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Product Review - AudioControl C-101SE Two-Channel Equalizer - March, 1999

Karl Suager


AudioControl C-101SE Two-Channel Equalizer

Maximum Input and Output: 8 Volts RMS

THD: 0.005%

Mfr. FR: 10 Hz - 100 kHz ±0.75 dB

Input Impedance: 100k Ohms; Output Impedance: 150 Ohms

Size: 3 1/2"H x 7"W x 11"D

Weight: 9 Pounds

MSRP: $799 USA

AudioControl, Inc., 22410 70th Avenue West, Mountlake Terrace, Washington 98043; Phone 425-775-8461; Fax 425-778-3166; E-Mail; Web

"EQ This Bucko!" I first thought when JEJ suggested reviewing AudioControl's C-101SE equalizer. All in all, I don't have much against equalizers, at least in principle. However, the purist audiosnob occupies as much of my cranium as the pragmatic music lover. I've had a couple of EQs in the past, both of which added enough of what I didn't want in my music (distortion) that I chose to leave them behind with the recordings I otherwise would have liked to Band-Aid.

To make a short story no longer than reasonably drawn out, the C-101SE arrived, I unpacked it, went through a cursory visual inspection, set it on a shelf, and left it there for some time while I mulled over whether or not I really liked EQ. A few weeks ago, my curiosity prodded me into pulling out the extra interconnects and slamming the box into the two-channel music system, and here we are.

The C-101SE is a special edition of the original classic C-101, essentially identical to the original, so I'm told, in every aspect other than cosmetic mods. Like the C-101 sans SE, the SE version is a 10 band, 1 octave graphic equalizer with an onboard spectrum analyzer of the same sort, complete with calibrated microphone. Features include an internal pink noise generator, display turnoff, display increment selector (2 or 4 dB/LED), EQ defeat, Tape Monitor (replacing the tape loop the C-101SE will most likely occupy), recording EQ, and an 18 dB/octave subsonic filter with a 20 Hz cutoff point. Sliders are adjustable  ±15dB individually for the left and right channels center at 32 Hz, 60 Hz, 120 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, and 16 kHz, representing 1 octave jumps across the audible band. Putting the left and right controls for each band adjacent to each other allows the user to easily match levels between channels. Although the ability to individually tailor each channel's response doesn't hurt itself, actually using that option can degrade imaging in many cases, as the unbalanced equalization (sliders for the left and right channels not in the same positions) will cause interaural phase shifts that smear localization cues in the time domain.

RTAs (Real Time Analyzers), like the spectrum analyzer within the C-101SE, can provide a rough picture of the system response, including the listening environment. That is quite a useful tool, in that it provides visual feedback by which to gauge the effectiveness of room treatment techniques and loudspeaker locations when attempting to optimize performance of an audio system. An EQ, when used in conjunction with an RTA, can compensate for room and loudspeaker artifacts, to some extent. However, one should consider that an EQ, even when used with an RTA, is a limited device in that application.

For one thing, a simple spectrum analyzer cannot capture information in the time domain, and therefore cannot differentiate between direct sound and reflected sound. So, what the spectrum analyzer shows is the average of the two. Because of this, if adjusted solely by the RTA, an EQ alters both the direct and indirect sound so that the two sum flat, although neither may be so individually. Human hearing works in a much more complex manner, so that although we may not hear the two (direct and indirect sound) as distinctly separate in most home environments, altering one to correct the other won't always work very well. One of the best examples of this is to get a dipolar speaker, which usually has a horrible pink noise response due to a high ratio of delayed, reflected sound from the rear wall. If you adjust an EQ to compensate for the RTA reading, you often get sliders shoved all over the place, and a very weird tonality. This is because the process of hearing somewhat compensates for the environment, and takes much of the comb filtering effects of reflected/direct sound interaction which skew the tonality of continuous pink noise, and puts it to use with impulsive signals to derive spatial cues about the environment. That's why bipolar/dipolar speakers tend to do such a great job providing a "they are here" presentation. Tangent aside, even though an equalizer can slightly compensate for room problems, if the room's broken, you're best off fixing the room.

Secondly, a spectrum analyzer, especially a 10 band, 1 octave jobbie, has limited frequency resolution, looking only across relatively broad sections. For instance, the frequency response may vary 10 dB up and down, but so long as it averages within that octave, appears perfectly flat on the analyzer. The corollary is that an equalizer with similar resolution cannot effectively compensate for narrow band response peaks or dips caused either by loudspeaker problems or extreme room modes.

