Enter the crossover frequency, driver impedance, and filter characteristics. The calculator outputs the exact capacitor and inductor values needed for both the low-pass (woofer) and high-pass (tweeter) sections of a passive crossover network.
- Slope
- 24 dB/oct
- Phase at crossover
- 0° (in-phase)
Low-pass (woofer)
High-pass (tweeter)
L = inductor (in series for low-pass, in parallel for high-pass). C = capacitor (in parallel for low-pass, in series for high-pass). Real-world inductors should be air-core for tweeters; iron-core is acceptable for woofers where DCR matters more.
How Passive Crossovers Work
A loudspeaker crossover divides the full audio frequency range into separate bands, routing low frequencies to the woofer, high frequencies to the tweeter, and (in three-way systems) midrange to a dedicated driver. Without a crossover, a tweeter receives low-frequency energy it cannot reproduce, causing distortion and potential damage, while a woofer attempts to reproduce high frequencies it handles poorly, smearing the response.
Passive crossovers use inductors and capacitors wired between the amplifier and the drivers. An inductor passes low frequencies and attenuates highs (low-pass filter); a capacitor passes high frequencies and blocks lows (high-pass filter). The combination of these elements, their values, and the circuit topology determine the crossover frequency, the slope of the roll-off, and the phase behaviour at the crossover point.
Butterworth vs. Linkwitz-Riley
Butterworth filters are “maximally flat” in the passband: each filter section is down 3 dB at the crossover frequency. When the low-pass and high-pass outputs are summed, the result is a +3 dB peak at the crossover point (for even-order) due to the in-phase combination of the two −3 dB outputs. Odd-order Butterworth crossovers sum flat but introduce a 90° phase offset between drivers.
Linkwitz-Riley filters solve the summing problem by cascading two Butterworth filters. Each section is down 6 dB at the crossover frequency, so the summed output is flat (0 dB) at the crossover point with 0° phase difference. This makes LR the preferred choice for most loudspeaker designs. LR crossovers are always even-order: LR2 (12 dB/oct), LR4 (24 dB/oct), LR8 (48 dB/oct).
Choosing the Crossover Frequency
- Two-way systems: typically 1.5–4 kHz. The crossover should fall well within both drivers’ operating ranges—at least one octave above the woofer’s natural rolloff and one octave below the tweeter’s resonant frequency.
- Three-way systems: common splits are 300–500 Hz (low/mid) and 2–4 kHz (mid/high). The midrange driver handles the most perceptually sensitive band (speech, vocal presence).
- Subwoofer crossover: typically 60–120 Hz. Higher crossover points make the subwoofer localisable, defeating the purpose of a separate sub.
Filter Order and Slope
| Order | Slope | Components per section | Notes |
|---|---|---|---|
| 1st | 6 dB/oct | 1 (L or C) | Simplest; gentle slope, wide overlap between drivers |
| 2nd | 12 dB/oct | 2 (L + C) | Most common DIY; moderate overlap |
| 3rd | 18 dB/oct | 3 | Good protection; inverted polarity on one driver |
| 4th | 24 dB/oct | 4 | Professional standard (LR4); steep, clean transition |
Practical Considerations
- These calculated values assume a purely resistive load equal to the nominal driver impedance. Real drivers have impedance that varies with frequency (rising at resonance, rising inductively at high frequencies). Use an impedance-compensating Zobel network for more accurate results.
- Standard component values may not match calculated values exactly. Choose the nearest standard value or combine components (capacitors in parallel add, inductors in series add).
- Inductor DCR (DC resistance) effectively attenuates the woofer’s output. Use wire gauges thick enough to keep DCR below 0.3 Ω for woofer-section inductors.