Equipment report
Esoteric MG-20

To coincide with its 20th anniversary, TEAC Esoteric expanded its product base during CES 2007 by adding a loudspeaker line. It was an appropriate moment to celebrate, and sharing a toast with corporate president Motomaki Ohmachi during the press function, I reflected on what turned out to be a most positive first impression. What is special about the MG-10 and MG-20 is that both feature an all-magnesium driver complement. The MG-20, a slim floor-standing tower, is outfitted with a pair of 6.5" cone woofers and a tweeter, while the bookshelfsized MG-10 uses a single woofer. My first take on the MG-20 tower was extremely positive: wonderful clarity, but without the metallic aftertaste that often accompanies metal-diaphragm drivers. For the record, this speaker immediately rose to the top of my list of review priorities for 2007.

If you were an electronics-based manufacturer with speaker-design ambitions, how would you go about realizing a final product? Esoteric had the good sense to partner with Tannoy in the U.K. for the engineering and manufacturing functions. Tannoy offers over 75 years of experience and has gained a solid reputation as a leader in various sound-reproduction fields. Esoteric’s system architecture called for a coherent and involving soundstage, an open and naturally detailed midrange, an extended treble, and effortless dynamics. Alex Garner, Tannoy’s technical director, nurtured these goals to maturation.

The path to success involved several critical ingredients. First, consider the MG- 20’s cabinet. It’s fairly light, but much of its mass is made up of a 1"-thick front baffle. And that’s where the rubber meets the road; it’s the part that takes all the pounding from the woofer baskets. Each action generates a reaction in the front baffle, and the less flexing it undergoes the lower its sonic contribution to the music. Next, note the trapezoidal cabinet shape, which minimizes internal standing waves. The front baffle is joined to the body of the cabinet using solid cherrywood siderails. Comprehensive internal bracing stiffens the cabinet further. Finally, behold the drivers, which are, of course, the star attractions.

In the beginning there was paper. While not particularly stiff in sheet form, it gains considerable strength when shaped into a cone. Its low density, ease of molding, and good internal damping made it the industry standard in the 1930s, and paper woofers have remained in production to this day. The ability of a woofer to behave as an ideal piston over an extended bandwidth is related to two basic physical parameters: stiffness and the cone’s sound velocity. Stiffness (as measured by Young’s modulus) is, for example, at least a factor of 100 greater for titanium than for paper. But that’s only part of the story. Cones and domes break up at a resonant frequency, which is proportional to the sound velocity of the cone material. For a given cone size, the higher the sound velocity, the higher the resonant frequency, giving the woofer a more extended range. Getting back to our example, titanium’s sound velocity is about a factor of four greater than that of paper. This means that a paper cone will breakup much sooner than a titanium cone. (Ironically, plastic/polypropylene cones, which became popular in the 1970s, offer an even lower sound velocity than paper.) A 6.5" magnesium-alloy cone woofer probably starts breaking up above about 4kHz. However, whereas paper cones can work fairly well in breakup mode, metal, being poorly damped, rings severely during breakup, which means that the working range of metallic woofers needs to be pushed about an octave below the onset of resonance. Still, in my experience, metal drivers are well worth it. Having worked in the past with some of the SEAS aluminum woofers, I was mightily impressed with their much greater pistonic precision relative to paper alternatives.

Esoteric feels that magnesium alloy (96% magnesium) provides better internal energy dissipation than aluminum or titanium. In addition, the woofer cone is corrugated and damped with two thin coatings (one of which is a ceramic layer) for enhanced resonance control. This diaphragm technology is said to have originated in Esoteric’s sound engineering department and is manufactured jointly with Nippon Kinzoku Company, a major metals-manufacturer in Japan. Esoteric believes that TEAC Esoteric MG-20 Loudspeaker these design features are essential to maximizing the sonic potential of magnesiumalloy technology.

It is worth repeating that, unlike the much more common scenario where the driver complement is a mix of paper or plastic woofers and a metal dome tweeter, the MG-20 uses magnesium-alloy diaphragms in every driver. As a result, when the dynamic/harmonic envelope blooms and expands, the MG-20’s character remains unchanged. The MG-20 was designed to speak with a consistent voice over its entire range. A soprano voice, for instance, may launch in the woofer’s sweet spot and seamlessly continue its upperregister ascent courtesy of the tweeter, never changing diaphragm material. (Yes, it’s true that cone materials do sound different, and for the same reasons that a violin or piano’s timbre is affected by the choice of woods and lacquers for the body of the instrument.)

The MG-20 is a three-driver, two-way design. Those of you familiar with loudspeaker design will readily identify the vertical layout (woofer, tweeter, woofer) as a D’Appolito configuration. Its advantages are a uniform vertical radiation pattern and an enhanced listening-seat sweet spot. Bass loading is the ubiquitous bass reflex with a front-firing vent. I would estimate the box tuning frequency at around 35Hz. (A low tuning frequency is beneficial in controlling driver excursions in the deep bass.) The crossover frequency is pushed down to 1.9kHz with a second-order (12dB/ octave) low-pass network for the woofer. The tweeter is protected with a third-order (18dB/octave) high-pass network, which I think is a wise choice. All crossover components are said to be high-precision, low-loss types. The network is hard-wired and glued to the backside of the terminal cup—there are no printed circuit boards. The terminals are bi-wireable and feature an “earth” or grounding point for the driver chassis, which is said to minimize RF interference. Internal wiring is van den Hul silver-coated copper. The speaker’s nominal impedance is rated honestly at 6 ohms. The minimum impedance is about 4 ohms, which together with a decent sensitivity rating, makes this an easy amplifier load.

