A Copernican View of the Turntable System

Dover: For whatever reason, cantilevered armboards appear to increase the bass volume and power, compared to non-cantilevered armboards. This is from my own experience, as well as from discussing these issues with other turntable designers.

Still, if I were to design an ultimate turntable, it would have a low-noise platter bearing, an ultra-rigid connection between platter bearing and tonearm pivot (ideally machined as one piece), a helluva lot of moment-inertia in the platter, and even greater moment-inertia in the plinth (which would be designed for low structural and cavity resonances).

The complete turntable would be integrated with a self-levelling air isolation platform, which would rest on a stone column that goes directly into the ground, without any contact with the floor of the listening room. Surrounding the turntable (but not contacting it) would be a double-wall acoustic shield, vacuum-evacuated between the walls to minimize energy transmission.

cheers, jonathan carr (using 60kg solid zinc plinth to connect platter to tonearm)

Hmmm Jonathan,
Sounds like a typical listening room to me? :^)
Lewm,
The shrinkage of concrete is greatly determined by the water content.....the greater the water content, the more the shrinkage. (George knows what I'm talking about).
I doubt that concrete designed to set under water has much shrinkage.
My experience has been that concrete, as it cures, tends to stick to its edge formwork tenaciously, with most shrinkage occurring within its main body via shrinkage cracks.
That's why great care is usually taken to coat the formwork with 'releasing' agents so that it can be stripped away fairly easily.
If one were worried, or had experiences of the concrete shrinking from it's mould.......one could ensure the internal face of the cylindrical mould was coated with a rough epoxy film to which the concrete would cling.

You actually pre-empted another design I had which was for exposed concrete armpods.
In this case, the metal cylinders would not be permanent formwork, but would be coated with form-release agents so that after initial cure took place, the concrete could be released from its mould by a hammer tap to its top or bottom. This would allow many pods to be cast from the same mould and even pods of different heights to be cast.
The bare exposed surface of the concrete pod cylinder could then be left 'as-is'......or painted as one wished.

Jonathan - nice to hear from a fellow 60kg SPZ plinth owner - only point I would debate would be the air suspension, still think the tt has to be grounded no matter how much mass you have in the plinth. Rf shielding in the wall & perhaps a sealed room with an assistant inside to turn the record over.. One point I note is the number of people who locate their turntables in resonant room corners or between the speakers where sound travels free and fast.

As time and my birthdays go by, I feel I am headed toward a Linn turntable, a solid-state integrated amp cum phono stage, and a pair of bookshelf speakers. My muscles and joints would love that system. Last night I had to carry just the power supplies for my new Sound Lab 845PX speakers up from my basement to my listening room. This awakened symptoms due to an old rugby injury to my cervical spine. It took four of us to uncrate the 845s and carry them into the house. (I timed their arrival to coincide with a visit from my son, from Tokyo, so I could count on his help.) I cannot lift my SP10 Mk3 in its 100-lb slate and wood plinth without assistance and can barely lift the L07D. I don't look forward to carrying my 90-lb tube monoblock amplifiers up the steps from my basement to the listening room, either. This is despite the fact that I lift weights, do push-ups, and do a cardio work out every day. This talk of massive pods and plinths puts me off, even though I subscribe to the theory. High end audio is for young athletes or for those of us with grown sons who have not yet left home.

Dear Lew, In the first place congratulation with your birthday. In the second with your Lab 845 PX. Since you are still working I assume that you are a young gentleman in
comparison with some other members. Except for those two facts
(the birthday and the Lab) I don't believe a single word of the rest of your complaints. I hope your Lab 845 PX will surpass your expectations.

Kind regards,