all audiobahn immortal and eternal are extremely insane.. they have been able to make awesome subs that are great .. the imortals are a lil more but eternals are great for price and sound.. i owned them for 2 yrs and they were excellent.. i have heard other top nothc and those subs stick with them especially in a ported box
How much are you paying for them? There might be something better and more reliable for your budget. Audiobahn subs are not that reliable and are by no means the pinnacle of sound quality. I'm sure acendant audio, RE, ect has something to offer in your price range.
I have heard an immortal before and was not impressed at all. for all that power handling and rediculously oversized magnet one would think the sub would excurse more then 16mm oneway. The acendant audio atlas can do that, and alot more efficiently. Of all their subs i am most impressed by the linear excursion series for spl and the alums for sq, but i would never consider buying one.