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The Silent Running Audio Ohio Class XL plus isoBASE™
(With a Second Look at the VR Series isoBASE)

Audio Equipment Review By: Stero Times, Frank Peraino

August 2004


For the flower child, there were good vibes and bad vibes. For the Beach Boys, we know they had good vibrations. With all due respect to Brian Wilson and company, for the audiophile, there ain’t no such thang as good vibrations – only bad vibrations. If you don’t buy into the philosophy that vibration and unwelcome resonances degrade the audio signal, I suggest you move on to something else. If, like me, you agree that component isolation is important, read on.

The Earth vibrates. Everything is prey to the planet’s fundamental resonant frequency of about 0.5 to 2 Hz, along with its seismic activity, winds, tides, etc. Add to this all the noise we humans generate: automotive traffic, railroads, airplanes, heating and a/c systems, refrigerators, dancing circus elephants. These vibrations lie primarily in the subsonic range but are large enough in amplitude to affect anything in contact with the ground, for our purposes, a house and the hi-fi system it encloses.

Audio vibrations can bring a host of detriments to the audio signal: image smearing, bloated, tubby bass, diffuse soundstage presentation, timbral coloration, homogenization of transient attacks, and opacity (as contrasted with transparency) just to name a few. I have spent considerable time and effort attempting to address these ills.


If you are like me (God forbid, in which case I feel for you), you have probably tried at least one if not numerous roads to gear isolation. In the ever-growing audio-accessory market, there has been an explosion in the number of tweaks and materials offered to deal with vibration. These products range from pucks, points, cones, ball bearings and combinations thereof (constructed of brass, ceramic, aluminum, titanium, etc.), to various platforms, racks and shelves (of various design and construction including pneumatic, spring loaded, sorbothane, carbon-fiber, acrylic, maple, Corian, granite, marble, etc., etc.).

I have both auditioned and lived with a great many of these products. Virtually all of them had an effect on my audio system, and not all of it positive. Some devices improved image focus or bass response but proved too analytical. Some ameliorated that nagging glare or edginess but produced an overly warm, fuzzy sound or resulted in a loose or tubby bass response. It seemed there was always a price to pay for what subtle improvement was gained. Approximately a year and a half ago, I began my search for state-of-the-art audio isolation platforms for my Tenor 75Wp OTL mono amps. My focus was on my amplifiers because I was now going to be placing them on the floor rather the bottom shelf of my former component rack. My quest led me to the Silent Running Audio Ohio Class XL isoBASES™ under review here. I first learned about Kevin Tellekamp, chief technical guru and designer of the SRA line, from a former colleague at Ultimate Audio. I had also heard and read various accolades about Kevin’s products from other reviewers and SRA owners. My objective was to find the best isolation product, period. I wasn’t looking to needlessly jettison gobs of cash on a wild goose chase. However, I was willing to spend what I needed to squeeze every ounce of performance I could from my amplifiers. After hearing and rejecting a number of static suspension systems and the usual suspects, the ball-bearing and cone systems, I called Kevin Tellekamp. That call led to many more and to my conclusion that Kevin is one of the true gentlemen in high-end audio and a gifted designer/engineer.


When SRA was seeking an effective principle to apply to audio isolation, a look back at Sir Isaac Newton’s theories provided guidance – “For every action there is an equal and opposite reaction.” Stated in audio speak: “Every motion [vibration] generates a counter motion [vibration].” The question then becomes: “How does one effectively attenuate this vibration [motion]?” The answer, which would likely meet with Newton’s approval, is to design and provide an effective counter-motion, (i.e., a suspension), which, if implemented properly, would generate friction and dissipate thermal energy.

Enter SRA’s top-of-the-line Ohio Class XL plus isoBASES™ as the ideal implementation of this Newtonian response. In case you are wondering where the “Ohio Class” designation comes from, Kevin has a background in submarine resonance control technology, which is what first attracted me to SRA. If the military entrusts Kevin with the sonic isolation of its hyper-sensitive sonar equipment in multi-billion dollar nuclear submarines, I could probably trust him with my stereo gear. The mission: to attack vibration.

