Ok, I have two sealed 12" in the car right now, each one rated at ~94dB. When I went from one to two, I know the sound didn't double (i.e. I'm no producing 180dB now). I'm not thrilled with the response so I was thinking about switching to a single 12 in a ported enclosure, which is rated at ~103dB max.
I guess my main question is: how does the SPL increase when you add speakers? How does one ported sub compare to two sealed subs purely in volume?