The XLm4 is the next generation of our most award winning driver. The XLm4 has aN added pole vent , redesigned top plate and T yoke, larger magnets wrapped in a stylish motor boot an 8 layer flat wound voice coil, upgraded cone and surround. We are always looking to make great even better and the XLm4 is again a step in that direction. Anyone looking for a subwoofer that not only sounds great but is a beast in the SPL lanes, look no further, you have found what you have been searching for.