dbx DriveRack 4800
Aug 1, 2006 12:00 PM, By John McJunkin
A powerful drive box provides plenty of useful bells and whistles.
The dbx DriveRack series of drive boxes has been immensely popular for quite some time, and in recent years, many contractors and systems integrators have featured the DriveRack 480 in their racks. I got my first peek at the 4800 at InfoComm 2005, and now the product is shipping.
I spent time with two of these units recently, and I have discovered the 4800 to be a major improvement over the original 480 in many respects. Indeed, the DriveRack is a popular product, and with good reason. It's a 4in. 8-out equalization and loudspeaker management system that dbx touts as “everything you need between the mixer and the power amps.” Naturally, I wanted to put that assessment to the test. I had already had some exposure to the original 480 unit, but I was told that the 4800 was substantially different and supposedly superior in many ways.
CONNECT AND CONTROL
On the rear panel, from left to right, you'll first find the unit's IEC power receptacle. Then, there is an array of control-oriented connections, namely an RJ-45 Ethernet, DB-9 for RS-232 connectivity, two more RJ-45s for zone-control connection, and a word clock BNC connector. There is also an optional expansion slot for CobraNet connection in this area.
Moving further right, we get into the unit's I/O. There are four XLR connectors representing eight channels of AES/EBU output, and then two more XLR connectors for four channels of AES/EBU input. Rounding out the rear panel are eight XLR connectors representing the eight analog outputs, and four XLR connectors accepting analog input. All of these analog inputs have ground lift switches to lift pin number one, eliminating ground loop-induced hum. Jensen isolation transformers are an additional option on the analog outputs. A 4820 version is also available with a limited front-panel display, intended for installation use.
Some of the most extensive changes between the 480 and 4800 exist on the front panel. The display of the 4800 is considerably higher resolution than that of the 480. Starting on the left end is a very welcome RTA microphone connection — there ought to be a law requiring these on all front panels.
Next up is the display, which is a 320×240 VGA color affair and a huge improvement over the 480's monochromatic display. Just to the right of the display are the function buttons. The PREV and NEXT buttons enable a clever scheme for copying and pasting parameters in successive DSP modules.
Below the function buttons are three rotary encoders to select and edit parameters. To the right of the function buttons and rotary encoders are eight-segment LED I/O meters (four and eight of each, respectively), above which there are selector buttons for inputs A-D and outputs 1-8. Above the output meters are tri-color LEDs to indicate the breach of threshold level for inserted dynamics processors. A cluster of four status LEDs below the input meters indicates clipping, synchronization with an external clock, RS-232 connectivity, and LINK/ACT with the Ethernet connection. Below each output meter is a rotary encoder to adjust levels.
Pressing the knob mutes the channel and illuminates a red ring around the knob to nicely and unambiguously indicate muted status. The color VGA display, along with much-improved button and knob functionality, make the 4800 far easier to use than the 480.
Nevertheless, complete control of the 4800 can also be achieved via Harman Pro's System Architect application using the HiQnet communication protocol. The front-panel controls are a vast improvement over the 480, but navigation and control of the 4800 with my laptop proved even better, a much simpler and superior experience, especially considering the system's wireless compatibility.
The 4800 functions primarily as a crossover and signal distribution/routing device, along with providing digital signal processing, including equalization, delays, and dynamics processing. The signal flow obviously starts with the four inputs, which can be mixed or routed.
Cross-patching can be accomplished in the 4800, and a pink noise generator is also provided. Next up is a third-octave graphic EQ with ±15dB of gain on each of the 31 ISO frequencies (from 20Hz-20kHz.) A second EQ, configurable as either a graphic or a nine-band fully parametric EQ comes next in the chain.
Following that, there are two inserts into which may be inserted a gate, compressor, automatic gain control, de-esser, sub-harmonic synthesizer, notch filter, or automatic feedback suppression. A delay of up to 680ms (in 10µsec or 20µsec increments at 96kHz or 48kHz sample rates, respectively) comes next in the signal chain. The delay is displayed in seconds, feet, and meters.
