Pick of the Hits - dbx® DriveRack PA + in Church Production

March 16, 2010

Audio Review: dbx® Driverack PA+ Loudspeaker Management System

Unit is particularly useful for churches that set up and tear down each week
by John F. McJunkin


dbx is well known for its speaker management products, ranging from simple speaker processors like the DriveRack PX up to sophisticated system management solutions like the DriveRack 4800. Included in this array is the DriveRack PA+, the new revision of the DriveRack PA. Considering the list of features included with this device, its $749 list price is astonishingly low. The original version was powerful, and this revision adds welcome and useful new features that not only increase the functionality of the unit, but make its operation simpler for the benefit of users who do not have any formal education or much experience (i.e. volunteers.)

The new version of the DriveRack PA continues to feature all the functionality of the original, and quite a bit more. First, to address the original unit's attributes: it features compression and limiting, parametric equalization, advanced feedback suppression, the dbx120A subharmonic synthesizer, and a 2x6 crossover matrix, accommodating up to a stereo three-way system. Moreover, all parameters are stored as part of system presets, and the system has presets for a spate of different speakers. The compressors feature dbx's famous "over-easy" knee adjustment to smooth out the onset of compression, which can pretty radically alter the nature of the compression. The original unit offers graphic equalization before the crossover stage - specifically dual 28-band graphic EQs. I'm not super fond of the user interface mechanism for the graphic. You select a frequency and either boost or cut it - a little tedious, but it still works. The included advanced feedback suppression utilizes up to 12 filters under the control of an intelligent system that "listens" for feedback, isolates it, and suppresses it by reducing a small range of frequencies. I tested this by placing a sensitive omnidirectional condenser mic less than three feet directly in front of a speaker. Not only did the feedback suppression system work very effectively, but it did not mangle the signal, and indeed, this system is intended for wringing feedback from the mains, not the monitors.

The system's dbx 120A subharmonic synthesizer has been a tried-and-true mechanism for live sound engineers to add a little girth to the low end, and in this case, it works just as advertised. The crossovers allow for up to three-way operation, with Butterworth filters at 6, 12, 18, and 24 dB/octave slopes, and Linkwitz-Riley filters at 12 or 24 dB/octave. After the crossover section in the signal flow, parametric equalization is available with up to 12 dB of boost or cut in three bands with a Q ranging from 0.2 to 16. Compression and limiting follows next, and features control over threshold, ratio, gain, and "over-easy" which is dbx' vernacular for the softness of the knee. Hard-knee is at 1, and soft-knee is at 10, and this helps to make the compression more transparent. One minor critique: An inexperienced volunteer can easily wind up with obvious, pumping compression. This unit is intended to simplify for the untrained volunteer, and largely excels at that notion. But there is no "volunteer-proof" mechanism to help a neophyte avoid mangling the signal with too much compression. Otherwise, dbx' compressors sound great when they're configured properly, as does the system's limiter, which also has the over-easy capacity to soften the knee.

Beyond the dynamics processing is an alignment delay, which is very welcome, facilitating time alignment between lows, mids, and highs. The unit's display shows a nice graphical presentation of signal flow, yet another convention to simplify operation for a volunteer.

In addition to an updated library of speaker and amplifier settings, the PA+ adds quite a number of new features. Specifically, there are now front panel mute buttons for each of the unit's six electronically balanced XLR outputs, continuous real-time analysis, and a suite of automated wizards to simplify for the benefit of volunteers. There is an auto-EQ wizard, an auto-level wizard, and an advanced feedback suppression wizard as well. One very welcome feature here: upon pressing the "set-up" button on the front panel, a complete process is started, with speaker choices and auto-leveling first, followed by auto-equalization, and finishing with feedback-suppression setup. Literally one button guides a green volunteer through the process of setting up the system - very simple. Another new feature is the unit's USB connection, which facilitates connection to a computer for vastly enhanced graphical control over the system. This is becoming a standard for virtually all digital equipment now, and very welcome here.

I test-drove the system and paid particular attention to the automated wizards. The setup button opened a dialogue asking me questions about the details: stereo or mono, main speaker choice, subwoofer choice, levels, presets, and then auto leveling. Upon completion of that process, the system immediately proceeded to auto-equalization, walking me through mic connection, pink noise level, choice of a target curve ("flat" is not the only available choice,) and then completion of that process. Finally, the system proceeded to the wizard for advanced feedback suppression, which again, held my hand through the process to set the filters. Upon completion of this entire process, the system was completely configured and ready to go. Of course, an advanced user can nevertheless go back and tweak parameters, but the lion's share of the work is done by the wizards.

The DriveRack PA+ is particularly useful to small churches like mine that set up and tear down each week - it enables the engineer to tune the PA for the room (even if the room changes from time to time) and get a handle on the signal going to the speakers. And that's not to say it's not useful for a permanently located church - there are thousands of such churches that don't currently have a speaker management device to tailor EQ, crossovers, dynamics, levels and so on - the DriveRack PA+ would be a significant improvement for such churches. The printed documentation is a bit lacking, in my estimation - for instance, there's precious little guidance in regard to the choice of an RTA [real-time analyzer] mic or where to place it. Despite that oversight, this system is largely automated, so intensely in-depth documentation is probably not as important.

In the spirit of the Hippocratic oath, I always insist first and foremost that signal processors like the DriveRack PA+ "first do no harm", meaning that the signal coming out should sound at least as good as it did going in. That is indeed the case with this processor. If anything, the unit's equalization and dynamics processing improved the overall quality of the output, and that's the main reason for this unit. But aside from sculpting the signal, there is also the issue of tuning the system to work in the space, which it also accomplished nicely. Finally, there's the issue of user-friendliness. Other than a somewhat lacking manual, this box does nearly all the work for you, more or less - and that is very welcome when volunteers are involved. The street price for the DriveRack PA+ is right around $500, and at that price, this unit is well worth considering to help improve the overall quality of your church's sound.

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