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How It Works
A passive crossover network splits an audio signal into separate frequency bands for different speaker drivers (tweeters, woofers, etc.). The crossover uses capacitors and inductors to create high-pass and low-pass filters at the desired crossover frequency. The filter order determines the roll-off slope: 1st order = 6 dB/octave, 2nd order = 12 dB/octave, 3rd order = 18 dB/octave, and 4th order = 24 dB/octave.
This calculator computes the component values for Butterworth-type crossover networks (all orders), plus Linkwitz-Riley, Bessel, and Chebychev alignments (2nd order), and Linkwitz-Riley, Bessel, Legendre, Gaussian, and Linear-Phase alignments (4th order). Enter the driver impedances and crossover frequency to get the capacitor (farads) and inductor (henrys) values.
Example Problem
Design a 1st-order Butterworth crossover at 3,000 Hz with Rₕ = 8 Ω (tweeter) and Rₗ = 4 Ω (woofer).
- Capacitor: C1 = 0.159 / (8 × 3000) = 0.159 / 24000 = 6.625 × 10⁻⁶ F (6.625 μF)
- Inductor: L1 = 4 / (6.28 × 3000) = 4 / 18840 = 2.1231 × 10⁻⁴ H (0.212 mH)
Higher-order networks produce more components. A 2nd-order Butterworth at the same frequency would yield C1, C2 (capacitors) and L1, L2 (inductors) using the coefficients 0.1125 and 0.2251.
When to Use Each Order
- 1st Order — simplest design, minimal phase shift, but gentle 6 dB/octave slope means drivers share a wide overlap band. Best when drivers can handle broad frequency overlap.
- 2nd Order — 12 dB/octave slope with multiple alignment choices. Butterworth is flat at crossover; Linkwitz-Riley sums to flat; Bessel preserves transient response.
- 3rd Order — 18 dB/octave for tighter frequency separation. Good for protecting tweeters from low-frequency power.
- 4th Order — steepest 24 dB/octave roll-off, excellent driver isolation. Linkwitz-Riley 4th order is popular in professional audio for its flat summed response.
Frequently Asked Questions
What is a passive crossover network?
A passive crossover network uses non-powered components (capacitors and inductors) to divide an audio signal by frequency. Unlike active crossovers, passive crossovers sit between the amplifier and the speaker drivers, requiring no external power supply.
What is the difference between Butterworth and Linkwitz-Riley crossovers?
A Butterworth crossover is −3 dB at the crossover frequency, meaning each filter passes half power at that point. A Linkwitz-Riley crossover is −6 dB at crossover, so when the high-pass and low-pass outputs are summed acoustically, the result is perfectly flat. Linkwitz-Riley is generally preferred for speaker systems because of this flat power response.
How do I choose the right crossover frequency?
The crossover frequency should fall within the operating range of both drivers. A common approach is to set it where both drivers can comfortably reproduce sound without distortion. Tweeter crossover frequencies are typically between 2,000 Hz and 5,000 Hz for two-way systems.
Why do the results show values in farads and henrys?
Farads (F) measure capacitance and henrys (H) measure inductance. In audio crossovers, typical values are in the microfarad (μF) range for capacitors and millihenry (mH) range for inductors. Multiply farads by 1,000,000 to get μF, or henrys by 1,000 to get mH.
Can I use this calculator for three-way speaker systems?
This calculator computes component values for a two-way crossover network. For a three-way system, you would design two separate two-way crossovers: one between the woofer and midrange, and another between the midrange and tweeter, each with its own crossover frequency.
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Reference: Dickason, Vance. 1991. The Loudspeaker Design Cookbook. Audio Amateur Press. 4th ed.