Isolation Platform for my Sota Cosmos?

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.

The SME suspension towers are heavily damped, so pushing down on the plinth does not get it to oscillate. Likewise, the Vibraplane is fed by a compressor, so as soon as one corner is pushed down, the air bladders immediately fill up and so it does not oscillate either.

I have not tried to defeat the suspension of the SME and listened to it on the Vibraplane. I only compared the table with and without the Vibraplane, and it is better with the Vibraplane inflated. The motor controller isolated on the Vibraplane also makes quite a difference.

Thanks for your suggestions. BTW, I thought that if they are 180 degrees out of phase, they would cancel, and it is only when they are in phase that the cycles amplify to cause problems.

I suspect all is fine, because I have never seen either move and the sound has never been better. But I wonder if the isolation is redundant. I'm going to try to defeat the isolation on my the SME towers this weekend and give it a listen.