Have you tried "doping" your speaker cones?

I recently "doped" my cones. I had read several discussions on it, on the Single Driver Website. It seems Damar varnish is the "dope" of choice. I couldn't find that brand so I used another. I thought it made a fantastic difference. The cones are much stiffer and there is better definition and smoother high end. Bass tightened up too. Had to make a slight adjustment in the "stuffing" in my transmission line tube to cut the bass back a little. They recommend two coats, so that's what I did. Anyone else tried it?