so what you are trying to say is that which subs will sound louder in dbs in the same set up... this is my opinion 1.Fi BL Xmax is 28mm 2.Fi Q Xmas is 28mm 3.RE SXX and SSA ICON have 20 and 20.5mm theres also a dude selling 2 15" crossfires xs v2 for $1,000 shipped on **** the xmax on those subs are in the mid 30s and thats the same price i paid my my 18s xs v2s lol if the xmax is greater you will hit the lows better, the subs are going to move up and down alot