If you are interested in a louder sound without an amp or mic, see my post of July 23, 2010 above.

I have changed what I do. Instead of using blu-tak, which flattens with time, I make pads from the rubbery material which is sold to line shelves. You can buy it in supermarkets or hardware stores. Each pad is about 1 inch by 1-1/2. It has four layers of the padding, and I sew them together with needle and thread - a single stitch in the center, which is then tied in a knot.

Four of these, set under the edge of the instrument, keep it from sliding and make it louder.