The Scan-Speak 18W/8542-00 is a generic replacement for the ProAc Studio 100 mid-woofer. It features the Symmetric Drive (SD) concept with copper in the magnet system which was invented by Scan-Speak. This high-quality magnet system design has thus been a key feature of Scan-Speak design since the company's inception. The Classic woofers are highly praised and are used in some of the worlds most exceptional high-end loudspeakers.