Most audio technologies, including microphones, electronics, and storage systems have one common element: they all handle the full range of audio frequencies. This means that higher frequencies are effectively modulated by the lower ones. An almost perfect analogy is the LP groove, where the wider swings contain smaller and even very tiny squiggles superimposed on them, these representing the lowest, middle and highest frequencies, respectively. As vinyl lovers know, these grooves can be portrayed with amazing accuracy even through this mechanical system that has been in use in various forms for well over a century.

      The one area of the reproduction chain that alters this relationship, and very substantially, is the speaker. In fact, it's not the speakers (or drivers) that do it, but the passive crossover that usually precedes them. In the very process of separating the higher frequencies from the lower, this relationship between them is altered, that is, the higher ones are no longer piggy-backed on the lower.

      It was a young engineer named Eric Alexander who recently realized the seriousness of this problem, and the kind of Doppler distortion that was created by the passive crossover's separation of bass and treble frequencies. It's almost a kind of negative Doppler, that is, it is the absence of the normal modulation of higher frequencies by lower ones inherent in the vibration of every microphone's single full-range diaphragm over the whole audible range. That's why full-range drivers like electrostatics and planars tend to sound more natural and coherent than multi-driver dynamic systems. The fact is, they are more coherent, the phase and timing relationships of the original audio signal unaltered by a crossover network.

      What Happens in A Typical Crossover

      In a typical crossover made up of resistors, capacitors, inductors, and other parts, the musical signal is altered as it is separated not only in the timing of these frequencies relative to each other, but in terms of relative electrical and acoustic phase, especially near the crossover frequencies. Milder crossover overlaps, those that cover a wider range of frequencies above and below the actual crossover point, so-called first order designs, generally have better electrical phase, but poorer acoustic phase, leading to bumps and dips through this region of frequencies. Conversely, higher order crossover slopes can have less of this lobing (as it is called) between the drivers acoustically because the drivers' ranges overlap less, but the actual electrical phase shift is often worse, resulting in greater timing errors, with the output of the tweeter usually leading that of the woofer by several milliseconds.

      Though many speaker engineers claim that this is not audible, speakers which do not have such problems inevitably sound more natural, because more of the music is in the right order coming out of them.

      The DiAural Solution

      Though both Jim Hayward and I are unable to discuss the crossover specifics, we have both been to Kimber in Ogden, Utah to see it demonstrated and to learn and discuss its technical specifics, and its implementation with various speaker configurations. Like over 100 speaker manufacturers to date, we signed non-disclosure agreements until the patent that is pending is finally awarded to DiAural Corporation.

      Ray Kimber expects that to be soon, and is in partnership with WordPerfect founder Bruce Bastion to develop and license the technology. DiAural Doppler decoding apparently puts enough bass into the tweeter to restore (or more correctly, maintain) the modulation relationship we've discussed, and therefore maintain good phase relationships between the drivers, whether there are 2, or 3, or more. This eliminates lobing, the acoustic reinforcement and cancellation effects near crossover frequencies, and makes the speaker system sound much more coherent, and the music much more real.

      This was dramatically demonstrated both on a pair of excellent compact 2-way speakers, and on behemoth 3-way PA speakers facing out a shipping door at the Kimber factory. In both cases, indoor or 100 feet outside the plant, respectively, the sound was amazingly spacious, coherent, and natural with the DiAural crossover. And the horn-loaded midrange drivers on the PA system didn't sound cuppy or megaphone-like at all. And inside, because of the absence of acoustic driver interaction, the sound was uniform everywhere we listened in the large plant space: coherent, in phase, whatever, everything sounded natural and musical, whether it be rock, classical, chamber music, or anything else.

      I had previously heard the effect at CES in a private listening room at the Alexis Park, but I was still awed that such good sound could be heard in such a large space as the Kimber factory, and be heard anywhere, near or far from the speakers. It appears that when you make them radiate with real coherence, that is, phase accuracy, the sound tends to stay that way even when reflected or carried over large distances. And the PA system demonstrated that this could also be achieved with pretty industrial-strength drivers: they may have lacked subtlety, but they sounded better than they had any right to, even when played at jackhammer levels.

      The audiophile system inside consisted of some very nice components,a Mark Levinson amp and preamp fed by a Denon DVD-5000 DVD/CD player. Of course, cabling was all Kimber Select. We listened to many CDs that weekend (March 22nd and 23d), as well as to some DVD Audio discs I'd brought, along with our new Chuck Israels jazz CD. Neither Jim nor I were ever less than impressed at what we heard, though I now want to try DiAural technology on more familiar speakers.

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