I've come to the same conclusion about the thread tension. Too tight and it doesn't sound right. It needs to be just tight enough to grip, but still loose enough for the weight and mass of the platter to do its speed stability thing without being hampered by the string.
I'm also using a twisted silk thread, which seems to be able to give me that little extra grip while still remaining a little loose. The thickness of the thread also seems to make a difference, with a thicker one sounding better to me. But it can't be too thinck or the knot size becomes a problem.
I'm using thread from here and recommend size 2 or 3 (in whatever color your heart desires): http://www.artbeads.com/stringing-materials-griffin-silk-bead-cord.html
I'm also using Mark's controller on my Hurst 600RPM motor. When it's dialed in I almost can't feel it running while holding it in my hand. Very quiet, but it does take a bit of tweaking to get to that setting. It also does vary with the clock setting a bit so I'm prone to finding the right thread and sticking with it rather than swapping them out and resetting the clock and "quietness" each time.
Bob
