The 21XR is a high efficiency, (96 dB 1watt / 1 meter) 21-inch woofer with incredibly linear frequency response characteristics. Our new and patented ground up motor design is a new approach to high-excursion woofers. The voice coil winding is always in the magnetic gap that is extremely wide. This feature ensures extremely low distortion across whole working range of this unique driver. Motor Design The magnetic design incorporates large neodymium magnets placed along the voice coil winding. This has allowed us to push the cone excursion to 50mm peak to peak. Unique gap venting ensures good air circulation and greatly improves the reliability of this driver. We have also developed a new technique for manufacturing deep copper caps that are implemented in this design and covering the whole voice coil movement.. The design further utilizes triple, uncommonly large, spiders, spaced with spacers, hot-pressed tinsel wires onto the top spider, reinforced cone edge, reinforced surround to cone joint, reinforced spider to basket joints, etc.