Turntable speed accuracy

In absolute terms there is no such thing as perfect speed stability. There is always a finite amount of instability. It's like saying a surface is smooth. A smooth surface looks like a mountain range under a microscope.

So the right question is what level of speed instability is audible? It is a fact that uneven drag from a stylus will affect platter speed. But is it enough to be audible?

To the novice it would seem that a good motor and a heavy platter will push instability into the in-audible range. Early work with digital encoding fell into the same trap. Who would have imagined that infinitesimally small timing errors in the tens of pico seconds would be audible. Well, it is clearly documented fact that these microscopic errors are audible. This tells us that our ears are far more sensitive to errors in the time domain than anyone would have imagined.

In my opinion achieving speed stability such that there are no audible artifacts is something that state of the art turntables approach but never quite meet. My experience has shown that there is always room for improvement when it comes to speed stability.

Correct speed with 500 arms? That is not a helpful statement since we don't know what the definition of "correct speed" is. What matters is to reduce the effect of a single stylus to below audibility. I don't think that anyone has been able to quantify what that specification is. But there is ample evidence that extremely small speed perturbations are audible.

It is is misnomer to assume that a massive platter fixes the stylus drag issue. A heavy platter results in a smaller perturbation spread over a longer period of time. A light platter will slow more but will recover more quickly. A heavy platter changes the problem but does nothing to eliminate it. I think that most people prefer the shallow but longer perturbation from a heavy platter, but ultimately it's a matter of taste, not superior stability.