SigTech TF 1120 Time Field Acoustic Correction System Page 2

While the SigTech is an extraordinarily complex and sophisticated piece of gear, once it's been properly set up it's quite simple to use: Pick the right input source, select the proper filter from four choices, and turn it on and off via the bypass switch. During six months of using it, I never had a glitch or problem that was not due to user error (usually I'd be on the wrong input on the TF 1120 or the EAD 9000 III D/A processor). Once properly installed, the SigTech unit operates invisibly, calling little attention to itself. Even after power-outages, brownouts, and other power-line weirdnesses, the SigTech refused to suffer any digital amnesia or dyslexia. In short, the SigTech exhibited the kind of reliability you'd expect from a professional product. Too bad this level of reliability is less than universal among high-end gear.

Rooms, problems, & pyramids
Let's face it: The weakest link in almost any high-end audio system is the listening room. Even acoustician-designed rooms are no guarantee of acoustic excellence—remember the first incarnation of Avery Fisher Hall? This single edifice makes a strong argument for removing the "dismal science" mantle from the shoulders of Economics and draping it funereally around those of Acoustics. Most more-than-mo towns have some new hall or amphitheater built in the last 20 years that was supposed to sound wonderful but turned out to be a sonic disaster. In short, most rooms suck, and many custom-built rooms have only inflated sonic-disaster scenarios to Towering Inferno proportions.

The first step in turning the average listening room into something fit for music is not to run out and buy a SigTech unit. No, the first thing any audiophile who values music should do is physically treat their rooms. Proper use of ASC, RPG, or RoomTune products is a good first step toward solving room-induced problems (footnote 1). Judicious placement of rugs and carpeting, attractive overstuffed furniture, and wall hangings can also help tame overly reverberant listening environments. Yes, I know, many people believe it's possible to so overdamp a room that it loses its "bloom" and character, but in 20 years of audiophilia I've encountered very few home listening rooms that suffer from this particular sonic malaise. Most are far too bright, reverberant, and alive. Physical room correction is always preferable to electronic correction.

Adjusting the physical locations of your speakers and primary listening position is the second thing to do in your listening room. I've found that even small adjustments in speaker and listening positions can have a major effect on room interactions. Once you've done all you can physically, then it's time to embark on electronic corrections.

My own listening rooms are good examples of the kind of problems and solutions possible in the real world. My large (20' by 24') room has a parquet wood floor over concrete slab, post-and-beam construction, irregularly shaped walls, a high pyramidal vault, and large openings into other rooms. Without any damping it's far too alive, with noticeable slapback echo off the ceiling, floor bounce, irregular bass-frequency leakage and augmentation, and sidewall reflections. Physical solutions to the room's problems included RoomTune Ceiling Clouds in all four corners of the ceiling vault, ASC Tube Traps in the corners of the room behind the speakers and behind the speakers themselves, ASC wall panels behind the listening couch and on the sidewalls of the vault, thick rugs on the floor, and extra blankets on the back of the listening couch. While this treatment eliminated slapback ceiling reflections and attenuated most early reflections above 1kHz, rear-wall bass cancellation and broadband midrange colorations were only slightly improved.

But if you look at figs.1 and 2 (SigTech graphs of frequency response of the Dunlavy SC-VIs before and after SigTech equalization—the left speaker is the blue trace in both graphs, the right speaker the green trace), you can see that the major SigTech corrections were below 1kHz. The first correction was to eliminate the bass notches at 42Hz in the left channel and 33Hz in the right. The next correction was to reduce the midbass bloom at 100Hz in the left channel and 90Hz in the right. The Sigtech then addressed the broadband dip between 100Hz and 1kHz in both channels. Above 1kHz, the SigTech did some minor overall smoothing of the frequency curve.


Fig.1 Dunlavy SC-VI in SS's big room, 1/3-octave smoothed, uncorrected response (left channel blue, right channel green, 5dB/vertical div.)


Fig.2 Dunlavy SC-VI in SS's big room, 1/3-octave smoothed, SigTech-corrected response (left channel blue, right channel green, 5dB/vertical div.)

And the correction also applies in the time domain. Figs.3 & 4 show the first 50ms of the spectral decay of the right Dunlavy's output before and after correction. Note the presence of resonant ridges in the uncorrected waterfall plot (fig.3) but the clean, quick decay once corrected (fig.4).


Fig.3 Dunlavy SC-VI, right, in SS's big room, cumulative spectral decay without correction.


Fig.4 Dunlavy SC-VI, right, in SS's big room, cumulative spectral decay with SigTech correction.

My small (13' by 16') listening room is of similar construction to my main room, and also has a pyramidal ceiling vault. Again, room treatment consists of ASC Tube Traps in the corners, RoomTune Ceiling Clouds at the corners of the vault, RoomTune panels mounted on the bifold closet doors behind the listening couch, RoomTune panels on either side of the Proton 27" monitor, ASC Shadow Casters on either side of the room, thick rugs on the floor, and RoomTune CornerTunes at the wall-ceiling junctions.

Since this is a bedroom with more regular dimensions, there are fewer differences between the speakers' response curves than in my large room. Look at figs.5 & 6 (SigTech response curves of the Avalon Eclipses, right and left channels, respectively). Even after all this treatment (this room is somewhat deader than my large room: same amount of treatment in a smaller space = greater final effect), the room had a noticeable bass bloom at 150Hz. Since the Avalon Eclipses have little bass output below 50Hz, the SigTech was programmed to begin its corrections above 50Hz. Again, the first problem was some rear-wall bass cancellation at 90Hz in the left channel, 100Hz in the right. Next, the room's prodigious 150Hz bass bloom was tamed. The next problem was the broadband dip centered at 300Hz. Above 2kHz, the SigTech again did only a bit of smoothing.


