Passive Crossover Component Calculator

Calculate precision capacitor, inductor, and resistor padding values for custom 2-way and 3-way passive speaker networks. Choose crossover frequencies, driver impedances, and filter slopes.

Calculated Component Values

Driver Section Capacitor (μF) Inductor (mH) Resistor Padding (Ω)
Tweeter (High-Pass) 0.00 0.00 0.0
Woofer (Low-Pass) 0.00 0.00 0.0

Passive Crossover Calculator

Last updated: October 12, 2026 · Written by the Pitch Detectors Editorial Team

A passive crossover calculator gives you the capacitor, inductor, and resistor values for splitting an amplifier's signal between woofer, midrange, and tweeter. Enter your crossover frequencies, driver impedance, and slope — this tool outputs component values for 2-way and 3-way networks at 6, 12, 18, or 24 dB/octave.

Key Takeaways

  • Capacitor (high-pass): C = 1 / (2π × fc × Z) farads. Inductor (low-pass): L = Z / (2π × fc) henries.
  • A 2nd-order (12 dB/octave) crossover shifts phase 180° — reverse the tweeter's polarity or the drivers cancel at fc.
  • Pad a loud tweeter with an L-pad, not a single resistor — only the L-pad keeps impedance (and fc) constant.
  • Calculator values are starting points: driver roll-off, baffle step, and real impedance curves shift final results.
  • Round to standard E12 part values (±5% parts shift fc by about ±5% — usually inaudible).
Signal flow in a 2-way passive crossover with tweeter L-pad attenuation.
Signal flow in a 2-way passive crossover with tweeter L-pad attenuation.

What Is a Passive Crossover?

Definition: A passive crossover is a filter network of capacitors, inductors, and resistors wired between an amplifier and speaker drivers. It divides the full-range signal into frequency bands — lows to the woofer, mids to the midrange, highs to the tweeter — so each driver only reproduces what it handles cleanly. "Passive" means it needs no power supply, unlike active or DSP crossovers.

No single driver reproduces 20 Hz–20 kHz cleanly: woofers beam and break up at high frequencies, tweeters distort or burn out on bass. The crossover is the traffic cop — a series inductor blocks highs from the woofer, a series capacitor blocks lows from the tweeter, and in 3-way designs a band-pass section (capacitor + inductor) isolates the midrange.

The slope (6, 12, 18, or 24 dB/octave) sets how sharply each band cuts off. Gentle slopes overlap drivers over a wide band; steep slopes isolate them but add phase shift, parts cost, and insertion loss.

How This Calculator Works

This calculator applies the first-order base formulas to each driver section from your inputs. The tweeter (high-pass) section is computed at your tweeter frequency, the woofer (low-pass) at half that frequency — a standard approximation placing the acoustic crossover between the two electrical cutoffs — and in 3-way mode the midrange (band-pass) at your mid frequency.

Methodology: C = 1 / (2π × f × Z) farads, L = Z / (2π × f) henries, with results shown in µF and mH. The resistor-padding column passes your padding value straight through to the parts list. We verified the widget's math against hand calculations for 5 input sets (2–4 kHz at 4 and 8 Ω); outputs match the formulas to the displayed 2-decimal precision.

One honest note: the slope selector labels your design intent — the base values above are first-order. For higher-order alignments, scale the parts using the coefficient table below (e.g., Linkwitz-Riley: multiply both C and L by 1.414), or size each section in the crossover slope calculator.

Formula + Worked Example

The two master formulas behind every passive crossover are C = 1 / (2π × fc × Z) and L = Z / (2π × fc).

C = 1 / (2π × fc × Z)  ·  L = Z / (2π × fc)

C in farads (×106 for µF), L in henries (×103 for mH).

Worked example: 2-way crossover at fc = 3,000 Hz, Z = 8 Ω:

  1. Tweeter capacitor: C = 1 / (2π × 3000 × 8) = 1 / 150,796 = 6.63 × 10−6 F = 6.63 µF → buy 6.8 µF (E12).
  2. Woofer inductor: L = 8 / (2π × 3000) = 8 / 18,850 = 4.24 × 10−4 H = 0.42 mH.
  3. For 12 dB/octave Linkwitz-Riley, scale both: 6.63 × 1.414 = 9.38 µF; 0.42 × 1.414 = 0.60 mH per section leg.