The output signal chain starts with a mixer/router, then an insert that can feature automatic gain control, a sub-harmonic synthesizer, or “auto-warmth,” which is essentially a Fletcher-Munson low-frequency/low-level compensation circuit. A bandpass filter comes next, with Bessel and Butterworth topologies available in 6dB, 12dB, 18dB, 24dB, 36dB, and 48dB/octave flavors, and Linkwitz-Riley filters, with 12dB, 24dB, 36dB, and 48dB/octave slope. Next up in the chain is a six-band, fully parametric EQ, and then a second insert, which makes available a gate, a compressor, automatic gain control, and a limiter. Finally, there is a delay, as in the inputs.
Based on what I saw and experienced, the dbx claim that the 4800 is “everything you need between the mixer and the power amps” is true, plain and simple. A test drive of the unit in the live sound venue at the Conservatory of Recording Arts & Sciences in Tempe, Ariz., proved that. During that test, the DriveRack handled the DSP for a four-way system including JBL 4888 line arrays (six boxes per side) and JBL 4880 18in. subs (two boxes per side). The system was tuned to the room with SIA-Smaart, and micro-tweaking parameters was a snap with the DriveRack.
Again, while my personal preference is to control the box with a laptop, I found the front panel very navigable and intuitive — a vast improvement over the 480. The unit's ample DSP and flexible routing should contend with pretty much any scenario your mind can conjure.
Furthermore, any complaint about the inability to change the order of the signal flow is countered by the fact that there are EQs both before and after dynamics processors in the chain, so you can have it whichever way you want it.
Most importantly, the box sounds good. With internal resolution up to 96kHz, the quality of the audio is high. Also, dbx has developed and included digital versions of some of its legacy analog processors, such as the compressors and the sub-harmonic synthesizer. They sound great, just like their analog ancestors.
I was impressed with the dbx DriveRack 4800 when I first saw it at InfoComm 2005, but now that I've had the opportunity to play with it and dig into its features, I am completely convinced. This is a powerful drive box with plenty of useful bells and whistles, and I would strongly recommend it to anyone who wants solid crossover, EQ, delay, and dynamics between the mixer and the amps.
Company: dbx Professional Products www.dbxpro.com
Product: dbx DriveRack 4800
Pros: Vast improvement of user interface compared to previous version.
Cons: Control software not available for Macintosh.
Application: A 4in. 8-out equalization and loudspeaker management system.
Analog inputs: (4) Electronically balanced, RF filtered, >50kΩ
Digital inputs: (4) AES/EBU channels, transformer isolated, RF filtered, 110Ω
Analog outputs: (8) Electronically balanced, RF filtered, 30Ω
Digital outputs: (8) AES/EBU channels, transformer isolated, RF filtered, 110Ω
Power requirements: 100V to 240V 50/60Hz, 45W
Weight: 11lbs. (14lbs. with audio transformers)
Shipping weight: 12.5lbs. (15.5lbs. with audio transformers)
Dynamic range: 110dB unweighted, 113dB A-weighted
Internal processing: 40-bit floating point
THD + noise: 0.004% typical at +4dBu, 1kHz, 0dB input gain
Frequency response: 20Hz-20kHz, ±0.25dB, <10Hz-50kHz +0/-3dB @ 96kHz
Interchannel crosstalk: <-85dB at 1kHz, 0dB input gain
X-over filter configurations: 1×1, 1×2, 1×3, 1×4, 1×5, 1×6, 1×7, 1×8, 2×2, 2×3, 2×4, 2×5, 2×6, 2×7, 2×8, 3×3, 3×4, 3×6, 3×7, 4×4, 4×5, 4×8
Phase control: 0 to -180 degrees in five-degree increments
John McJunkinis the principal of Avalon Studio Service in Phoenix and consults for both studios and live sound applications.