down firing or front firing sub?

It depends on the application. All good points above, but, in some instances front firing sub(s) might have some advantages. Those that have neighbors below them, might find front firing subs more suitable. So might those that might not have the firmest flooring. In the near field a front firing sub might offer better driver integration with the main speakers.

If you're crossing low enough (<80hz or so), I suspect that the distinction isn't terribly meaningful. If you take the same sub and position it both ways (some models are designed for this), I'd have to think that room position would have way more impact than driver orientation.

That said, I've never done the A-B, so take this FWIW>

Marty

Thanks for the responses guys. I'm looking at constructing my own with a tapered back chamber with the Rythmik 12" + direct servo amp and position will / could have a bearing on its outer construction.

The only reason I'd avoid a down firing sub is if someone lived below me. Aside from that, both can sound good. Taste and budget are going to be your final qualifiers.