I recently purchased 2 zvx-15s and it occurred to me that most SPL subs have a large, high excursion, surround that is 2-3" wide. Thus subtracting from the useable cone area. Many moons ago when it was Rockford Fosgate, alpine, JL, and so on.... the surrounds were 1/2" wide, 1" at the most when Eclipse introduced the aluminums. We all know there is a sound difference between 8s, 10s, 12s or 15s. I feel each size has its own unique sound as 2 10s still do not give the sound of a 15" Measuring the cone area on the zvx-15 I noticed it's only 10". Useable area of 12" at the most, including half the surround. Does this mean, if I wanted actual 15" I need to buy 18"? If I wanted 12" then buy the 15s?