Passive Crossover Calculator
Compute inductor and capacitor values for 1st and 2nd-order low-pass and high-pass crossovers, with response curves.
Inputs
Schematic
How it works
A passive crossover splits the amplifier signal into a low band for the woofer or sub and a high band for the mains, using coils (inductors) and capacitors. Inductors pass low frequencies and resist high ones; capacitors do the opposite.
1st order: L = Z / ω C = 1 / (ω · Z)
2nd order: L = Z / (Q · ω) C = Q / (ω · Z)
ω = 2π·fc, Z = speaker impedance
Q: Butterworth 0.707 · Linkwitz-Riley 0.5 · Bessel 0.577The low-pass has a series inductor and a shunt capacitor across the speaker; the high-pass swaps them: a series capacitor and a shunt inductor. The Q sets the shape of the knee. Higher Q gives a sharper corner but a peak; lower Q gives a smoother, more damped one.
Practical advice: passive crossover parts for subwoofer frequencies are huge and costly (tens of millihenries, hundreds of microfarads) and waste power in the coil’s resistance. In car and home audio, subwoofers almost always use an active crossover (a 24 dB/oct Linkwitz-Riley filter) ahead of the amplifier. These formulas are still great for the high-pass side that protects small speakers from bass, or for passive mid/tweeter designs. They assume a purely resistive load: real drivers have inductance and resonance peaks, which shift the actual crossover point.