crossover filter calculator

What is a crossover filter?

A crossover filter splits audio into frequency bands so each speaker driver handles only the range it is built for. In a typical 2-way speaker, the woofer gets low frequencies and the tweeter gets high frequencies. This improves clarity, reduces distortion, and protects the tweeter from damaging low-frequency energy.

How this calculator works

This calculator uses ideal textbook formulas for passive crossover design. You provide crossover frequency and nominal impedance, then it computes capacitor and inductor values.

1st order (6 dB/octave)

• High-pass (tweeter): one series capacitor
• Low-pass (woofer): one series inductor
• Simple design with gentle slope and fewer parts

Formulas:
C = 1 / (2πfZ)
L = Z / (2πf)

2nd order Butterworth (12 dB/octave)

• High-pass (tweeter): series capacitor + shunt inductor
• Low-pass (woofer): series inductor + shunt capacitor
• Steeper slope than 1st order and better band isolation

This page uses ideal Butterworth coefficients for a classic 2nd-order passive section. Real-world values often need tuning based on measured driver behavior.

Practical design tips

1) Start with measured driver data

Nominal impedance (like 4Ω or 8Ω) is only an average. Real drivers have impedance peaks and dips across frequency. For accurate crossover work, use measured impedance and frequency response files.

2) Choose component quality wisely

• Use air-core inductors for low distortion when possible.
• Use film capacitors in the tweeter path for better stability and lower loss.
• Check component tolerance (5% or tighter is usually preferable).

3) Verify power handling

Crossover parts dissipate heat. Confirm wire gauge, resistor wattage (if using padding networks), and overall thermal margin.

4) Expect fine tuning

Even excellent first-pass calculations usually need adjustments after listening tests and measurements. Baffle effects, driver spacing, and polarity all affect final performance.

Passive vs active crossover filters

A passive crossover sits between amplifier and drivers. It is simple and requires no extra amplifier channels, but it depends heavily on changing speaker impedance. An active crossover works at line level before power amplification and gives far more control (slope, delay, EQ), often producing better precision in advanced systems.

Frequently asked questions

What crossover frequency should I choose?

Select a point where the woofer still has smooth output and the tweeter can operate safely with low distortion. Common ranges for 2-way speakers are around 1.8 kHz to 3.5 kHz depending on driver size and design goals.

Are these values exact?

They are mathematically correct for ideal conditions. Real loudspeakers are not ideal, so treat these results as a strong starting point, then validate with measurement software and listening tests.

Do I need polarity inversion?

Some crossover alignments and physical driver offsets benefit from reversing one driver's polarity. Verify summation around crossover frequency using measurements.