its really funny to see people try and calcualte cone aress.
for example, 18" subwoofer dont have 18" cones. they are genearlly 18.5" from the edge of the basket.
the cones are closer to 16" tops.
take a tape, measure from the outside of the surround to the inside of the surround on the other side... this is a close... slightly over aprox. of the active cone area... for an 18 is about ~0.11 square meters for a given high excursion driver.
for a 12" is about ~0.049 square meters for a given high excursion driver.
18's generally have more cone area than two 12's, but we're forgetting a critical piece of information.
its not about displacement, its about sensitivity, For a 12" woofer, takes its sensitivity number and add 3dB two it every time you double down...
for example if our 12 pulls 86dB, then two pull 89 and four pull 92.
this is because we are doubling the cone area and then of course halving the current to each driver. It winds up being a +6 -3 tradeoff or net 3dB.
You also have to consider than 2 twelves prolly have better thermal proprieties than a single 18" with only 1 voice coil so in theroy ytou might be able to run te 12's with more power.
But the 18 might have a displacement advance which will come in handy in the low octaves... its just not so simple.....
sensitivity, displacement and power handling, you just look at any one.
