SELENIUM 18WS600 Woofer Bumped back plate and extended pole piece for maximum excursion Multi-cooling system forces cool air across the voice coil The 18WS600 is specially designed to provide high impact low frequency output in all pro sound applications. Two counter-balancing, distortion canceling, polyester-cotton-fiber spiders Strong reinforced cast aluminum frame also acts as a heat sink Bumped backplate and extended pole piece for maximum excursion Multi-cooling system forces cool air across the voice coil 4" diameter copper wire voice coilNon-pressed long fiber pulp cone for linear response and strength Two counter-balancing, distortion canceling, polyester-cotton-fiber spiders Strong reinforced cast aluminum frame also acts as a heatsink