Impedance Equalization (Zobel) Circuit Designer / Calculator Help
Use the Impedance Equalization Circuit Designer.
Impedance Equalization Circuits, also know as Zobel circuits, are used to counteract the rising impedance of a voice coil caused by inductive reactance. This problem mainly occurs in sub woofers because of their large coils. A Impedance Equalization circuit is usually placed after the crossover.
Impedance Equalization Circuit is simply a capacitor (C) and a resistor (Rc) in series, in parallel with the driver.
![Circuit](circuit.gif)
Re = Driver DC Resistance in Ohms
Le = Driver Inductance in mH
![Formula](formula.gif)
Example: Say you have a 8 Ohm tweeter with a Re of 5.7 Ohms with a Le of .08 mH The impedance curve for the driver would look like this.
Actual Driver Resistance
Desired Driver Resistance
![Graph](graph.gif)
The impedance of the tweeter rises because of the voice coils inductance at high frequencies. Using the above formulas, C = 1.58 uF and Rc = 7.13 Ohms. Using the capacitor and resistor will help to flatten out the impedance curve. Experimentation is recommended to achieve the desired result.