The BPSD21 Sub Engine S2 is a new and improved version over our series one BP-SD21. It now comes with the most powerful low frequency transducer we have ever found. It boasts folded-horn output from a box one half the size of one of our WH folded horns. The 21” Neodymium woofer has a 6” voice coil that can handle 2000W RMS, 4000W Program and 8000W Peak. When it is used with a bridged 6000W amplifier, the low frequency output is staggering. The frequency response curve is 3db down at 32 Hz. The BPSD21 Sub engine also comes with a detachable dolly board for easy transport.