13 cm (5") woofer with robust polypropylene membrane for very compact subwoofer. Designed for multi-purpose applications due to 2 x 4 ohms double voice-coil, with excellent properties as 8 ohms drivers in series configuration. The enormous membrane displacement for its size as well as the very low resonance frequency allows a considerable sound pressure level, the one does not trust such a small speaker.
(1) one voice coil not connected
(2) both voice coils in series
(3) both voice coils in parallel