RSIIIb diffraction mat

[bendoggie]

After spending a long time looking for RSII woofers,buying and repairing them. I found an excellent pair of RSIIIb just minutes from my house, very ironic. The RSIIIb's need only one thing, the foam mat that sits around the mid and tweeter. What can replace this ? Felt?
thanks
Augie

 

[Tedrick]

You can use felt, or either 1/8" or 1/4" regular charcoal-R open-cell foam from the Foam Factory.