Passive Crossover Calculator
Capacitor and inductor values for a first or second order passive crossover, from the crossover frequency and the driver impedances.
Results
Capacitor, first order high-pass
7.9577
µF
Inductor, first order low-pass
0.5093
mH
Capacitor, second order high-pass
5.6270
µF
Inductor, second order low-pass
0.7203
mH
Capacitor in the low-pass leg
5.6270
µF
Inductor in the high-pass leg
0.7203
mH
First order slope
6.0
dB/oct
Second order slope
12.0
dB/oct
Wavelength at that frequency
13.72
cm
One octave below
1250.0
Hz
What this tool does
A passive crossover is one capacitor and one inductor doing arithmetic with frequency: the capacitor passes what is above, the inductor passes what is below, and where they cross is set by the impedance they work into. The values here are for a nominal resistive load. **A real driver is not a resistor** — its impedance rises at resonance and with frequency, so these are a starting point to be measured and adjusted, not a finished design.
Formula
1st order: C = 1 ÷ (2π f Z), L = Z ÷ (2π f) · 2nd order Butterworth: C = 1 ÷ (2√2 π f Z), L = √2 Z ÷ (2π f)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
fc | Crossover frequency | Hz |
zw | Woofer impedance | Ω |
zt | Tweeter impedance | Ω |
C1 | Capacitor, first order high-pass | µF |
L1 | Inductor, first order low-pass | mH |
C2 | Capacitor, second order high-pass | µF |
L2 | Inductor, second order low-pass | mH |
CL | Capacitor in the low-pass leg | µF |
LH | Inductor in the high-pass leg | mH |
SL | First order slope | dB/oct |
S2 | Second order slope | dB/oct |
WL | Wavelength at that frequency | cm |
OC | One octave below | Hz |
Worked example
- Crossover frequency2500 Hz
- Woofer impedance8 Ω
- Tweeter impedance8 Ω
- Capacitor, first order high-pass7.9577 µF
- Inductor, first order low-pass0.5093 mH
- Capacitor, second order high-pass5.6270 µF
- Inductor, second order low-pass0.7203 mH
- Capacitor in the low-pass leg5.6270 µF
- Inductor in the high-pass leg0.7203 mH
- First order slope6.0 dB/oct
- Second order slope12.0 dB/oct
- Wavelength at that frequency13.72 cm
- One octave below1250.0 Hz
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.