Crossover Calculator - Passive 2-Way Component Values

A crossover calculator is an electronics tool that sizes the capacitors and inductors in a passive speaker crossover from driver impedances and a chosen crossover frequency. Enter your tweeter and woofer impedances, pick the filter order, and read off the four reactive component values you need to wire a 2-way passive crossover. The tool supports 1st-order Butterworth, 2nd-order Butterworth, and 2nd-order Linkwitz-Riley alignments, which cover the most common DIY speaker designs.

• • DIY 2-way bookshelf speakers: Home audio builders use it to pick the series capacitor and parallel inductor values that route highs to a tweeter and lows to a woofer.
• • Audio engineering coursework: Students use it to confirm textbook formulas and explore how impedance and crossover frequency interact with component size.
• • Studio monitor repair: Technicians look up the original design value from the driver impedances and crossover frequency when replacing parts.
• • Custom car audio upgrades: Car audio installers size 2-way passive networks between aftermarket tweeters and woofers.

A passive crossover splits the full-range signal from an amplifier into a high-frequency band for a tweeter and a low-frequency band for a woofer. Because the components are passive, no extra power supply is needed, which is why passive crossovers are the standard inside most home and car speakers. A 2nd-order crossover adds a parallel inductor to the tweeter branch and a parallel capacitor to the woofer branch for a 12 dB/octave slope.

Before you wire the four components from this crossover calculator, sanity-check the capacitor behavior with the Capacitor Charge Time Calculator to confirm the RC time constant matches your crossover frequency.

The tool uses the standard capacitive and inductive reactance formulas, scaled by filter-type constants, to compute one capacitor and one inductor for the tweeter branch and one of each for the woofer branch.

• Z: Nominal impedance of the tweeter or woofer in ohms, usually 4 Ω or 8 Ω, taken from the driver datasheet.
• f: Frequency in Hz where the high-pass and low-pass responses intersect, usually 2000 to 3500 Hz.
• k_C: Dimensionless filter constant: 0.1592 for 1st-order Butterworth, 0.1125 for 2nd-order Butterworth, 0.0796 for 2nd-order Linkwitz-Riley.
• k_L: Dimensionless filter constant paired with k_C: 0.1592 for 1st-order Butterworth, 0.2251 for 2nd-order Butterworth, 0.3183 for 2nd-order Linkwitz-Riley.

For each driver, the calculator scales the constant by impedance and crossover frequency. Capacitance values come out in farads and are converted to microfarads (μF); inductance values come out in henries and are converted to millihenries (mH). A 1st-order design uses one capacitor and one inductor total, while a 2nd-order design uses two of each because of the steeper 12 dB/octave slope.

The math is grounded in X_C = 1/(2πfC) and X_L = 2πfL. Solving for C and L at the crossover point and applying a Butterworth or Linkwitz-Riley alignment gives the closed-form constants. The 2nd-order Butterworth constants come from √2/(4π) and √2/(2π); the Linkwitz-Riley constants come from 1/(4π) and 1/π.

According to DiyAudioAndVideo 2nd-order Butterworth crossover table, The 2nd-order Butterworth crossover constants 0.1125 (capacitor) and 0.2251 (inductor) match published component tables for 2 Ω, 4 Ω, and 8 Ω drivers from 80 Hz to 12 kHz.

To confirm the current that flows through the crossover network at the crossover frequency, run the same impedance through the Ohm's Law Calculator with the amplifier voltage to size downstream components.

Before trusting the four numbers from this tool, it helps to understand the four building blocks the formula relies on: impedance, crossover frequency, filter order, and filter alignment.

These four concepts are interdependent. Raising the crossover frequency shrinks both the capacitor and inductor values; lowering it inflates them. Choosing a Linkwitz-Riley alignment instead of Butterworth doubles the inductor size relative to the capacitor.

The same resonance reasoning behind the Vibration Natural Frequency Calculator explains why real speaker cones have a usable frequency range, which sets practical bounds for the crossover frequency input.

Enter four values, then read the four component sizes you need to wire a 2-way passive speaker crossover.

