well we all know some subs get louder than others. otherwise we would all be running cheap stuff. some subs are more efficient even at this high level. a split 4" coil is very heavy and not very efficient so the test results dont surprise me.
the only test i know of was done by a great competitor, not just some guy that "thought" he knew what he was doing. it wasnt a difference of a few DB of course, but every tenth helps.
feel free to not believe me. i realize it is just hearsay and i cant give the exact, needed, details of the test or even give proof that it happened. but i do see tons of people talking about the SMD like it was a sub forged by the gods. they have no testing results... no one seems to question it...