for a 15 sealed 1.5 ft net per sub (I recommend putting 2 pounds of polyfill to had a little bit more low end and get a 1-2 decibel gain along with lowering the Otc but thats just me you don't have too)
for a 15 ported 2.8 ft net per sub tuned anywhere from 28-35 hz depending on personal preference with either 2 4" aeros or 1 6"
for a 12 sealed 0.8 ft net per sub (use 1 pound of polyfill which is optional)
for a 12 ported 1.3 ft net per sub tuned anywhere from 28-35hz with 3 3" aeros or 1 6" or 1 5"