Gziw 12inch. I have it in a 68 (internal) liter box with a 6.4 Inch Ported. The sub literally does wonders. For its price, there are no words. Extremely high-quality speaker construction. Sweet deep low boots! The company recommends 600-700 MAX RMS depending on the box, of course. I personally listen to the company and give it just 600. For about 8 months, whether it's loud or relaxed, it doesn't feel it. Of course, you need to have the right box; otherwise, you won't hear it properly! I don't have an SPL number. I don't have a meter to measure; I imagine that a 135-138 at 40 Hz with the right box will easily give you that at Min. At least that's what it gives me! At its price, you won't find anything better. If you have the difference for the 15-inch, grab it too yesterday!