Yeah, but after writing that I was remembering a popular brand sub, can't remember which but most certainly JBL, Infinity, or another mass market product of the same price range, that was a downfiring sub that you could switch the feet out to another facet on and make it a front firing sub. I really couldn't wrap my head around it so I've forgotten the brand, on purpose. Seems like it would really mess with the response, perhaps there's a compensation switch on the amp or something. Anyway, it's been done.
I've found that a simple Radio Shack SPL meter and a test CD to be invaluable in setting up subs (make sure to download the correction curves for the RatShack meter, just google them up). Of course an RTA with a calibrated mic and some good software would be better, but you can get a major improvement with the cheaper setup. The settings you end up with are not intuitive and are much different than you end up with setting by ear alone. We don't differentiate bass tones well and it sounds so much better when helped by a SPL meter.
