This is the 4641 subwoofer.

This is a 600 watt subwoofer featuring an advanced technology 460 mm (18 inch) low frequency transducer.  The 2241H transducer utilizes the same patented Vented Gap cooled process as the 2242 transducer in the 4645C.  This has a usable response to 25 Hz and is THX approved.