How to isolate turntable from footstep shake or vibration


Even while the Oracle turnable that I use has a built-in springs suspension by design there is a low or even sub-low frequency boom every time someone walks in a room. This becomes really bad with the subwoofer’s volume set high as the low frequency footsteps make straight to subwoofer where they are amplified shaking everything around. It seems the cartridge is picking up the footsteps very efficiently as even a lightest foot down becomes audioable. What can be done to attempt to isolate the turntable from the low frequency vibrations? Interesting, that the lower the volume of the subwoofer, the less the footstep shake is evident and with the subwoofer turned off it is a barely a problem at all. 
esputnix
Mijo, I am rather surprised at your attitude toward isolating "electronics".  Perhaps you eschew the use of tube equipment as absolutely as you prefer spring suspended turntables, but anyone who does use tube equipment will know full well that tubes are sensitive to vibration, because all tubes are at least to some degree microphonic, and many types, especially some of those with larger glass envelopes, can be very microphonic.  Some of the more expensive tube equipment makers (e.g., Allnic) even go to the trouble of isolating tube sockets in an energy-absorbent gel. Without exception, I have found tube preamplifiers (phono and linestages) to benefit from isolation, and tubes benefit from "dampers".  As to transistors, according to Wiki one of their main advantages over tubes is a lack of sensitivity to mechanical vibration. And yet, many do use expensive isolation devices, for good or ill, with transistor gear.  Those persons would tell us what a huge improvement they experienced. Certainly, CD and DVD players do benefit from isolation, for obvious reasons related to the laser reading the disc.

Now, as regards the F22, in order for that airplane to fly, its piloting computer must be oriented in space at all times, so it can "know" how to maintain level flight and issue the correct commands in response to its pilot.  I have no doubt that its piloting computer must be encased in some sort of module that keeps it aware of level flight and is isolated from vibrations, because, like a phonograph stylus, if it is vibrating, even though its component parts are not sensitive to vibration, it might not be able to sense how to create stable flight.  Or perhaps it senses its own micro-instability and corrects for that.
I just suspended my audio rack, not the 70 pounds power amp, from the ceiling with ajustement screws, and a foam insert to the bottom to prevent excess of mouvement.
My experience with a "VibraPlane" isolation device was that it not only isolated a turntable from the sub-sonic problems mentioned by the OP, but that even the placement of other equipment, like a CD player or DAC produces a surprising improvement in clarity and focus. I understand that they are used with electron microscopes to improve the clarity of the images. There seem to be quite a few used ones for sale on EBay from about $400 to $4000. It works, but they are HEAVY !!
@lewm, the Russians used tubes in their military avionics until the mid 70s I think. You would think just looking at a tube with it's delicate appearing insides that it would be sensitive to vibration. Is this reality or lay instinct? I use a tube phono stage which uses 6922's. It is not the tiniest bit sensitive to vibration, at least as far as I can hear and I have done some pretty crazy things. I have 25 foot long RCA interconnects from my Krell amplifier days so we put my turntable and phono stage on top of a subwoofer just for fun and to prove that the Sota was impervious to vibration. I had no intension of testing the phono stage. But, tonearm interconnects are only so long so the phono stage went with the turntable. I'll bet you can guess the results. I think the high end was slightly rolled off but my brain would think that anyway because it knows to much about the effect of length on single ended interconnects. Otherwise, everything sounded exactly the same as before I moved the turntable set up. But again this was subjective and only an indicator.  I have never seen any proof that tube electronics are sensitive to vibration. If you have seen some I would love to see it. As far as what people hear?  Subjective evidence is an indicator. It does not rise to the level of proof. Lay instinct is a horrendous trap I think most of us have fallen for at one time or another. I certainly have which is probable the reason I treat these issues more cautiously. I am not about to go out and spend money on an anti vibration platform for my phono stage. I have no reason to.
Do what I did - move to a residence built on a continuous slab......silent as a tomb. Of course, the motive of the move was not to exorcise demonic vibration hobgoblins from my stereo systems, but it was a factor in my decision to buy this particular town-home that is now mi casa. My Thorens TD 160, 160 Super, and TD-320 have now been rendered impervious to the vagaries of heavy footfalls.....the only worry is that a cat might decide to use one of the 'tables as a trampoline while it's playing.