Speaker Crossover Calculator

Passive crossover formulas

Let f be the target frequency, ω = 2πf, and R the driver impedance used for the ideal resistive-load calculation.

For a first-order section:

• Woofer low-pass series inductor: L = R ÷ ω
• Tweeter high-pass series capacitor: C = 1 ÷ (R × ω)

For a second-order low-pass section:

• Series inductor: L = R ÷ (Q × ω)
• Capacitor across the woofer: C = Q ÷ (R × ω)

For a second-order high-pass section:

• Series capacitor: C = Q ÷ (R × ω)
• Inductor across the tweeter: L = R ÷ (Q × ω)

This calculator uses Q = 1/√2 for second-order Butterworth and Q = 0.5 for second-order Linkwitz–Riley. Each ideal Butterworth section is about 3.01 dB down at the selected frequency; each ideal LR2 section is about 6.02 dB down.

Worked 2,500 Hz example

With an 8 Ω woofer, an 8 Ω tweeter and a target of 2,500 Hz, the ideal values are:

The values become different between branches when woofer and tweeter impedances differ. That is why the calculator accepts the two impedances separately.

Why nominal impedance is not enough

A driver labelled 8 Ω is not an 8 Ω resistor across the audio band. Resonance, voice-coil inductance and the enclosure change both impedance and phase. Dayton Audio’s DATS documentation shows how a woofer’s rising upper-frequency impedance can prevent a textbook low-pass network from reaching its intended cutoff. Its OmniMic measurement guide likewise explains that useful crossover optimization needs driver frequency-response and impedance data with consistent level, delay and measurement distance.

Electrical filters also combine with each driver’s natural acoustic roll-off and physical offset. Linkwitz notes that an electrical filter cannot deliver its intended acoustic result when the mounted drivers lack suitable overlap, flatness or phase alignment. For LR2, the ideal electrical branches are 180° apart and one branch is reversed in the textbook model, but practical polarity should be decided from the measured acoustic sum and reverse-polarity null.

Component and wiring limits

Calculated capacitance and inductance do not determine capacitor voltage rating, inductor current capacity, wire gauge, power handling or thermal safety. Real capacitor ESR, inductor DCR and component tolerance alter response and amplifier load. Disconnect the amplifier before changing wiring, discharge capacitors, check the tweeter manufacturer’s minimum crossover recommendation, and begin prototype testing at low level.

Technical references: Texas Instruments loaded LC-filter derivation, Linkwitz Lab crossover notes, Linkwitz Lab filter notes, Dayton Audio OmniMic measurement guide, and Dayton Audio DATS LA manual.