it is tuned to 35 hz.... it is said to have a fs of 24.5hz. , ........ i wanted to be loud, which it is, but it does not play the lows in a manner in which i am use to. the Xcon still wanted more power... the SAZ-1500d definetly is a power horse but that 18" Xcon wantss even more.... I am old school in that 18"s were said to be sloppy...... ha ha ha , yeah right.... it does dam good at plating low notes.... the tried and true song, Bass I Love You is represented beautifully.... the bass notes hit very loud and the lower ones, create quit the eye candy. the 18" SSA XCON has no problem being equall to a 12" subs reputation for tight accurate bass, only ou move aalot more air with this beast.... air, doors, roof panels, everything is moving, lol. The Sundown Nightshade was a 12" sub, but let me tell you, the S.O.B. is bullet proof. With the right power behind it, wow, it does like magical sh*t to your music. the lows are very tight and the bass is crazy loud . We have played with it with some serious power going to it and it still just keeps wanging. I can only imagine the larger diameters and what thier output would be. The 4 12"s we had in the F150 had more potential still. However for a cheaper brand , they did not disapoint me any. they were in dual prefab boxes stacked... needed a single enclosure speced out to thier needs.... uh, i guess by my experiances and todays technology the diameter is not a big issue...... cone area will equal more air being moved but it also matters more importantly having the right amount of air space and tunning with the right amount of power to back em up. chop It is hooked up in my Jimmy right now with my saz 3000d and it is insane, It is just as loud as my Xcon, without the getting low factor. But overall I liked them both. Very good companies with very good products.