Where I can find acoustically clear foam?

Guilford of Maine - http://www.acousticalsolutions.com/products/fabrics/guilford.asp

I don't know how big these speakers are but the foam filters made for air conditioners that are about 1/4 inch thick is the type I've seen used on other speakers. I think the type is called open cell foam

Hope this helps a little

Great idea!

Thank you.