SRA’s implementation of its counter-motion technology via its “raft” and “suspension” system is not easily described. The Ohio-Class XL plus isoBASE is actually two isolation units in one. Kevin developed the upper housing with derivatives of what the audio world commonly refers to as coupling and rigidity. The lower section’s design conversely employs the concepts of de-coupling and mass. Rather than utilizing a “one-size-fits-all” approach, other than its budget priced Tremor/Less audio islation platform, all SRA products are component-specific designs with a number of factors taken into account before construction begins. These factors include component size and weight; location and weight distribution of interior and exterior parts, (e.g., large transformers, drive units, outboard flywheels, etc.); equipment typography; and the materials used in the component’s construction. In addition, the end-user’s listening room also figures into the design equation. After all this information is compiled, the following design/manufacturing process begins.

  1. Modeling. A data stream processes no less than 130 entries to produce a platform: The component’s blueprint if you will.
  2. The main housing assembly. A proprietary, high-pressure nanoparticle composite of over 250 distinct products and chemicals are compiled under a nitrogen blanket, which is to say, in an airless environment consisting of hundreds of thousands of microscopic vacuums.
  3. The raft isolation frame system. SRA’s military-grade isolation system can be compared to the frame of your car. This element of the design allows SRA the opportunity to deal with the thermal energy dissipated during the counter-motions discussed above.
  4. The raft isolation suspension system. Because SRA begins the design process with exact specifications, SRA can then set precise suspension parameters. The isolation system is dynamic by design and specific to its component. Kevin provided an analogy: Compare the size, weight distribution, materials and design differences between a school bus and a Ford Taurus. Both vehicles have a suspension system consisting of shocks, springs and/or struts. However, no one in his right mind would claim that you could use the Taurus’ suspension system under the bus or vice versa, and so it is with our stereo systems. Audio isolation components are of different size, weight, materials and purpose. Thus, if one is going to develop a suspension to effectively counteract each motion a particular component generates, in order to operate optimally, the suspension system must be designed to counteract the motion (vibration) for that particular component.

"Needless to say I was delighted to find that my bass response, while more articulate (as was the case with the both the VR series and many of the cones and footers I have tried), was deeper with an improved harmonic texture."

Through the storage and dissipation of thermal energy, this enormously complex suspension system has the ability to rapidly alter its properties as required. These changes are triggered by room-borne, air-borne, and/or equipment-borne episodes. Inside the SRA housings are bladders filled with a thermally reactive copolymer that, according to Kevin, can change its darometer, (i.e., its stiffness or softness), with extreme speed. Viagra should be so versatile. Think of Jell-O and the way it moves from liquid to solid. The relative volume and chemistry of the copolymers can then be varied in order to match the isoBASE to its component. If this sounds like mad chemistry to you – it did do me too, until I heard what it produced.

But why not use air you might ask? Kevin is not a big proponent of air as an isolator, especially if the design is inexact and non-specific. As Kevin puts it, “Air carries the music from your speakers to your ears at 1200-1300 feet per second at 70 degrees F (at about 50 Rh). Why would you want to use air as the ideal isolation medium?” Makes sense to me.

The Jell-O analogy is useful to a point, but it doesn’t provide any indication of the much more difficult task of building the custom isoBASE. The copolymers used by SRA in its isoBASES achieve a liquid state only in an air-free environment!. This, as mentioned above, requires SRA to assemble the isoBASES under a nitrogen blanket. Design overkill? Not so fast oh skeptical one! The result is an air-tight platform containing a thermally reactive Jell-O -like substance capable of changing its density in response to the specific vibrations caused by that component’s typography. I know of no other isolation product that can make such a claim.

Protruding from the bottom of the isoBASE are spiked footers. Their cylinders also contain copolymers, but whose reaction capability has been chemically blocked, enabling the high-tensile steel spikes to operate as shock absorbers. The isoBASES are then coated with an aggregate that includes ground rubber and crushed glass, its purpose, to dampen vibration and shield for RFI. For the final touch, the piano-gloss-black finish of my Ohio Class XL plus isoBASES is on par with any speaker and even any automobile finish I’ve ever seen. Nothing I’m aware of in the way of acoustic isolation compares with SRA’s attention to detail, design, technology and manufacturing process.