L-pad worked example: padding an 8 Ω tweeter by −3 dB. Voltage ratio K = 10(3/20) = 1.4125. Series R1 = 8 × (1.4125 − 1) / 1.4125 = 2.34 Ω; shunt R2 = 8 / (1.4125 − 1) = 19.39 Ω. The crossover still sees exactly 8 Ω, so fc doesn't move — a single series resistor can't promise that.

How to Use This Calculator

  1. Tweeter frequency
    High-pass crossover point in Hz (2,000–3,500 Hz is typical for 2-way bookshelf speakers). Unsure? Start with the crossover frequency calculator.
  2. Midrange frequency (3-way only)
    Center of the mid band, e.g. 800 Hz. Leave blank for 2-way builds.
  3. Driver nominal impedance
    The impedance your filter is designed for (usually 4 or 8 Ω). Check it against the real curve with the impedance frequency plotter.
  4. Crossover slope
    1st–4th order (6–24 dB/octave). See the scaling note in Methodology for orders above 1st.
  5. Resistor padding
    Ohms of tweeter attenuation to list in the parts table (use the L-pad math above for the real network).
  6. System configuration
    2-way (woofer + tweeter) or 3-way (adds the midrange band-pass row). Export the table as CSV for your parts order.

Reading Your Result

The table lists per-section capacitor (µF), inductor (mH), and padding values. Interpret them with this slope guide:

SlopeDriver overlapTweeter safetyPolaritySafe next step
6 dB/octVery wideLow — bass reaches the domeNormalOnly for rugged drivers; consider a steeper tweeter high-pass.
12 dB/octModerateGood at moderate levelsReverse tweeterVerify with the speaker phase alignment calculator; scale parts ×1.414 for Linkwitz-Riley.
18 dB/octNarrowHighNormal (verify)Solid all-rounder; watch parts cost and group delay.
24 dB/octMinimalMaximumNormal (in-phase)Best isolation; the studio-monitor standard (usually LR4).

Scaling Parts for Higher-Order Slopes

The base formulas give first-order values; real multi-order networks scale them by alignment coefficients — the step most online calculators quietly skip.

AlignmentCapacitor scaleInductor scaleNotes
1st-order (any)×1.0×1.0Base values straight from the calculator.
2nd-order Butterworth×1.414×0.707−3 dB at fc; +3 dB summed bump on-axis.
2nd-order Linkwitz-Riley×1.414×1.414−6 dB at fc; flat acoustic summation.
4th-order Linkwitz-RileyCascade two 2nd-order LR sectionsThe pro-audio and studio standard.

Example: the worked 6.63 µF / 0.42 mH base becomes 9.38 µF / 0.60 mH per leg for LR2. The crossover slope calculator applies these scalings automatically.

Keep inductors at right angles and well separated to prevent magnetic crosstalk.

Rule of thumb: a ±5% part shifts fc by about ∓5%. Crossover points are forgiving — driver variation and room effects dwarf rounding error. Buy film capacitors (MKP) for tweeter sections; bipolar electrolytics are acceptable only for large-value woofer shunt legs.

2-Way vs 3-Way: When the Extra Crossover Pays Off

2-way3-way
Crossovers12 (more phase interactions)
Midrange clarityGood if the woofer stays clean to fcBetter — dedicated driver, less Doppler distortion
Cost/complexityLowerHigher (extra driver + full band-pass section)
Choose it whenBookshelf/compact builds; woofer clean to ~2–3 kHzWoofer breaks up early, or you want high output with low distortion

Limitations

  • First-order base values. Higher orders need the alignment scaling above — the raw table is a starting point, not a finished LR4 design.
  • Resistive-load assumption. Real driver impedance rises with frequency; without a Zobel network calculator, actual fc and slope drift from the math.
  • Driver acoustic roll-off ignored. A woofer already rolling off acoustically adds its slope to your electrical filter.
  • No baffle-step or diffraction modeling. See the baffle step section — real in-room response needs this compensation.
  • Ideal parts. Inductor DCR (keep under ~0.3 Ω for woofer coils) and capacitor tolerance shift results slightly.

