+1 for:
The sweet spot... MyMats is two.
FWIW:
I have a lot of experience with dampening materials. I've used both the Michael Percy & Parts Connexion variety (as well as sorbothane but I don't recommend that). Both Percy's & Part Connexion dampening sheets are effective. The stereo rack I had prior to my current one was .5" plate steel (not ideal BTW) & had those sheets on both sides. It worked well. I've also dampened many a chassis with the parts connexion sheets. They both do what they are designed to do.
