I just had a custom box built for my 2 10 inch RE Audio SE Pros. It was built exactly to specs tuned at 36hz. I just unistalled my 15 RF T1also in a custom box tuned to 36hz. Both were powered by my JL Audio 1000/1 V2. Honestly i cannot hear a difference between my 2 10s and 1 15. The 15 is obviously deeper but my 2 10s keep up stride for stride. Their bass response is very deep as well. I drive a Toyota 4-Runner. What gives? Why is the difference between the two so small? I know 1 15 has more cone area.