Product: Material for decoupling feet
Manufacturer: Bilz vibration technology AG - Germany
Recommended Retail Price: approximately 10€ per panel depending on size and thickness
Reviewer: Piero Canova - TNT Italy
Reviewed: April, 2021
Often I happen to read articles expressing very strong opinions about the performance and merit of accessories for our Hi-Fi systems. Many times the positions of these commentators are completely opposing and the consequences are endless discussions. Even leaving aside those comments based on badly hidden secondary opinions or where partisan positions are taken regardless of the obvious facts, it is difficult to explain how people having both a long experience and a true intellectual honesty can hear completely different results from the same tweak. Perhaps, what's missing, is a more scientific approach that takes into consideration not only the modification, but also of what's around it, in short the boundary conditions.
Today I have decided to venture into the dangerous territory of decoupling feet. These products, for me, are all those devices that have the purpose of changing the frequency of the vibrations transmitted by the shelf where our equipment rests. Since very low frequencies (below 20 Hz) are outside those we are interested in, if I place an object that has its resonant frequency in this very low range, it will adsorb the frequencies of the shelf and will remove the energy without disturbing our music signal. Normally these feet are made from soft rubbery materials based on rubber polymers with different fillers or plasticizers to obtain the right consistency. Some feet use mechanical systems to absorb vibrations such as springs, either flat or spiral, sometimes with soft materials to lower the resonant frequency of the spring. The last category is made by feet using solid materials with a specific crystalline structure like graphite. In my system, I have a mix of mechanical systems (G-Flex) and soft feet (Vibrapods). Occasionally also some graphite blocks. How I chose them is completely random with a perfect application of the “try it and see” method. What I have now seems to be OK for me, but it is tough to recommend the same solutions to somebody else. Recently I have discovered an interesting material I want to introduce you together with the related documentation, which I think is quite interesting.
The problem of vibrations is very interesting, not only in the Hi-End domain, but also in several industrial and R&D fields. Take, as example, very high precision scales, electronic microscopes, laboratory equipment, medical devices and many others. Most of them will produce inaccurate results if subject to vibrations. The difference is that while we can, "by ear", find if our system is correctly isolated, you can't do the same for an electronic microscope so the company selling and installing them must rely on well-tested and predictable anti vibration materials. Bilz Vibration Technology AG was established in 1985 and is specialized in vibration insulation systems of a different kind. Many are designed for very heavy equipment thus out of our interest, but if you visit their website you will find some very interesting solutions. My interest was caught by the "Insulation Pads": they are some greenish slabs, heavy and of variable size, made from some polymer with several fillers. I did try to take a picture with my microscope: the image confirms there are several different materials inside a rubbery matrix, but you can't go much further.
Among the differentmodels available I have chosen the "B30W" with the lozenges only on one side: the technical specification is shown here below.
If your last examination in physics was some time ago, the graph above indicates that applying to one of these panels a pressure (Belastung) of 30 N/cm2 (approx. 29,5 Kg/cm2) will resonate with a vertical frequency of approximately 37 Hz while horizontally at 19 Hz; if you increase pressure to 39,2 Kg/cm2 the frequency drops to 34 Hz and 18 Hz. This graph contains very valuable information: it isn't enough to know the characteristics of the feet you use, but also how you apply pressure on it. The feet you have chosen will behave in a very different way if you put on top a 20 Kg class A power amplifier or a 4 Kg CD player. It is no surprise that you will have different results and thus different listening impressions are possible and expected.
The insulation pads can be worked easily with any tool for wood. You can use a band saw, hacksaw, holesaw, etc. They are almost odourless and do not mark any surface so you can put them on top of expensive wood furniture without problems. They have a very high friction coefficient so your electronics will stay firmly in place. The only problem is that a pressure of 35 Kg/cm2 isn't very common in High-End equipment, but with a bit of creativity we can resolve any issues. It is easy enough to make up a feet of two parts: the first is a piece of Insulation Pad you have cut while the second is an embedded insert threaded for bolts of varying sizes. In this way, we reduce the contact area thus increasing the pressure. If we use three feet each with an M4 screw for equipment weighing 10Kg, each foot will have a pressure of 27,05N/cm2 so well inside the requirements of the material shown in our graph. We will have slightly less than 20 Hz horizontally and approximately 38,5 Hz vertically which is a fair result. If we use 4 feet each with an M3 screw we will increase pressure to 36,1 N/cm2 obtaining 18 Hz horizontally and 37,5 Hz vertically. By playing with number and screw diameter you can manage systems from 3Kg to 40 Kg which is a comprehensive range for our needs.
My reference for feet is the G-Flex (see our review), but they are out of production and they also were too expensive. Vibrapods (see our review) are a bit dark for me, they do deform in time and if you put them on a painted surface they simply remove the paint probably because the plasticizer that makes them soft migrates into the paint. The Insulation pads have the same performance as the G-Flex, but they are much cheaper so you can make all the tests you want costing pennies. They do isolate without adding any color to the music, as it should be. With a bit of proper design, you can also make a version that can be adjustable vertically so they can be placed below a turntable or any device that needs accurate leveling.
Defects: I found two. The first is that on the graph the curves tops at 40 N/cm2 and there is no indication of what happens next. They should have written "kaputt" because above 40 N/cm2 the material breaks and your screw sinks inside it. If you plan to work in that region be sure you never put anything on top of your equipment or you will see it slowly sinking. The second defect is the availability: I have contacted Bilz Italy and they are super kind, but normally their customers order industrial quantities so a customer ordering one or two panels worth a few Euros is understandably a nuisance and you will have to wait until there is room in their shipment from Germany of the panel you have chosen.
If you are looking for nice-looking feet with marine chroming this isn't for you, but if you want to isolate your equipment in a predictable way the Insulation Pads are cheap and perform very well. With a bit of care and craftmanship, you can make them very nice looking too.
If you really want the very best and you have some quite heavy equipment then look in the Bilz website for the air suspensions "FAEBI 50 Soft + BR7-1". They are the industrial translation of the deflated bladder under a shelf, but with easy leveling. The smallest with a load of 9,81 Kg per foot resonates at 6,5 Hz. They are more expensive at approximately 100€ each and the only device of better insulating performance is just a maglev system.
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