Placebo effects are always a concern in any test situation*, but I would have to question your blind test as when you compare different subwoofer types, there
are differences. I got a guy in AVF to do this for himself here:
http://www.avforums.com/forums/15833269-post292.html
and he is reporting the very same experience I describe and others also agree with. There are cases where subwoofers will sound very similar and are almost indistinguishable, but not when you are comparing different design types. Again, I would ask as to your reasoning as to why different types of subwoofers exists if they simply sound the same once they are eq'd flat. I dont wish to be impolite, but I have to question your testing if you cannot distinguish the difference between a high end ported and a high end sealed subwoofer, when both are capable of reference level playback. Even more so, less capable subwoofers are harder to match to each other due to performance limitations. Once I get myself a good system again, I will invite you for a listening session, and we can do this together and come to our conclusions.
We can quote group delay, harmonic distortions, spectrograph results, in room response measurements to our hearts content, but until this test is performed its all theory. I have done these tests myself and know the outcome, and have urged others to also do the same, and the vast majority have come to the same conclusions.
One final thing I would ask, is why do you think I would turn my back on ported designs if what you state is true. Sealed designs are more expensive if you want high spl output to be produced cleanly to low frequencies. You typically need a pair of drivers and at least double the clean power to match the output of a ported sub, so why would I pay these costs if there is no additional benefit from it.
*I do not agree that high end cables make a difference. A clean reproduction from an amplifier is clean no matter the cost, so a more expensive amplifier doesnt always make any real difference. High end power cables are pointless. Thes are things I believe, and its my belief that if you have the correct specification, then the end result is good, even if the cables etc are cheap.