As long as both subs were in the same place when you were playing them, and you were sitting in the same listening position each time, your test seems valid.

I think we would all be happier if your SVS turned out to be defective -- we were having a heck of a time coming up with another good explanation after a while.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8