Contrary to popular belief, downfiring subs are fine on carpet. Bass waves are so long, the thin carpet (relative) is not even a factor to bass response. Infact, firing into a carpet (port as well), if anything, would elimiate some high frequency distortion if at all present. Downfiring designs have this advantage. Still, your main concern with any bass woofer is location and coupling to the room, in relation to where your ears are located.