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Turntable platforms Halcyonics/MinusK/vibraplane

I have a turntable with an external motor (TW Raven AC) and wondered what the right way to use one of these "lab quality" platforms is... do you keep the motor pod on the same platform with the table. That would seem right to me, as you seek to isolate the entire system, not just one element of the system.

It's a bit of an academic questions, but arises b/c the only platform that suits my living area (aesthetics) is the Halcyonics "Silencer" which is 19wx17"d, so not nearly big enough to hold the entire table, as my motor is in the back and really needs about 22" depth though width is fine.

As an alternative, I could create a piece of slate that runs under the table ( from front to back) and exits out the back with an overhang on which the motor can sit on (like a plank off a ship, but meant to be stable). The slate would be 19" wide to fit the profile, and 22" deep. So table and motor sit on slate (with motor on overhang bit) and slate sits on platform. Does that reduce effectiveness of the system?

Thanks in advance.
hatari
3 responses Add your response
sdlevene
13 posts
 
Hatari,

You probably do not want to mount the motor on a separate platform because cogging of the motor will excite resonances of the damped suspension system. This will occur even with a Halcyonics or Minus-k platform. I have a a VPI TNT turntable supported on a Minus-k BM-8 isolator. The turntable's outboard motor rests on the BM-8 platform supported by a granite tile on top of three sorbothane hemispheres. There are many possible configurations of sorbothane components that can used for isolation; consult the downloadable program on the sorbothane website, which calculates the resonant frequency of a sorbothane part as a function of supported mass, shape, size, elastic modulus (durometer rating), etc. You can optimize your setup by reducing the resonant frequency of your motor support as far below the lowest frequency of the motor as possible.

With this setup wow and flutter measure in the 0.02 to 0.03% range. Speed stability (SDS stabilized) is in the 0.1% range.
syntax's avatar
syntax
2,193 posts
 
Some time ago there was a discussion here about these supports.
There is probably the information you are looking for.
t_bone
1,182 posts
 
On mine I have them on one platform. The theory has always seemed to be to keep belt driven TTs and their motors on the same one, but I for one don't think it is absolutely necessary. If they are separate, you could experience small changes in belt tension based on either up and down movements or, worse, side-to-side movements but for most of the very small movements (which are the ones which matter most to the TT), I expect they would not be problematic. Never having tested the theory, I cannot speak from experience, and someone with experience, or abetter grasp of the physics involved, might feel differently.
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