WL218-sw is premium, high-performance, dual 18-inch subwoofer designed for suspended or ground stacked use in most demanding touring or installed concert applications. With an impressive combination of punch, low-frequency extension and accuracy, the WL218-sw is an ideal companion for QSC's acclaimed WideLine as well as other professional sound reinforcement systems. Sound system designers and operators are increasingly turning to subwoofer systems that are flown with the main array for more seamless acoustical transition from bass to the low-mid region. With simple, three-point suspension design that is essentially scaled up version of the QSC WideLine system, the WL218-sw fulfills the requirement while also delivering powerful and stunningly accurate low frequency output. Suspension of the array requires one AF218-sw for each subwoofer array. The AF218-sw is simple, heavy-duty array frame constructed of welded, aviation-grade 6061-T6 aluminum and intended for suspension of up to eight WL218-sw subwoofers with 10:1 design factor. For ground-supported applications, the subwoofers may be stacked using interlocking feet and recess features machined into the enclosure's end caps. 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 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. 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 WL218-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 the same plywood as the enclosure. Each woofer is protected by heavy-duty, 14 gauge, powder coated steel grille and housed in its own, separate chamber to prevent failure of one driver from causing damage to the other.