Personally, I'm running a single Obsidian Audio 15" on an APSM-1500 in 3.5 cubes @ 30-32 hz (somewhere in there lol) via a single 6" aeroport. While I will say the Obsidian woofers are amazing for the price, all of the companies listed by myself have solid products. Jacob, the owner of Sundown Audio, has had a hand in the design of Obsidian and Skar woofers. Furthermore, Obsidian is a joint venture between Jacob of Sundown Audio and Nick of Stereo Integrity... google if you have to, but both of these companies have proven track records. Honestly, I wouldn't hesitate to run any of the woofers in my vehicle. However, the Obsidian is considered by a lot to be more SQ than SPL oriented by many. I like beatin' the block down... but the Obsidian provides incredible accuracy, even on my super-budget amplifier. Tuned as low as I am, I still get the fast bass from metal, as well as the crushing sub-30hz notes from chopped and screwed music.
