sub in the fireplace

It's not a fireplace; it's a custom sub enclosure.

That chimney would make a helluva transmission line, wouldn't it?

Expensive Duraflame log? I think they're going to have to experiment with that one and then post the results. Elgordo - whats the best listening position for that transmission line? Would it be in the basement or on the roof? Streetman, good luck to your parents.

I thought I was the only crazy to do this. I sealed off my fireplace with expanding foam and carved out a nice shell and painted it flat black. The sub is down-firing and side ported. My firebox sits about 10" off the floor. It sounds great, and it's a great conversation piece. People look at my speakers and are in awe at how low they go. I just laugh. Plus, it hides an ugly big square box that clashes with the room. I say go for it if it works for them. Works for me.