Stereophile: MartinLogan Monolith loudspeaker

MartinLogan Monolith loudspeaker

J. Gordon Holt, March, 1985

Most Stereophile readers are aware by now of why the full-range electrostatic should, in theory, be the ideal transducer. (If you aren't aware, see the accompanying sidebar.) Acoustat was the first manufacturer to design a full-range electrostatic that was so indestructible it came with a lifetime warranty. (MartinLogan is now offering a three-year warranty on their speakers, and is considering going to a lifetime warranty). But Acoustat was never able to solve another problem that has plagued all flat-panel speakers: treble beaming.

Until recently, all push-pull electrostatic designs were flat panels, and when sound is produced from a flat panel, interference patterns cause the high frequencies to be radiated from the panel's center in a beam whose width becomes narrower with increasing frequency. Most designers of full-range electrostatics have attempted to circumvent this beaming through the use of several narrow vertically oriented panels arranged in a gently convex curve but, while this seemed to increase the apparent HF dispersion of the system, it did so at the expense of imaging precision. The reason is that the more discrete radiating sources there are (horizontally), the more each source interferes with all the others. With only one panel per side (as in Acoustat's Models 1 and 1+1), a flat-panel electrostatic can produce incredibly specific imaging for a listener positioned dead-center between the speakers (the so-called "sweet spot"), but the imaging deteriorates if you move to either side by more than a few inches. Adding additional panels to each side broadens the seating area from which one can hear acceptable imaging, but at the same time degrades imaging heard from the sweet spot.

It has long been assumed that the electrostratic's beaming problem would be eliminated if the large diaphragm's width could be accomplished via a single, curved diaphragm, but this was generally dismissed as an impossible goal b¢cause, regardless of the shape of a flexible membrane's outer edges, any tension on it acts to flatten its center area. This brings us to the MartinLogan Monolith.

Curved Panels
Rather than building their electrostatic as a series of panels, MartinLogan uses a diaphragm that is curved in the horizontal plane over its entire surface. The diaphragm is held in place at top and bottom to curved structural members, but it was necessary for ML to develop a special manufacturing process to keep it curved over its entire horizontal dimension. The result is the first beam-free electrostatic (footnote 2).

The Monolith is a two-way hybrid system that uses a large electrostatic radiator to span the range from 100Hz upwards, crossing over to a 12" woofer below 100Hz. The Monolith's woofer "isolation" from the power amplifier is minimized through the use of a huge crossover coil—about the size of those two-gallon plastic jugs of distilled water sold in supermarkets.

MartinLogan contends that the driver blending is "seamless" and that although it is possible to bi-amplify the system, this is not necessary. But even before I audidoned the Monolith, I had doubts that its 12" woofer would be able to mesh properly with the much faster electrostatic upper range.

At the time of first testing these speakers the two best amplifiers I had in the house were the solid-state Electron Kinetics Eagle 7A and a pair of the mono Paoli SOB tube units. I would judge both to be state-of-the art designs, but each has its unique areas of almost unchallenged superiority. With the Eagle that superiority is in its low-end range, where it possesses impact, detail, and control—in abundance. But it has never sounded very good through its higher-frequency range with electrostatics. The SOB, on the other hand, has the sweetest, most delicately musical high end of any amplifier I have ever heard, and has proven to be the most nearly perfect complement to every electrostatic speaker I have tried it on. But, while it exercised better LF control than most tube amplifiers, it still has less control than the beefiest solid-state amps.

I started my tests using the Eagle because I was particularly curious to find out what the speaker's woofers could do under the best of circumstances, since woofer "meshing" is the most common problem with hybrid speaker systems. For example, experimenters have been trying for years to come up with a cone subwoofer for the Quad ESL-63 that can match its transient agility, and the Monolith's electrostatic section does not sound a whit slower than the ESL-63.

Sound
I found the Monolith's low-end extension to be remarkably good—subjectively flat down to almost 35Hz in my listening room, with usable output to slightly below 30Hz. Low-end detail, however, was not very good, though I am not at all sure that the problem results from a poor meshing between the woofer and the electrostatic. The problem seems to start at a frequency much higher than the system's crossover. The diminution of attack and detail sounded as if it set in at around 500Hz.

