"can you simulate how 8 of my sealed flat packs with SI 18's compare with 2 of these Marty cubes?"
if you are thinking about repurposing your drivers, marty isn't the only option. designing up another large low-tuned custom super system might be kind of fun. :-) although, you could always just copy what 'not did!
instead of different numbers of different subs, here is 1 of each. all with 1100 watts.
there are no filters applied here. this is just raw response.
3.75 cu ft sealed, martycube, and full size marty (tuned to 17hz, though you could go 16, 15, or even a hair lower if you wanted a little extra extension in exchange for a db or so of output just above the tuning frequency).
each time that you double the number of cabs (and power of course), just add +6db across the entire curve.
four subs would be +12db across the entire curve.
eight subs would be +18db across the entire curve.
these are of course model results. Donny did some measurements and finds that they are reasonably accurate for what can be expected +/- a db or two here and there.
as for the orbit shifter, it is probably rolling off very fast under 25hz or so because in that region it is pretty much just a sealed sub. of course the top end is fully loaded horn, so that spl would be very high. a full martysub will have more lowend cab for cab.