I've been able to round up all the older drivers and the crossover I need to build a center channel speaker to match my older Polk Monitor series... they're all designed to work together so all I have to do is build a box. The unit will be MTM. The problem is shielding. Neither the tweeter nor the 6.5" midwoofer is shielded. I have bucking magnets I can put on them, but from what I've read - while it helps - that won't allow me to put the speaker on top of the TV. Worst case, I'll have to build a shelf or in some other way mount the center in position far enough away from the TV. So I have two questions.. first, what is the rule of thumb (rules of thumb?) regarding driver or magnet size and distances and magnetic interference? Of course I can just put the driver close to the TV and see what happens, but I'm wondering what is considered "usual" or minimum distance? There is a VCR shelf under the TV.. I considered building the center into that slot. Second.. is there a way to add some shielding beyond bucking magnets? Would it help to line the interior of the cabinet (or maybe just the bottom?) with metal? Any insight, ideas or recommendations are appreciated. Thanks.