SourDeez - the cone does not affect the sound other than how much you get unless it bends/resonates or distorts (that's strictly a higher frequency issue, not a subwoofer issue). We can go into details but i'll keep it short: Larger speakers be it (tweeters, midrange or woofers) are better across the board. Sometimes you need narrow drivers for ultra high frequencies to prevent directionality issues, but low frequencies are so low, its not even a question. More cone area means more displacement and less current and movement to get it (a win win), but they also tend to need larger motors to prevent high Q issues and non-linear frequency response - that's not a sound quality issue, but rather a system design issue/consideration. The best subwoofers are always 18's or 21's - not entirely ideal for car audio because of size issues, but don't send a 12 to do a 15's job and expect it to do it better.... it won't. If you measure a good 18's vs a good 12 there is not one single objective number you can say that the 12 does better in expect for being smaller.
simple proof: by math we can model two (lets use 12's ) as one by doubling all the parameters. We wind up with identical Qts, Fs and 3dB higher sensitivity, and double the BL^2/Re (which gives us that +3dB). This means that from a mathematical standpoint two identical drivers are exactly equal a single larger one expect that for every watt of power, you get twice as much sound. - clearly two drivers are better than one and i think from general intuition you would agree....
Keep this in mind: An 18 is just bout the size of two 12's...... continuing......
however this mathematical model of the sum of these two drivers is simply one with a cone twice as large, moving mass twice as heavy, suspension twice as stiff and twice the motor force factor thus we could also create a larger driver that met these same parameters and was therefore twice as good as the single smaller one, do this for N+1 blah blah and my induction we can prove not only that two are better than one , but a larger driver is better than a smaller and so fourth...
I use a very expensive 12" for my home theater (over $1000 for the driver) not because it sounds better, but because i don't have too much space, but it happens to be a very good 12 on quite of bit of power thus makes plenty of sound. I would use an 18 if i had a larger room or more space and it would be better.
