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 (L_e). A schematic of a impedance equalization circuit (zobel) is shown below. The impedance equalization circuit is usually placed after the crossover circuitry.

Where:

• R_e is the DC Resistance of the driver [ohms]
• L_e is the Voice coil Inductance of the driver [H]
• R_z is the calculated Zobel resistor [ohms] and
• C_z is the calculated Zobel capacitor [F].

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

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