Author: Ken Pohlman
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Originally appeared in the September/October 1994 issue of Car Stereo Review magazine.
Reprinted with permission.
© All rights reserved.
Way back in the winter of 1991 (ah, I remember it well), I tested Rockford Fosgate's Symmetry, a unique analog/digital system that, like a 300 pound gorilla, could do almost anything it wanted to. My January/February 1992 review reported that this modular and expandable system (built into twin racks the size of small microwave ovens) contained a power supply, preamplifier, time-alignment system, auto system equalizer, real-time analyzer, active crossover, and power amplifiers, all controlled via a dandy wired remote. Basically, it's an audio computer. Even before I switched it all on, I figured that its designer, Wayne Harris, had time traveled about 10 years into the future and brought this beauty back with him. And when I was finished testing it, I said that it was simply the most remarkable audio system on the road. Now it appears that Wayne has checked into the 21st millennia again, this time bringing back the EPX, son of Symmetry.
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.
Hideaway processors are as easy to install as light bulbs. I mounted the EPX in my front trunk near my power amplifiers using self-tapping screws: I made sure that the input panel – and its sensitivity controls – were accessible. A CD head unit served as the source with its front line outputs wired into the EPX's inputs. I left the head's rear outputs unconnected, since fading is handled by the EPX; this will be especially good news if your head unit doesn't have rear outputs.
Then I wired the EPX outputs to my amplifiers. The front high-pass outputs drove two front tweeters and woofers, the rear band-pass outputs drove two rear woofers, and the constant-bass low-pass drove two subwoofers. My Porsche's front trunk layout made it a snap to run the data cable through the firewall and on to the RDAT. Finally, I trussed up the power, chassis-ground, and remote-turn-on leads.
Fully wired, the EPX was now ready to help me tweak the daylights out of my system A main menu appears when you power up the unit with prompts titled PREAMP, EQl, XOVER, GLOBAL, LOCK, SETUP, and ABOUT. Hitting the function key tied to one of these prompts accesses a corresponding submenu that lets you get down to the dirty work of cleaning up your system's sound. Volume can be adjusted at any time using those dedicated keys, but note that the remote's display only shows a volume bargraph when you're in the main menu.
To start the ball rolling, I tapped the SETUP key; its submenu includes CODE, CHIRP, MEMORY, and LEVELS prompts. I selected LEVELS and followed the on-screen instructions from a spot just outside my trunk; the instructions include 11 easy-to-follow steps for optimizing sensitivity. Very cool. Sensitivity adjusting completed, I slammed the trunk closed and took o seat behind the wheel.
I found that CODE lets you enter or change a four-digit PIN number just as if you were withdrawing money from the ATM machine in your local bank's vestibule (the factory default is 1234) – no PIN, no music. Tapping LOCK lets friends, interlopers, and sound-off competitors listen to your system, but it keeps them from screwing it up: Once you enter your PIN, system settings can't be changed until you enter it again. At the same time, system volume won't exceed the level at which it was locked – no matter how much the volume-up button is tapped. Prod the CHIRP option and the RDAT will emit a chirp every time you press one of its buttons; prod it again and it will chirp no more. If you like the chirps, you can even change their pitch. The MEMORY option should be used only if you want to reset all system presets to their default factory settings. Be careful of that one...
The PREAMP functions are easy to use. Its submenu offers SOURCE, FADER, and TONE options. SOURCE lets you select one of your two sources (A or B). The fader option displays two bargraphs, one for balance and the other for fader; you use the left/right multipurpose keys to adjust the former, their up/down counterparts for the latter. To reset either parameter to its center position, punch the center multipurpose key. The TONE option puts up a bargraph for bass and one for treble. You use the left/right keys to select bass or treble and the up/downers to boost or cut; the center key dials in flatness.
Tapping the EQl button calls up a submenu offering A, B, C, D, and ADJUST options. The four letters refer to the equalizers four preset banks. Tapping a letter gets you into the corresponding bank; recall that each bank can hold up to four preset equalizer curves. All of the presets are set for flat (unequalized) response when you first power up the EPX.
To customize a curve, tap the ADJUST button. This accesses a screen with two readouts, one for frequency and one for amplitude. The frequency readout has a horizontal bargraph with a cursor you use to select the band you want to adjust as well as a numerical display of the center frequency. The amplitude readout uses a vertical bargraph that displays the current level and numerical readout in dB. Pressing the left/right keys moves you through each preset's 14 bands, and the up/down keys boost or cut the level of the selected band. A SAVE function lets you store a curve. Tapping the center key flattens the selected band.
The XOVER submenu displays LP (low-pass), BP (band-pass), and HP (high-pass) prompts. To adjust the low-pass, you hit the LP function key; the display shows a numeric denoting the cutoff frequency and a crude graphical representation. You can adjust the crossover frequency with the left/right multipurpose keys; changes are automatically saved. The high-pass filter is adjusted the same way, except you must first select whatever you want to work on the front or rear outputs. For the band-pass filters, you punch the far-left function key to access the filter's low side and the far-right key to adjust its high side.
The GLOBAL function takes you to a submenu with LOAD, SAVE, and AUTO prompts. The LOAD option lets you access a previously stored global preset; hit the function key and select from A, B, C, or D. The SAVE option lets you store a new global preset in A, B, C, or D; all system settings except for source and volume will be stored. As noted, the EPX can also automatically switch between your A and B global presets following the volume level designated using the VDISC function. To access this ultra-cool function, hit AUTO and check out the display showing ENGAGE, BYPASS, and a volume bargraph. Then set the volume to the level at which you want the switch to occur and hit ENGAGE. At this point, global A will be active whenever the volume level is below the threshold and global B will kick in when the level exceeds the threshold. BYPASS lets you turn off the VDISC feature.
Throughout this lengthy – but enjoyable – routine, I found that working with the EPX was a piece of cake. Most of the routines are intuitive, and it only takes a few minutes to get comfortable with the software's basic character – a very rare thing in the software world. I really appreciated the fact that the EPX let me sit in my Porsche's driver's seat while I was adjusting my system's EQ and crossover points – it's much easier than crawling around in the trunk with a screwdriver. You can actually hear what you're doing while you're doing it! And remember that the EPX's EQ and crossover are free of potentiometers – parts that traditionally prove to be a weak link and make a component noisy by allowing dust and dirt to crawl into its guts. The EPX gels a big, healthy thumb's-up as a user-friendly device.
All of the convenience in the world is useless unless the component that grants it also sounds great. To gauge the EPX's performance chops, I hit the road with my reference collection of classical and rock music, listening for any kind of system noise, computational error, A/D or D/A nonlinearities, or other funny stuff. And I came away happy as a clam. The EPX is extremely clean, and it does an excellent job of running the analog audio in and out of the digital domain. In addition, the digital signal processing itself was of truly audiophile caliber. If you want to feel guilty about not crawling around in your trunk and think that there must be some sonic penalty, go ahead and think it – but you'll be spinning your wheels.
Once again, Wayne Harris and Rockford Fosgate have let us peek into the future. Their EPX demonstrates that the trend is toward the digitization and integration of audio functions with remote software control. And this processor shows that it can be done without demolishing your credit line. Clearly, break-through products such as the EPX are beginning to drive nails into the coffin of hard-wired dedicated audio products.
-Ken C. Pohlmann