So if we take out thermal compression and only address Bl non-linearity via xmax and Sd, we can draw some conclusions.
(One of the Mbentz links gets even more interesting. Check out the abreviated poster http://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Klippel_Nonlinearity_Poster.pdf
Lets take LTD02's thought of wanting to keep peak content to 50% xmax as the base idea and go from there...(bass idea!)
I'm going to bring this to the home theater front instead of rock concerts since it has more application here.
Most home theater environments use an 80 Hz 2nd order HP filter on mains, so lets use that in the model as a starting point.
Lets consider the SEOS speakers and use them represetatively to other designs
Kit (alignment): driver, xmax, sd, power at 50% xmax, spl (1m) at 50% xmax
Fusion 6 (sealed): FaitalPRO 6FE100, 5.25 mm, 143 cm^2, 19 watts, 102 db @ 1m
Fusion 8 (vented):Eminence Beta-8A, 3 mm, 210 cm^2, 14 watts, 105.5 db @1m
Fusion-10 Pure (vented): Eminence Delta-10A, 3.5 mm, 345 cm^2, 45 watts, 113 db @1m
Fusion-12 Tempest(vented): Eminence Delta Pro-12A, 4.6 mm, 532 cm^2, 90 watts, 117 db @1m
Fusion-15 Sentinal(vented): B&C 15PS76, 7.5 mm, 855 cm^2, 375 watts, 123 db @ 1m
We know that we don't listen at 1 meter away, but are more like ~3 meters. This distance is a a -9 db penalty (-6 db for 2 meters)
We also know that woofers have to contend with baffle step, so lets figure a -4db penalty.
We know that you need +20db of dynamic headroom.
So we can take this information to figure out what is the maximum reference level for each of these speakers
RealRef=db@ 50% xmax -9 db (distance) -4 db (baffle step) -20db (peak headroom)
Fusion 6 = 69 db (75 db in MTM)
Fusion 8 = 72.5 db (78.5 db in MTM)
Fusion 10 pure= 80 db (86 db in MTM)
Fusion 12 tempest= 84 db (90 db in MTM)
Fusion 15 sentinal= 90 db (96 db in MTM)
Note #1: If you use a higher XO, you can gain a few more db headroom. If you lower, you lose headroom.
Note #2: THX theater ref is 85 db. Home ref is often set to 75-85 db.