ideal is any very firm board. 7/16" plywood, 1/4" luann, or even just a
few layers of corrigated board.

Mark Oppat


"William Sommerwerck" wrote in message
...
You didn't indicate what type of "barrier" you put over the front of the
driver. I'd be inclined to use a piece of solid plastic; cardboard
wouldn't
be sufficiently puncture-proof.