Calculate the capacitor and inductor values for a passive 2-way speaker crossover from your target frequency, driver impedance, and filter order.
Results
Calculated
High-pass capacitor
—
Wire in series with the tweeter
Low-pass inductor
—
Wire in series with the woofer
Filter slope
—
Attenuation beyond the crossover point
Wavelength at fc
—
Sound wavelength in air (v = 343 m/s)
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How to use the Crossover Calculator
Enter your target crossover frequency, the driver's nominal impedance, and choose a 1st order or 2nd order (Butterworth) filter slope, then click Calculate to get the capacitor and inductor values for a passive 2-way speaker crossover.
The formulas
A passive crossover splits an amplifier's signal between a tweeter (high frequencies) and a woofer (low frequencies) using capacitors and inductors instead of active electronics. For a first-order (6 dB/octave) network:
High-pass capacitor (tweeter): C = 1 / (2π × fc × Z)
Low-pass inductor (woofer): L = Z / (2π × fc)
where fc is the crossover frequency in hertz and Z is the driver's nominal impedance in ohms. A second-order Butterworth (12 dB/octave) network multiplies both values by √2 ≈ 1.4142, trading one extra component per driver for a steeper roll-off.
Choosing a crossover point
The crossover frequency should sit inside the range where both drivers perform well — above the woofer's breakup region and below where the tweeter starts to distort or is driven outside its safe range. Most small dome tweeters aren't rated much below 2,000 Hz, and many mid-size woofers begin beaming or breaking up somewhere between 3,000 and 5,000 Hz, so 2,000-4,000 Hz is a common starting point for 2-way designs.
Interpreting the results
The capacitor and inductor values are the theoretical component sizes assuming a purely resistive load equal to the driver's nominal impedance. Real drivers have impedance that varies with frequency, so treat these values as a solid starting point — many builders fine-tune the final network by ear or with measurement software after wiring up the calculated components.
Frequently Asked Questions
What is a crossover frequency in a speaker system?
The crossover frequency (fc) is the point where a passive filter network splits the audio signal between drivers: frequencies below fc are routed to the woofer through a low-pass inductor, and frequencies above fc are routed to the tweeter through a high-pass capacitor. A typical 2-way home speaker crosses over somewhere between 1,500 Hz and 4,000 Hz.
How do you calculate crossover capacitor and inductor values?
For a first-order (6 dB/octave) crossover, the tweeter's high-pass capacitor is C = 1 / (2π × fc × Z) and the woofer's low-pass inductor is L = Z / (2π × fc), where fc is the crossover frequency in hertz and Z is the driver's nominal impedance in ohms. A second-order Butterworth (12 dB/octave) network multiplies both values by √2.
What is the difference between 1st order and 2nd order crossovers?
A first-order crossover uses a single capacitor or inductor per driver and rolls off at 6 dB per octave outside the crossover frequency. A second-order Butterworth crossover adds a second component per driver (an inductor paired with the tweeter's capacitor, a capacitor paired with the woofer's inductor) for a steeper 12 dB per octave roll-off, which better protects each driver from frequencies it wasn't designed to reproduce.
Why do tweeters need a capacitor and woofers need an inductor?
A capacitor blocks low frequencies and passes high frequencies, protecting a tweeter from low-frequency energy it cannot handle. An inductor does the opposite: it passes low frequencies and blocks high frequencies, keeping a woofer from trying to reproduce highs it reproduces poorly. Used together, they form a passive crossover network.