Are you talking about reinholtz resonator (Bass Traps) ?

because they need to be several feet thick depending on frequency and engineered to properly trap bass. ie.. x amount of holes per cubic foot.

Correct me if I am wrong but as far as I know foam unless it is very thick does nothing for bass absorbtion the length of the bass wave is too long for the foam to have any friction or absorbtion properties.

I could just build a baffle wall so only the grill is showing but that eliminates the rear wave which for must midfi sub designs is critical.



Thanks for the replys

Regards,

Peter