Both coils work, but they rub that's why is being sold for parts.

The Rockford Fosgate RFD2215 15" Subwoofer is a high-quality car audio product designed for powerful and immersive sound performance. With a dual 4 ohms design and an RMS power of 1200W, this subwoofer delivers exceptional bass response for a truly cinematic audio experience in your vehicle. Made in the United States by the renowned brand Rockford Fosgate, this enclosed powered subwoofer is a top choice for car audio enthusiasts looking to upgrade their sound system with a reliable and high-performing component.