Scan Speak - 28W/4878T00 - Woofer 28cm 4 Ohm Revelator

Datasheet

The Revelator woofers and subwoofers features very rigid cones in paper or aluminium 
that operates as a piston over a wide frequency range, in combination with ScanSpeaks low-loss linear suspension and the patented Symmetrical Drive (SD-1) it 
results in very low distortion and a smooth and well behaved frequency response as 
well as perfect transient reproduction.