The 21LW2500 is a 21" (533 mm) extended low frequency loudspeaker, designed for use in vented enclosures. The loudspeaker is designed to withstand high power levels without damage while providing clean and undistorted LF reproduction at a very high SPL. For optimum results we recommend amplifiers able to deliver 3600 Watt program power. The 21LW2500 features a unique motor featuring a high grade ferrit magnet assembly in a structure optimized for thermal and magnetic efficiency. 21LW2500 features include a large displacement suspension system which, in conjunction with a composite reinforced, straight ribbed cone and the Eighteen Sound proprietary Double Silicon Spider (DSS) technology, allows an ultra-linear piston action and provides full mechanical control across the entire working range. The 100mm (4 in) state-of-the-art voice-coil utilizing Interleaved Sandwich Voice coil (ISV) technology, provides high levels of thermal stability and durability. The ISV technology achieves a balanced linear motor unit exerting an exceptionally high force factor.