Boom, did you check the phasing between the 2 subs.
from 0 to 180 degrees, there could be a difference in total output of 6 dB or more.
if i remember right, this is done before syst. calibration, using a SPL meter at the MLP, (right between the 2 ears).

Last edited by J. B.; 05/28/15 12:35 PM.