SB ACOUSTICS SB56WBAC25-4, 64mm ALUMINUM CONE FULLRANGE 4OHMFeatures Geometrically furrowed aluminum cone for extended usable frequency range Copper cap for increased high frequency output, reduced phase shift at higher frequencies and improved power handling capability Low damping surround and non-conductive voice coil former to ensure dynamics and an open/transparent sound character with excellent detailing/resolution Linear neodymium motor system for reduced distortion Vented voice coil former for reduced compression Specs Nominal Impedance 4 Ω DC resistance, Re 3.6 Ω Voice coil inductance, Le 0.15 mH Effective piston area, Sd 20 cm2 Voice coil diameter 25.4 mm Voice coil height 8.3 mm Air gap height 3 mm Linear coil travel (p-p) 5.3 mm Magnetic flux density 1.02 T Magnet weight (NEO) 0.02 kg Net weight 0.14 kg Free air resonance, Fs 115 Hz Sensitivity (2.83 V / 1 m) 83.5 dB Mechanical Q-factor, Qms 6.0 Electrical Q-factor, Qes 0.77 Total Q-factor, Qts 0.68 Moving mass incl. air, Mms 2.5 g Force factor, Bl 2.9 Tm Equivalent volume, Vas 0.43 liters Compliance, Cms 0.77 mm/N Mechanical loss, Rms 0.3 kg/s Rated power handling* 20 W * IEC 268-5, high-pass Butterworth, 200 Hz, 12 dB/oct, T/S parameters measured on drive units that are broken in.