SB ACOUSTICS SB12PACR25-4, 12cm ALUMINUM CONE MIDWOOFER 4OHMFeatures Vented reinforced plastic chassis Anodised aluminium cone Low damping rubber surround Large vented motor system Long stroke linear suspension Light weight CCAW voice coil Non-conducting fibreglass coil former Non-resonant long life lead wires Specs Nominal Impedance 4 Ω DC resistance, Re 3.1 Ω Voice coil inductance, Le 0.25 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 1.03 T Magnet weight 0.40 kg Net weight 0.86 kg Free air resonance, Fs 52.5 Hz Sensitivity (2.83 V / 1 m) 87 dB Mechanical Q-factor, Qms 5.0 Electrical Q-factor, Qes 0.33 Total Q-factor, Qts 0.31 Moving mass incl. air, Mms 6.1 g Force factor, Bl 4.35 Tm Equivalent volume, VAS 5.3 liters Compliance, Cms 1.50 mm/N Mechanical loss, Rms 0.4 kg/s Rated power handling* 30 W * IEC 268-5, T/S parameters measured on drive units that are broken in.