Before shipping, all SRA products are tested with military-grade procedures. (SRA also does work for the Defense Department.) The test equipment runs the gambit from accelerometers to oscilloscopes to anechoic chambers, with a few more items between. All this sophistication and technology won’t amount to a hill of beans, however, if the SRA isoBASES aren’t effective at both controlling unwanted resonance and which translates to an improvement in the sound of your system – so read on!


My adventures with SRA began with the mid-level VR 3.0 isoBASE. I initially bought the VR 3.0s for my former reference Tenor 75Wp OTLs and immediately noticed their positive effect. The VR Series isoBASES are fine looking products with a gray textured coating. The units range from 2”- 3” in thickness and cost from $300 to around $800 per platform. Although I was thoroughly satisfied with the results, Kevin offered to custom-build a set of Ohio Class XL plus bases without obligation for comparison purposes. Who am I to argue with him? I asked him how much better he thought the Ohio Class XL plus would be than the VR 3.0’s. (I had the two-piece platform with a “pre-base” for use on my floor with thick carpet). He opined that the Ohio Class XL plus would likely give me a 10-15% improvement. It turns out that Kevin was being conservative and I’m getting ahead of myself.

When I first placed the VR 3.0 isoBASE under my Tenor OTLs, I was pleasantly surprised at how easily I noted the improvements. I actually expected, notwithstanding the sophisticated design, to have to strain to hear differences, if any, over the other isolation products I’ve tried. Those other isolation methods did provide some benefits, largely subtle. For the most part, those changes were a relatively modest tightening of bass response and an equally modest improvement in image focus. However, those other products also produced certain negative effects, ranging from added brightness to a disagreeably analytical sound. One of the first things I noticed with the SRA VR 3.0, and even more so with the Ohio Class XL plus isoBASES, was an increase in both the width and the depth of the soundstage. But the even greater surprise was that the residual glare or brightness imparted by the other products I tried was now gone. With no glare or brightness I was sure I would be sentenced to tubby or wooly bass. Needless to say I was delighted to find that my bass response, while more articulate (as was the case with the both the VR series and many of the cones and footers I have tried), was deeper with an improved harmonic texture.

After about four months with the VR Series isoBASES, I switched to the Ohio Class XL plus with my typical Doubting Thomas attitude expecting to hear little if no improvement. What did I hear? Well, I have to take what, at first, looks like the easy way out -- I got more of everything I heard with the VR Series. An experience with one of my audio fraternity brothers best illustrates the impact of the Ohio Class XL plus isoBASE in my system.. My buddy Brian has been with me through most of my audio journeys and is now a certified audio sicko in his own right. He too now fights the seemingly never-ending battle of extracting the most from his system. He had been by for a listening session during the last week the VR Series isoBASES were in place. I hadn’t told him that I was getting the new Ohio Class XL plus isoBASES. He came by one night the next week and we put on two or three of our reference discs. He asked me what in hell I’d done with my system! He was convinced I had changed, at a minimum, speaker cables or interconnects. Like me, he judged the bass to be deeper and more articulate – in fact, the best he had heard in my system yet, and he also thought that it sounded harmonically richer and illuminating - more sparkle with less glare was his supplemental diagnosis. It took a bit of convincing to make him believe that all I had changed was the platforms under my amplifiers.

This episode notwithstanding, it wasn’t until I got more used to the SRA isoBASES under the Tenors that I began to realize what I now had was a much more realistic musical landscape. If you’ve ever gone from a conventional 4:3 aspect television to a wide-screen 16:9 ratio television, you know that when you first fire up that new baby there are those nagging wide spaces on the sides of the screen. The picture is being squeezed into a square because the station is transmitting a 4:3 ratio to your 16:9 screen. Your television’s remote has an aspect button that lets you expand the 4:3 image to sort of “fit” your new screen size. The resulting problem, however, is that the faces and images are now somewhat distorted. People and images on the screen seem heavier and distorted. That anorexic super model now looks nearly normal and that person with a few extra pounds is now virtually obese. As if that isn’t bad enough, the picture’s top and bottom is now cut off. However, if a station is actually broadcasting in 16:9 or if you rent a movie which is formatted in a16:9 ratio, when you watch that channel or pop that DVD into the player, voila! – all is right with the world.

