they are just physiclly different. No woofer keeps the same exact specs when going from a different coil configuration but normally they are very small changes that no one can physiclly tell. People dont go in to a stereo shop saying they want the D# of ____ woofer because it sounds better/louder/cleaner then the D# or S# version. Oh and resistance itself is also not a 100% measurement. Just because you have a dual 2 doesnt mean u will meter exactly 2 ohms on the coil. Hence why FI states them as .7 and 1.4 In all reality all they are doing is giving a little better idea over the rounded numbers. And every spec is related to one and other. You cant just magiclly raise or lower something and expect all the other paramaters to stay the same