Iknow the 18 has more cone area but which would be louder considering motor force. I have 2 12" FI btls (fully loaded) but looking into a solo x or something along those SPL lines. Will not be used for competition. Only daily. They will be going in a 4 door f150. I took the whole backseat out for my audio. . Subs will be in correct enclosure and power . Or has a 18 they would trade for the FI btls and cash.