I didn't make very much progress today. I finally wound up with a layer of 7/16" OSB, a layer of 30# roofing felt, and another layer of 7/16" OSB on top of that. The stage actually sounds VERY solid now! Yay!
The sad part is that I managed to make three runs to Home Depot, one run to my office in TechShop (hunting for my 1/2" router collet), at least an hour or two rummaging in the garage for the same collet, and at least an hour driving! I hate wasting time looking for tools and materials!
My plan at this point is to
1. Use a flush trim bit to smooth out the OSB sandwich that spills over the stage edge,
2. tack two strips of 1/2 x 3/4" stock to the edge all the way around,
3. follow around the tacked strips with a roundover bit for carpet.
I just ordered, reluctantly, a replacement 1/2" collet for my router. I have to wait until TUESDAY to do anything more!
Maybe while I wait I'll see about ordering some linacoustic for the screen wall.