Associated Equipment:
Digital Front End
Power Conditioning
Buggtussel Tegmentum Subwoofer

Sweet and Low

Jon T. Gale

15 May 2003


Frequency Range: 16 Hz-200Hz
Nominal Impedance: 4 ohms
Amplifier Requirements: 50-500 watts
LF unit Driver: 12" viscous damped, spun aluminum
Crossover: Optional: Thalamus; Active: Adjustable frequency, Slope and Q Dimensions: 27" 18" 32" (H W D)
Weight: 155 lbs.
Price (Standard finishes):
Internal Amp-$2600.00
External Amp-$2850.00

Buggtussel, LLC
1701 B. Vanderbilt Ave.
Portage, MI 49024
(ph) 269.321.9660
(fax) 269.321.9661


Introducing true low frequencies into a listening room can be fraught with difficulties. Simply accommodating the size of a large separate low frequency transducer into a room is enough to make a grown man pucker up when factoring in the Spouse Acceptance Factor. And considering the girth of the subject of this review, the Buggtussel Tegmentum subwoofer, this is a subject better left for later in this review. The masking effect to the midrange is the next subject for consideration. Most listening rooms not sufficiently treated to control room resonance suffer greatly in this regard, often degrading the overall transparency of the main speaker system. Lastly, improper placement and calibration by the end user, not understanding the complexities involved with the integration of a true sub-based system to the room, has resulted in the subwoofer being relegated to the Home Theater audience by the, sniff, serious "audiophile". To those who disdain subwoofers as a genre, to those who have "never" heard a sub they liked, I will argue:

  • They have never heard a well-placed and calibrated subwoofer

  • They have never heard a well-treated room

  • They have never heard the Tegmentum subwoofer

The reviewing community and sales personnel - in my opinion - have failed badly in educating the end user concerning the proper integration of a subwoofer. The importance of location, location, location, in relation to room boundaries in order to get the smoothest standing wave pattern in a room, cannot be stressed often enough. As little as four inches, at times, can translate into a completely different set of acoustic measurements! A little elbow grease goes a long way here. It takes a few listening sessions and some perspiration, but the sonic benefits will be vast. A modest understanding of crossover points and slopes will pay off greatly also, especially in accelerating the set-up process. A wonderful side benefit develops from the place/test/listen/repeat process: You will become a far more discerning listener and more aware of subtle changes in your system's performance. With that, in the set-up portion of this review I shall attempt to give you an idea of the effort it takes, (or in the case of the Tegmentum, the lack of), to properly calibrate a subwoofer to a system/room.


Big. Real big. As in: "You gotta' be kidding me!" big. The laws of physics enter here big-time pal. Go low, go large. Period. This is especially true with transmission-line loading. Folding the rear wave output back and forth inside the cabinet takes volume, no getting around it. The added benefit from the required internal channeling is one very well braced cabinet, especially with the Tegmentum subwoofer. Its designer, Dr. Kevin Blair, and Buggtussel business manager Doug Knudsen off loaded this beast into my basement listening room, with the Tegmentum initially sited along the plane of the main speakers, tight against the right side wall. A couple hours of pleasantries and a quick tutorial on the wide range of adjustability the Tegmentum offers, and they were off on their four-hour drive back to Portage, Michigan.

Optional with the Tegmentum is a dedicated amplification and equalization module. This module is also offered built in, with controls along the top rear of the subwoofer cabinet. And it is just this hefty 200watt module that clearly sets the Tegmentum apart from most competitors in the marketplace. You see, it's not the power; it's the dual-crossover network along with two parametric equalizers, each with its own "Q" setting and independent circuit activation. Now how cool is that? This crossover/equalization circuitry makes the Tegmentum one of the most adjustable subwoofers on the market, and I simply cannot envision the room in which it could not be very successfully integrated. The amp module was connected with a 25ft set of MIT 330+ interconnect to the second set of pre-outs of my BAT VK3i, and an 8ft set of Luminous Audio Renaissance speaker cable to the Tegmentum.


