M.M.D., driver that is usually found only on Infinity's top of the line speakers. Inside these drivers an aluminum layer is sandwhiched between two layers of ceramic, stiffness and flexibility for extra responsiveness and less resonance. Inside the speaker shell there is a 1" C.M.M.D. tweeter, a 4" C.M.M.D. midrange, dual 6-1/2" C.M.M.D. woofers.