X-18 V.2 D2 - Sundown Audio 18" Dual 2-Ohm X V.2 Revision 2 Series Subwoofer Xmax = 30mm one-way by 70% BL | RMS Power = 1500-watts Specifications: DC Resistance (Re): 3.80  | Resonance Frequency (Fs): 26.4 Hz | Equivalent Volume (Vas): 154.0 L | Electrical Q Factor (Qes): 0.44 | Mechanical Q Factor (Qms): 5.16 | Total Q Factor (Qts): 0.40 | Voice Coil Inductance (Le): 2.71 mH | Force Factor (BL): 25.4 NA | Moving Mass (incl. Air Load) (Mms): 449.0 g | Suspension Compliance (Cms): 0.08 mm/N | Sensitivity: 90.0 dB 1w / 1m Box Recommendations: Sealed Enclosure Suggestion: Not Recommended | Ported Enclosure Suggestion: 7.0 cu. ft. | Displacement: 0.23 cu. ft. | Depth: 10.25 in | Outside Diameter: 18.42 in | Cutout: 16.69 in | Recommended Tuning: 32 Hz | Recommended Port Area: 112 sq. in.