Antone,
I should have looked at my test results before that last post, I did several different box tests in 2008 and did not remember them correctly.
Your larger box tuned lower should give less (not more) excursion in the 45-55 HZ range than my smaller (per cone) box.
However, the sensitivity in the smaller box went up almost 3 dB in the 35-60 HZ range, I decided the extra sensitivity was an advantage that offset the excursion disadvantage, and I did not have space for the larger box anyway.
My actual measured excursion results using about 24 volt sine wave input (around 100 watts per cone) with 2)Lab 12 in one 7.76 cubic foot box tuned to 36 HZ were 13 mm peak to peak at 30 HZ, 5 at 35, 8 at 40, 12 at 45 and 50, tapering off to less than 2 mm above 110 HZ.
Using a single Lab 12 in a 6.5 cubic foot box with a 27 HZ tuning, the results with the same drive were 19 mm peak to peak at 25 HZ, 12 at 30, 11 at 35, 13 at 40, 6 at 45, 5 at 50-60, and down to less than 2 above 90 HZ.
I’d expect your box to be similar to those excursion levels, which would definitely be over the rated 13 mm Xmax at 400 watts.
I would be curious how the actual measured (with a ruler) results compare with the box predictive model. If you do try the real test, be advised that 49 volts (400 watts at 6 ohm) will make the speakers stink within a very short period of time, I’d suggest only using 24 volts and just do the theoretical doubling of excursion.
Also wondering if you have noticed a difference in distortion between the push pull arrangement and both cones firing the same direction?
Art Welter