The floor is the best place by far. Its very difficult to make a rack that is as good as the floor. I know. Mine was on the floor for years. When I finally developed a turntable rack better than the floor this is what it looks like https://systems.audiogon.com/systems/8367 Its a massive 750 lbs of solid cast concrete shelves, legs, and granite, with sand beds for the phono stage and turntable.
Mass is sort of the basis of a really good turntable rack. There's lots of different ways it can be done. You could more easily build a sand box and put that on top of any reasonably sturdy rack.
However you do it, this is only the foundational first step. Next is springs. Because its all about vibration control. A lot of mass solves only a part of the problem because high mass physically cannot move a lot. It takes too much energy. It does however vibrate all by itself. Everything does. So what the mass does is eliminate large amplitude vibrations. Then springs are used to further reduce small amplitude vibrations.
I've used the mass approach for decades and it works great. Recently I've started working with springs and they are great on the floor. So I have some ordered, hopefully they will be tuned to work well with the turntable, and will be able to let you know for sure. But for now, go with what we know for sure will work.
Mass is sort of the basis of a really good turntable rack. There's lots of different ways it can be done. You could more easily build a sand box and put that on top of any reasonably sturdy rack.
However you do it, this is only the foundational first step. Next is springs. Because its all about vibration control. A lot of mass solves only a part of the problem because high mass physically cannot move a lot. It takes too much energy. It does however vibrate all by itself. Everything does. So what the mass does is eliminate large amplitude vibrations. Then springs are used to further reduce small amplitude vibrations.
I've used the mass approach for decades and it works great. Recently I've started working with springs and they are great on the floor. So I have some ordered, hopefully they will be tuned to work well with the turntable, and will be able to let you know for sure. But for now, go with what we know for sure will work.