1. 1 Choose the filter order and alignment: Pick 1st-order Butterworth for a simple build, 2nd-order Butterworth for the standard 12 dB/octave slope, or 2nd-order Linkwitz-Riley for a flat summed response.
2. 2 Enter the tweeter impedance: Type the nominal tweeter impedance in ohms, almost always 4 Ω or 8 Ω, from the tweeter datasheet.
3. 3 Enter the woofer impedance: Type the nominal woofer impedance in ohms. If the tweeter and woofer share the same impedance, enter the same value twice.
4. 4 Enter the crossover frequency: Pick a hertz value inside the overlap range of both drivers, typically 2000 to 3500 Hz.
5. 5 Read the four component values: Use the two capacitor values for the high-pass and low-pass filters, and the two inductor values to complete the 2nd-order topology.
6. 6 Wire the components into the network: Place Capacitor 1 in series with the tweeter, Inductor 1 in parallel with the tweeter to ground, Inductor 2 in series with the woofer, and Capacitor 2 in parallel with the woofer to ground.

A hobbyist building a 2-way bookshelf speaker chooses 2nd-order Butterworth, enters 8 Ω tweeter, 8 Ω woofer, and 2500 Hz crossover, and reads C1 = C2 ≈ 5.6 μF and L1 = L2 ≈ 0.72 mH. They wind L1 and L2 from 1 mm enameled wire on a 25 mm bobbin, then place C1 in series with the tweeter, L1 across the tweeter, L2 in series with the woofer, and C2 across the woofer.

After wiring the components, use the Decibel Calculator to predict how much insertion loss each filter branch adds at the crossover point and adjust your amplifier gain if needed.

A purpose-built speaker crossover calculator removes the manual algebra from passive speaker design and replaces it with a single click on a live form.

• • Skip the closed-form math: Instead of solving X_C = 1/(2πfC) and X_L = 2πfL by hand for each driver and filter constant, type the four inputs and let the tool return the four component sizes.
• • Compare filter alignments instantly: Switch the filter order dropdown between Butterworth and Linkwitz-Riley to see how the same drivers and frequency produce different capacitor and inductor values.
• • Match real E24 standard parts: Component values are reported in microfarads and millihenries, so you can round each result to the nearest E24 standard part without re-scaling.
• • Sanity-check manufacturer designs: When repairing a speaker, enter the driver impedances and the crossover frequency stamped on the original board to see if the tool returns sizes close to the installed parts.
• • Plan the physical layout: Bigger inductance values need larger coils and smaller capacitance values need tighter-tolerance capacitors. The tool lets you preview sizes before ordering parts.

These benefits compound when you are iterating on a design. Tweaking the crossover frequency up by a few hundred hertz lets you see whether the new inductor values still fit on the crossover board, while tweaking the filter order lets you decide whether the extra 6 dB/octave of slope is worth adding two more reactive components.

Pair the values from this crossover calculator with the RMS to Watts Calculator so you know how much amplifier RMS power each branch needs to deliver at the chosen crossover frequency.

Five variables control the four outputs from this tool, plus a few practical limits that you should know before you commit to a build.

• • The tool models driver impedance as a constant. Real speakers vary in impedance with frequency, so the formula gives a starting point rather than a measured response.
• • The tool supports 2-way passive crossovers only. Three-way designs that add a midrange driver need a low-pass filter for the midrange and a band-pass filter pair, which this calculator does not compute.
• • The tool assumes a single crossover frequency for both drivers. Asymmetric crossovers with different slopes on each side require separate calculations.

Impedance tolerance and crossover frequency are the two inputs that change the outputs the most. Doubling the crossover frequency halves both the capacitance and inductance values, while doubling the driver impedance doubles the inductance and halves the capacitance for the same driver.

According to DiyAudioAndVideo 2nd-order Linkwitz-Riley crossover table, The 2nd-order Linkwitz-Riley crossover constants 0.0796 (capacitor) and 0.3183 (inductor) produce a flat summed response through the crossover.

When the impedance of your drivers changes with frequency, use the Frequency Calculator to convert the crossover hertz value into a period and check where the filter rolls off relative to the driver resonance.