You can use the EQ to boost a bit below the low-end cutoff of loudspeakers to gain additional extension, though I only recommend trying this with sealed enclosures, as ported speakers tend to simply unload the cones below the ported frequency if boosted significantly. I did this with some M&K satellites for kicks, boosting 15 dB at 32 Hz, and 4 dB at 60 Hz. It actually didn't sound too bad, although a bit strange to get significant output that deep with a 5" mid-bass. The drawback, though, comes two-fold, in terms of limited dynamic range. 15 dB equates to a boost of about thirty two times. That means you're going to need a lot of power to generate even moderate SPL at those frequencies, making the possibility of clipping an amp that much more likely. And, with that kind of power, the voice coils in most small drivers will warm up quickly, resulting in dynamic compression at lower output levels than usual, assuming the motor doesn't fry itself and melt in the gap! Couple that to the fixed excursion limitations of those drivers, and you're patching a dam with toothpaste.

The subsonic filter didn't have any audible effect for my listening since I didn't have many discs that went that deep, and my main speakers only go down to 27 Hz. It might be pretty useful with turntables that pick up acoustic feedback in that area, but I don't own a turntable.

That said, the C-101SE remains a powerful and productive tool for pulling enjoyment out of audio. The analyzer provides more information than a simple SPL meter, and can accompany more specific test tones than pink noise, such as warble tones and sine wave tests, should you have a generator or a test disc. The 10 band EQ, though not as precise as a 1/3-octave unit, has far more finesse than typical bass and treble tone control knobs. In fact, for average recreational use, a 10 band EQ seems to have just about enough sliders to scratch all the right spots, but not so many as to make the adjustment ponderous.

The user may set up the C-101SE two different ways, either through the tape loop, or between the amplifier and preamplifier. I chose the second option since my passive controller lacks a tape loop at the present, although I saw the necessary parts at a specialty electronics store a couple of weeks ago. Configured after the passive controller, the C-101SE provided an excellent buffer in bypass mode. Because of the 100 kOhm input impedance, as opposed to the 22 kOhm input impedance of both of my Aragon amplifiers, the system demanded less current from the CD player output. I don't know that it actually improved the sound in any real way, but it didn't seem to hurt much either.

For the sake of going through appropriate motions, I messed around with the onboard RTA and pink noise generator. If AudioControl went through the trouble to build it in, than I suppose I should at least try it. I mean, it is half the product after all, and if I hadn't already used AudioControl's 1/3 octave analyzer to help set up the system, I might have found out something new. Not surprisingly, the RTA on the C-101SE showed what I already knew. The overall balance wasn't bad, but slightly bass heavy, likely due in part to the smallish room dimensions of 13'X20'X8'. The display did prove entertaining when listening to prerecorded material, adding another dimension to the fray as instruments and vocals threw their own shifts to the energy spectrum. For the most part, though, I made tonal adjustments by ear for each recording, the same way I think most people would eventually use the C-101SE.

For controlling the tonality of listening material, the C-101SE excels. Many recordings, which I considered absolutely substandard, made it back into my CD player, and actually stayed there for more than a few minutes. With this tonal food processor, a few sliders slipped a dB or three worked wonders just shy of a minor miracle. While the C-101SE couldn't completely compensate for errors, i.e., "artistic choices" in microphone selection/placement and the mixing process, it could tweak the overall effect to good measure.
A slight lift between 2 kHz and 8 kHz brought out Jewel's vocals on her "Pieces of You" album, otherwise sunken and muffled. A bump between 32 Hz and 120 Hz coupled with a gradual lift 4 kHz and up brought some innards-smacking punch and sparkle back to Soundgarden's "Bad Motor Finger." Fiona Apple's "Tidal" sounded slightly cleaner and tighter with a 4 dB cut at 32 Hz, while The Cure's "Disintegration", a completely dead-sounding disc, became listenable with a hefty lift at 8 kHz and 16 kHz. And it's not just pop material that can benefit from equalization. "Canciones de Llamas", a Latin mix of guitar and rhythm by Tony Lasley, sounded more than up to snuff, even by audiophile standards, with a little massaging. A 6 dB cut at 32 Hz, a 2 dB boost at 60 Hz, and a little tilt from 2 kHz and above a few dB cleaned up the boom while lifting the veil on a host of reverberant information.

