What would be the advantages of powering each voice coil seperately on a dual coil driver? I have an amp that's 2x240W @8ohms (it's 2x420W into 4ohms) that I'm going to use to power my new sub. From what I understand, the driver in my sub (a Shiva M2) has a sensitivity of about 91dB @ 1W with both coils wired in parallel (thereby reducing it's impedance to 4Ohms). BUT, if I wire each coil seperately the sensitivity drops to 88dB (at 8ohms per coil). Doesn't that mean that it would take twice as much wattage to push this driver if both coils are driven seperately? SO, would that mean that I would have to push 2x420W at 8ohms to equal a single 420W channel at 4ohms? I know the following is true: 91dB senitivity @ 1W = 88dB sensitivity @ 2W but am I missing something? Ack... this is confusing.