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Reviewer: Kari Nevalainen
Analogue source: La Nouvelle Verdier with Ortofon RMG-309), EMT 930 with RF-297; Ortofon SPUs, Denon DL-103 cartridges and others
Digital Source: Audiomeca Kreature transport, Sentec DiAna DAC (various mid-fi digital cables)
Preamp: Shindo Aurieges, Dynaco PAS (heavily modified)
Power Amp: Shindo Montille, 6V6 special design, Sony integrated
Speakers: PHY/Fostex based single-driver speakers
Cables: PHY, Kimber, Belden, Supra
Power Cords: basic stock cords
Sundry Accessories: Sound Organization rack, Final, SID and other isolator pads
Power Line Conditioning: None.
Room Size: 4.5m wide by 5m long by 2.8 m high, one side wall partly open
Review Component Retail: Aerius feet €140/3, Stab 1 + Aerius €360


Am I justified to believe that what I just heard is true? That there really was that difference in the sound I thought there was? Some people bypass this question by taking their personal perceptions at face value. And that's fine. I've always admired their certainty and envied the trouble-free attitude they have towards what their ears tell them. But that's not me. I have to struggle. Not always of course. Sometimes I'm pretty confident that my ears told me the truth. But then there are moments when I slide into scepticism and accuse myself of intellectual dishonesty. And I'm not at all worried about the possible sources of errors in the perception process like mood, stress, biased preferences. Those errors are overrated.


What agonizes me is that some of my personal findings seem to live an isolated, self-sustaining life entirely independent of the facts of the natural world when in fact, there should be some link between them. I'm not a science fanatic. This is just common sense to me. If there's going to be a change in the sound, it must be a result of some change at the natural Physics level. The alternative concepts simply don't fit my head.

It would help if something we know about the natural world could explain my making the sort of perceptions I make. For example, my seeing the skyline red at sunset is explained by low angle scattering of light from dust and other particles. This humans typically see as red (or purple and orange). I don't have to know all this in order to be justified to believe that the sky really is red. But what if somebody comes and claims that the skyline is olive green? Thanks to what we know about sunsets and human perception, we recognize he's either bluffing or the part of his visual cortex that's responsible for color reception really makes him see the sky as olive green.


See what I'm getting at? What's the theory or set of
theories regarding the natural world that would assist me in explaining the sort of perceptions I make with respect to audio accessories? But let's not move so fast. Let's move first to Italy, to a small town called Sacile. It's located in the province of Pordenone, not far from beautiful Venice.


Italian know-how
Gregorio Giust is a long time hifi enthusiast and audiophile. But first and foremost, Gregorio's an expert in the maintenance of electric engines and pumps. In this capacity, he's very familiar with all manner of vibration-related problems that are threatening the fine workings of electric engines - shortening of the useful life span, performance instability, decrease of quality, noise problems, energy losses etc. Gregorio has 40 years of experience studying and eliminating vibrations in numerous applications.


Put those two facts together and what you get is a man who has decided to combine his passion for music and sound reproduction with his skill and know-how in the field of vibration control. It all started, as it often does, by first offering prototypes to his audiophile friends. Encouraged by the positive responses, he's now offering to the audio community anti-vibration devices under the name of Gregitek, sister company to Giust Electrotechnical.


The goal of the firm is to design and manufacture anti-vibration products that are based on solid technical knowledge and hence work. In addition to the Stab1 + Aerius equipment platform under review, Gregitek also makes equipment racks (Stab Tower) and anti-vibration supports for bookshelf speakers. More is to come soon.


The + between the Stab 1 + Aerius nomenclature signifies that the Aerius feet are an independent product whereas the Stab 1 is not. You can buy the feet without the table but not the reverse. Or maybe you can but there would be no point as you'll see shortly. The Aerius feet follow the fairly popular construction concept whereby a ball is placed between two cylinders. In the case of Aerius, there's a cavity in both cylinders. The feet are made of aluminium. The choice of material was based on measurements and listening, as were the shape and other physical characteristics. If you thought that the trick was just to have a ball ride between two metal cylinders, you thought wrong. There are plenty of details that go into designing feet like these.


