One 12 Inch vs Two 10 Inch Subwoofers: Which Setup Wins?

On representative cone area figures, yes. A 10 inch driver has an effective cone area of roughly 56.7 square inches, so two of them together total about 113.4 square inches, compared to roughly 81.7 square inches for a single 12 inch driver. Those are conventional, representative figures for effective radiating area rather than a spec pulled from any one driver, and the actual Sd for a given model is published on its own data sheet and can vary from these numbers. Even accounting for that variance, two 10s generally out-total one 12 on combined cone area.

There is a second effect worth knowing: when two identical drivers share the same signal and sit close together in a common or coupled enclosure, they gain roughly 3 dB from mutual coupling on top of whatever their combined cone area and power handling would predict on their own. That gain assumes matched drivers wired and mounted the way the design intends, not two mismatched subwoofers thrown into a box together.

Cone area is not the only number that changes with driver count. Two 10 inch subwoofers generally need a combined net volume that is larger than what a single 12 inch driver requires, and depending on the specific drivers chosen, that combined volume can approach what a single, larger 15 inch driver would need on its own. The manufacturer's per-driver recommended volume, multiplied by two and adjusted for any shared internal bracing, is the number to build to, not a guess based on the 12 inch box the setup is replacing.

This is where a lot of two-10 builds run into trouble: the cone area and coupling gain look appealing on paper, but the vehicle's available space was sized around a single 12 inch box, and two 10s in a properly built enclosure simply do not fit the same footprint. Running the sealed box volume calculator or ported box volume calculator for the actual drivers chosen, before assuming the swap is a drop-in, avoids that surprise.

Two 10 inch subwoofers typically split the amplifier's power between them rather than each receiving the same power a single 12 inch driver would get on its own amplifier channel, unless the amplifier and wiring are sized specifically to feed both drivers at their full individual rating. Dual voice coil 10 inch drivers give more wiring flexibility, series, parallel, or a series-parallel combination across two drivers, which can be used to hit a target impedance the amplifier is comfortable driving. Check the amplifier's rated power at the resulting impedance, not just its headline power figure, before assuming two drivers will each get full power.