In general, the Monolith's middle-range performance was quite a bit better than that of most audiophile speakers. It has none of that laid-back, unctuously over-rich coloration so admired by LS3/5A lovers. The Monoliths reproduce cellos, lower brasses, and piano bass strings better than do most other perfectionist speakers and, perhaps because of this, they have more apparent dynamic range than the speakers I have grown resignedly accustomed to auditioning these days. They are far superior to the Acoustats in this regard, which is perhaps why so many observers have complained about the Acoustats' lack of authority during fortissimos. The Monoliths are also very efficient (for electrostatics), playing cleanly at near ear-shattering levels with amplifiers rated at (only!?) 100 watts/channel.

Relative midrange superiority notwith standing, the Monoliths still exhibited, with the best amplifiers I had, some deficiency of "gutsiness," compounded by a distinctly ill-defined low end. Bowed double basses lacked delineation (ie, the feeling that one could count the cycles), and plucked bass strings and kick drum sounded soggy and shy of attack. With piano, progression of notes descending into this region sounded as if the piano's hammers had become less hard; some of the percussiveness just disappeared. Kettledrums had sharp attacks but undercontrolled and somewhat aimless decays, like harmonics in search of their fundamentals. And this, remember, was with the Eagle 7A power amplifier, which has better LF detail and control than any amplifier I know of.

There were some other less-than-appealing things to be heard from this system with the Eagle. To begin with, the Monoliths had what I feel to be too much high end (above 10kHz) content—far more, relative to the lower ranges, than one would ever hear from live musiC. They were also exceedingly bright-sounding, to the point of steely hardness. (By "bright" "I refer to excessive apparent output in and about the 5kHz range—the mid-treble range—not the range around and above 10kHz that many audiophiles incorrectly call the "brightness" range. Since I pioneered the use of this terminology in the first place, I can define its meanings without risk of contradiction—I should hope!)

And that was only half of the problem with the Eagle! On top of the hardness was an overlay of harsh grittiness. Since the Eagle sounds superb with a number of other speakers (all of them cone speakers, by the way), this only confirmed my contention that you cannot judge an amplifier except in terms of the speaker it is being used with. And vice versa.

So, I switched to the Paolis. These amplifiers effected improvements in some areas and regressions in others. Expectedly (in view of what I knew about the SOBs), the extreme high end became softer and more musical, but the middle high-frequency content increased and the bass became a little less tight—not what the Monoliths needed. I still considered the sound to be totally unacceptable.

I also borrowed the BEL 2002 amplifier (favorably reviewed in Vol.7 No.6). This elicited smoother and more natural upper-range sound from the Monoliths than did either of the previous two amplifiers but, oddly enough, had markedly less ability to control the 12" woofer than did the other two amps. The bass with the BEL was inordinately heavy and woolly. Clearly, none of these amplifiers was ideal for these speakers. (ML tells me they have gotten excellent results with Threshold and Krell power amps. I have arranged to re-borrow the Threshold S/500 for further testing of the Monoliths.) Next, I decided to try biamplifying the speakers.

Footnote 1: When a large-diaphragm panel is "aimed" directly at a listener, putting him the same distance from the left and right sides of the panel, all of the radiated `waveforms will reach his ears simultaneously and in step with one another. But if he moves to the right of the panel's axis, sounds from the panel's right-hand side will reach his ears slightly before those from its left-hand side, and the resulting interference between them will cause partial cancellation of each signal. The effect is wavelength-related; it is most pronounced at the higher frequencies, and the subjective result is the well-known electrostatic "hot spot"—a tendency for the panel to radiate an on-axis "beam" of treble that becomes progressively narrower with increasingly frequency.
Footnote 2: The Quad ESL-63 is inherently as beamy at high frequencies as any other flat-panel system, but it utilizes delay lines and annular rings of radiator diaphragm to simulate electrically the behavior of a curved diaphragm.

Each Monolith has external strapping which makes bi-amping (and bypassing of the internal crossover components) relatively simple. I used an M&K 100Hz passive crossover to feed the BEL for the high end and the Eagle at the bottom. There ws some improvement in quality across the board, but not as much of an improvement through the lower midrange and upper bass as I had hoped for. The low end remained rather ill-defined and still had what I felt to be entirely too much high end, but biamping produced the best sound up to that point in my testing.

Equalization
A phone conversation with ML'S Gayle Sanders revealed that I was not the first person to complain about the Monolith's brightness. Indeed, ML was already making available a passive equalizer that could be connected to the electrostatic element (via the back-panel strapping) to tame the aggressive upper range. Gayle offered to send me a pair of them.

