“His solution was to make a drive unit that coupled a very light diaphragm with a carefully optimized foam substrate, to produce a loudspeaker with the speed and stiffness required for audio reproduction. The difficulty faced with this design—it transpired—was that it doesn’t ‘scale’ well. Where pioneering plastics technologists in the 1930s quickly found a way to mass-produce their materials, the need to create a foam substrate of varying size across the driver meant Emil Podszus’ [sandwich cone] remained essentially a bespoke design that could only be produced in tiny numbers. A very high performance design, undoubtedly, but one that precluded being supplied to the audio mass market. This kept the Podszus name out of the mainstream audio world, but the Zellaton brand that came out of this technology was resilient. Dr. Emil handed the concepts down to his son Kurt, who then subsequently passed the baton down to his son Manuel.”
Manuel Podszus is still making his grandfather’s drivers—and still making them by hand in a process so painstakingly exacting that it takes several weeks to complete each cone (all materials and adhesives are also subjected to several months of testing and optimization). It is commonplace today for loudspeaker manufacturers to brag about their high-tech tweeters, midranges, and woofers, but, frankly, a good deal of the fabrication and assembly of those drivers is farmed out to specialty companies that have the machinery to produce parts precisely to order—and in sufficient quantity. This is not the way Zellaton works. It makes diaphragms the way Patek Philippe makes watches.
The Reference MkII is a three-way floorstanding loudspeaker with a single 2" true cone tweeter (not a dome or an inverted dome but a cone), a single 7" mid/woofer (which, by itself, covers the range from 250Hz to 6.5kHz—part of the reason why the Reference MkII sounds so much like a single-driver speaker), and three 9" woofers, all housed in a unique, gorgeously finished, multi-layered, matrix-braced, open-backed enclosure (see below for more details). Every single one of the Reference’s drivers uses Emil Podszus’ sandwich cone (which his grandson Manuel has improved by “using modern materials and sophisticated, purpose-designed processes without changing the basic formulation that has been employed for decades”). Utilizing a single type of driver made of precisely the same materials—rather than a mix of cones and domes made of a variety of materials, as is the case with almost every other dynamic or hybrid loudspeaker I know of—is another reason why the Zellaton Reference MkII sounds so remarkably ’stat-like and of a piece.
What is a Zellaton driver? Essentially, it is a three-piece sandwich cone comprising a micro-thin layer of aluminum film (0.006mm thick in the case of the tweeter) atop a layer of ultra-stiff aerated foam (still hand-made and hand-cured using Emil Podszus’ “top-secret” formula), and backed by a proprietary layer of treated paper. Zellaton cones are incredibly light (the Zellaton tweeter’s diaphragm weighs approximately 0.16 grams!) but also incredibly stiff, giving them what is claimed to be “ideal pulse response.” All of the Reference’s drivers also use computer-optimized magnet systems (pure iron with 20,000 gauss magnetic flux, in the case of the cone tweeter) with a “largely linear field along the entire height of the pole plate”; proprietary spiders and surrounds (which have a softer “feel” that other surrounds I’m familiar with—just touch one of the woofers’ surrounds and see for yourself); and high-temperature voice coils on titanium-film formers. Each driver is “subjected to multiple control measurements and fine adjustments,” with its frequency response logged and documented and pairs matched to the highest tolerances. The drivers are linked to each other via crossover networks that use ultra-high-end Duelund Coherent Audio caps, coils, and resistors, and wired with ultra-high-end Schnerzinger cable.
The Reference MkIIs’ enclosures are just as handcrafted as their drivers. Intricate in design, damping, bracing, composition, and finish, their multi-layered wooden walls vary in thickness from 34mm to 50mm. At the rear, the enclosures are mostly open from top to bottom—an unusual configuration (nowadays) that reduces or eliminates compression of the tweeter, midrange, and woofers’ backwaves, and gives the Zellatons something very like the dipolar radiation pattern and easy, boxless openness of membrane speakers—another reason why the Reference MkIIs sound like ’stats on steroids.
Of course, the main reason that the Zellaton Reference MkIIs are reminiscent of electrostats is the forehead-slapping realism with which they reproduce voices and so many acoustic instruments. This is in equal parts the result of extremely high resolution (virtually as high as you can get at low to moderately loud levels with cones), extremely lifelike reproduction of timbre, extremely natural and linear reproduction of transients (with none of the edge or “zip” of metal domes and none of the subsequent timbral, dynamic, and imaging discontinuities between the midrange and the upper octaves—every instrument speaks with the same voice no matter where in its range it plays, just as in life), and extremely low driver/box coloration with none of the usual sense of the box or the backwave of the drivers selectively adding spurious, spring-like energy to the presentation, which, despite the manifest increase in thrills this “super-charging” gives the sound, is not something one—or, at least, this one—hears in a concert or recital hall.
With really great recordings of acoustic music, the result is a truly remarkable sense of being in the presence of actual vocalists and instrumentalists. As I’ve noted before, this level of realism—where a voice or an instrument is conjured up so completely that the mind does a double take—is not something we are used to from stereo systems. We expect hi-fi’s to sound at least a little like hi-fi’s. It is what they are, after all—and hell, we’re looking right at them. In spite of this, at its best the Zellaton Reference MkII makes you forget where the sound is coming from.
All this talk about Zellatons and electrostats raises an interesting question: Why not just buy a ’stat or hybrid ’stat instead? After all, even the best of such speakers costs far less than a pair of Reference MkIIs.