X-18 V.2 D4 - Sundown Audio 18" 1500W RMS Dual 4-Ohm X V.2 Series Subwoofer Xmax = 30mm one-way by 70% BL | RMS Power = 1500-watts Specifications: DC Resistance (Re): 6.1  | Resonance Frequency (Fs): 27.7 Hz | Equivalent Volume (Vas): 137.7 L | Electrical Q Factor (Qes): 0.54 | Mechanical Q Factor (Qms): 5.12 | Total Q Factor (Qts): 0.49 | Voice Coil Inductance (Le): 4.0 mH | Force Factor (BL): 29.8 NA | Moving Mass (incl. Air Load) (Mms): 454 g | Suspension Compliance (Cms): 0.07 mm/N | Sensitivity: 89.2 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.