Well, so it is with the Ohio Class XL plus isoBASES. I get a more coherent and a more natural and balanced presentation. I’m able to hear deeper into the music because the size, images and placement of the performers is 16:9 rather than 4:3. It is the sonic equivalent of your television’s “aspect.” Button if you will. I also found my system to be producing a more organic sound. Instruments and voices, while more clearly delineated, are melded together in a mellifluous way that allows the listener to enjoy both the fine detail and the big picture simultaneously and without effort. I have always felt that the most delicate balancing act in both designing equipment and in compiling and matching the components in your own system relates to the ability to extract detail and resolution without making the end result sound analytical or fatiguing. Every time I think I have coaxed the last drop of resolution and detail from my system, that it is impossible to extract more from my source material, I find something that proves me wrong. Enter the Ohio Class XL plus. These bases are remarkably more effective than any isolation product I have tried and at least 20-25% better than SRA’s own VR Series. As I was listening to a disc by Doc Kupka’s Strokeland Superband, I was amazed that I could now understand previously undecipherable lyrics. (The liner notes don’t provide them.) A lowered noise floor might also account for my sense of increased clarity.

Be that as it may, this latest assault on vibration has produced the most natural, unforced, refined and panoramic presentation I’ve heard coming from my system thus far. I finally found an isolation product that doesn’t produce as many ill effects as it does sonic benefits. The Ohio Class XL plus isoBASES are not only the most visually stunning and technologically advanced isolation product I have ever used, they are, by a large margin, the best sounding and, alas, most expensive I’ve ever used.

As noted above, I am by nature skeptical, particularly with respect to audio accessories. Admit it, tell me you haven’t looked at a $4,000 interconnect or speaker cable or a $2,500 power cord or that $500 footer and asked yourself, what’s in there that can possibly be worth that kind of money? I certainly have. Now before all you good and honorable designer cable manufacturers ride me out of town on a rail, let me explain. One, cables and power cords can make a significant difference. Two, not all high-priced cables and power cords justify their cost of admission. However, I have defended a number of effective mega-buck cables by offering this hypothetical: Two of my all-time favorite artists, Stevie Wonder and Ray Charles, are sitting around talking about their audio systems. One day an audio dealer drops in and says to the guys; “Hey, we’ve pulled out a $500 component from your system and replaced it with a $3,000 equivalent. Let me play a few of your favorite cuts and see if you like it”. If Stevie and Ray enjoy and value the improvement in the system’s performance, would they care if that replacement piece was an interconnect rather than an amplifier? I think not. The problem is, we look at that meager power cable or interconnect and their apparent lack of intrinsic value and it just doesn’t seem right that we should pay as much as we pay for a good amplifier, which is, after all, big, heavy, and stuffed with parts. However, if that meager interconnect or power cord has as dramatic of a positive effect on our enjoyment our system, why should we balk at the price? Easier said than done, I know.

So, I again warn you, these SRA Ohio Class XL plus isoBASES™, visually stunning as they are, do an excellent job of concealing the intensive labor, materials, attention to detail, design and testing that goes into them. Do not make the mistake of judging this book by its elegantly simple cover. The Ohio Class XL plus isoBASES are an upgrade equal in all respects to a major component replacement.

Downsides? Once again, the Ohio Class XLs are expensive. Conventional wisdom recommends against a $2,000 platform under a $2,000 amp. The money might be better spent on a $4,000 amp. Better yet, the VR Series or SRA’s new low-cost Tremor/Less bases might be just what the vibration doctor ordered. Moreover, one of SRA’s chief selling points – that the isoBASES are custom built specifically for your component – can also be a negative if you replace components as often as Osama bin Laden changes bedrooms. You may have a harder time selling the isoBASE than a one-size-fits-all butcher block. However, if you have a state-of-the-art component or one you intend to keep for the long haul and you want a truly effective isolation platform to allow you to extract everything, ideally, that component has to offer, I submit that nothing comes close to the Ohio Class XL plus isoBASE. We live in an age of “smart” cars, “smart” computers and even “smart” household appliances. Add to that list, the SRA Ohio Class XL plus isoBASE. It is not only a “smart” isolation device it is indeed the class valedictorian! My highest and an unequivocal recommendation!

Component-specific, custom-built audio isolation platforms conforming to the width, depth, weight distribution, equipment typography, construction and, if applicable, the irregular contours of the components they support.

Price: Varies Based on audio isolation component

by Frank Peraino



© 2006 Silent Running Audio