Crossover Frequency Calculator

Last updated: October 31, 2026 · Written by the Pitch Detectors Editorial Team

A crossover frequency calculator gives you the inductor and capacitor values for passive speaker crossovers. Enter the crossover frequency, speaker impedance, filter order, and alignment — get exact low-pass (woofer) and high-pass (tweeter) component values instantly.

Key Takeaways

• A crossover splits audio so the woofer gets lows (low-pass) and the tweeter gets highs (high-pass).
• 1st order: L = R/ω, C = 1/(ωR); 2nd order scales both by the alignment's Q factor.
• Butterworth = flattest response; Linkwitz-Riley = in-phase summing (studio standard); Bessel = cleanest transients.
• 2nd-order filters flip polarity 180° — wire the tweeter reversed or accept a response null.
• Real drivers' impedance varies with frequency, so treat calculated values as starting points, not gospel.

What Is a Crossover Frequency Calculator?

A crossover frequency calculator computes the inductor (mH) and capacitor (µF) values needed to build a passive speaker crossover at a chosen frequency, impedance, filter order, and alignment. It answers the DIY speaker builder's core question: "what parts do I buy to split 3000 Hz between my woofer and tweeter?"

Passive crossovers sit between amplifier and drivers, dividing the signal with coils and caps — no power supply needed. This tool covers 2-way designs: a low-pass section protecting the woofer from highs, and a high-pass section protecting the tweeter from lows.

How This Calculator Works

The tool starts from textbook first-order formulas, then scales them for higher orders and your chosen alignment's Q factor. Inductors block highs (series for low-pass), capacitors block lows (series for high-pass) — the reactances equal the load impedance exactly at the crossover frequency.

Methodology: with ω = 2πf, first order uses L = R/ω (henries) and C = 1/(ωR) (farads), converted to mH/µF. Second order divides both by the alignment Q (Butterworth 0.707, Linkwitz-Riley 0.5, Bessel 0.577); higher orders cascade sections. The tool also reports the filter's phase shift. Validation method: enter 3000 Hz / 8 Ω / 1st order and confirm L ≈ 0.42 mH and C ≈ 6.63 µF — the closed-form check anyone can verify by hand.

Last reviewed: October 2026. Formulas follow standard passive filter theory.

Worked Example: 3000 Hz, 8 Ω, 2nd-Order Butterworth

Designing a 2-way with crossover at 3000 Hz into 8 Ω drivers:

1. ω = 2π × 3000 ≈ 18,850 rad/s
2. First-order values: L = 8/18,850 ≈ 0.42 mH; C = 1/(18,850 × 8) ≈ 6.63 µF
3. 2nd-order Butterworth (Q = 0.707): scale both by 1/Q → L ≈ 0.60 mH, C ≈ 9.38 µF
4. Low-pass (woofer): series 0.60 mH inductor + shunt 9.38 µF capacitor
5. High-pass (tweeter): series 9.38 µF capacitor + shunt 0.60 mH inductor — and reverse the tweeter's polarity (180° phase shift)

Buy the nearest standard values (0.60 mH → 0.60 mH air-core; 9.38 µF → 9.4 µF or 10 µF film cap) — 5–10% tolerance is normal and shifts Fc only slightly.

How to Use the Crossover Calculator

1. Crossover frequency: enter Hz — 2500–3500 Hz is typical for 2-ways with 1" tweeters.
2. Speaker impedance: select the driver's nominal Ω (4, 6, 8, or 16).
3. Crossover order: choose 1st (6 dB/oct) through 4th (24 dB/oct).
4. Crossover type: pick the 2nd-order alignment — Butterworth, Linkwitz-Riley, or Bessel.
5. Read both result boxes: low-pass L and C for the woofer, high-pass C and L for the tweeter, plus phase shift.
6. Buy standard values nearest the results; wire per the diagram, minding tweeter polarity.

Reading Your Result: What the Values Mean

Which Alignment Should You Choose?

The alignment (Q factor) decides the filter's character — this is the choice competitors gloss over:

Can't decide? Linkwitz-Riley 2nd or 4th order is the safest all-round choice — its in-phase summing avoids the response dip that plagues mismatched designs.

The 180° Phase Flip (and the One-Wire Fix)

Every 2nd-order filter shifts phase 90° per section — and with two sections (LP + HP) the tweeter ends up 180° out of phase with the woofer at the crossover point. In-phase drivers sum; out-of-phase drivers cancel, carving a deep null right where the two bands meet.

The fix is one wire: reverse the tweeter's +/− connections. This is standard practice in 2nd-order designs, not a hack — commercial speakers do it routinely. (4th-order Linkwitz-Riley stays in phase and needs no reversal; 1st and 3rd order shift 90°/270°, where the answer depends on driver offset.) If your fresh build sounds hollow in the midrange, reversed tweeter polarity is suspect number one.

Limitations

• Nominal impedance is a fiction. Real drivers' impedance swings with frequency (peaks at resonance, rises with voice-coil inductance) — textbook values assume a flat 8 Ω that doesn't exist. Consider a Zobel network to flatten it.
• Parts have tolerance. 5–10% tolerance on caps and coils shifts Fc noticeably; buy 5% film caps for the tweeter path at minimum.
• 2nd-order values scale by alignment Q in this tool — verify critical builds against a crossover design reference or measurement before ordering expensive parts.
• No baffle-step or diffraction compensation. Real designs add level correction the textbook math omits — measure the finished speaker if you can.

Safety: passive crossover parts are low-voltage, but always disconnect the amplifier before wiring, and keep soldering irons away from flammable materials.

Crossover Orders Compared

Frequently Asked Questions

Related tools: passive crossover calculator for full networks, crossover slope calculator, Zobel network calculator for impedance flattening, impedance calculator, and impedance frequency plotter to see real curves.