Speaker Crossover Calculator
Enter your speaker impedances, crossover frequency, filter order, and filter characteristic to get the exact capacitor and inductor values for a passive crossover network. Works for 2-way (tweeter and woofer) and 3-way (tweeter, midrange, woofer) designs. Results update instantly as you type.
Formula
Worked example
A 2nd-order Butterworth 2-way crossover at 2500 Hz with 8-ohm woofer and 8-ohm tweeter: Butterworth g-values are [1.4142, 1.4142]. Woofer L1 = 1.4142 x 8 / (2 x pi x 2500) = 0.721 mH. Woofer C1 = 1.4142 / (2 x pi x 2500 x 8) = 11.26 µF. Tweeter C1 = 1/(1.4142 x 2 x pi x 2500 x 8) = 11.26 µF. Tweeter L1 = 1/(1.4142) x 8 / (2 x pi x 2500) = 0.360 mH.
What is a passive speaker crossover?
A passive crossover is a network of capacitors and inductors placed between the amplifier and the speaker drivers. Its job is to divide the full-range audio signal into frequency bands, routing low frequencies to the woofer and high frequencies to the tweeter. Without it, a tweeter would receive bass frequencies that could damage the voice coil, and a woofer would produce muddy high-frequency distortion it was not designed to handle. Passive crossovers work without external power and sit inside the speaker cabinet in almost every bookshelf and floor-standing loudspeaker.
How this calculator works
This calculator uses the normalised LC-ladder prototype method. For a chosen filter characteristic (Butterworth, Linkwitz-Riley, or Bessel) and order (1st through 4th), a set of normalised element values - called g-values - are looked up from standard filter tables. These are then denormalised to the target impedance and crossover frequency using two formulas: for a capacitor, C = g / (2 x pi x fc x Z); for an inductor, L = g x Z / (2 x pi x fc). The high-pass section uses the dual transform, swapping inductors and capacitors and replacing each g-value with its reciprocal 1/g. A 3-way design applies the same procedure twice: a low-pass filter at the lower crossover frequency for the woofer, a band-pass (cascaded high-pass and low-pass) for the midrange, and a high-pass at the upper crossover for the tweeter.
Butterworth, Linkwitz-Riley, and Bessel filters compared
Butterworth filters are the most popular choice for loudspeakers. They produce the flattest possible amplitude response in the passband with no ripple, and the high-pass and low-pass sections each measure -3 dB exactly at the crossover frequency. Linkwitz-Riley filters, developed by Siegfried Linkwitz and Russ Riley in 1976, are a cascaded pair of Butterworth filters of half the order. Their key property is that the high-pass and low-pass outputs sum to a flat total response at all frequencies, which is extremely useful when the two drivers overlap acoustically. At the crossover point each section is at -6 dB. Bessel filters prioritise constant group delay over amplitude flatness, meaning transients (the sharp attacks in music) pass through with less smearing. The trade-off is a slightly slower roll-off than Butterworth at the same order.
Practical tips for building a crossover
Real drivers do not present a flat resistive impedance across frequency. The impedance of most woofers rises steeply above resonance, which shifts the effective crossover frequency upward. A Zobel network - a resistor in series with a capacitor placed across each driver - flattens the impedance curve and makes the crossover behave as calculated. Use film or metallised polypropylene capacitors (not electrolytic) for best audio performance. For inductors, air-core types have zero saturation distortion but need more wire turns; ferrite-core types are more compact but can saturate at high current. Choose inductors with a DC resistance well below 1 ohm relative to speaker impedance, or the effective impedance seen by the crossover will be wrong, shifting frequencies and eating efficiency.
Filter order comparison
| Order | Roll-off rate | Components per section | Characteristic | Phase shift at fc |
|---|---|---|---|---|
| 1st | 6 dB/octave | 1 capacitor + 1 inductor | Simple, minimal | 90 deg |
| 2nd | 12 dB/octave | 2 capacitors + 2 inductors | Common in hi-fi | 180 deg |
| 3rd | 18 dB/octave | 3 caps + 3 inductors | Good driver protection | 270 deg |
| 4th | 24 dB/octave | 4 caps + 4 inductors | Excellent separation | 360 deg |
Approximate characteristics for each crossover order. Component counts are per section (low-pass or high-pass).
Frequently asked questions
What crossover frequency should I choose?
Match the crossover frequency to the capabilities of your drivers. The crossover frequency should sit well within the range that both adjacent drivers can reproduce cleanly. A typical 2-way speaker with a 6-8 inch woofer and a 1-inch tweeter crosses over between 2000 Hz and 4000 Hz. Subwoofer crossovers are usually set between 80 Hz and 120 Hz, with 80 Hz being the THX standard. If your drivers have measured frequency response data, cross over at a point where both drivers are at least 10 dB above their roll-off floor.
Why do the high-pass and low-pass component formulas look like reciprocals?
The high-pass section is derived from the low-pass prototype by the LC duality transformation: every capacitor becomes an inductor and vice versa, and each element value g is replaced by 1/g. This swaps the roles of the components so that the high-pass filter passes high frequencies and attenuates low ones, which is the mirror image of what the low-pass does.
My drivers have different impedances - does that matter?
Yes. The component values depend directly on the driver impedance. If you use the wrong impedance, the crossover frequency will shift. If your woofer is 8 ohms and your tweeter is 4 ohms, enter each value separately into the corresponding field. Note that nominal impedance (printed on the driver) is an approximation - the real impedance varies with frequency. For critical builds, measure the driver impedance with a measurement system and consider impedance compensation.
What is a Zobel network and do I need one?
A Zobel (or impedance compensation) network is a resistor in series with a capacitor, connected directly across a driver. Its purpose is to cancel the rising impedance caused by the driver voice coil inductance, presenting an approximately flat resistive load to the crossover across the audio band. Without it, the effective crossover frequency shifts upward as the driver impedance rises. For precision results, especially with 2nd-order and higher crossovers, a Zobel network is recommended. The values are: R_Z = 1.25 x R_DC and C_Z = L_voice_coil / R_DC^2.
How accurate are these component values?
The calculations are mathematically exact for ideal resistive loads at the nominal impedances you enter. In practice, standard capacitor values come in a E12 or E24 series, so you will need to combine values to get close. Inductor tolerances are typically 5-10%. Real driver impedance is not purely resistive. For most home audio applications the calculated values will get you within audible range; fine-tuning by ear or with measurement software (such as REW) is common for critical builds.
What is the difference between 2-way and 3-way crossovers?
A 2-way crossover splits the signal at one frequency point into two bands: a low-pass for the woofer and a high-pass for the tweeter. A 3-way crossover uses two crossover frequencies to create three bands: a low-pass for the woofer, a band-pass (formed by a high-pass cascaded with a low-pass) for the midrange driver, and a high-pass for the tweeter. The 3-way design gives each driver a narrower frequency range to reproduce, which generally improves clarity and reduces intermodulation distortion, at the cost of more components and greater complexity.