the SX has pretty good SQ. I can't directly compare it to the type R though. If you want SQL you can't go wrong with either. the 2 12" type R's would have the advantage in SPL though over a single SX. 2 SX would be louder though with the the right power and setup
I whould take the 2 12 type R's because overall it has the potential to get louder and sound alot better SQ wise and take the same amount of power or less then the SX
2 12" type r's can get rediculously loud imo.. i just finished a ported box for my friend hes got an explorer.. its so loud you almost cant stand it.. his roof flexes a good inch and a half lol
i had them in a 1.7 cu ft per chamber box with a slot port until i changed it to a 1.25 sealed. i like the sealed better probably cause the ported box i had was a poor design. i don't even know what it was tuned to cause the place that sold it to me said "huh" when i asked what is it tuned to.
