Crossover Frequency Calculator — Speaker Crossover Design

Formula

How this is calculated

A passive crossover uses inductors (coils) and capacitors to route different frequency bands to the correct driver. An inductor acts as a low-pass filter: it passes low frequencies to the woofer and blocks high ones. A capacitor acts as a high-pass filter: it blocks low frequencies and lets highs through to the tweeter. The crossover frequency fc is where each filter is 3 dB down — both drivers share the load equally at that exact frequency.

For a first-order (6 dB/octave) crossover, each section needs just one component: a series inductor L = Z/(2πfc) for the woofer, and a series capacitor C = 1/(2πfc·Z) for the tweeter, where Z is the nominal speaker impedance (commonly 4, 6, or 8 Ω). First-order crossovers sum flat at the crossover point with correct polarity and are simple to build, but their gradual roll-off means both drivers reproduce a wide overlap band.

A second-order Butterworth crossover (12 dB/octave) uses two components per section and attenuates the stopped band much more steeply, reducing driver overlap and improving power handling for the tweeter. The Butterworth alignment (Q = 1/√2) gives a maximally flat response without peaking. This calculator gives component values for the standard series-first topology; adjust for shunt-first or higher-order alignments (Linkwitz-Riley 4th order, Bessel) as needed. Real-world values should be rounded to the nearest standard (E12/E24) series inductor or capacitor.