[cherepashka]

Not just take the foam away, but cut-out the inner part of the foam and leaving outer ring. (because getting rid of all foam changes 650 sound in not a good way imo.) Then put some nylon (got some pantyhose?

) in place of cutted-out middle portion of foam. Here's a pic - what part of foam it's better to leave unremoved:

 

[tbonner1]

I tried no foam, nylon, cotton and a hole cut in the foam.

The hole cut allowed more highs but the remaining foam damped out some of the sound reflections and was the best of the above mods.