All this experimenting made a point worthy of notice. If a listener were to judge the performance of a system based on their subjective impressions of a handful of their favorite recordings (usually the case), they may place disproportionate blame or credit for the total sonic performance on the playback system, and tailor that system to respond synergistically with those specific recordings, possibly hampering the potential of the system as a whole.

For instance, had I chosen a system to complement The Cure's dead-sounding album, I might have ended up with a very bright system that caused listening fatigue on more balanced material. To contrast, had Jewel's album been the reference, the ideal system to fit my taste would have slightly rolled off the very top octave and starved the lower midrange to gain an anemic yet overly forward upper midrange. Perhaps I'd simply call the system very revealing in order to rationalize my choice in equipment, and leave myself open to more expensive upgrades in the future. Anyway, you get the idea. I think this problem is far more common than most people in the industry would like to admit.

Is it possible, or even likely, that so many experienced professionals would glance over this aspect intentionally? You bet. Possibly because they'd like to sell you more stuff that leads you open to buy yet more stuff instead of providing a box which addresses the issue at hand. I once read an anecdote somewhere, I forget the source, about a salesman who, when asked why high-end preamps lacked tone controls, said something to the effect of, "I don't know, but I'm glad they don't. We'd sell a lot less speakers if they did." Perhaps in the future we will have digital EQ that you set for each CD, DVD, or whatever, and each time you plunk the disc in your player, the digital EQ section recognizes that disc and recalls the specific EQ you set for it.

The C-101SE is a pretty attractive box for those who'd take control rather than jumping from different speakers, cables, and preamps every few months. It's sure a lot quicker between tracks. If the tonal flavor of the music doesn't match you or your system, you can make it! Not that I've anything against trying new components. I thrive on it. First time I had a tube-based preamp and listened, I thought, "Whoa, now this is pretty neat!" Nor am I proposing that an EQ can compensate for lousy electronics or speakers. I am proposing what many have adamantly stated for years, that a good EQ can make many recordings more enjoyable in any system, regardless of personal taste or the sonic character of that system, simply because it allows optimization of the subjective experience. With an EQ of this high quality, the compromises, if any, are minimal. And, if hooked up via the tape loop, the C-101SE can become more transparent than any electronic device, simply by disengaging the loop.

With the unit I tested, the noise floor was lowest in bypass mode, and slightly more with the EQ engaged, in turn a good step below the acceptable levels inherent in some surround processor/preamps for the sake of comparison. With the RTA display kicked on, noise leaked into the audio path with a weird character, like a tweaked out fax machine with a ground loop, at a moderately high level. It was not really that high in a total sense, but it was high for me since I had the EQ hooked directly into the 28 dB gain of the amplifier. This hookup method would be equivalent to the noise level if the EQ were in the tape loop of an active preamp with the volume knob cranked to about 1 o'clock, enough to drive an amplifier at full output with a typical CD. The noise may have been particular to the individual unit I got, as AudioControl claims that shouldn't happen. Whether or not that's the case, the noise wouldn't pose much of a problem if the unit were hooked up via the tape loop, as mentioned, since it places any noise from the EQ before the preamp, attenuating that noise at most volume settings.

Aside from a small increase in noise floor, the C-101SE is one of the more neutral pieces of electronics I've listened to. To be fair, it doesn't provide gain or volume control, but at $799, it goes head to head, in terms of transparency, with some of the best two-channel audiophile preamps on the planet under the $1.5k mark, and embarrasses a few at more than quadruple that. Though certainly not a fix-all, the unobtrusive control in the audio chain makes the C-101SE a real treat for the music lover and a tempting dalliance for the audio purist. The thought of its departure hurts. I don't think AudioControl is getting this one back just yet. If they can send me a Diva (an eight channel digital EQ, review hopefully coming soon), we can talk about it.

Karl Suager

Associated components used for this review:

Infinity Renaissance 90 Loudspeakers
M&K LCR-55 Satellite Speakers
Aragon 8008BB Power Amplifier
Aragon 8008x3 Power Amplifier
Sunfire Stereo Amplifier
Passive Controller w/50kohm Nobel Pot
DH Labs Silver Sonic Interconnects and Speaker Cables
Audioquest Diamond Interconnects
Liberty Emerald CL-3/14-4 Speaker Cable
JVC XL-Z1050 CD Player
Audio Power Industries Power Pack V Line Conditioner
Bybee Technologies Prototype Power Purifiers
Bybee Technologies and M D'or Custom Shielded Power Cords

© Copyright 1999 Secrets of Home Theater & High Fidelity
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