The JRX218S is driven by a massive JBL 18" woofer with a cast frame and 3" voice-coil.    

Features :

• 18 in. compact subwoofer. 350 W (continuous), 1400 W (peak) power capacity.
• The rugged enclosure is constructed from 19 mm (.75 in) MDF (Medium Density Fiberboard) using advanced adhesives and mechanical fastener technology for durability and improved low-frequency performance.
• The enclosure is covered in black carpet.
• A top mounted, cast aluminum 36 mm pole mount receptacle can receive an optional SS3BK pole to facilitate use of the JRX218S as a base for a midhigh speaker cabinet.
• Non-resonant, all steel handles are used.
• Attractive 18-gauge perforated steel grille protects components from damage.    
• Specifications   Power Rating  :   350 W / 1400 W
• Frequency Range (-10 dB)  :   34 Hz - 250 Hz
• Frequency Response (±3 dB)  :   53 Hz - 250 Hz
• Sensitivity (@1m)  :   98 dB Nominal Impedence  :   4 ohms Recommended
• Amplifier Power  :   350 W to 700 W into 4 ohms
• Maximum SPL  :   133 dB peak, @1 m (3.3 ft)
• Dimensions (H x W x D)  :   605 mm x 508 mm x 551 mm  (23.8 in x 20.0 in x 21.7 in)
• Net Weight  :   32.2 kg (71 lb)
• Low Frequency Driver  :   M118-4
• Input Connectors  :   Neutrik® Speakon® NL-4 (x2); parallel
• Grille  :   18-gauge, powder-coated steel