SB ACOUSTICS SB23NBACS45-8, 23cm BLACK ALUMINUM CONE WOOFER 8OHMFeatures Soft low damping rubber surround for improved transient response Geometrically reinforced aluminium cone for improved break-up control Shorting ring in motor system for reduced distortion Vented pole piece for reduced compression Vented cast aluminium chassis for optimum strength and low compression Shallow design Non-conducting fibre glass voice coil former for minimum damping CCAW voice coil for reduced moving mass Long life silver lead wires Specs Nominal Impedance 8 Ω DC resistance, Re 5.7 Ω Voice coil inductance, Le 0.37 mH Effective piston area, Sd 216 cm2 Voice coil diameter 45.5 mm Voice coil height 19 mm Air gap height 6 mm Linear coil travel (p-p) 13 mm Magnetic flux density 0.9 T Magnet weight 0.8 kg Net weight 2.7 kg Free air resonance, Fs 25 Hz Sensitivity (2.83V/1m) 87.5 dB Mechanical Q-factor, Qms 5.54 Electrical Q-factor, Qes 0.43 Total Q-factor, Qts 0.40 Moving mass incl. air,Mms 31.2 g Force factor, Bl 7.9 Tm Equivalent volume, Vas 93.4 liters Compliance, Cms 1.43 mm/N Mechanical loss, Rms 0.8 kg/s Rated power handling* 60 W * IEC 268-5, T/S parameters measured on drive units that are broken in.