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
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
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.
Going To The Next Step...
To that end, Jim and I are planning
soon to visit another signer of the non-disclosure agreement, Newform
Research's John Meyer to modify two of my four R-830 speakers with
a DiAural crossover. That way we'll be easily able to compare them
with the normal crossover, and more exactly determine how effective
it is. Check back with AIG Online in a few days for more on this.