X-15 V.2 D4 - Sundown Audio 15" Dual 4-Ohm X V.2 Revision 2 Series Subwoofer X-15 V.2 D4 - Sundown Audio 15" Dual 4-Ohm X V.2 Revision 2 Series Subwoofer Specifications: DC Resistance (Re): 6.1  | Resonance Frequency (Fs): 29.5 Hz | Equivalent Volume (Vas): 59.5 L | Electrical Q Factor (Qes): 0.50 | Mechanical Q Factor (Qms): 4.92 | Total Q Factor (Qts): 0.45 | Voice Coil Inductance (Le): 3.61 mH | Force Factor (BL): 28.8 NA | Moving Mass (incl. Air Load) (Mms): 365.3 g | Suspension Compliance (Cms): 0.08 mm/N | Sensitivity: 86.7 dB 1w / 1m Box Recommendations: Sealed Enclosure Suggestion: Not Recommended | Ported Enclosure Suggestion: 4.25 cu. ft. | Displacement: 0.22 cu. ft. | Depth: 10.85 in | Outside Diameter: 15.51 in | Cutout: 13.83 in | Recommended Tuning: 32 Hz | Recommended Port Area: 68 sq. in.