built a box (2 cubes @ 35 hz) for a single 12, for a co-worker yesterday. he had a d2 cvr, and a d4 pioneer in a prefab, lol. I said i'd build it for his old prefab, and whichever sub he didn't end up using. needless to say, it was more of a favor than anything else as I have no use for prefabs and junk subs... anyways, i told him that the cvr, wired in a series, is the only reasonable option since he is using a class ab 2 chan, bridged. We put it in, it sounds ok for a single 12. Guess he was expecting more, because the first thing he does is pick up the pioneer and say, "Imma put this in instead, it looks better". smh. oh well.