Suspensions on turntable...really effective?

Go to the Minus K website for some real good info on isolation. You can get one of their platforms for around $2500.

Diamonddears, I'm no mechanical engineer, but a spring has a resonant frequency (it's "rate"), above which it isolates whatever is sitting on it from whatever the spring itself is sitting on, and below which it does not---the mechanical energy passing right through the spring, un-attenuated. The isolation resembles an electronic filter, with a roll-off slope beginning at the center frequency.  A turntable suspension, therefore, should have as low a resonant frequency as possible, 3Hz being an attainable number. The lower the desired frequency, the "looser" the suspension, and the slower the table will bounce when pushed down upon. A table tuned to a low resonant frequency will have soft springs, like an old Cadillac. 

By the way, Diamondears, a spring need not be a metal coil---air can also function as a spring. A DIY isolation platform can be made by placing a barely-inflated inner tube (the lower the pressure, the lower the spring rate/resonant frequency) between two Baltic Birch plywood shelves. The discontinued Townshend Audio Seismic Sink was just such an isolation product, though fabricated of metal. Townshend now offers the Seismic Pod, a metal coil inside a rubber bellows, available in different rate versions (for different mass loads). The Townshend site has technical information, including a video demonstrating the Pod in use, explaining the theory behind the Pod.