Springs under turntable

Yes Uberwaltz, you are right but the resonance frequency of the suspended units is so low. In Boston after the Big Dig a concrete paneled ceiling in one of the tunnels broke and collapsed on a car killing I think it was two people. Traffic though the tunnel created very low frequency rumble exciting the panels cracking them.
Again, they are so heavy there is not near enough energy produced by even the largest system to get the concrete "ringing"
That would apply to apartment buildings, office buildings and skyscrapers. Not to mention you can't play a system very loud in those buildings without pissing someone off.
Most of us I would assume (maybe I'm wrong) have reinforced concrete slabs sitting on compressed stone dust, a wonderful floor for a Media room. 

I think you just described my room Mijo, lol.

And which is why despite the too large amounts of glass it still works pretty well for me as my music room.

I would still think there maybe some slight differences but not sure how  you would start to prove it.

Lewm, exactly right. The springs have to have the exact same rate and they have to be located exactly the same distance from the center of mass. Unfortunately, this is not so easy to find without harming the turntable. The result is that is is extremely difficult to get this right at a frequency below 3 Hz. It is far easier to create an unstable system than a stable one. INHO if you want a suspended turntable, and I believe everyone does even if they don't know it, buy a well engineered suspended turntable or a MinusK platform. This of course eliminates the Linn LP12:)

I made a big mistake. It is not a resonance frequency I was talking about above but the energy or power required to move the concrete. If you could pluck the cables holding up those concrete slabs the frequency would be very high because the cables are stretched tight and they are not very long. In buildings I believe the concrete is going to be placed on steel girders. The resonance frequency of the floor would be determined by the weight of the floors and the flex of the steel girders. The only thing I could hear when I lived in a 19 story apartment building was a low frequency boom when someone upstarts jumped down on the floor. A person weighting around 150 lb is going to put way more energy into the floor than any HiFi could. I had RH Labs subwoofers at the time and the only complainers were my next door neighbors. Nobody up or down ever complained.

Uberwaltz, you measure it!  Check out this https://www.parts-express.com/dayton-audio-omnimic-v2-acoustic-measurement-system--390-792. My room control system essentially does the same thing. It measures each individual speaker. The frequency response above 10 kHz is significantly different in my right ESL than in the Left one. The only difference is the right one has a window in front of it on the side wall. The system corrected it but beforehand the window was smearing the image.
To produce the best image the frequency response of both speakers has to be identical or the image will smear to the side that is louder at any given frequency. There are always differences from one speaker to another of the same type not to mention that the speakers occupy different positions in the room. If you measure your system you will be amazed if not terrified at the variations in frequency response particularly below 100 Hz. The curve will look like a profile of the alps. 
It is a lot of fun to measure other people's system and show them how bad things are. 

So, Uberwaltz, do not downplay those windows. More than likely they are having a significant effect on the sound. But, it is hard to predict how. If you want to know measure it. But if you are not planning to get a room control unit don't bother. Ignorance is bliss.