as a suggestion (which may be completely unwarranted and without any form of merit-
next panels perhaps try slat on one side (Heimholtz resonator) and just fabric over the insulation (especially for drums)
I'm not sure if 2 reflective sides is going to have the desired result (and as RawD mentioned) you may be 'aiding" the resonant ability of your wall, rather than hindering it (and it may be very frequency specific
my hats off to you for persevering with hand tools- thta's determination !
