2, Here is the speaker specification of HiVi D6.4MKII as following

Rated impedance Z=4 Ω

Resonant frequency Fs=53 Hz

Rated power Pnom=50 W

Maximum power Pmax=100 W

Sensitivity (2.83V/1m) E=87 dB

Weight W 1.37=kg

Voice coil diameter ∅=76 mm

DC resistance Re=3.6 Ω

Voice coil width H=12.8 mm

Voice coil wire = copper clad aluminum

Voice coil bobbin = aluminum

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Force coefficient (BL value) BL=7.85 N/A

Magnetic gap height He=6.0 mm

Maximum linear displacement Xmax=3.5 mm

Compliance Cms=412 uM/N

Mechanical Q value Qms=2.29 -

Electric Q value Qes=0.41 -

Total Q value Qts=0.35 -

Vibration mass Mms=20.6 g

Equivalent volume Vas=8.5 L

Recommended net volume of box Vb=13.5 L

Inverter tuning frequency Fb=46 Hz

Cabinet in free field -3db frequency F3=50 Hz