First off, just changing subs isnt going to change the "loudness" very much. If you want substantally louder bass, you need a bigger/more powerful amp. Or, if you have a sealed box, a ported box will produce more output as well.
In fact, if you just change subs, you might not even be able to tell a difference in loudness, but they will likely sound "different". I prefer JL to all of these brands, they just have such a clean sound.
