How to best isolate TT from vibration?

Wall mount recommendations are right on.

FWIW foot fall induced vibrations are vertical and NO isolation system is going to eliminate them completely, not spring systems, nor isolation devices of any type. Believe it or not unsuspended tables acually deal better with foot fall problems than suspended ones. Think about it a bit and you will figure out why.

In addition to Nsgarch's suggestion, have you considered reinforcing the floor under your turntables rack. Assuming you're on the first floor, can you get under the house?

I do agree w/ Newbee's exception: If you have a concrete slab-on-grade floor (or a 1 foot thick steel-reinforced floor in a hi-rise or loft,) then a stout rack (like a Billy Bags) spiked right into the floor will do it (or for the cost of a few concrete blocks and some mortar, you could build your own TT pedestal for pennies!

I also think unsuspended tables are the way of the future ;--)

I don't have Newbee's faith in jacking joisted floors. Which isn't to say that it can't work. It's just that a lot of the existing floor's construction details have to be just right.

Tips about wall shelves:

Mount them on any masonry wall, if it works out OK for you in that location.

Second choice, an outside wall -- heavier studs and thicker surfaces (more mass -- less vibes)

If you're in a new, cheap, tract house, on an inside partition wall -- don't despair. Wall shelves are usually 2 stud spaces wide (16" + 16" = 32") Get a 48" wide (4 ft) by 2ft high by 1" thick piece of Scandinavian plywood (the kind with many pretty laminations, like used in furniture), finish it natural or to match the wall and lag bolt it to four studs (16" + 16" + 16" = 48".) You can mount the TT shelf on the plywood panel with lag screws, but if you're really cool, you'll pre-install T-nuts on the back side of the panel to receive bolts thru the wallshelf after the panel is mounted to the wall. It'll look great and be stiff as a board (did I say that?)
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Unfortunately, (continuous) very low frequency seismic vibration forces the entire house or apt. to move up and down. Thus, wall mounting is only partially effective for isolating in the vertical direction - a "de-coupling" device is required to "de-couple" the audio component from the seismic vibration.

Note: My company specializes in vibration isolation.

Seismic vibration is at too low a frequency to be audible, and too low in amplitude to cause mistracking (unless you happen to be in an earthquake!)

If the problem is ground transmission of things like trucks, trains, or military ordinance (very) nearby, you'll be needing to soundproof/isolate the whole room, so the TT issue will take care of itself ;--)

Wall mounting is still the best solution.
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Dear Jim: skipping when you walk in the room?

Maybe and just maybe the problem is not exactly a isolation one: I don't know which cartridge do you use and if the set-up is right and if the resonance frequency between the arm/cartridge is in the safe range. Do you already try with the higher manufacturer recomended VTF?

If everything is fine then the Jfrech advise is a best one. Stay away from Aurios or similar design devices for this kind of problem.

Regards and enjoy the music.
Raul.