In the British hi-fi tradition, Esoteric recommends a classic setup with the speakers toed in toward the listening seat. It is suggested that the driver axes for the left and right channels intersect about two to three feet in front of the listening seat. There is no question that this is an excellent recipe for obtaining as wide a soundstage as possible, while enlarging the sweet spot, but I discovered that tonal balance also plays a role in dialing in the optimum toe-in angle. My in-room on-axis measurements showed that the lower treble, the range from 8–12kHz, is rolled off gently relative to the midrange and then flattens out to beyond 20kHz. Listening off-axis further decreases output at 8kHz, slightly reducing treble air and immediacy. On the other hand, aiming the speakers directly at the listening seat gave the treble a hint of assertiveness. The best overall compromise, in my listening room, between soundstage width and treble immediacy turned out to be a toe-in angle that did intersect the tweeter axes in front of the listening seat. Of course, you should experiment in this regard to obtain the sort of balance that agrees with your personal preferences. Optional aluminum isolation bases are available. They’re rather expensive at $1080/pair, but are probably a very good idea when positioning the speakers on a carpeted floor. Samples were not yet available for evaluation at the time of this review. A final world of caution: A lengthy (200-hour) break-in is required to fully smooth out this speaker. It’s pretty good right out of the box, but keeps improving for the first few weeks.

The MG-20’s most compelling attributes were instantly obvious: clarity and transparency to die for! It felt as if layers of veiling were lifted from the soundstage, making for a stronger connection to the original performance. It was a sensation similar to the experience of listening to a live microphone feed versus a mastertape. The microdynamic intensity, kinetic energy, and rhythmic drive of the music were that much more believable. Good grief, how can anyone return to the world of plastic and paper cones, after having sampled the “forbidden fruit”? As if a giant searchlight illuminated the soundstage, it was possible to make out its inner recesses. Now, that’s transparency taken to the max! Reverberant information, decaying gossamer-like into the recording’s noise floor, was faithfully reproduced—and to a degree even fine electrostatics would have difficulty duplicating. The MG-20’s controlled midrange dispersion pattern relative to that of a dipole radiator gives it the edge in low-level resolution, as there is less reflected energy to interfere with the direct sound.

And just as important, there was absolutely no metallic sizzle in evidence. Sibilants were negotiated without exaggeration. Violin overtones, a severe test for any dome tweeter, especially a metal one, were reproduced with convincing sheen and luster. Vinyl surface-noise was not prominent, and in fact sounded a bit subdued—an added benefit of the way the upper octaves were equalized by the design team. This is not a bright-sounding speaker. Its detail resolution is earned the old-fashioned way through superior transduction of the input signal, rather than distortion of the tonal balance in favor of the presence or lower-treble regions. Sadly, too many audiophile speakers fall into the latter category. I’ve seen it with my own eyes: These are the speakers that receive the “oohs” and “aahs” at shows. They represent the antithesis of the concert hall experience, but bright speakers do turn heads.

I have to respect a speaker that does not impose its personality on the music. A colored speaker might be fun for a while, or even complimentary to a few recordings, but over the long haul I prefer a speaker such as the MG-20 that is faithful to the original recording. The payoff is incredible timbral accuracy. Listening to the Lesley double-LP, David Manley’s 1992 recording on the Vital Sound label, was most telling. This recording of my wife Lesley, is of course, an album that I am intimately familiar with and enjoy often. I was present at the live-to-two-track recording session at Manley’s studio in Chino, California (which was, I’m sad to report, dismantled a few years ago), and was privileged to hear the musicians, not only live, but also via the mike feed to the studio monitors. And, finally, auditioning the mastertape and vinyl lacquers, I have stored away in my memory banks a vivid impression of what the live sessions and transfers were all about. To be honest, very few speakers get this right. The MG-20 is one of the few that does. It reproduced the essence of Lesley’s timbre cleanly across its entire dynamic range.

The range from 300Hz to 20kHz (the upper limit of my measurement system) was very smooth with no observable response glitches through the crossover region. There was plenty of midbass energy and the upper bass was sufficiently solid to properly flesh out the power range of the orchestra. The surprisingly strong bass foundation was a pleasant surprise and made it possible to fully enjoy orchestral music. Deep bass extension was limited to about 45Hz in my room, which serves most music well enough. The pistonic precision of the magnesium cone woofers was very much in evidence. It translated into exceptionally tight bass lines. Jazz bass boogied with what I can only describe as paranormal (for a speaker) pitch definition.

Generating an adequate impression of space is a challenge for a two-channel audio system. Planars, given sufficient breathing space, do a credible job of generating a concert hall perspective, while mini-monitors excel in maintaining tight image focus. When properly set up, the MG-20 imaged much like a mini-monitor. However, I have to give credit here to the Bybee Speaker Bullets, which caused image outlines to fully snap into tight and palpable focus. The soundstage unfolded as an organic whole, with excellent depth and width. Massed voices were distinct, allowing me to focus on a particular vocal line—and that’s not easy, as many speakers blur closely spaced spatial outlines into a blob.