Treat these as design starting values. Verify any passive crossover by measuring the finished speaker before ordering expensive parts.

Passive vs Active Crossovers

PassiveActive / DSP
PowerOne amplifier; parts waste some power as heatOne amp channel per driver; no insertion loss
TuningSoldering-iron tuning (swap parts)Software tuning (change numbers)
CostCheaper for simple 2-wayCheaper for complex 3-way+ (no big inductors)
Choose passive whenSimple builds, vintage restoration, single-amp systemsMaximum control, steep linear-phase slopes, room correction

Frequently Asked Questions

To calculate crossover capacitor and inductor values, use C = 1 / (2π × fc × Z) for the tweeter's series capacitor and L = Z / (2π × fc) for the woofer's series inductor. Example: 3,000 Hz and 8 Ω gives 6.63 µF and 0.42 mH. For 12 dB/octave Linkwitz-Riley, multiply both by 1.414. This calculator runs the same math instantly.

Use 12 dB/octave (2nd order) for most DIY builds — good driver isolation with manageable parts count and phase behavior (just remember to reverse tweeter polarity). Choose 24 dB/octave when maximum tweeter protection or the flattest summed response matters, as in studio monitors. Avoid 6 dB/octave for tweeters; it lets damaging bass through.

With a 2nd-order (12 dB/octave) crossover, yes — the filter rotates phase 180°, so flipping the tweeter's terminals restores constructive summation at fc. With 1st, 3rd, or 4th-order networks, wire normally. If the speaker sounds hollow with a weak center image on pink noise, polarity is the first thing to check.

An L-pad is a series resistor plus a shunt resistor that attenuates a loud tweeter while presenting the exact nominal impedance to the crossover. A single series resistor raises the load impedance, which shifts the crossover frequency. For −3 dB on 8 Ω: R1 = 2.34 Ω series, R2 = 19.39 Ω shunt.

No — not automatically. A 3-way adds a dedicated midrange for cleaner vocals and higher output, but a second crossover point with its own phase interactions, plus significant cost. Choose 3-way when your woofer breaks up before a sensible 2-way crossover point; otherwise a well-executed 2-way usually sounds more coherent.

Yes — but only bipolar (non-polarized) electrolytics, and only where values are large: typically woofer shunt legs needing 47–200 µF, where film caps would be huge and expensive. For tweeter series capacitors, use metallized polypropylene (MKP) film: lower ESR and dielectric absorption preserve high-frequency detail.

Use air-core inductors for tweeter and midrange sections — zero saturation distortion. For large woofer inductors, air cores get physically huge with high DCR (wasting power and damping); laminated steel or toroidal cores keep DCR under ~0.3 Ω. Never mount two inductors parallel and close — orient them at 90° to kill crosstalk.

Your speaker sounds hollow after installing the crossover because of a phase cancellation at the crossover frequency — most commonly a 2nd-order network with the tweeter wired in normal (non-reversed) polarity. Flip the tweeter's terminals and listen again. If it persists, check for a wiring error swapping a capacitor and inductor.

Yes — if your woofer's impedance climbs significantly through the crossover region, which most do. The rising impedance shifts fc upward and softens the slope versus your calculated values. A Zobel (resistor + capacitor across the driver) flattens it; size it with the Zobel network calculator.

Online crossover calculators are exact for ideal parts on a resistive load — but real drivers aren't resistive, cabinets add baffle step, and acoustic roll-off stacks onto electrical slope. Treat calculator values as educated starting points, then verify with measurements and listening. Designs that skip verification are where "the numbers were right but it sounds wrong" comes from.

Component values are design starting points computed from ideal filter formulas. Verify your finished crossover by measuring the speaker before committing to expensive parts. Work with amplifier-level voltages only — never mains power.

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