Crossover Frequency & Slope Calculator
Design 2-way and 3-way passive speaker crossovers. Pick the slope (6, 12, or 18 dB/oct), the alignment (Butterworth, Linkwitz-Riley, Bessel), and the driver impedance — the tool computes every L and C, picks the driver polarity that flattens the summed response, and plots the actual simulated network response (not just the ideal curves).
Input
Result
Choosing a Slope & Alignment
A passive crossover splits the audio signal into bands so each driver only sees the frequencies it's good at. Two design choices dominate: the slope (how fast each filter rolls off, in dB per octave) and the alignment (the mathematical filter response that defines exactly what happens at and around the crossover frequency).
Slopes
6 dB/oct (1st order) — the gentlest slope. One inductor for the woofer, one capacitor for the tweeter. Cheap, simple, and has zero phase shift at the crossover, but the drivers overlap broadly so both reproduce a wide region together. Demands well-behaved drivers without nasty out-of-band breakup.
12 dB/oct (2nd order) — the standard "good enough" slope. Sharper rolloff means less driver overlap, less out-of-band stress, and looser driver requirements. The trade-off is a 180° phase shift at the crossover, which is why 2nd-order crossovers usually wire one driver with reversed polarity to flatten the summed response.
18 dB/oct (3rd order) — sharper still. Very little overlap; ideal when you need to keep a tweeter well above its resonance, or protect a small driver from low frequencies. Wires up with normal polarity for both drivers (Butterworth 3rd-order sums flat in magnitude). Component count and cost go up.
24 dB/oct (4th order) is not offered here. Fourth-order passive crossovers are technically possible but rare in well-designed loudspeakers — the singly-terminated 4th-order ladder is extremely sensitive to component tolerances and driver-impedance variation. When 24 dB/oct is needed, the standard solution is an active Linkwitz-Riley crossover built from cascaded op-amp Sallen-Key sections (which is well covered by our other filter calculators).
Alignments at 12 dB/oct
Butterworth (Q = 0.707) — maximally flat amplitude. Each driver is −3 dB at the crossover; the sum has a +3 dB bump there. The classic choice when you want flat response in the passband.
Linkwitz-Riley (Q = 0.5) — the audiophile favourite. Each driver is −6 dB at the crossover; the sum is perfectly flat (0 dB) when one driver is wired with reversed polarity. The trade-off is the −6 dB acoustic crossover means more driver overlap.
Bessel (Q ≈ 0.577) — between the two. Most natural transient response (linear phase), favoured in studio monitors. Drivers are about −4.8 dB at the crossover and the sum is close to flat (within a dB) at fc.
Why polarity matters
Filters introduce phase shift. When two drivers overlap, they can add (in phase) or cancel (out of phase). The tool automatically picks the polarity combination — normal or inverted — that gives the flattest combined response at the crossover frequency. For most 12 dB/oct designs that means inverting one driver; for 6 dB/oct and 18 dB/oct Butterworth, both drivers stay normal.
Driver impedance — the lie that's mostly fine
These formulas assume the driver looks like a constant resistance R across the whole band. In reality drivers have a resonant rise around their free-air resonance, a mostly-resistive midband, and a voice-coil inductance rise at the top. The calculator's output is the ideal starting point — for a finished design you'd add a Zobel network on the woofer (to flatten its high-frequency impedance rise) and possibly an L-pad to attenuate a too-loud tweeter. Always measure the in-box response.