“A bunch of the boys were whooping it up at the Malamute Saloon.” All of the claims of huge breakthroughs over the years do bring to mind this opening line of Robert Service’s famous poem. But sometimes these claims of radical improvements that change what is possible in audio and offer new vistas of excellence... sometimes one or another of these claims is actually the unvarnished truth, not whooping it up at all, but a matter of straightforward fact. DALI claims that its Epicon Series speakers embody a new kind of magnetic structure that reduces odd-order harmonic distortion in dynamic drivers to the point of its being all but unmeasurable. Interestingly, the even-order harmonic distortion remains unchanged: the Epicons have low but not unprecedentedly low total harmonic distortion. But the odd-order parts are, they say, all but gone.
And the Epicon 6 speaks for itself on this matter: I do not think anyone listening to it, audiophile or no, would fail to observe how pure and liquid is the sound, how reminiscent indeed of the ultra-low harmonic distortion of electrostatics. Once heard, this liquidity is unmistakable and likely to be unforgettable as well. Lars Worre, the chief executive of DALI, explains the new magnetic structure in some detail (www.youtube.com/watch?v=PTPSelj4g8M), and I shall summarize the principles of it later. But the effect is surely heard independently of the explanation being offered, interesting though the explanation is. This is not something one has to talk oneself into hearing!
There is far more to speaker design than low-distortion drivers, of course. But driver behavior is fundamental. I shall go later into how the Epicon 6s perform in other aspects. But their low distortion already makes them not only interesting as a product but something of a landmark in audio history.
How the Reduction in Distortion Works
A driver consists of a magnetic structure surrounding a “voice coil,” the voice coil being attached to the part of the driver you see, the part that moves the air. The voice coil is moved by the magnetic force: When current goes through the coil, force is exerted on the coil and the coil is thus accelerated. And the force on the voice coil is ideally exactly what it should be as determined by the current flow in the coil. But in practice, the magnetic structure is usually made of metal. And the metal conducts electricity. So the coil with its varying current generates, via electromagnetic induction, current in the magnetic structure’s metal. This current in the magnetic structure in turn alters the magnetic field, inducing an unwanted and uncalled for extra force on the coil. These induced currents, “eddy currents” as they are called, are a source of distortion. The idea of the DALI driver is to get rid of them by making the magnetic structure effectively non-conducting so that eddy currents are prevented. [See also the discussion of driver eddy currents in my review of the Magico Q7 in Issue 229.—RH]
The eddy current problem occurs also in transformers, which is why laminated structures are used for them, the lamina being separated by thin layers of insulation so that current is unable to flow across lamina. A more extreme form of the idea of a non-conducting magnetic structure was developed by the Danish company Grundfos. Its idea was to make a material consisting of iron particles—so that it is magnetic—but to coat the particles with a non-conductive layer before forming the material by pressing the particles together. The result is in effect laminated in all directions at once and does not conduct.
The non-conducting magnet structure and eddy-current reduction is responsible for about half of the lowering of odd- order harmonics. The rest of the distortion reduction is the result of aluminum and copper rings within the magnetic material that create an optimally shaped magnetic field that is more linear. The rings also decrease inductance. Together, the unique magnetic material and the rings produce a magnetic linearity that remains constant regardless of signal current, signal frequency, or cone position.
This idea was in fact developed by Grundfos for high-speed electric motors, not for speaker drivers at all. But, fortuitously, Grundfos is close to DALI in Jutland in Denmark, about ten miles away, and after a while the subject of using the idea for speaker magnetic structures came up (the idea was actually suggested by Grundfos, according to Worre in the video link). Of course, some work was needed on how to carry this out, but the idea has a fundamental rightness to it that strikes one immediately. Like many really good ideas, once this one has been brought up, it seems entirely natural.