Sorry to say this but just simply swapping subs wont really give you an noticeable increase in SPL. Off the same power, in the same car with all the same equipment you may notice a SQ difference but you simply wont be flexing your windshield with 1 brz1700but like it said it definitely doesn't give me the nice back massage/windshield flex I am looking for from subs Hopefully these SA-12's will satisfy my bass craving.
Obviously unless your switching from 1 10 to 2 18's you will but same cone area off the same amount of power it should have close to the same output. This isnt true in extreme cases either (switching from cheap $50 sony xplods to fully loaded btl)
You WILL be happy with SA12's (i went from type R's to sa12's 2 years ago) but soon after upgraded to the brz2400 and dual batteries
I don't come near flexxing my windshield off a brz2400, two yellowtops, custom box. Then again my trunk is like 18ft away from my windshield