BY KEN C. POHLMANN
When spectators crowd around a car to admire its sound system, their attention is often initially drawn to the power amplifiers. Truly, there's nothing quite so impressive as row after row of hot extruded aluminum, the raw power, and the spl they represent. Speakers are pretty impressive, too -- all those square inches of cone material and the enclosures they ride in, letting you visualize what the sound must be like. Head units are less impressive, but at least they garner some attention because they're the master control panel and the source of the sound.
All but lost in the shuffle are the equalizers. They seem to be viewed as insignificant trivialities that just complicate the wiring plan; why, they're almost as bad as crossovers. If some components are as exciting as a wealthy and charming bikini-contest winner with a Ph.D, then an equalizer is about as dull as Nancy Reagan on Sleep-Eze.
That, at least, is the impression that many people have of equalizers. And that's a shame, because equalizers are the mortar that holds an install's bricks together. A good eq adds sonic sugar and spice to soften the rough edges that grate on the ear. Without proper equalization, all the watts 'n' woofers in God's creation just won't sound good.
Moreover, eqs allow manipulation of frequency response to whatever contour you desire, whether it's flat or wildly aesthetic. Although purists will shudder at the latter notion, it sure is a whole lotta fun to wank on a car's frequency response. In particular, good equalizers let you dial in the coolest amount of bass -- and the difference between lame bass and killer bass may only be a crucial decibel or two. In short, whether for accuracy or for kicks, expert audiophiles know that equalizers can make huge differences in attaining sonic goals.
DEI's Model 4000 equalizer ($210), a member of the company's Mobile
Power Series, isn't physically huge; its half-DIN-size chassis measures
only 1 x 7.25 x 4.25 inches (h/w/d), but it is designed to have a huge
effect on your system's sound. It offers four-band equalization with a
maximum of 18 dB boost/
cut, a dedicated subwoofer output with an adjustable low-pass filter,
and a master volume control.
The 4000's front panel is principally occupied by eight push-to-recess potentiometers and some cleverly hidden controls. The first potentiometer, labeled volume, controls overall system gain (both main and sub output). The adjacent potentiometer (fader) provides fader control over front/rear levels; it has a center detent.
Two potentiometers control a dedicated subwoofer output channel. One, labeled sub freq, adjusts the cut-off frequency (from 30 to 300 Hz) of an active low-pass filter; the other, sub vol, controls the volume of the dedicated sub channel.
The last four potentiometers control filter gain (+/-18 dB) on each of four channels: sub, low, mid, and hi(gh). Inset to the left of each level control, and accessible with a screwdriver, are four internal potentiometers that allow adjustment of the center frequency of each band. The frequency ranges for the four bands are labeled as sub, 30 Hz-70 Hz; low, 150 Hz-400 Hz; mid, 1.5 kHz-4 kHz; and hi, 10 kHz-20 kHz. A small cd/radio pushbutton to the left of all of the potentiometers selects either of two line-level inputs.
Unlike a true parametric eq, the 4000 lacks controls for bandwidth (Q). The Qs of the bands change only as center frequency is changed. DEI informs us that Qs vary from low to high as center frequencies are changed from low to high. For the sub channel, at 27 Hz (which is slightly lower than the labeled figure), Q is 1.6; at 70 Hz, it's 3.2. On low, at 150 Hz, Q is 1.5; at 400 Hz, it's 3.5. For the mid channel, at 1,500 Hz, Q is 1.3; at 4,000 Hz, it's 3.9. And for hi, at 10,000 Hz, Q is 1.4; at 20,000 Hz, it's 2.0. As you can see, the bands are broader with low center frequencies and pointier with high center frequencies.
The rear of the unit has 10 gold-plated connectors. Four RCA jacks (input radio l and r, input cd l and r) handle left and right radio and CD input, while four other RCA jacks provide left and right front and rear output (output front l and r, output rear l and r). Two additional RCA jacks provide left and right subwoofer output (sub out l and r).
Power, ground, and remote turn-on are connected via a socket that plugs into the unit. Two recessed potentiometers on the chassis top (cd gain l and r) provide gain adjustment of the active preamplifiers accepting the CD input (or, as DEI informed us, they provide "attenuation of the input signal to provide level matching").
