This concept is getting some consideration as the new plinth for the TD150 project. The theme is for a build-up using alternate constrained layers of aluminum and pvc (vinyl) plates which are adhered with polyurethane adhesive. In this model, as much emphasis is placed on rigidity of the base as is for resonant damping. The motor mounting plate is bolt-down and does not touch the the load-bearing plate used for hanging the suspended sub-chassis, which is also bolt-down. Once all the layers are layed up with adhesive, pressed in a special fixture and cured, the table will assemble its mechanical parts from the top side.
It is thought that the massively layered design of this base will at once absorb and restrict the emanation of resonance from the AC synchronous motor, as well as any resonance that might otherwise enter the structure from the outside through supporting structures.
Previous experience with the constrained layer sub-chassis frame gives evidence to not only the adequate structural rigidity of this type of frame construction but also its ability to stop the propagation of platter bearing resonance before it reaches the tonearm. (Testing by way of stethoscope.)
The compression springs that support and isolate the standard TD150 sub-chassis have been replaced with tubular, fiber-reinforced, neoprene. Also known as automotive heater hose, the short length hose acts at once as both a structural stand-off spacer and resonant isolator between the plinth and sub-chassis. The isolation capabilities of this new suspension has been evaluated previously with excellent results in the standard TD150 cabinet. Isolation is as good or better than with springs. Compliance is evident, when testing by hand pressure, as being slightly resilient but not at all bouncy. The sub-chassis hangs with vastly reduced motion. In return the dimensional distance between motor-pulley and platter is far more stable, the drive belt encounters less stretching motion and the end result is a more solid and constant pitch speed at the platter. One of the key goals in this project. Sonically, this gives a much better sense of pace, rhythm and emotion to the music being played. (ie. more goose-bumps.) A very significant upgrade according to my ears.
Above pic: Testing the new constrained layer sub-chassis frame with tubular isolators in the old plinth. The tubular isolators replace the conical compression springs. These isolators are very effective in this particular application. . These isolators have not yet been tested with the standard Thorens sub-chassis frame.
The completed table less platter mat and tonearm. Tonearm will be the SME 3009 S2 improved, at first.
above pic: a footer. build-up is the same as with the turntable base construction. Alternating plates of pvc and aluminum bonded with polyurethane adhesive. More details to come. For now a brief description: The steel ball separates the upper and lower portions of the footer. The upper portion is bolted to the turntable base. The ball and the lower pad are loose. The weight of the turntable and gravity holds it all together. The slightly concave shape of the contact surfaces above and below the ball will cause the table to self center on the three feet. The constrained layer blocks will damp resonance to a degree while the contact between upper and lower surfaces is restricted to two very small area points on the ball. Resonance can only pass through at these points of contact. A resonant bottle neck coming and going. Rigid decoupling.
Speed selection will be done by removing the outer platter and moving the belt, by hand, to the second pulley run. At this point it is unclear if there will be an on/off switch mounted to the plinth or to a separate outboard power supply. Certainly, the plinth would be more solid and inert without having to provide any tunnels for cables and a pocket for the ac mains terminal. With an outboard PS, a single plug at the back of the plinth would feed power to the motor. Details yet to be worked out.
It is still very much a Thorens TD150, but I think a greatly improved one.