Isolation Platform for my Sota Cosmos?

Peterayer, that is way cool. Your turntable and platform look very good. I'm sure the sound is fantastic. I have an ARC preamp and it throws a deep/wide sound stage but never forward of the front plane of the speakers. It goes deep instead. My analog soundstage goes beyond the speakers and almost to the side walls (24ft across). My digital soundstage is just as deep but not nearly as wide. I also think that the better isolation reduced surface noise on my records. I can't really prove that however.

The fly in the ointment when using suspended turntables on isolation devices such as Vibraplane is that if the resonant frequency of the turntable's suspension is close to that of the isolating system the two systems can interfere with each other. Like a car going down the street with two shock absorbers for each wheel, linked in series. The passengers in the car will have a very bumpy ride. One way to test this theory is to disengage the turntable suspension and see wa' happen.

If you want to go on the cheap, a good home-made isolation platform that I have used for years is to buy several wheelbarrow inner tubes at your local hardware store and a large cement paver block. Place the block on the inflated inner tubes and your turntable on that. Sounds silly, but I learned this trick in graduate school where we needed to isolate a monolayer trough from building vibrations and my graduate advisor had me do the same thing (he was cheap). I tried a lot of other solutions but nothing worked as well as the massive block on the tubes. I think there are some commercial products such as the Townsend Audio Seismic Sink and others that use this principle but will cost you a lot more. Good luck.

Geoffkait, that is an interesting post. I never really considered that. I may try to lock down my SME suspension and listen to the result. The other alternative is to tune either the Vibraplane or the SME towers to different frequencies. They are adjustable, but I don't know how to measure the respective resonant frequencies. Thanks. One more thing to play with.

Peterayer, the suspension Fn on your tt is likely in the 1-3 Hz range. At least my Sota is around that. So you can maybe measure it with a stopwatch since it is slow enough. Just excite your plinth and try to count as many cycles as you can while running a stopwatch. Then just divide the no. of cycles you counted by the time on the stopwatch. What Geoffkait says is possible. If the Fn's of both the tt and the platform are the same, then they can excite each other and if they get 180 degrees out of phase, then be ready to catch your tt. :) When you excite your plinth by pushing down on it, just watch to see what the platform does. Maybe it is dampened so that it does not respond to the tt mass moving up and down.