Two sets of balls are included, steel and ceramic (Delrin). The idea is that hobbyists can experiment which of the two yield better sonic results. The same goes for the rubber O rings on the backside of both cylinders. The main (but not sole) purpose of these rings is to provide a better contact between feet and surface, necessary to comply with international security standards regarding the safe use of such devices. But the rings are removable. Gregitek urges hobbyists to also try the feet upside down (with the larger diameter cylinder lowest) and listen carefully to possible benefits. The Aerius feet are available in three finishes -: black, silver and gold. The set of three will thin your wallet by 140 euros.


The Stab 1 platform (450 x 350 x 25mm) is a perfect partner for the Aerius feet not just figuratively but literally. It is made of massive wood (also in favor with Italian ski makers) whose major characteristics are its reactivity and elasticity. The platform is made of boards which are joined to each other using a unique method. For example, tonality of each board counts. The method is similar to that utilized by local piano manufacturers.
The novelty of Stab 1 is a chromium-plated metal disc that hangs from an elastic coupler at the center point of the bottom side. I'll tell you more about its function later. The disc too has a removable rubber ring around it.


The finishing of Stab 1 is simply breathtaking. The lacquer surface meets the highest possible Italian standards. The surface of the platform has such a shining brilliance that one feels intimidated to touch the platform with bare hands. I don't think I have an unconscious desire to be a butler but I still more than welcomed the included pair of white gloves. It's a shame to cover the platform with a CDP or other component but what to do. 360 euros including the Aerius feet seems more than a reasonable price for this product. But not just to watch it.


Does this platform kill vibrations?
To a simple question, a simple answer: Yes. Below is certain evidence that it does. Note that in these measurements carried out by the manufacturer, only one strong excitation (192Hz) was used to test and study how the platform works under maximum stress caused by vibrations.


I didn't attempt to repeat Gregorio's measurements and verify the results. I have absolutely no reason to distrust them. As far as I can judge, the test arrangement and the equipment (SKF vibration generator, Sony Sound Forge program etc.) seem fit for the purpose. Secondly, I once reviewed a similar anti-vibration platform by a Scandinavian company and did similar measurements through similar procedures and obtained similar results. By comparison, certain spikes under B&W 805s measured substantially worse. In the above measurements, the average attenuation of vibration obtained was approximately minus 22dB.



A dynamic damper
A Soviet leader once visited Finland. He was taken to the countryside where the host demonstrated their new tractor model in a field. The leader was impressed: "Okay, that seems to work fine in practice." Then he added: "Does it work in theory too?" This is a joke, an old and well-known one. Nevertheless, the question at the end is excellent. Understanding why something works as it does is a prerequisite for all learning and development. Knowing why anti-vibration devices work is the first step in bridging the gap between personal perception and the facts of the natural world.


When I've reviewed anti-vibration devices in the past, I've always contacted relevant experts in technical universities and research centers, to hear their view of the underlying working principles. What I've learned from those contacts is that while some topics -- e.g. the physics of springs -- are relatively well known and understood, it's not always clear even to experts what exactly the physical basis of various anti-vibration devices could be.


Anyway, based on the information I got from Gregorio and talking to a researcher at the Helsinki University of Technology (thanks K.K.), I can tell that with these Gregitek devices, we need not worry about the grey zone. The Stab 1 + Aerius work as a passive dynamic damper or a mass-spring absorber as it's sometimes called. Dynamic dampers are used both for preventing external vibrations from getting into a unit and for controlling and reducing vibrations generated by the unit itself.


Let's assume, first, that Stab 1 without the metal disc beneath it is placed on the Aerius feet. When an excitation is directed at it, this mechanical system will start vibrating laterally at its natural resonant frequency, this being a function of the radius and curvature of the ball-bearing cavities. Thus, Aerius feet work like springs on the horizontal plane. Whatever the resonant frequency is -- presumably very low -- the feet isolate the platform from vibrations whose frequency is at least twice the base frequency.