Each equalizer consists of an inductor, resistor and capacitor, all paralleled and connected in series with the signal line. The effect of this network is to depress the range above 4kHz, with a flattening-out shelf above 8kHz (to prevent progressive attenuation of the extreme upper range). I won't say this transformed the speakers, but it sure put them in the right ballpark.

Extreme highs were still a little excessive, but the apparent brightness of the speakers now corresponded pretty well with the known attributes of the amplifiers used on the high end. (The Eagle, for example, is somewhat bright, which is one reason it makes so many speaker systems sound almost shockingly real and alive.) With the equalizer in, the high end from the Eagle/Monolith combination corresponded well to the qualities of the various program sources. The grittiness I had previously noted was entirely gone and, with the best available source material the Eagle/Monolith's high end sounded as palpably real as anything I have heard. HF detailing was so incredible that the sound would have been totally unlistenable had I been using a preamp with the slightest tendency toward harshness or grittiness. (I was using a tubed preamp known to have an unusually sweet, clean high end—the Conrad Johnson PV-5).

Yet, while this sound was tremendously exciting, it did not have quite the effortless ease that makes live music so easy to listen to. For that quality I must keep returning to the Watkins WE-1s (footnote 3).

By comparison, the BEL amplifier sounded sweeter and more "listenable," but some of that reach-out-and-touch-someone aliveness had been lost. With the Paolis, the extreme high end was right on, but the middle high-end brightness was once again excessive. (I like less high-end content than do most audiophiles who frequently complain that live music is lacking in treble. I should also add that I feel that most loudspeakers have entirely too much HF output; I am not singling out the Monolith for this criticism.)

Imaging
One thing that remained consistently superb throughout the testing was the Monoliths' imaging. To hear electrostatic-type detail, smoothness, and attack, without the usual on-axis sizzle and off-axis dullness and imaging deterioration, was a rare privilege. What this means in terms of stereo imaging has to be experienced to be believed! The Monoliths image almost as well as any system I have ever heard, and is even capable of the remarkable holographic effects I have previously heard only from a couple of satellite systems. (By "holographic" I refer to the impression that closely miked sounds are located out in front of the speakers, floating spookily in space a few apparent feet in front of my face.) The soundstage is wide and deep, and front-to-back perspectives replicate those of the recordings themselves about as well as I have heard from any speaker system.

Interestingly, though, while the Monolith has no high-end directivity, it does have some in the middle range. To either side of the speaker's "axis" the sound loses some of its body and impact, and if the speakers are not toed-in towards the center of the listening area there is a significant shift in lateral image position as one moves from side to side. There are speakers which provide more uniform lateral localization from a wider listening area, but all of these have a "shaped" directivity pattern in which the apparent output from each driver diminishes as you approach a location directly in front of it. (The dbx "Soundfield" speaker is a prime example of this directivity shaping.) But, all in all, the imaging from the Monoliths is as good as I have heard from any other kind of speaker, particularly any electrostatics.

That's where things stood—lots of potential, but not the overall satisfaction you should get for this kind of money when Electron Kinetics' John Iverson paid me a visit, carrying a cute little new Eagle amplifier under one arn. (Try to do that with the 7A!) It was an Eagle 2, rated at 120Wpc and priced, at that time, at $850. (It has since risen to $895.)

Revelations
We tried the new Eagle with the Monoliths (which were back to being mono-amped), and I was flabbergasted to hear this little amp dramatically outperform its big brother in every way. The low end was much tighter and suddenly had real concussive impact from kick drum. The high end was sweeter, more open, and more musically euphonic, and the entire audio range had superior detail. The sound of good recordings was astoundingly alive—and except for that lower middle range deficiency—was far better than anything I had ever previously heard in my own listening room! I was really bowled over, and after several months of living with this system, I still am. I won't go as far as to say this is the best sound reproduction I have heard anywhere, but in most respects it comes close.

But what, then, is the "sound" of the ML Monoliths? On the basis of what I know about the sound of the amplifiers I used with it, I'd say it is (with the "equalizer" noted above) extraordinarily detailed, a little bright and forward (although not hard, with the right power amp), somewhat uppish at the high end, and very extended but still a shade woolly at the bottom.

ML's assurances notwithstanding, this system does benefit from tube amplification (using an external passive crossover). The low end is tighter, deeper, and better-controlled, and the rest of the range is slightly but definitely cleaner and detailed.