In the beginning, I wanted to see just how good the un-equalized Tegmentum was, so I ran it "straight up", just the standard placement, phase and crossover adjustment doctrine was used. In the initial side-wall placement, the Tegmentum proved to exacerbate my 40hz room resonance more than most subs that have performed well in this position. Performance was good, but in lowering the gain to control the room mode, most of the low bass was absent. Moving it to the center, front wall position helped greatly, smoothing slightly the room peak. (Being centered on the short wall, there should be a dip in the response as the short room dimension standing wave null is in the center). But I was still troubled by what I thought, given the size of this monster, was a curious lack of extension and power. I next turned the Tegmentum 90 degrees, with the driver and port "front" of the sub firing parallel with the front wall. NOW things started to take shape! Thus far, the performance of the Tegmentum, using what have become the industry standard phase/crossover adjustments, was very, very good. And this wasn't even close to the performance after full calibration.


Using the equalization of the Tegmentum may be a bit daunting at first, but one quickly comes up to speed once you have an understanding what all the dials do. Each eq circuit has a gain setting, with adjustments marked from -9db to +6db. These adjust the gain centered on the frequency set on the dial next to it, the frequency adjustment. This dial has calibrations marked from 30hz to 175hz. Next to this, is the "Q" control, which adjusts the systems resonance. This was never set on anything but "0". (Zero being the "tightest" setting.) Like I said, it sounds a little daunting at first, but here is how it plays out in practice:

My main speakers having output into the upper 20hz region on their own, I initially set the crossover at just under 40hz. The crossover is unique in that it has two independent crossovers used to adjust the crossover point. To quote the manufacturer, "They are fully independent 2nd order Butterworth filters adjustable down to 35Hz. When they are set at the same frequency they combine to form a 4th order Linkwitz-Reiley. When used at different frequencies they vector to provide a more complex response". While I was able to obtain wonderful blending with any speaker tried using the dials set to the same frequency, the flexibility is here to use separate points to end up with a very complicated staggered slope. After setting relative levels, a run through the test tones revealed a dip at the 50-60hz region, a fairly large peak centered at 40hz, (and its multiples), and nothing usable below a very strong 20hz. Now it gets really cool. I first raised the crossover setting to 60hz, which perfectly filled in the dip in that region, but doing so made the 40hz peak that much more obnoxious. I then activated one of the eq circuits and set it centered just below 40hz, and dialed in what was to become -4db. This took care of most of the room resonance, while leaving it just a bit on the pleasingly plump side. I took advantage of the second eq network by dialing in +3db gain centered at 30hz, to bring up the very bottom. After re-setting the overall gain to match the main system, I now have the smoothest bass and sub-bass response I have ever had in my room. And here's the kicker: this calibration took all of 30 minutes, not including determining the proper location. The Tegmentum is simply the easiest subwoofer I have ever dialed in, and easily the most adjustable I have ever used. While there are some other subwoofers on the market that incorporate some form of extra adjustability, none I know of offer the kind of well thought out and user friendly calibration as the Tegmentum.

In Use

Establishing a smooth response does not in itself insure quality bass reproduction. Doing so also requires a Herculean driver well fed by gobs of current, and an exceedingly tight, non-resonant enclosure. All of which the Tegmentum has in spades. At any levels just short of insane, I could not get this driver to "double". (Example: A low bass note should just go Wooooo in the room. Doubling sounds like Woowoowoowoo. Sigh. Doubling is rather hard to describe in print.).

The 12" driver used in the Tegmentum seems to be a goodie, quick but very robust. The driver is a light weight, but ultra-pistonic, viscous-damped, spun-aluminum diaphragm with a proprietary FerroFluidic gap-suspension and a mechanical suspension of Nomex and Santoprene. The cabinet is very, very inert. The external walls are made of laminated " MDF, with the front panel increasing to a 1 " thickness. Internal bracing varies in thickness, but given the complexity of the transmission line loading, the external walls are effectively braced every six inches. The non-resonant nature of this enclosure allowed the Tegmentum to blend quite nicely with speakers much smaller than I had expected. Representing the monitor category during this review period were the Buggtussel Cingulate, Tyler Acoustics Reference Monitor and Von Schweikert VR-1 loudspeakers. All three fine monitors with disparate sets of colorations and room interaction. In all cases I was able to obtain very good integration, particularly so with the Cingulate and Tyler Ref. Monitor. Crossing over at 80hz, along with the required custom equalization for each speaker, seamless blends were once again obtained in mere minutes.

