Scanspeak 26W/4558T00 Discovery 10 inch 4 ohm Sub Woofer.
Rugged audiophile quality high power sub bass speaker with ultra rigid alloy cone providing tight, solid lower registers with excellent speed, texture and extension. A popular unit with a low resonance of just 21 Hz and a maximum excursion of 56mm - capable of high sound pressure levels without stress. Ideally suited to both domestic and in-car applications. A full datasheet can be downloaded from the bottom of this page.
A matching passive radiator can be found here: 26W/0-00-00