Hi oscer, I had a problem with close neighbours and could not have any vibe getting away and so had to isolate the hammer totally. I talked to an anti vibration engineer and came up with this, which works well and no shock at all is felt outside of the floating concrete inertia block.
It's a pit in the floor of the workshop with an 8" thick floor all reenforced with steel. Then build a big box to fit in it with a gap all around and 6" shorter than the depth of the pit. the stacks of anti vibe rubber shock absorbers (in my case 20 of ) placed around underneath. Fill the box full of concrete ( 9 tons ) and hey pesto.
All of the variables were fed to the engineer- how heavy- how hard it hits- how fast it hits- and so on. with this he worked out what density of rubber - how many thicknesses - how many pads and so on.
Don't know if this is useful but here it is.
P.S. to get the floor level with the box of concrete was another equation on how much the rubber shocks would take up when the box was filled.