How to use the speaker crossover component calculator
- Choose the filter type: first order, second order Butterworth or second order Linkwitz-Riley.
- Enter the crossover frequency and the nominal impedance of the woofer and the tweeter.
- Read the coil and capacitor for the woofer low-pass section and for the tweeter high-pass section.
- Check the parts list and the steps, then compare the values with parts you can buy.
Formula
w = 2 x pi x crossover frequency
First order: low-pass coil L = R / w; high-pass capacitor C = 1 / (w R)
Second order: L = R / (w Q) and C = Q / (w R)
Q = 0.7071 for Butterworth and Q = 0.5 for Linkwitz-Riley
R is the impedance of the driver the part feeds. Butterworth sections are 3 dB down at the crossover frequency, while Linkwitz-Riley sections are 6 dB down, so with one driver wired in reverse polarity two ideal sections sum flat.
A 3 kHz split for 8 ohm drivers
A second order Butterworth crossover at 3,000 Hz with 8 ohm drivers needs a 0.6002 mH coil and a 4.6891 uF capacitor for each section: the woofer gets a series coil with a capacitor across it, and the tweeter gets a series capacitor with a coil across it.
The Linkwitz-Riley version needs 0.84883 mH and 3.3157 uF. A first order split at 2,500 Hz with a 6 ohm woofer and a 4 ohm tweeter needs a 0.38197 mH coil for the woofer and a 15.915 uF capacitor for the tweeter.
First order or second order
A first order filter uses a single part, rolls off at 6 dB per octave and keeps the phase simple, but the drivers must handle a wide overlap. A second order filter rolls off at 12 dB per octave and protects a tweeter better. Linkwitz-Riley is popular because the two outputs sum to a flat level at the crossover frequency; second order sections are 180 degrees apart in phase, so one driver is usually wired in reverse polarity.
The resonance and impedance of the parts can be explored with the RLC impedance and resonance calculator. For converting a gain or loss in decibels use the decibel calculator, and for a box that suits the woofer see the sealed speaker box calculator.
Why measured drivers differ
A real driver is not a resistor. The impedance of a woofer rises with frequency as its voice coil adds inductance, and a tweeter has a resonance dip. The values here assume a flat resistive load, so they are a first draft. Builders refine them by measuring the impedance and the response in the enclosure.
Assumptions and limits
- Each driver is treated as a pure resistor equal to its nominal impedance.
- The sections are passive, with the low-pass filter on the woofer and the high-pass filter on the tweeter, and no baffle step or level matching network.
- Capacitor and coil values are theoretical and must be matched to parts you can buy, with suitable ratings.
- The crossover frequency must be between 20 and 20,000 Hz.
Frequently asked questions
How do I calculate crossover capacitor and inductor values?
For a second order Butterworth filter, C = 0.7071 / (2 x pi x f x R) and L = R / (2 x pi x f x 0.7071). At 3 kHz and 8 ohms that is 4.689 uF and 0.600 mH.
What is the difference between Butterworth and Linkwitz-Riley?
Butterworth is flat in its own passband and is 3 dB down at the crossover. Linkwitz-Riley is 6 dB down there, so the two outputs sum to a flat level when one driver is wired in reverse polarity.
Can I use different impedances for the woofer and tweeter?
Yes. Each part is calculated from the impedance of the driver it sits with, so the two sections can have different values.
Do I need a third order or higher filter?
Not always. Higher orders protect the drivers better and cut the overlap, but they use more parts and add phase shift. Start with the order that suits the drivers you have.