The necessity of a plinth

Dazzdax, You raise an interesting question, and I am glad that Raul responded with his experience. One logical reason for a heavy plinth on the SP10 was put forward by Mark Kelly, a person whose opinion commands respect. Mark noted that because of the torque of the SP10 motor and that of other tts with torque-y motors, a heavy plinth will serve to counter the tendency of the motor to twist itself and the chassis frame to which it is attached. I have thought about this a lot; I am not sure how or whether high torque motors would create an audible problem, once the platter is up to speed. (The full torque of the motor is only applied during the instant after turn-on when the platter is still at rest, I would think.) Albert Porter's plinth deals with motor/bearing vibration in a novel way that might mitigate the need for a super heavy plinth. (Go to the Sound Fountain website to see a depiction of Albert's idea.)

Here's the way I try to think of the difference between an idler and a DD as regards plinth design: In the idler, the motor and idler itself are "external" sources of noise and vibration, whereas the rotation of the platter and the bearing can be just as inherently silent as that of a belt-drive table. A high mass plinth can drain away the motor/idler noise before it reaches the platter/bearing. That makes sense to me. On the other hand, in a DD table, the motor is a priori and inseparably associated with the bearing/platter. In a way, it's a closed system. So it is not obvious to me how a high mass plinth per se can efficiently interdict the transfer of noise to the platter from the motor. That's why I admire the thinking that has gone into Albert's plinth; there is an attempt to drain spurious noise into a heavy iron block via a threaded rod that contacts the base of the motor/bearing assembly. So instead of going upward into the platter, the spurious motor and bearing vibrational energy has a low impedance path downward into the iron block. In theory, it makes a lot of sense and similar strategies could be adapted to other DD tables. The high mass plinth may just be icing on the cake, to dampen chassis vibration and provide a solid base for the total structure. (I guess other plinth-makers have used a similar strategy to Albert's; I am not assigning a patent on the idea.)

This has absolutely nothing to do with the differences between DD tables and idler tables, but IMO a cone-shaped footer can be an asset IF one first determines the loci of standing waves on the shelf (which would be based on the resonant frequency and is best located with a stethoscope) and then places the tip of the cone on a vibrational node (i.e., a point where the shelf is not vibrating). This would then prevent the shelf from transmitting vibrations up into the equipment, because the equipment would only "see" the null points in the shelf. Like you guys, I don't quite see how a cone will prevent transmission of energy in the other direction. However, is not a diode a one-way device? Ergo, we have a mechanical diode. Maybe the term "diode" is not semantically appealing in this case.