SB ACOUSTICS SB20PFCR30-4, 22cm FIBER CONE WOOFER 4OHMFeatures Vented reinforced plastic chassis Proprietary cone material with natural fibers made in-house Soft low damping rubber surround for improved transient response Large spider for improved linearity Optimized motor system Vented coil former for low compression Non-resonant long life lead wires Specs Nominal Impedance 4 Ω DC resistance, Re 3.4 Ω Voice coil inductance, Le 0.71 mH Effective piston area, Sd 216 cm2 Voice coil diameter 30.5 mm Voice coil height 16.5 mm Air gap height 5 mm Linear coil travel (p-p) 11.5 mm Magnetic flux density 1.2 T Magnet weight 0.54 kg Net weight 1.42 kg Free air resonance, Fs 34 Hz Sensitivity (2.83V/1m) 92.5 dB Mechanical Q-factor, Qms 2.78 Electrical Q-factor, Qes 0.37 Total Q-factor, Qts 0.33 Moving mass incl. air,Mms 22.4 g Force factor, Bl 6.6 Tm Equivalent volume, Vas 66.2 liters Compliance, Cms 1.0 mm/N Mechanical loss, Rms 1.7 kg/s Rated power handling* 50 W * IEC 268-5, T/S parameters measured on drive units that are broken in.