Well what you are lookin for is how much THD(total harmonic distortion) is increased from 4ohm load to 2 ohm load to 1 ohm load. Taking a wild guess but sounds like a you may have an Alpine set up? Cause thats exactly what my numbers come out to be. Im running 2ohm load, or wire the 4 ohm sub voice coils parallel, and its fine. Some amps you wanna keep it at 4 ohm load to keep the bass cleaner, but it depends on the amp really. Alpine amps THD doesn't change from 4 ohm to 2 ohm.