Order	Slope	Components	Phase	Character
1st	6 dB/oct	1 each	90°	Gentle, wide overlap
2nd	12 dB/oct	2 each	180°	Common, good isolation
3rd	18 dB/oct	3 each	270°	Better isolation
4th	24 dB/oct	4 each	360°	Steep, excellent isolation

Crossover Frequency Calculator

Last updated: October 12, 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 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 works like this:

ω = 2π × 3000 ≈ 18,850 rad/s
First-order values: L = 8/18,850 ≈ 0.42 mH; C = 1/(18,850 × 8) ≈ 6.63 µF
2nd-order Butterworth (Q = 0.707): divide both by Q → L ≈ 0.60 mH, C ≈ 9.38 µF
Low-pass (woofer): series 0.60 mH inductor + shunt 9.38 µF capacitor
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 air-core; 9.38 µF → 9.4 µF or 10 µF film cap) — 5–10% tolerance is normal and shifts Fc only slightly.

2nd-order crossover topology. Suggested alt text: "Schematic diagram of a second-order passive speaker crossover"

How to Use the Crossover Calculator

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

Reading Your Result: What the Values Mean

Each result is one part of the filter network — buy and wire all of them. This table decodes the output:

Result	What it is	What to buy
LP inductor (mH)	Series coil rolling off highs to the woofer	Air-core inductor, nearest mH value, rated above your amp's current
LP capacitor (µF)	Shunt cap completing the low-pass	Film/foil capacitor (cheap electrolytics don't belong in the signal path)
HP capacitor (µF)	Series cap blocking lows from the tweeter	Film capacitor — this one directly shapes treble clarity
HP inductor (mH)	Shunt coil completing the high-pass	Air-core inductor, same current care as LP
Phase shift	90° per order per section	2nd order = 180° → reverse tweeter polarity

Which Alignment Should You Choose?

The alignment (Q factor) decides the filter's character — this is the choice most calculator pages gloss over.

Alignment	Q	Character	Choose it when…
Butterworth	0.707	Maximally flat passband, −3 dB at Fc	You want the flattest response; PA and general hi-fi default
Linkwitz-Riley	0.5	−6 dB at Fc, drivers sum flat and in-phase	Building studio monitors or MTM designs — the modern audiophile default
Bessel	0.577	Linear phase, best transient response, gentle knee	Transient purity matters more than flat amplitude (niche, purist builds)

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)

A 2nd-order filter rotates phase 180°, so the tweeter's output arrives 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 a fresh build sounds hollow in the midrange, reversed tweeter polarity is suspect number one.

Tweeter polarity and the crossover null. Suggested alt text: "Graph showing crossover response null fixed by reversing tweeter polarity"

LR2 vs LR4: Specify the Order

"Linkwitz-Riley" alone doesn't tell you the slope. LR2 is the 12 dB/octave version; LR4 is the 24 dB/octave version — and the one most people mean when they say "Linkwitz-Riley." Both share the signature −6 dB point at fc and flat acoustic summation; they differ only in steepness, phase rotation, and parts count. When following a design or forum advice, confirm which one is meant.

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 calculator 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 when possible.

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

Crossover Orders Compared

Order	Slope	Strengths	Costs
1st	6 dB/oct	Phase-coherent, simplest, cheapest	Poor driver protection; tweeter sees lots of low-frequency energy
2nd	12 dB/oct	The sweet spot: good protection, manageable phase	180° flip needs tweeter reversal
3rd	18 dB/oct	Strong protection, asymmetric option	Complex; 270° shift complicates phasing
4th	24 dB/oct	Brick-wall separation, LR stays in phase	Most parts, most cost, group-delay artifacts

Frequently Asked Questions

To calculate crossover capacitor and inductor values, use L = R ÷ (2πf) henries and C = 1 ÷ (2πfR) farads for first order, then convert to mH and µF. At 3000 Hz into 8 Ω that gives 0.42 mH and 6.63 µF. Higher orders cascade these sections and scale by the alignment's Q factor — or enter your numbers in the calculator above and read the results.

The safe crossover frequency for most 1" dome tweeters is 2500–3500 Hz with a 2nd-order (12 dB/oct) high-pass. Never cross below roughly twice the tweeter's resonant frequency (Fs). Smaller tweeters and 1st-order slopes need higher points. When in doubt, cross higher — a tweeter playing too low distorts and fails early.

It depends on your priority. Butterworth (Q=0.707) gives the flattest individual response; Linkwitz-Riley (Q=0.5) gives flat summed response with drivers in phase — the modern default for studio monitors and serious DIY. Choose Butterworth for simplicity and PA; Linkwitz-Riley when imaging and flat summing matter most.

You reverse the tweeter's polarity because a 2nd-order filter shifts phase 180°, putting tweeter and woofer out of phase at the crossover point — they'd cancel and carve a deep null. Reversing the tweeter's +/− wires restores in-phase summing. It's standard practice, not a hack; 4th-order Linkwitz-Riley needs no reversal.

Use 2nd order (12 dB/oct) for most 2-way builds: solid driver protection without the parts count and phase headaches of higher orders. Use 1st order only with robust drivers crossed high; 4th order when you need brick-wall separation and can afford the complexity.

Yes, often for the woofer: a driver's impedance rises with frequency due to voice-coil inductance, which skews textbook filter values. A Zobel (resistor + capacitor in series, shunted across the driver) flattens it back toward nominal. Size it with the Zobel network calculator.

Yes, but only non-polarized (bipolar) types — and film capacitors (polypropylene) are the better choice for everything in the signal path. Electrolytics are cheap, but they drift with age and sound worse in the tweeter path. Save them for shunt positions in budget woofer sections only.

Your DIY crossover sounds wrong most often because of three suspects: tweeter polarity not reversed (hollow midrange null), real driver impedance differing from the nominal value used in the math (shifts Fc), or parts wired to the wrong driver. Verify polarity first, then measure or estimate actual impedance — textbook values assume a perfect resistor.

Online crossover calculators are exact for ideal components and resistive loads — excellent starting values. Real builds deviate because of parts tolerance (5–10%) and drivers' non-flat impedance curves. Treat results as precision starting points, then verify by ear or measurement and tweak.

Q factor describes the filter's shape at the crossover point: Q=0.707 (Butterworth) is maximally flat, Q=0.5 (Linkwitz-Riley) sums flat in phase, Q=0.577 (Bessel) preserves transient shape best. Higher Q means a peakier knee; lower Q means a gentler, more gradual transition.

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

Speaker Tools