I have seen SPL subs. As for a definition no, I don't know exactly what defines SPL other than the fact that its designed toward being loud over accurate.
I did read that the type X has great precise and SQ for being such a loud sub. I also believe the type X to be louder than type R's with the right amount of power.
I can handle being wrong but you don't have to be a douche about it. I started the thread to get information. Not to argue.
I don't really see what the point the argument is anyways. I just want to know a good combination of volume, port area, and tuning to make this sub pound hard and loud.