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Audio Review: dbx Professional Products DriveRack PX

Nov 1, 2008 12:00 PM, By John McJunkin

A welcome optimizer for powered loudspeakers.

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I test drove the system in a semi-professional environment with drums, bass, electric and acoustic guitars, and four vocalists. The loudspeakers were a pair of Mackie SR1530s (three-way powered loudspeakers with 15in. woofers). No subwoofer was employed. In this application, a digital mixer with limited dynamics processing is normally used, and I disabled the compression on the mixer's mains in order to hear the dbx compression. After inserting the DriveRack PX between mixer and loudspeakers, I launched the setup wizard from the front panel. After informing the unit that there would be no sub and that I was using a “custom” loudspeaker configuration (rather than a factory preset), the system proceeded to establish proper left-right balance. The system then proceeded on to the Auto-EQ wizard, in which I connected the RTA mic (which was placed in the center of the audience area) and pressed the RTA input button. I was presented with five different curve choices (including a flat one). I chose a subtle “disco smile” curve with slightly pronounced low end and high end. Next up, the pink noise appeared from my loudspeakers, and the system auto-equalized for the room and the curve I chose. After auto-equalization, the AFS wizard came next. In realtime, I gradually raised the master fader on the mixer to the performance level while the filters automatically sought and eliminated feedback.

After running the wizards, I manually inserted the compressor, limiter, and subharmonic synthesizer. I stored the preset and turned the controls over to the front-of-house mixer, who reported that his mix sounded brighter with much more satisfying low end. I moved around the audience area throughout the performance and discovered the overall quality of the sound to be substantially improved. The main reason I chose the bass and treble-enhancing curve in the DriveRack PX is that I have always found those two domains lacking when I have mixed front of house with this system in this venue. The digital version of dbx's OverEasy compressor was subtle but effective. At no point did the performance ever reach levels above the limiter's threshold, but my experience with dbx dynamics processing of all kinds has been very good. During spoken-word non-musical segments of the program, an omnidirectional head-worn mic was employed, and the feedback elimination was very effective. The 120A subharmonic synthesizer is another of dbx's classic processors, and the digital adaptation of it is great. It subtly mixes in a clone of the bass note an octave below the program bass. This sounds substantially better to me than simply pumping up the low-end EQ, and in this particular venue with this particular system, it did just the trick.

It seems to me that contractors will be thrilled to have a simple, easily used solution to enhance the quality of powered loudspeakers. As I said before, anything that moves the fidelity toward that of a tuned, multi-amped component system is very welcome, and the DriveRack PX effectively accomplishes that goal. It's simple, it's powerful, and if you wish to vastly improve the results with your powered loudspeakers, you'll definitely want to check it out.


  • Company: dbx Professional Products
  • Product: DriveRack PX
  • Pros: Significant improvement of powered loudspeaker fidelity and control.
  • Cons: EQ navigation a bit dodgy.
  • Applications: Optimization of powered loudspeakers.
  • Price: $599.95


Analog Inputs

  • Impedance: >40kΩ
  • Max input line level: +20dBu
  • Input CMRR: >45dB
  • RTA mic EIN: >-110dBu, 22Hz-22kHz, 150Ω

Analog Outputs

  • Impedance: 120Ω
  • Max output level: +20dBu

A/D Performance

  • Type: dbx Type IV conversion system
  • Dynamic range: >110dB A-weighted, 107dB unweighted
  • Type IV dynamic range: 123dB (transient) A-weighted, 22kHz BW; 121dB (transient) unweighted, 22kHz BW; 115dB typical with program, A-weighted, 22kHz BW
  • Sample rate: 48kHz

D/A Performance

  • Dynamic range: 112dB A-weighted, 110dB unweighted

System Performance

  • Dynamic range: 110dB A-unweighted >107dB unweighted
  • THD+N: 0.002% typical at +4dBu, 1kHz, 0dB input gain
  • Frequency response: 20Hz -20kHz, ±0.5dB
  • Interchannel crosstalk: <-110dB, 120dB typical

John McJunkin is the principal of Avalon Podcasting in Chandler, Ariz. He has consulted in the development of studios and installations, and he provides high-quality podcast production services.

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