What is the ideal weight/mass for a turntable?

Thank you, Teres Audio, for the clarification.

How about a carbon-fibre frame filled with lead-shot and/or sand?

Would that reduce the cost of the plinth while giving the benefits of rigidity?

"An intelligent answer for once!

Granite rings like a bell: please explain, any data or proper observations on this?"

Hi,
This one is easy to answer. Granite is one of the worst possible materials for a turntable for the simple reason that sound travels through it several times faster than it does through water. It is made up of crystalline particles which are bound tightly, so there is no damping offered at all. It is pretty, however. Choosing such a material just because it is heavy, or looks good, which is the likely reason, is a big mistake, if the goal is better sound. One may as well use glass. Actually, using glass would be an improvement, although slight. It is a no-brainer, really.

Here is one reference. A search found it in less than one minute.
http://www.sv.vt.edu/classes/ESM4714/Student_Proj/class95/physics/speed.html

Regards,
mosin

I fail to see the relationship between the speed of sound in materials and the material's damping qualities. The speed of sound in the material just indicates the delay for the vibration to be felt (or influence) at the receiving end, has nothing to do with the the amplitude of the vibration, which is, indeed, influenced by the mass of the conducting medium.

Bob P.