bimasta, The idea of using no plinth with a DD was the subject of a lengthy and some times contentious thread, me being one of those on the "nay" side of that argument. The reason is this: Newton pointed out that "for every action, there is an equal and opposite reaction" (Newton's 3rd Law of Motion). This means that any torque delivered to the platter has an equal and opposite rotational effect on the chassis; it "wants" to spin in the opposite direction. Only gravity and the resulting friction between the chassis and the shelf is keeping a DD from spinning in both directions at once, around the spindle as an axis of rotation. Ergo, it makes sense to add mass to the chassis in the form of a heavy and dense plinth. Even leaving out the effect on damping of resonances, adding the mass increases the friction force between the chassis and shelf and assures that the work being done by the motor is diverted only to the motion of the platter.