SB ACOUSTICS SB12NRXF25-4, 12cm NOREX PAPER CONE MIDWOOFER 4OHMFeatures Proprietary cone material with natural fibres made in-house Foam surround for maximum transparency and midrange resolution Vented pole piece for reduced compression Vented cast aluminium chassis for optimum strength and low compression CCAW voice coil for reduced moving mass Long life silver lead wires Non-conducting fibre glass coil former for minimum damping Specs Nominal Impedance 4 Ω DC resistance, Re 3.1 Ω Voice coil inductance, Le 0.27 mH Effective piston area, Sd 50 cm2 Voice coil diameter 25.4 mm Voice coil height 15 mm Air gap height 5 mm Linear coil travel (p-p) 10 mm Magnetic flux density 0.84 T Magnet weight 0.32 kg Net weight 0.75 kg Free air resonance, Fs 61 Hz Sensitivity (2.83 V / 1 m) 87 dB Mechanical Q-factor, Qms 5.3 Electrical Q-factor, Qes 0.53 Total Q-factor, Qts 0.48 Moving mass incl. air, Mms 5.8 g Force factor, Bl 3.6 Tm Equivalent volume, VAS 4.1 liters Compliance, Cms 1.17 mm/N Mechanical loss, Rms 0.42 kg/s Rated power handling* 30 W * IEC 268-5, T/S parameters measured on drive units that are broken in.