Tjoeb 4000, the California Audio Labs CL-20, a Marantz PMD430 stereo cassette recorder and a Rega Research P25 turntable outfitted with a Rega Research RB600 tonearm and the superb low output Grado Statement Master tweaked with a Ringmat 330 through a Rogue Stealth phono preamp. I also referenced a set of superb headphones with the Mesa Tigris, the accurate andnon-fatiguing Grado RS1.

By any standard, this a fine reference system.