Impedance Measurement Procedure

Two-resistor method:

1. Connect 10Ω resistor in series between signal source and speaker
2. Measure V₁: voltage before resistor
3. Measure V₂: voltage across speaker
4. Calculate at each frequency:

Z_speaker = 10 × V₂ / (V₁ − V₂)

REW automated procedure:

REW can perform swept impedance measurement automatically with a supported audio interface:

1. REW → SPL Meter tab → Set up reference resistor value
2. Connect interface: Output → resistor → speaker; Input Ch 1 (reference), Input Ch 2 (speaker)
3. Sweep → saves impedance curve automatically

From impedance curve, extract:

Re = Z at very low frequency (near DC)
Fs = Frequency of impedance peak
Qes = F_s × (R_e / Z_max − Re) × √(Z_max/Re) / (f2 − f1)

Where f1, f2 are frequencies where Z = √(Re × Zmax) on either side of peak.