Subwoofer manufacturers make subs with dual voice coils (DVC) to take advantage of this difference in wiring schemes, so the user has more freedom of system design. A DVC 4-ohm sub can be wired into a system as a 2-ohm or as an 8-ohm load. A DVC 2-ohm sub can have a total impedance of 1 ohm or 4 ohms.
Also question is, what is a dual voice coil subwoofer?
The key difference between single and dual voice coil subwoofers is the multiple wiring options DVC subs offer: Parallel: A dual 4-ohm voice coil subwoofer with its coils wired in parallel presents a 2-ohm load to your amplifier.