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DEQX advances the art of speaker correction

DEQX room and speaker correction processors can transform the sound of very good hi-fi and home theater systems, and make them great.


I've listened to a lot of speakers over the past thirty-odd years, and I can tell you this, they're all imperfect.

No hi-fi or home theater sounds like live music, and not a single one of the most exalted high-end speakers has truly flat frequency response.

Of course, everyday speakers are less accurate, which is why just about every receiver sold today has a calibration system that corrects speaker anomalies and tames room acoustic problems.

That's all fine in theory, but most speaker calibration systems only change rather than improve the sound of a hi-fi or home theater. So I'm a bit of a skeptic about the benefits of this type of processing, but I finally heard a correction system that delivered the goods. It's the DEQX HDP-Express. I listened to it over a very high-end system (owned by DEQX's publicist).

The sonic transformation was at once subtle and dramatic. I first listened to the system without any correction, and the sound was excellent. The speakers were large floor-standing towers (Focal Utopias). I played a few recordings I know well, and the sound was beautifully balanced and natural.

Ah, but then my host switched on the DEQX speaker correction, and the sound of the "Wynton Marsalis & Eric Clapton Play the Blues" CD snapped into focus. Every instrument in the large jazz band was clearer and more present. High-frequency detailing and "air" were much improved, and bass definition firmed up. Then we turned on the DEQX's room correction, and the sense of listening to a live performance was heightened. Switching off the processing was a letdown; the music became less present and realistic.

The HDP-Express uses dual 32-bit floating-point digital signal processors running DEQX's patented technology. The playback system had the HDP-Express connected between the analog preamplifier and power amp, but the HDP-Express can also work directly with digital sources.

Of course, the processor can also be used with multichannel home theater systems, where speaker and room correction pay even larger dividends.

Setup involves taking speaker measurements with a microphone, and the HDP-Express then calculates corresponding correction filters. Once the speaker is corrected the HDP-Express measures the speakers again from the listening position and the results are displayed graphically on the setup PC. Typically only three to six bands of equalization are required to resolve in-room bass issues and can be set automatically or manually to preference. The HDP-Express has a three-band tone control on the remote, and up to four different combinations of speaker and room correction settings can be stored.

The processor offers a vast range of adjustments, and may require the services of a qualified installer to fully exploit its sound enhancement potential. The HDP-Express retails for $1,950.