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How to select capacitors for crossovers

Updated July 20, 2017

Choosing the right components when building an audio system can have a great impact on the performance of the system. It’s not enough that you have a high-end audio player that sends a crystal-clear signal to the speakers if the speakers don’t know how to play it properly. High-performance audio systems use crossovers to separate the frequencies that go to each speaker, ensuring that every speaker receives only the frequencies it can handle. Capacitors are the simplest form of high-frequency crossovers because they filter out sounds below a certain frequency, called the crossover frequency.

Check the speaker’s specifications sheet to find out the recommended frequency range for the speaker. The crossover will have to eliminate any frequency below the minimum of the speaker’s frequency range, so that minimum frequency will be your crossover frequency.

Go to the Basic Car Audio Electronics site (see References) and scroll down to the online calculator.

Type your speaker’s impedance in the “High Frequency Impedance” field.

Leave the “Low Frequency Impedance” field empty, as it is used to calculate the value coils used for low-pass filters.

Insert the crossover frequency in the “Crossover Frequency” field and click on “Go Figure.” The value for the capacitor you need will be displayed in the calculator.

Tip

If the resulted value of the required capacitor exceeds the minimum or maximum value of available capacitors, you can combine multiple capacitors in a series or parallel connection to obtain the proper value. A series connection will divide the total value by the number of capacitors of the same value connected together. A parallel connection will result an output equal to the sum of the values of the connected capacitors. You can also calculate the value for the capacitor manually by using the following mathematical formula: 1 / (2_Pi_crossover frequency*impedance). The result will be the value of the capacitor you need in Farads. To convert the value to microfarads, the default measuring unit for capacitors, multiply the value in Farads by 1,000,000.

Warning

Always use non-polar capacitors for audio crossovers. Polarised capacitors are not suitable for any audio application. The voltage rating of the capacitor is also important. A capacitor with a voltage rating of 100 Volts should be enough for a system of up to 2500 Watts in 4 Ohms. However, it’s better to choose a capacitor with a higher rated power than the required power instead of one with a lower power.

Things You'll Need

  • Speaker specifications sheet
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About the Author

Vladimir Khavkine has been writing since 1971. He has written for various online publications. Khavkine has a Doctor of Philosophy degree in mathematics and physics from the USSR Academy of Sciences.