The speaker's high-end sound with the BEL amp suggested that some amplifiers do not need the equalizer. The Threshold or Krell amps may turn out to be just the ticket, but after having lived with the Monolith/Eagle combination (with the equalizers) for a while, I have decided that that is, at least as of now, my preferred combination. I like this combination better in some respects (imaging, depth, deep-bass range, extreme high end, and aliveness) than the Eagle/Watkins pairing, but still find the latter more convincing in its portrayal of large brasses, cellos, and piano bass strings.

One thing which energ.d clearly from my tests is that the Monoliths are both unusually amplifier-sensitive and amplifier-critical.

These are not necessarily the same thing. The speakers are amplifier-sensitive in that their low-end control is drastically affected by the power amp used. They seem to need something with tremendous LF current capability in order to sound respectably disciplined at the low end. They are amplifier-critical in that their incredib1e detail and slight brightness make them exceedingly revealing of the merest traces of distortion in the power amp and preamp.

There are probably so few power amps out there that meet both criteria that I could only recommend the speakers with some strong qualifications or with specific amplifier recommendations. And I haven't tried enough amps yet to be able to recommend at this point any but the Eagle 2 or MartinLogan's suggested Threshold Stasis units. (Although I would guess the big Krells or the new Rowland Research amps might do fine too. We have a Rowland on hand, and I'll report in the next issue on how it goes with the Monoliths. The Krell amps are still with Antony H. Cordesman on the East Coast, so I don't know when I'll be able to comment on their abilities with the Monoliths.)

In short, the MartinLogan Monolith is yet another example of the truism that nothing is perfect. This system images so well, and has such hair-raising dynamic range, definition, and clarity (through most of its range) that its small imperfections seem less forgivable. It's rather like going to heaven and finding that it's everything you expected except that it never stops raining!

Some of the Monolith's shortcomings could, I think, be easily eliminated by some more creative equalization. I would, for example, like MartinLogan's HF equalizer to do just a little more of what it does now. And I know some hyping of the 300–800Hz range would enhance the speaker's ability to reproduce the large brasses, cellos, and so on. If it doesn't measure flat then, who care? After all, we keep telling ourselves, the "bottom line" in audio is how something sounds, not how it measures.

The low-end 1ooseness with many amps may be harder to remedy. This is, as I said, only a minor problem with the Eagle 2, but was really bad with some other power amps. Some of this is, I believe, related to the subjective shortage of mid- and lower-midrange contribution, but that's clearly not the whole story on the Monolith's low end. I suspect it is also caused by the system's 6dB/octave crossover, which allows the woofer to operate well up in the lower midrange before dropping out of earshot. (MartinLogan is currently working on a powered woofer system with integrated amplifier—see my editorial in Vol.7 No.5) that should effect a marked improvement in bass quality.)

Summing Up
There are so many things I love about the Monolith that I hate to qualify my review of it. One could argue that the degree to which it does practically all of the right things is probably worth the $4850/pair price, but the fact remains that there are some areas where its performance will not be up to what most buyers would expect from a speaker in this price class. There is just no point in trying to pretend that the Monolith will be all things to all listeners.

The add-on equalizer, which I feel should be made available without additional charge to the buyer (or, better still, incorporated into the speaker's internal crossover), is a step in the right direcfion. I hope there will be more such steps, and I shall watch further developments at MartinLogan with great interest.

J. Gordon Holt returned to the Monolith in March 1986 (Vol.9 No.3):
While I (currently) favor the MartinLogan Monoliths because of their incredible you-are-there realism, I still go back to the Infinity RS-1Bs from time to time for their awesome quality of power and excitement. The Infinities can give me goosebumps more often than any other speakers I've had on hand; every audiophile needs that kind of a fix from time to time.

After awhile, though, the RS-1's peculiar (apparent) sluggishness gets to me, and I start to long once more for the delicacy and transparency of the Monoliths. Which just goes to show once again that, no matter how good a loudspeaker system is, there's always another one that does some things better. I am not just waffling when I say that I would hate to have to choose one or the other of these to live with exclusively. Although that doesn't help you make a choice, does it?—J. Gordon Holt

Footnote 3: Note that the "version" of the Watkins that I so much like with the Eagle is the original one. Current versions of the speaker may or may not be so ideal for use with that amplifier.