Fig.5 Avalon Eclipse in SS's small room, 1/3-octave smoothed, uncorrected response (left channel blue, right channel green, 5dB/vertical div.)


Fig.6 Avalon Eclipse in SS's small room, 1/3-octave smoothed, SigTech-corrected response (left channel blue, right channel green, 5dB/vertical div.)

The point of SigTech treatments is not to "overcorrect" so as to make all speakers sound alike, or to "sterilize" the sound, but to eliminate the largest room-induced frequency anomalies. In both of my rooms, the SigTech accomplished this goal admirably. It should be noted that, according to SigTech representative Denis Doyle, my rooms had far fewer sonic problems than most studio monitoring and home listening rooms he's tested. Even without SigTech treatment, they're both good-sounding rooms. Still, it was obvious that neither room was anywhere near perfect, and each had its own particular sonic aberrations.

How did things sound with SigTech treatment? Surprisingly, in my large room the differences were subtle. Audience applause on E-Town DATs and my own recordings sounded more natural with the SigTech treatment—the slightly hollow quality to the midrange was attenuated, and there was suddenly more dimensionality. On music the midrange sounded slightly warmer, tenor voices having a touch more presence and body. Female voices, like those of Janis Ian or Emma Kirkby, sounded more harmonically complete. Midrange bass bloom was noticeably reduced by the SigTech treatment, the result being that lower bass transients were cleaner and better delineated; midbass slam, specifically on kickdrum, was attenuated. On some material, like Joan Osborne's Relish CD, kickdrum didn't have quite the impact and dynamic extension with the SigTech in the circuit.

The sonic changes in the small room were more pronounced. The most noticeable change was the attenuation of the midbass room bloom. Again, on some material the loss of midbass slam, especially with Avalons, which lack any true low bass, made music less exciting and robust. Midrange response was more harmonically complete with the SigTech, adding to the verisimilitude of female and male voices. Inner detail sounded slightly better with the SigTech, allowing easier access to deeply buried musical minutiae. This was probably a result of the reduction of any small peaks in the midrange that might obscure the musical information just above or below the dominant frequency. Dimensionality and focus were not impaired by the SigTech, demonstrating that it certainly did not compromise the phase characteristics of the program material.

Was the SigTech treatment without sonic drawbacks? Almost, but not quite. In both systems I noticed that the SigTech added a wee bit of grain to the texture of the music. The differences with and without SigTech were similar to the differences between a Class B and a Class A CD transport—I was reminded of the sonic disparities between the PS Audio Lambda and the C.E.C. TL 2. Perhaps the SigTech added some jitter to the digital datastream. I even gave the SigTech the benefit of AT&T optical connections, while the comparison direct feed between transport and D/A was handled by an AES/EBU cable. While the difference was noticeable, it didn't make my nose wrinkle up in disgust; in a physically well-treated room, SigTech's contributions to a system may be almost balanced by this increase in grain.

If you're an analog devotee (and what semi-insane audiophile is not?), the SigTech's A/D section will not please you. Like most consumer-grade A/Ds I've heard, this one dries out the top end, reduces dimensionality, and adds a sandy, artificial edge to the texture of the sound. I found the "digitized" analog inputs less than satisfactory, and bypassed the SigTech when listening to analog sources.

The SigTech Acoustic Correction System is an elegant solution to the problem of acoustically corrosive environments. Like any engineering solution to an environmental problem, it should be used after all physical solutions have been exhausted. But in situations where no further physical room corrections are possible or economically feasible, the SigTech can offer a way to improve your room acoustics without heavy demolition. Though not inexpensive, the SigTech system is reliable, flexible, easily reconfigured if speakers and/or their placements change, and an invaluable sonic evaluation and correction tool. While not sonically transparent—it adds a wee bit of grain to the sound, and lacks an adequate A/D to keep analog-lovers content—the improvements it manifested in my listening rooms make the SigTech the first Class A room equalizer I've ever heard. If your pricey audio system doesn't sound as you know it should in your listening room, and you've tried room treatments, acousticians with slide-rules and beanies, even voodoo audio gurus—maybe it's time you tried the SigTech.

As both LA and JA have pointed out many times in these pages, the true bottom line of any equipment report is whether or not a reviewer thinks enough of the product to plunk down his own money and keep the thing. When it was first installed in my system, the SigTech 1120 D seemed to me to be the kind of product I was adamant about not purchasing—it was simply too expensive to justify. Now, after six months of living with it in both my systems, I've realized its insidiousness—I've gradually become addicted to it.

No, I don't use it constantly, though I do engage it about 60% of the time. I go back and forth a lot during critical listening sessions: When harmonic accuracy is my top priority, I use the SigTech. When I'm listening to analog sources or am concerned with music's textural characteristics, I remove the SigTech from the circuit.

Am I going to buy it? I'm still not sure. Convincing my wife that I need to plunk down an additional chunk of cash for another black-and-silver box is no simple matter. Persuading her to let me buy the Dunlavy SC-VIs was relatively easy—all I had to do was put on some music she loved and make her cry. (I can be ruthless when it comes to getting my way.) The SigTech won't be such an easy sell. So, as in the serial adventures of yore...tune in next month to see if our sometime hero can extricate himself from yet another fine mess he's gotten himself into.

Footnote 1: If you send Acoustic Sciences Corporation an accurate floor plan of your listening room, they'll generate a set of recommended placements for their Tube Traps and other room-treatment products. RoomTune offers a similar service.
Cambridge Signal Technologies, Inc.
(company no longer trading, 2021)