The SCM20SL Passive low-frequency section is a hybrid design incorporating a 150mm bass cone with a grafted 75mm soft dome for mid-range assist. The woofer magnet assembly utilizes ATC's unique "SL" technology to greatly reduce third harmonic distortion and reveal mistakes and details. The tweeters are ATCs new dual suspension high powered tweeters. They do not use ferro fluid for cooling so will last a lifetime. A newly redesigned crossover ensures a smooth transition across all frequencies. All ATC drivers are manufactured in-house to exacting tolerances and are legendary for their many design innovations.