On there site (JL's ) I did not see them stating it voiding your warranty, but it may be i the manual. I do know that Rocdford Fosgate did this. Only using one coil (if you guys didnt check out JL's site) Will over work the coil you are powering. As it tries to move the woofer the second coil is dead weight, this is added mass that the manuacture did not intend this woofer to receive causes it to strain (it will also have less xmax, since the magnetical field wil be greater than expected thus changing parameters of the woofer too.)
Here is a whole FAQ on DVC's
http://www.jlaudio.com/tutorials/dvc/index.html Check out the one "What is a dual voice coil speaker"
Maybe you will see what I mean by one coil now being dead weight.
