Esoteric MG-20 LOUDSPEAKER

Technology in the Service of Music

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.)