SB ACOUSTICS SATORI MW13TX-4, 13cm TEXTREME CONE NEODYMIUM MIDWOOFER 4OHMFeatures Advanced TeXtreme® cone Vented aerodynamic cast aluminium chassis Soft low damping rubber surround Advanced BIMAX spider Powerful optimized low distortion neodymium motor system Extended copper sleeve on pole piece Non-conducting fiberglass voice coil former Vented pole piece and voice coil Light weight CCAW voice coil Long life silver lead wires Specs Nominal Impedance 4 Ω DC resistance, Re 3.8 Ω Voice coil inductance, Le 0.16 mH Effective piston area, Sd 70 cm2 Voice coil diameter 30.5 mm Voice coil height 15 mm Air gap height 5 mm Linear coil travel (p-p) 10 mm Magnetic flux density 1.08 T Magnet weight 0.1 kg Net weight .79 kg Free air resonance, Fs 38 Hz Sensitivity (2.83V/1m) 89 dB Mechanical Q-factor, Qms 5.08 Electrical Q-factor, Qes 0.27 Total Q-factor, Qts 0.26 Moving mass incl. air,Mms 7.4 g Force factor, Bl 5.0 Tm Equivalent volume, Vas 16 liters Compliance, Cms 2.38 mm/N Mechanical loss, Rms 0.3 kg/s Rated power handling* 40 W * IEC 268-5, T/S parameters measured on drive units that are broken in.