I'm replacing the 12" subwoofer speaker in a Sony subwoofer unit. The
original speaker (a POS) failed, has a single voice coil, and it says 6
ohms on it.

I happen to have a 12" Cerwin Vega dual voice coil subwoofer lying around.
Each of the coils on the Cerwin Vega are 4 ohms. How should I hook this up
in the Sony box? Is it OK to hook up just one of the coils? Will that
sound OK ? Or is it necessary to hook up both coils in series ? Both in
series would be 8 ohms, which is more than the original POS speaker's 6
ohms, but using a single coil would be 4 ohm, which is less. What to do?

Any advice?

Thanks.