I think you are right about the three pulley system. Even though the key way bearing noise could be transmitted would be through the belts, it could have been audible. I agree with Plato that the three pulley system was probably developed to avoid one-sided pressure on the bearing. After VPI changed to another bearing system, this was no longer necessary, so the three pulley system isn't incorporated in recent VPI designs.
You raise two points about the dual motor system: speed and noise. The speeds of the motors are coupled through the common "pulley," which is actually a flywheel. The stronger motor may be supplying more torque, but the flywheel is rotating at only a single speed at any given time. I believe the weaker motor is getting a little boost, and the stronger motor is working a slightly greater load. The two are probably rotating at the same speed. The speed is fine tuned at the platter to be correct using the SDS controller and a strobe system.
The noise of the two motors would be transmitted primarily through the belts. As you know, the stand alone motor chassis doesn't touch the plinth. The noise transmission from the motors is further buffered by the flywheel, i.e., the noise must go through the flywheel first, then the belt, to reach the platter. Perhaps the decision to use two small motors instead of one big motor was partially based on a lower noise level generated by two small motors. Where does the noise go? Well, I think a lot of it actually does disappear into the air. As Pmotz suggested, how much gets transmitted through to the platter is better judged by listening rather than analyzing the engineering. I would guess not many people have really noticed a lot of motor noise. Have you had a listen yourself?
You raise two points about the dual motor system: speed and noise. The speeds of the motors are coupled through the common "pulley," which is actually a flywheel. The stronger motor may be supplying more torque, but the flywheel is rotating at only a single speed at any given time. I believe the weaker motor is getting a little boost, and the stronger motor is working a slightly greater load. The two are probably rotating at the same speed. The speed is fine tuned at the platter to be correct using the SDS controller and a strobe system.
The noise of the two motors would be transmitted primarily through the belts. As you know, the stand alone motor chassis doesn't touch the plinth. The noise transmission from the motors is further buffered by the flywheel, i.e., the noise must go through the flywheel first, then the belt, to reach the platter. Perhaps the decision to use two small motors instead of one big motor was partially based on a lower noise level generated by two small motors. Where does the noise go? Well, I think a lot of it actually does disappear into the air. As Pmotz suggested, how much gets transmitted through to the platter is better judged by listening rather than analyzing the engineering. I would guess not many people have really noticed a lot of motor noise. Have you had a listen yourself?