Gee I didn't know I was touching on something close to the second cousin twice removed from the truth. How is it that the fingernail tap evokes a signature that is revealing of comparing felt and rubber? I never tried rubber, but I have turned from felt to Ringmat. They would have you believe that such a tap would not be helpful because of the interaction of cork, paper and cut-out shapes in parallel to the resting surface. Then again maybe that is a crock, but I do like it better than felt at higher SPLs.