How do I calculate earphone total impedance? Earphone impedance calculations; you can wire the earphones in series or parallel. Wiring earphones in series doubles the total impedance of the earphones i.e. 300 ohm earphones in series = 600 ohm total impedance. Wiring earphones in parallel halves the total impedance of the earphones i.e. 300 ohm earphones in series = 150 ohm total impedance.