IDMAX15 V.4 D4 - Image Dynamics 15" Dual 4-Ohm IDMAX V.4 Series Subwoofer 15" Dual 4 ohm ID MAX V.4 Series Subwoofer | Pressed paper composite cone woofer | Parabolic EPDM rubber surround | Over 2" long linear excursion | RaDiaToR cooling system for heat dissipation | Radiant Diametric Torsional Reinforcement High compliance suspension design | Flat spider with NOMEX cloth woven tinsel leads | High-temperature flat wire, flat wound voice coil | Inverted dust cap with logo | Powder coated alloy proprietary basket DC Resistance (Re): 3.10  | Resonance Frequency (Fs): 29.61 Hz | Equivalent Volume (Vas): 109.03 L | Electrical Q Factor (Qes): 0.75 | Mechanical Q Factor (Qms): 1.47 | Total Q Factor (Qts): 0.5 | Frequency response: 20-250 Hz Peak Excursion (Xmax): 44 mm | Force Factor (BL): 11.40 Tm | Piston Area (Sd): 934.79 cm2 | Sensitivity: 87.60 dB 1w/1m Mounting Depth: 10.40 in | Outside Diameter: 16.22 in | Cutout: 14.80 in