Thebreeze wrote:jorge said....."Sanding the underside of the skin makes it thinner in the middle which does not optimize the sound."
I don't understand how sanding the underside makes the skin thinner in the middle unless whoever sands it does not do it uniformly. You have to make sure that you do it " UNIFORMLY " so that the entire surface of the underside gets sanded equally. I have done this several times with different heads to date and I can only say that I have had great results. We all have different experiences and results so while someone has bad results, others have good results.
The key word you used is "uniformly", which can be tricky. The mistake I made sanding the underside of a conga skin the first couple of times about 35 or 40 years ago was to sand across the diameter of the skin and rotate it. Each sanding stroke went across the center of the skin, but started and ended in a different area of the outside part of the skin near the bearing edge. Imagine making a lot of Xs using the diameter of the circle, all lines pass through the center but they are much farther apart around the outer edges. So the center part got much more sanding than the outer parts and wound up thinner than the outer parts. Those skins sounded terrible when I put them back on the drum. Finally I figured out that to remove thickness evenly over the whole area of the skin, I had to make an effort to sand the outer parts as much as the center part. It still did not work as well as choosing a skin of the right thickness for the drum from the beginning. The sanded skin, which is kind of soft and fuzzy underneath, seemed to sound different, project less, and be harder to play than a skin of the right thickness that has not been sanded. It has been many years since I did this and I don't remember more details, but I did decide to stop doing it. Choosing the right thickness skin for a particular drum is a skill that needs to be developed by trial and error over a long period of time and trial and error with skins can get expensive especially at current prices.