The 4000 is housed in a metal chassis; a pair of screw holes on each end can be used to secure a metal mounting bracket. No brackets were supplied with our test sample, but DEI says that two brackets and eight screws are usually supplied. DEI does kindly include a plastic screwdriver (for adjusting the recessed potentiometers) as well as an in-line fuse.
Inside, the circuitry is mounted on a double-sided glass epoxy board.
The board is neatly laid out with good-quality parts. The active filters
are designed around bi-fet op-amps, and a mosfet switching power supply
provides the juice. The 4000 has a 3-year limited warranty when installed
by an authorized DEI dealer; the warranty goes down to 1 year when installed
otherwise. Price: $210. DEI, Dept. CSR, 2560 Progress St., Vista, CA 92083;
800-288-4474. Web site: www.directed.com.
THE INSTALL
Installation of the 4000 was a snap. I ran a stereo input from my head
unit, and then four main outputs and a stereo subwoofer output to my power
amplifier. I added three power wires, and, presto, I was in business. I
adjusted the input gain using the top-mounted recessed potentiometers,
and then slung the equalizer under my mule's dashboard using a bracket
to hold it up. (My trusty CSR mule, as you'll recall from prior tests and
evaluations, is a 1986 Oldsmobile Ciera.)
Everyone should take an extra minute when setting the 4000's input
gain to make sure that the unit won't clip even when you dial in +18 dB
at a high volume setting. After doing so, I noticed that the fader control
was backward; this was easily remedied by switching the front and rear
output pairs to the power amplifier. I later noticed a slip of paper inserted
into the unit's owner's manual (emblazoned with the banner headline, "important!"),
advising of this minor problem, and DEI says it's been fixed in current
production models.
PERFORMANCE
Once I was properly wired, I spent some quality time getting a feel
for the 4000. The subwoofer cut-off frequency and level controls are useful
for dialing in your preferred bass response. I appreciated the ability
to locate a low-pass cut-off frequency from 30 to 300 Hz before cranking
it up. Some day, all head units will have independent subwoofer controls;
until then, external control is fine.
I next turned my attention to the four eq bands. DEI advertises the 4000 as a parametric equalizer, but this is akin to advertising Salisbury steak as sirloin. By definition, a parametric equalizer provides control over gain, center frequency, and bandwidth. The 4000 only permits control over the first two; hence, it's not a parametric equalizer. It's a function of the filter circuit employed that the bandwidth increases as center frequency increases; at best, DEI should call the 4000 something like "quasi-parametric" or "semi-parametric." But they shouldn't call it a full-blown parametric unless they want to get hauled into court -- either the court of public opinion, or that of the legal kind.
Truth-in-advertising issues aside, the four-band equalizer did a pretty good job of providing frequency-response adjustment with relatively little interaction between band controls. Just for the heck of it, I hooked up a real-time analyzer (RTA) and shot some pink noise into my car's system, using the 4000's filters to dial up problem areas in the frequency response so I could bump or cut as needed.
You'll need more than four bands to even hope for a flat response, but these controls were useful for general-purpose curve setting. However, if a problem area falls between two bands, the relatively little overlap between bands means that you may have to dedicate two bands to tackle it -- so those two bands can't handle other problems. And even with two bands working on one problem, it may be difficult to achieve the result you desire.
Unfortunately, the four filter potentiometers on my test unit didn't have center detents; I'm told by DEI that this has been fixed in current production. My biggest gripe, of course, is the lack of bandwidth control. The unit's relatively broad bands (especially with low center frequencies) give good general control, but you're outta luck if you need to pinpoint a narrow region. Also, it's important to remember that center-frequency adjustments must be made with a screwdriver. This would make sense if the 4000 was a set-and-forget device, but it isn't. It's a hands-on unit, and one for which you need a screwdriver to make primary adjustments. This is a problem.
From a sonics standpoint, however, the 4000 didn't give me any grounds for complaint. The noise and distortion levels are low, and the unit didn't display any clipping or headroom problems. The output signal can be cranked to a generous 8 volts rms. All of the front-panel potentiometers have a smooth, tactile feel, and they're nicely back-lit with green lighting. In a more perfect world, the 4000 would also have adjustable bandwidth; leds for power on, input clipping, and output overload; and a defeat switch to bypass the equalization.