@mijostyn
If it does not bounce between 1 and 3 Hz it is not isolated and the amount of noise passed on by the environment is easy to see. Hook the output of your phono stage to an oscilloscope and put your stylus down on a record with the turntable stopped. Tap on your granite rack and watch the oscilloscope jump. All that wiggling going on in the background is environmental rumble. On any good suspended turntable you will not see any of it. The tracing won’t be dead quiet as the cartridge is capable of picking up air currents in the room.
I don’t care about noise I can’t hear! 1 - 3Hz ???
When I play record there is nothing under 20Hz and I don’t hammer my turntable when I listen to the music. I should concern only about frequency range comming from the speakers withing vinyl record frequency range, the speakers are near. I have absorbers and diffusers on the walls and ceiling in my listening room.
Sitting in Russia and listening to my favorite vinyl I don’t care about seismic vibration from Japan, aliens rarely use their weapon in my area since the Tunguska event in 1908, we are fine. I don’t have to glue some springs to my slippers before I come to flip the record.
Audio-Technica AT616 Pneumatic insurator are super effective in 50Hz - 20kHz range. Pneumatic is super effective at 200Hz. Overall they are effective at 20Hz - 50kHz and there are graphics of the measurements in the manual. They are also level adjustable and ideal for some turntable plinth! I liked them under wooden plinth of Technics SP-10mk2, Denon DP-80, Victor TT-101 (because stock feet sucks) ... I the AT/616 under my huge Tannoy “15 DMT MK2 monitors on the front side only (to change the attack angle).
Regarding other turntables I want to remind you again that Luxman PD-444 is suspended on its stock level adjustable feet. I don’t use AT-616 under my Lux PD-444 turntables, because this plinth is a perfect design, But I use custom racks (they are metal filled with sand).