From the Manufacturer
With the addition of SB218 subwoofers, the low frequency response of the V-DOSC system is extended down to 25 Hz. The SB218 subwoofer enclosure has been specifically designed to complement V-DOSC and all OEM factory presets are optimized for the SB218. The SB218 contains two 18-inch transducers, front-loaded in an optimally-tuned and vented enclosure. Power handling is 1100 Wrms continuous program (4400 Wpeak) at a nominal 4 ohm impedance. Connection is made via Speakon NL4 connector and DOSUB cables are used to connect to amplifier racks (one SB218 per LA48a amplifier channel). Usable frequency response is 28 to 140 Hz (+/- 3 dB) with -10 dB response at 25 Hz referenced to the average level of the usable response. The SB218 features critically-damped tuning characteristics with an enclosure tuning frequency of 32 Hz. The central, large-area port enhances large-signal dynamic capability while minimizing nonlinearity due to port turbulence effects. The 18-inch transducers employed in the SB218 have a 4.5 inch diameter edgewound copper ribbon voice coil, 9 mm peak excursion capability, weatherproof cone body, diecast aluminum frame, massive vented magnet structure and utilize advanced high temperature adhesives in their assembly. Loudspeaker components feature low thermal power compression, long term reliability and low distortion output. The SB218 is constructed of 24 mm baltic birch and is internally braced with steel corner plates and joints that are sealed, screwed and rabbeted in order to remain free of vibration at extreme sound pressure levels. Dimensions are 550 mm (21.7 in) high, 1300 mm (51.2 in) wide and 700 mm (27.6 in) deep and enclosure weight is 115 kg (233.7 lbs). The finish is brown gray (RAL8019) structured polyurethane paint and the front of the enclosure is protected by a black powder-coated, 1.5 mm thick steel grill grille covered with 10 mm (0.4-in) thick acoustically-transparent open cell foam. The SB218 has two recessed flytrack sections mounted on both sides for rigging purposes. An accessory flying bar is available that allows for rigging of arrays up to 8 enclosures deep with greater than 5:1 safety factor. Six recessed handles are located on the sides of the enclosure and a front mounted dolly board attaches to the enclosure using two locking pins and two front baffle-mounted dolly locator studs.