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Passive Crossovers
Formulas & Calculators

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  • Capacitor and Coil Calculator
  • Narrow Band Pass Calculator
  • Zobel Calculator



    • Capacitor and Coil Calculator line

    Use these formulas to calculate for first, second, and third order low pass, high pass, and band pass filters. Do not use these for narrow band pass filter calculations.
    Before clicking for the crossover component values, enter the impedance level and the desired crossover frequency. Values should be rounded off to the nearest hundredth.

    If you need a 16 mHy coil, you can series a 12.8 mHy coil and a 3.2 mHy coil. If you need a 70 µfd capacitor, you can parallel two 35 µfd capacitors.When the exact value of a coil or capacitor is not available, you can substitute values of ± 5%.

     

    Impedance

    Ohms    		 Crossover
    Frequency

    Hertz (Hz)






    1st Order (6 dB per Octave) (diagrams) line
    L1 (mHy) = (1000 x Impedance) / (6.283 x Crossover Frequency)
         		 Coil - L1  

    Millihenries (mHy)
    C1 (µfd) = 1,000,000 / (6.283 x Impedance x Crossover Frequency)
         		 Capacitor - C1  

    Microfarads (µfd)

    2nd Order (12 dB per Octave) (diagrams) line
    L2 = L1 x 1.414 Coil - L2  

    Millihenries (mHy)
    C2 = C1 x .707 Capacitor - C2  

    Microfarads (µfd)

    3rd Order (18 dB per Octave) (diagrams) line
    L3 = L1 x 1.5 Coil - L3  

    Millihenries (mHy)
    C3 = C1 x .1.33 Capacitor - C3  

    Microfarads (µfd)
    L4 = L1 x .5 Coil - L4  

    Millihenries (mHy)
    C4 = C1 x .667 Capacitor - C4  

    Microfarads (µfd)
    L5 = L1 x .75 Coil - L5  

    Millihenries (mHy)
    C5 = C1 x 2 Capacitor - C5  

    Microfarads (µfd)

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    Narrow Band Pass Filter Calculator line

    Use these formulas to calculate values for Narrow Band Pass filters only! These are completely different formulas than the ones used above, and should only be used when the low pass frequency is less than 20 times the high pass frequency. Remember, the low pass frequency (F2) is higher than the high pass frequency (F1).
    Before clicking for the crossover component values, enter the net impedance level and the desired crossover frequencies. Values should be rounded off to the nearest hundredth.

    If you need a 15 mHy coil, you can series a 12.8 mHy coil and a 3.2 mHy coil. If you need a 70 µfd capacitor, you can parallel two 35 µfd capacitors.When the exact value of a coil or capacitor is not available, you can substitute values of ± 5%.

     
    Net
    Impedance

    Ohms    		 High Pass
    Frequency

    Hertz (Hz)    		 Low Pass
    Frequency

    Hertz (Hz)
     

     
     

     

    1st Order (6 dB per Octave) Narrow Band Pass (diagram) line Formulas for first order only, calculate for L1 first, then C1.
    L1 = Net Impedance / [(F2 - F1) x 6.283] x 1,000 = L1 in (mHy) Coil - L1  

    Millihenries (mHy)
    C1 = 1 / (39.472 x [L1/1000] x [F1 x F2]) x 1,000,000 = C1 in (µfd) Capacitor - C1  

    Microfarads (µfd)

    2nd Order (12 dB per Octave) Narrow Band Pass (diagram) line Formulas for second order only, calculate for C1 first, then L2, C2, L1.
    L1 = 1 / (39.472 x C1 x [F1 x F2]) x 1,000 = L1 in (mHy) Coil - L1  

    Millihenries (mHy)
    C1 = .707 / (Net Impedance x 6.283 x [F2 - F1]) x 1,000,000 = C1 in (µfd) Capacitor - C1  

    Microfarads (µfd)
    L2 = 1 / (C1 x [6.283 x (F2 - F1)]2) x 1,000 = L2 in (mHy) Coil - L2  

    Millihenries (mHy)
    C2 = 1 / (39.472 x L2 x [F1 x F2]) x 1,000,000 = C2 in (µfd) Capacitor - C2  

    Microfarads (µfd)

    3rd Order (18 dB per Octave) Narrow Band Pass (diagram) line Formulas for third order only, calaculate for L3 first, then C2, C3, L2, L1, C1.
    L1 = 1 / (.499849 x [6.283 x (F2 - F1)]2 x C2) x 1,000 = L1 in (mHy) Coil - L1  

    Millihenries (mHy)
    C1 = 1 / (39.472 x [F1 x F2] x L1) x 1,000,000 = C1 in (µfd) Capacitor - C1  

    Microfarads (µfd)
    L2 = 1 / (39.472 x [F1 x F2] x C2) x 1,000 = L2 in (mHy) Coil - L2  

    Millihenries (mHy)
    C2 = 1 / (1.4884 x [6.283 x (F1 - F2)]2 x L3 x 1,000,000 = C2 in (µfd) Capacitor - C2  

    Microfarads (µfd)
    L3 = (.5 x Net Impedance) / (6.283 x [F2 - F1]) x 1,000 = L3 in (mHy) Coil - L3  

    Millihenries (mHy)
    C3 = 1 / (39.472 x [F1 x F2] x L3) x 1,000,000 = C3 in (µfd) Capacitor - C3  

    Microfarads (µfd)

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    Zobel Calculator line

    Use these formulas to calculate values of a capacitor and a resistor needed to construct a Zobel.
    Before clicking for the capacitor and resistor values, enter the nominal impedance of the speaker and the frequency where the impedance has doubled. Capacitor values should be rounded off to the nearest hundredth.

    If you need an 8 omh resistor, you can series two 4 ohm resistors. If you need a 3 µfd capacitor, you can parallel two 1.5 µfd capacitors. When the exact value of a capacitor is not available, you can substitute values of ± 5%.

     

    Nominal
    Impedance

    Ohms    		 Frequency
    Impedance
    Doubles

    Hertz (Hz)
     
     

     
     
     

     

    Zobel (diagram) line
    C (µfd) = 1,000,000 / (6.283 x Impedance x Frequency Impedance Doubles)
         		 Capacitor - C  

    Microfarads (µfd)
    R = 1.25 x Nominal Impedance Resistor - R  

    Ohms

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