Hi Foster 9
Jameswei is got it right. I actually work with spray foam and here is my suggestion. First wrap/bag your speaker with plastic,place it in the box and then spray foam the gaps.The stuff expands a lot so don't use much,the only thing that cleans uncured foam is lacquer thinner.Be careful not to overspray on on surfaces thought,so do it outside.
George
Jameswei is got it right. I actually work with spray foam and here is my suggestion. First wrap/bag your speaker with plastic,place it in the box and then spray foam the gaps.The stuff expands a lot so don't use much,the only thing that cleans uncured foam is lacquer thinner.Be careful not to overspray on on surfaces thought,so do it outside.
George