Moving to the Tegmentum's more logically intended loudspeaker size pairing, The Tyler Reference Monitor was used with its mass module stand along with the Von Schweikert VR-2 and my reference, the Von Schweikert VR-4 SE. I am a firm believer that once you have a speaker with the resolution and frequency output of the VR-4, which is good to the upper 20hz region in my room, the addition of a high quality subwoofer competes squarely in the "Super System" category, at a fraction of the price. Having a modestly large loudspeaker as the "satellites" has the huge benefit of facilitating a much more cohesive blend as they simply play lower, the character of the bass staying the same as the upper bass.

Enough with the blending. On to the Sound!

Different. Wonderfully different. Not the proverbial room pounder for sure. The Tegmentum had the very same beguiling lack of room pressurization effect only the Dunlavy SC IVa has had in my room. This is not to say it lacked extension, the Tegmentum has very strong output to 16hz, thank you very much, and it also possessed sternum-rattling concussive punch when called for. It is the strangely addictive "flow by you" concert hall bass rather than the "pressurize the room" sensation that has me so enamored with the Tegmentum. First and foremost, is the quality and resolution of the all important mid/upper bass blending area of the Tegmentum. Playing an assortment of juicy jazz recordings featuring stand-up bass, the calibrated Tegmentum refused to "pop" certain notes louder than others, a sure sign of proper room mode excitation. More than this, the resolution, the texture if you will, remained relatively the same regardless of the loudspeaker used as mains. The Tegmentum has high enough resolution to resolve the texture, or burr-on-the-edge, of the synthesizer low bass recordings in my collection, usually in cases I had previously not heard.

Of course, the real fun begins with the musical "big stuff". I simply dare you to pull out any of your favorite bass warhorses and tell me you don't hear more resolution, texture and image enhancement with this subwoofer than you ever have before.
In any room, save the largest, if it's on the recording, the Tegmentum delivers. I'm still pondering how it can launch such serious low frequencies into a room while avoiding most of the "pressurization" effect other, lesser subs can impart on the performance. (Can it be the added square inch radiation area of the TL vents, thus simulating a "wave launch" rather than a relative point source launch? I doubt it is as simple as this, and not being a TL theorist, I'll let this question be answered with a hopeful manufacturers comment.) The few pipe organ recordings I have were simply astounding in not just power, but also in articulation. Clearly heard now deep into the bass was the acoustic environment in which the recording was made. The Tegmentum clearly resolved large hall room reflections deeper into the bass than any other subwoofer I have ever owned. Ditto for well-recorded rock recordings, but in the inverse. The Tegmentum being tight and articulate enough to expose the isolated drum booth with added on electronic ambience most rock records possess.

With the exception of pipe organ recordings, most music simply does not contain sub-bass information. The music genre that solicited the most "What the hell was THAT!" response was electronic ambient/techno/industrial/whatever. There were many times in my listening where I'd be digging the tight gut punching transient response of the Tegmentum and all of a sudden the room just loaded up and shook, then, gone, vanished. Granted, I have a very bass trapped room, which greatly assists such performance. But all of the subwoofers I have used were in the very same environment, and none have showed such strength in so many vital areas.

The Tegmentum proved to me that quality sub-woofing can be accomplished. High enough in resolution and low enough cabinet resonance to keep up with the highest caliber main speaker, with more than enough electronic flexibility to mate well with any room. Enough power and dynamics to fulfill all but the most ham-fisted headbanger out there, and the ability to go deep, way deep.


As a reviewer, it is always the rare pleasure to find the over-achieving product from the unexpected source. The Tegmentum subwoofer is just this sort of rare pleasure. In every single parameter that I use in evaluating this genre of product, it met or exceeded expectations. I urge you to audition this subwoofer even if you are not currently in the market, or have given up the quest in trying to augment low bass to your existing system. I can say with certainty you will at least come away with a newfound respect for what can be accomplished.

