GP218-sw is premium, high-performance, rectangular dual 18-inch subwoofer designed for ground stacked use in the most demanding touring or installed concert applications. With an impressive combination of punch, low-frequency extension and musical accuracy, GP218-sw is an ideal companion for the acclaimed QSC WideLine series as well as other professional sound reinforcement systems. For suspension in permanent installations each GP218-sw subwoofer comes with total of sixteen (16) threaded M10 inserts (four per side). For ground-supported applications, the subwoofers may be stacked horizontally using their interlocking feet and recess features machined into the enclosure's top panel. 18-inch woofers incorporate double layer spider and triple roll surround for extended and controlled excursion at extreme power. The 4-inch voice coil is wound on a fiberglass former to prevent deformation at high operating temperatures and is extensively vented to reduce power compression. An aluminum demodulating ring is employed for low distortion. The extremely musical yet powerful performance of subwoofer is the result of carefully balancing the transducer selection, cabinet volume and port tuning. The resulting system offers plenty of punch while maintaining ample extension so the musically important and satisfying fundamentals are solidly and accurately reproduced. Enclosure of the GP218-sw is constructed of premium quality birch plywood finished in an environmentally friendly, waterborne, polymer finish that stands up to life on the road while also being field repairable. Extensive internal bracing is employed to eliminate acoustic losses due to panel resonance. Further contributions to cabinet rigidity come from vent walls constructed of same plywood as the enclosure. Woofers are protected by a heavy-duty, 14 gauge, powder coated steel grille and housed in separate chambers to prevent failure of one driver from causing damage to the other. Despite the extremely large amount of air moving in the ports, careful attention to detail has resulted in a system that is free of port distortion chuffing. Ample port area allows massive amounts of air to move freely with minimal turbulence and the ports are arranged so as to eliminate asymmetrical loading of the woofers, which can result in distortion and voice coil failure related to rocking-modes.