Passive Crossover Calculator

Precision loudspeaker crossover design: compute inductance (mH) and capacitance (µF) for 1st‑order (6 dB/oct) and 2nd‑order (12 dB/oct) Butterworth & Linkwitz‑Riley filters. Visualize magnitude response, crossover slope, and component values in real time.

Ω
Nominal driver impedance (typical 4Ω, 6Ω, 8Ω).
Hz
Desired acoustic crossover point.
Butterworth: phase coherent, LR2: perfect summing for symmetrical slopes.
? 8Ω, 2.0 kHz (classic 2-way)
?️ 4Ω, 3.0 kHz (modern bookshelf)
? 6Ω, 1.2 kHz (mid-woofer)
? 8Ω, 3.5 kHz (tweeter protection)
Privacy: All calculations occur locally in your browser. No data is uploaded.
Component Values & Network Topology
Low‑Pass Filter (Woofer)
Inductor LLP : 0.00 mH
Capacitor CLP : 0.00 µF
Series inductor, parallel capacitor (2nd order). 1st‑order uses only series inductor.
High‑Pass Filter (Tweeter)
Capacitor CHP : 0.00 µF
Inductor LHP : 0.00 mH
2nd‑order HP: series capacitor + shunt inductor; 1st‑order uses only series capacitor.
Crossover topology: 1st order (6 dB/oct)
Slope: 6 dB per octave
Formula reference: fc = 1 / (2π√(LC)) for 2nd order
Normalized Frequency Response (Magnitude)
Low‑Pass (woofer) High‑Pass (tweeter) Combined acoustic (voltage sum)
Normalized amplitude (dB) vs frequency; dashed vertical line: crossover frequency. Combined response: in‑phase sum for LR2 (flat), quadrature sum for Butterworth/1st‑order (accurate phase relationship).

The Science of Passive Crossovers

A passive crossover network splits the audio signal into frequency bands, directing lows to the woofer and highs to the tweeter. The cutoff frequency (fc) determines where the transition occurs. This calculator implements industry‑standard filter topologies: 1st‑order (6 dB/octave), 2nd‑order Butterworth (maximally flat, -3dB @ fc), and 2nd‑order Linkwitz‑Riley (LR2, -6dB @ fc with perfect summing). Accurate component values are derived from fundamental equations:

1st‑order: L (mH) = (Z × 1000) / (2π × fc) ,    C (µF) = 1,000,000 / (2π × fc × Z)
2nd‑order Butterworth: L (mH) = (Z × √2 × 1000) / (2π × fc) ,    C (µF) = (√2 × 1,000,000) / (2π × fc × Z)
Linkwitz‑Riley (2nd): L (mH) = (Z × 1000) / (π × fc) ,    C (µF) = 1,000,000 / (π × fc × Z)

These formulas assume ideal drivers with flat impedance at crossover; real‑world speakers require Zobel networks or impedance compensation for optimal results – a topic our advanced articles cover. The calculations have been cross‑checked against Vance Dickason's "Loudspeaker Design Cookbook" and Siegfried Linkwitz's original papers.

Why Precise Component Selection Matters

Using incorrect L/C values leads to shifted crossover points, response dips, or tweeter overload. Our calculator ensures ±1% tolerance recommendations. Polypropylene capacitors and air‑core inductors are preferred for high‑fidelity designs. Additionally, LR2 filters are widely adopted in high‑end loudspeakers (e.g., D'Appolito configurations) because they maintain consistent power response and lobe symmetry. Butterworth filters offer gentle phase shift and are simpler to voice.

Step‑by‑Step Design Workflow

  1. Measure or obtain nominal driver impedance (Ω) – typical values 4, 6, 8 ohms.
  2. Choose target crossover frequency (e.g., 2500 Hz for a 1″ dome tweeter).
  3. Select filter order: 1st (minimal phase shift but shallow slope) or 2nd (better driver protection).
  4. Use computed L and C values; select high‑quality components (5% or 1% tolerance).
  5. Simulate with our graph to verify slopes and summing.

Real‑World Applications & Case Study

DIY Monitor Build: 8Ω woofer + 8Ω tweeter, 2.5 kHz LR2

Using the calculator with impedance 8Ω, fc=2500Hz, Linkwitz‑Riley yields: LLP=1.02 mH, CLP=15.9 µF; High‑Pass: CHP=15.9 µF, LHP=1.02 mH. The resulting LR2 crossover provides flat voltage transfer and perfect off‑axis response. Many studio monitors (Genelec, Neumann) employ such topologies. The graph confirms -6dB at Fc and 12dB/oct slopes.

Component Selection & Parasitics

  • Inductors: Air‑core recommended to avoid core saturation. DCR below 0.5Ω for minimal loss.
  • Capacitors: Metallized polypropylene (MKP) yields low ESR and long‑term stability.
  • Wattage: Passive crossovers handle full amplifier power – use 50W+ rated components for home hi-fi.

Frequently Asked Questions

Butterworth 2nd order has a -3 dB dip at crossover and 90° phase shift; LR2 has -6 dB at crossover and 0° phase difference between drivers, resulting in perfect polar response. LR2 is often preferred for symmetrical MTM designs.

Yes, apply it for low‑mid and mid‑high sections independently. Each bandpass requires a high‑pass and low‑pass filter, but careful impedance and band overlap compensation is needed.

For Butterworth and 1st‑order filters, the drivers are 90° out of phase at crossover, leading to a quadrature sum which appears as a small ripple. For Linkwitz‑Riley (LR2) the combined response is perfectly flat (0 dB) because we sum in‑phase voltages – our graph correctly implements this.

Impedance rises due to voice coil inductance. A Zobel network (RC parallel) can flatten impedance, making the crossover behave as designed. Our calculator provides baseline values for nominal impedance.

Reputable suppliers: Parts Express, Mouser, DigiKey, or audio specialty shops like Jantzen Audio and Mundorf.
References: Dickason, V. "Loudspeaker Design Cookbook" (9th ed.); Linkwitz, S. "Active Crossover Networks for Noncoincident Drivers"; AES Convention papers on passive filter topology. This tool adheres to IEEE/AES standard formulas and has been reviewed by the GetZenQuery tech team (last full verification: May 2026).