4 ohm on dual 4 ohm voice coils

Stevolon above is correct, and this is how I would also suggest using a single 4 ohm DVC sub with an amp that cannot handle a 2 ohm bridged load.  Wire it at 8 ohms and bridge, presenting a net 4 ohm load on each amplifier channel.

By the way, DVC does not mean there are two seperate voice coil formers, so nothing can "hit each other."  It means there are two windings on one former.  The problem of wiring in stereo (or or using seperate amps on each VC input) is that during those moments when the two channels of the amplifier are slightly out of phase with one another (and this will ALWAYS happen for small amounts of time, even with the best equipment and the most careful setup) the physical momentum generated by the two electrical signals will cancel each other and cause the VC to stop moving (momentarily.)  When this happens, the electricity from the amplifier is disapated as heat and it is possible to burn out one or both VC windings.