What Is a Speaker Crossover Capacitor Calculator?
A passive crossover splits an audio signal between a tweeter and a woofer so each driver only receives the frequencies it can handle cleanly. This calculator finds the component values for the simplest possible crossover — a single capacitor feeding the tweeter (a first-order high-pass filter) and, for reference, the matching single inductor that would feed the woofer (a first-order low-pass filter) at the same crossover point.
This is the same formula found in loudspeaker design references and DIY speaker-building guides for a basic 6 dB/octave crossover network.
How to Read Your Results
High-Pass Capacitor (Tweeter)
This capacitor, wired in series with the tweeter, blocks frequencies below your crossover point and lets higher frequencies through. Use a non-polarized capacitor rated for audio use (film or bipolar electrolytic).
Low-Pass Inductor (Woofer)
This inductor, wired in series with the woofer, blocks frequencies above the crossover point and lets lower frequencies through — the complementary half of a basic two-way crossover.
Crossover Frequency (-3 dB)
The frequency at which the filter has attenuated the signal by 3 decibels, generally considered the effective cutoff point of the filter.
Filter Slope
A first-order filter rolls off gradually, at 6 dB per octave. Steeper second-order (12 dB/octave) or third-order (18 dB/octave) filters need more components and separate calculations.
Real-World Example
A common tweeter crossover point is around 3,000 Hz on an 8-ohm driver:
| Crossover frequency | Impedance | Capacitor | Inductor |
|---|---|---|---|
| 2,000 Hz | 8 ohms | 9.95 µF | 0.64 mH |
| 3,000 Hz | 8 ohms | 6.63 µF | 0.42 mH |
| 5,000 Hz | 8 ohms | 3.98 µF | 0.25 mH |
Notice that a higher crossover frequency needs a smaller capacitor and a smaller inductor — the components scale inversely with frequency.
Tips for Building a Passive Crossover
- Match capacitor voltage rating to your amplifier's output — audio-grade film capacitors rated 50V or higher are typical for home speakers.
- Air-core inductors are usually preferred over iron-core for woofer crossovers to avoid magnetic saturation at high power.
- First-order crossovers are simple but wide, so choose drivers with overlapping usable ranges around the crossover point.
- Always verify with a multimeter that real-world component values are close to the calculated ones — tolerances of ±10% are common.
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Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team