The metal disc beneath Stab 1 further attenuates vibration. When Stab 1 + Aerius start vibrating due to excitation, the lateral movement will also strive to produce vertical displacement, waking up the metal disc below Stab 1. Its spring, mass and shape carefully calculated, the disc starts to vibrate at the appropriate frequency but in opposite phase, thereby stopping the platform from vibrating entirely. From that point onwards, only the disc will continue to vibrate and dissipate energy (omnidirectionally in the horizontal plane). Simple and effective.


It's the properties of the disc that largely determine the frequency band in which the platform is most effective. Stab 1 + Aerius has been tested to be effective against excitations between 20 and 350Hz. The Aerius feet work very well in reducing very low frequency external vibrations but the platform as a whole is designed to provide best performance in the 200 - 300Hz range. It's here where the rubber O-rings reenter the picture. Their purpose is not just to provide an anti-slide function but to participate in tuning the platform's performance in the critical frequency range. As Gregorio points out, the balls, the shape of the cavity of the feet, the rubber O-rings, the resonance disc, the wood type and construction etc. are all active components in achieving the definite goal of the platform.


200 - 300Hz? Gregorio spent much time in determining which frequency range is the most detrimental to the sound and found that the killer frequency is 200Hz and that the optimal range extends half an octave higher. This applies especially to CD players but not exclusively so. Here's something very important to keep in mind when considering Gregitek's anti-vibration products and their underlying rationale: each component or gear has its own resonant behavior (e.g. they're not equally rigid), and therefore requires a specific treatment, not a universal one. This is why Stab 1 + Aerius permit alternative settings. They are not there just for the fun of experimenting but for identifying the best means for attenuating vibrations in each particular case.


Finally, a few general notes on dynamic dampers:
  • It doesn't matter whether vibrations enter the system from above or below.
  • Dynamic dampers have the advantage of working (almost) irrespective of the mass of the gear placed atop. However, Gregitek recommends that the component should weigh at least 3 kg for best results.
  • Dynamic dampers are especially good at reducing torsional vibrations caused by cyclical movements with a constant RPM.

The missing link
Now we have positive measurements and at least some rudimentary theoretical knowledge to explain the results. Do we have a sufficient link between an audiophiles' subjective perceptions and Physics? No. The worst part is yet to come. The big question is not whether equipment platforms and anti-vibration devices in general reduce vibrations. If they are competently designed like Gregitek's platform, they do. That's a fact. The million dollar question is how sensitive hifi components are to vibrations and whether we can hear the difference. What we would want to have ideally is a theory that tells us what it is in each gear that subjects it to vibration control measures eliciting different sonic characteristics that enter the threshold of human hearing. A theory like that would have to combine physics, electronics and psycho acoustics. Do we have such a theory currently?


It's arguable that there could be agreement on why most turntables and at least some speakers could benefit from a vibration controlling system (although even in these cases, the explanation would not always be straightforward). Likewise there could be some consensus on the reasons why amps with microphonic tubes and big transformers might gain from being placed on anti-vibration platforms. What about CDPs? Are crystal oscillators microphonic? Converter chips? The semi conductors in the output stage? If so, is their extent enough to where vibration reduction has audible effects? Many of today's top CD players already are built with adequate vibration damping in mind.


I'm not saying that we lack competent hypothesis. Gregorio for instance believes that it's the error correction circuitry that makes a CDP particularly sensitive to vibrations. The less the lens-coil assembly is forced to vibrate and the more linear the remaining vibration is, the less the error correction circuitry gets invoked and the better the sound is. And he may very well be correct in this. But there is hardly agreement on any existing hypothesis. I therefore believe that we still miss the final link between personal observations and Physics which we would want to have. In the absence of such a link, the only way we can solve the disputes and study the effects of various anti-vibration devices is to resort to listening and trust our ears. But it's no discredit to our hobby if we acknowledge that this situation is far from ideal in this regard.