After all this, I'd be crazy not to nominate this as a Stereo Times "Most Wanted" component. It certainly is one of mine. In fact, I purchased the review sample. Well done Gentlemen. Very well done indeed.

BTW, I did say it was rather large didn't I?

Manufacturers Response

The case of the missing dimension (dementia?)

"How long is it?" This is commonly the first question asked about a Transmission Line speaker. I usually reply, "It's long enough." Then slowly I'll add, "That is to say, the acoustical length of the line is appropriate for the system tuning of the bass driver into our understanding of how Transmission Line loading actually operates. In the case of the Tegmentum-12, that's 16 Hz." The next question usually slurs into many such as: "Is it quarter-wave length?" "How do you calculate line length?" So I respond, "Ah yes, quarter-wave length but, of which frequency? Driver free air resonance? What about driver electro-mechanical and mechanical-acoustical parameters? At what amplitude, the commonly utilized small-signal values or more applicable large-signal values? What about the interactions of the cabinetry on these parameters? " "Calculate? Well, I use a cheap electronic slide rule, similar to the one that got me through calculus, before the PC was invented." I'm not really trying to be a smart-ass, it just seems that way.

Theory and execution of Transmission line bass loading has not evolved much since its inception several decades ago. Unlike sealed box and Helmholtz-resonator (reflex/passive radiator) based woofer loading, filter-theory approximation approaches seem to have slipped by most of the Transmission Line encampment. This is largely the fault of proponents starting with an oversimplified model (thinking) of the line as its name-sakes' electrical circuit equivalent, plugging this propagation string onto the drivers' electrical circuit model and then confirming their hypothesis by non-rigorous validation techniques. Being an experimental scientist by training and a data junky by nature, Buggtussel Transmission Lines evolved a little differently. Taking a step back, we asked the not so simple question of "Just what kinds of reactances/resonances occur in a conceptualized Transmission Line loudspeaker? How do they interact with a given driver to generate system tuning? How does changing, in a controlled manner, variables such as line length, line surface area, line geometry, line losses, driver coupling, driver electro-mechanical and mechanical-acoustical parameters contribute to the changes in system tuning and performance?" Once you have a handle on these contributors, you can start to hypothesize a model.

Line resonance models are initially lumped into two classes: 1) wavelength is greater than line length exemplified by open- and capped-end pipe resonance (quarter wave phenomena); 2) wavelength is less than the physical dimension, exemplified by transmission line/waveguide resonance (propagation delay phenomena). Add in a subterfuge of mass/compliance (sealed box), anechoic (infinite baffle), secondary coupled mass/compliance (Helmholtz) and decoupled (muffler) resonances to account for the driver, box, and their mutual and room coupling and you begin to see the picture. In essence box volume, line length, line diameter, dampening, etc., are calculated to optimize the system transfer function as required by the drivers' electro-mechanical and mechano-acoustical properties at small and large cone displacements. Dampening dissipates back wave energy in a frequency (wavelength) dependent manner and controls line harmonics, line/room impedance matching (coupling) via the large vent area is superior to that obtainable by classic Helmholtz resonators. Thus, at frequencies generally greater than 100Hz, the driver is the primary radiator while the back wave sees a true infinite baffle, no reflections. Through the mid-bass, the line acts as a three-dimensional propagation delay line to augment driver output. From low frequencies down to system tuning, the line is a pipe driven by the driver and is the primary radiator, providing superior extension, output, damping and control compared to the same driver in either a sealed box or a bass reflex enclosure. Thus was born q-TSAL (Quasi Thiele-Small Actuated Labyrinth.) Alas, I never really do answer the question.

That being said, we at Buggtussel would like to thank Jon Gale for taking the time to do such a thorough and insightful review. We appreciate the dedication that Jon showed in spending the time to properly position and fine-tune the Tegmentum. Knowing the size and weight of the sub, we know this was not a task for the faint-of-heart.

Kevin L. Blair, President
and the staff of Buggtussel, LLC.













































Buggtussel Tegmentum Subwoofer