The dual Lab 12 has almost identical low frequency output in a smaller box with the same Fb as the BC18SW115-4.The BC18SW115-4, given twice the power, will get about 3 dB louder than the Lab 2x12.But it takes a bigger box to do it.The exterior dimensions of the box I used to test the BC18SW115-4 are 36 x 24 x 17 inch, 8.5 cubic feet compared to 7.76 for the 2x12. In all but the 38 Fb test, the magnet was outside the box, effectively adding about .56 of a cubic foot. That said, bigger is better (until Xmax is exceeded before Pmax) but the boxes are very close in volume.The BC18SW115-4 with the 37 Hz tuning almost exactly overlays the Lab 12, were it not for the lower upper filter on the Lab 12 , they would look more identical.Art Welter