PRO AUDIO REVIEW
DiAural Crossover Circuit Design for Improved Speakers K imber Kahle has recently debuted a breakthrough crossover design that is claimed to eliminate most speaker phase shift, enhance clarity and impact, as well as prevent tweeter burnout. It requires only two or three parts and replaces the crossover in existing speakers.

New design
Invented by Eric Alexander of Kimber Kable, the crossover circuit is being promoted by DiAural, a new company started by Ray Kimber and WordPerfect founder Bruce Bastion. The crossover design will be licensed to speaker manufacturers for a reasonable fee. Each manufacturer would build its own speak­er-specific crossover, based on the circuit. The DiAural design actually uses the back-EMF from the drivers to achieve its benefits. Energy that is absorbed and lost in a conventional crossover is fully used in the DiAural crossover.

The new crossover claims to solve a problem that has always existed in mul­tidriver loudspeakers. The problem actually starts with the recording. Imagine a micro­phone picking up a low organ note and a high trumpet note simultaneously. As the low note moves the mic diaphragm in and out, this motion modulates the frequency of the high note - a phenomenon called Doppler distortion.

During playback of this recorded signal, however, the Doppler distortion is canceled out by complementary motion of the speaker diaphragm. The high trumpet note is played by a diaphragm that is also playing the low organ note. That's assuming playback over a single-diaphragm speaker, or headphones. In a multidriver speaker, the cross­over separates the highs from the lows, so that the high frequencies no longer ride on the lower frequencies. The woofer puts out lows but does not produce any highs. Consequently, the highs are not modulated by the low-frequency cone motion and the Doppler distortion recorded at the microphone is not canceled out by the woofer. As a result, we hear IM distortion, which puts a veil over the sound. Single-diaphragm speakers, such as elec­trostatics, don't have this problem. That's one reason they sound so clear and coherent. Unfortunately, according to Kimber, pure electrostats tend to have a problem handling loud music and deep bass. The DiAural crossover is said to combine the purity of electrostatics with the depth and dynamics of moving-coil speakers. With the new crossover, all the drivers are essentially modulated with a full-range signal, although they reproduce only the highs, mids or lows. This restores the Doppler compensation, giving purer repro­duction of the high notes. The Doppler effect, "encoded" during recording, is prop­erly "decoded" during playback. According to Kimber, the Doppler encoding happens with any mixed signals, such as in multitrack recordings. Mixing two different tones electrically results in Doppler encoding, and so does mixing two different tones acoustically with a microphone.

Decreased phase shift
Another major feature of the DiAural crossover is elimination of most phase shift across the audio band. According to Kimber, inductors and capacitors in crossovers cause phase shifts in the musical signal. Meaning that a typical crossover changes the timing or phase of the lows and highs relative to each other.

In some speakers, at the crossover fre­quency, the woofer and tweeter are in phase. But an octave away, the phase dif­ference could exceed 180 degrees. In con­trast, the DiAural crossover keeps the dri­vers in the same phase quadrant from 20Hz to 20kHz.

In addition, the off-axis response and polar patterns are said to be dramatically improved. Keeping the drivers in phase at all frequencies makes the off-axis signal much more coherent.

There are other side benefits as well. The company claims that sensitivity tends to increase, while efficiency stays the same. Power handling is sometimes much higher because the woofer protects the tweeter, and vice versa - making the speaker much more reliable. The impedance-vs.-frequency curve is flatter. Frequency response stays basically the same. Kimber and Alexander are working on an active DiAural crossover that works the same way as the current passive DiAural crossover. The new circuit has some poten­tial drawbacks.

Some drawbacks
Not all driver combinations or drive/box combinations are compatible. Speaker designers lose the ability to fine-tune each driver's response by means of a fancy crossover. If good drivers are used in the first place, however, this should not be a problem. Biwiring is not possible with the DiAural circuit, but the improvement in sound quality overrides the lack of biwiring.

In a nutshell, here are the claimed bene­fits of this new crossover design:

• Speaker manufacturers can produce better sounding, more reliable speakers, with potential savings. This applies to multiway studio monitors, sound reinforcement speak­ers and consumer speakers.
•Recording engineers can hear their mixes with more clarity and realism. Their clients should be more impressed with the quality of the recording.
•House sound mixers should have an easier time mixing because the speakers will sound more natural.
•Consumers will enjoy more natural repro­duction and will have fun relistening to their record collection with new clarity.

I urge speaker manufacturers to check out the DiAural circuit and decide for themselves.

Contact: Jason Thomas for license infor­mation, at DiAural Corp. at 801-334-5510; e-mail jason@diaural.com.

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