The EPX packs some of Symmetry's most universally useful functions in a neat little black box. (Now you con enjoy synergy with Symmetry without having to own a Winnebago.) The reduction in features and sheer chassis size means a lower price tag and a lower install fee. In other words, this is a Symmetry for the rest of us. And we like what it does.
The little EPX chassis houses a dual-input preamplifier, a 14-band equalizer, and a three-way 10 channel active crossover; all are controlled in real time via a wired remote control, which Rockford has dubbed the RDAT (remote data access terminal). All inputs and outputs are analog.
The remote has a backlit LCD readout that provides both numeric and graphic displays. While most users will want to mount it on the dash or use it as a handheld device, the remote also grants system control from outside of the vehicle, a perk for soundoff competition. The best thing about the RDAT is that it lets you make adjustments from the driver's seat – that's the spot where you'll be doing most of your listening (unless you're an incredibly talented stud). That's right, with the EPX (or the full Symmetry rig, for that matter) you can forget all about jumping back and forth between your trunk and front seat while trying to tweak your system. Logic is a beautiful thing, isn't it?
The RDAT looks just like the remote that controls Symmetry, though the original's dorky putty color has been switched to black. It's actually a microcomputer that employs a software driven menu system to prompt you through system setup and tweaking chores; the remote's display even helps you along the way by displaying instructions for some of its many functions.
Brain work is handled by the RDAT's 20 MHz 16 bit microcomputer, which comes complete with 32 Kbytes of program memory and 8 Kbytes of nonvolatile memory. Technoids will be happy to learn that all of the EPX software is written in assembly language, which saves storage space and results in speedier execution of your commands. The RDAT's LCD provides a two-line, 40-character-per-line display that feeds menus and other information to the user. To select any given function, just press the associated function key. The remote interfaces with the EPX via a 9,600 baud RS-232 serial data port and a supplied data cable. All of the data lines are optically isolated from the EPX's audio circuitry to help keep the nasty, dirty digital stuff away from the delicate, fine-washable analog stuff.
The remote's keypad has 25 keys. Both the LCD and keypad are backlit. Five function keys occupy a place of honor on the RDAT. Their functions are determined by the menu that's on tap; whatever they happen to be at any given time is indicated by labels in the LCD. Three keys that don't access variable functions control volume up, volume down, and mute. Four multipurpose keys marked with arrows and a central key provide various functions, including alphanumeric input. There is a 12 key pad for entering numeric data, an escape key for canceling an operation, and a reset button (in case the microcomputer gets hung up).
Using the RDAT, you can control the preamp's volume, tone, balance, and fade functions, switch the mute function on or off, select either of the two sources, and set input gain. Volume is adjustable over an 80 dB range in 2 dB increments, while balance and fade each vary over a 40 dB range in 2 dB increments. Independent bass and treble controls vary the signal over a +/- 12 dB range in 1 dB increments; the bass corner frequency is at 45 Hz, the treble corner at 15,000 Hz.
The RDAT also taps into the 14-band stereo equalizer, which offers half-octave control below 1,000 Hz and full-octave control from that point up. Half- octave centers are fixed at 32, 45, 60, 90, 125, 180, 250, 375, and 500 Hz; full-octave centers ore fixed at 1,000, 2,000, 4,000, 8,000, and 16,000 Hz. Each band can be adjusted over a +/- 12 dB range in 1 dB increments.
The fadable three-way active crossover provides high-pass, low-pass, and band-pass filters with a total of 10 discrete outputs: front left/right high-pass, front left/right band-pass, rear left/right high-pass, rear left/right band-pass, and constant-bass left/right low-pass. The crossover points for each of the five groups can be adjusted independently. The front and rear high-passes run from 1,820 to 20,000 Hz; the low side of the front and rear band-passes run from 115 to 3,000 Hz, their high side from 650 to 20,000 Hz. The low-pass runs from 57 to 3,000 Hz. Butterworth-type filters are used throughout, with a rolloff of 12 dB per octave. Each filter can be set to one of 256 frequencies; the owner's manual does the math, noting that this provides 12 quadrillion unique crossover combinations. Crossover points are represented both graphically (over a logarithmic frequency scale) and numerically (frequency in Hz).
Don't overlook the crossover network's fadability; this means that front and rear levels can be adjusted independently. This degree of control is essential if you want to nail down a realistic balance between your front stage and rear fill – and you won't have to worry about your system's bass output, because the low-pass outputs are of the constant-bass variety. In other words, your subwoofer system will stay on full tilt no matter where you position the fader. All high-end xovers should be equipped this way.
The EPX also provides a nice software perk: GLOBAL and VDISC (Volume Dependent Interactive System Control). Using them, you can preset four different combinations of preamplifier, equalizer, and crossover settings; tie in VDISC and the EPX toggles between two presets automatically depending on the volume setting. The presets can cover typical changes in the road-going environment –top-up and top-down driving, for example, and/or low- and high-volume listening. This is really freakin' cool.
Unlike its Symmetry forebear, the EPX is a closed system, which means that it can't be expanded. Its software driven nature does mean that new versions of EPX software can be incorporated, however. My review unit was shipped with software version 1.05, for example-a step or two beyond what's listed (and discussed) in the owner's manual. One of version 1.05's perks lets you name all of your global presets, both source units, and the equalizer banks.
The EPX chassis is designed to be hidden away in any convenient location. One panel sprouting four phono jacks accepts inputs from two stereo sources (designated as A and B by the software); four pots let you adjust input sensitivity for each channel of each input source, which is the only way to go. A three pin Molex connector accepts a mate that handles power, ground, and remote turn-on; there's also a jack for connecting the RDAT as well as an LED that lights when the EPX is powered. All of the outputs are arranged on the opposite panel; 14 phono jacks do the honors. There are stereo pairs for front and rear high-pass, band-pass and all-pass as well as a stereo pair for constant-bass low-pass. Rockford kindly throws in a power wiring harness, an 18-foot cable for connecting the RDAT, mounting screws, and Velcro.
A peek inside the EPX chassis reveals another picture-perfect Rockford Fosgate construction job, complete with discrete surface-mount components. It's an absolute joy to see what truly talented electrical engineers can do with circuit-board layout and general construction details. As in other car units, the switching (30kHz) power supply provides DC-DC conversion to power the EPX; it's a self-oscillating design, however, that allows complete isolation between power ground and signal ground. This type of isolation helps minimize alternator whine and similar grounding nightmares. In addition, this design helps reduce radio-frequency interference (RFI) that could mess with your system's radio.
The preamplifier employs a differential input; this helps to reject common noise on the input lines by accepting only the difference signal (that's the audio stuff) between the lines. In addition, each set of audio inputs has its own audio ground; this helps to avoid ground loops when you're "having more than one" source and each one tries to be the common audio and power ground. Finally, the software controlling the preamplifier's input sensitivity controls (variable from 500mV to 2.5 V) features a level-setting procedure that helps optimize signal-to-noise ratio and headroom. Speaking of dynamic range, the audio output from the EPX is in the neighborhood of 10 volts; that pushes system noise way down. Nice, nice, nice. Price: $749. Rockford Fosgate, Dept. CSR, 546 S. Rockford Dr., Tempe, AZ 85281.
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