An Impedance Equalization Circuit, also know as a Zobel circuit, can be used to counteract the rising impedance of a voice coil caused by inductive reactance. The cause of this impedance rise is due to the speaker’s voice coil inductance (Le). A schematic of a impedance equalization circuit (zobel) is shown below. The impedance equalization circuit is usually placed after the crossover circuitry.


  • Re is the DC Resistance of the driver [ohms]
  • Le is the Voice coil Inductance of the driver [H]
  • Rz is the calculated Zobel resistor [ohms] and
  • Cz is the calculated Zobel capacitor [F].

Use this online calculator to determine the required Zobel resistor and capacitor. Simply enter Re and Le into the boxes below and click the CALCULATE button. Use the CLEAR button to reset all the values.

NOTE: This online calculator requires that JavaScript be enabled on your browser.

Re [ohms]
Le [mH]
Cz [µF]
Rz [ohms]

Comments closed