Speaker Crossover Capacitor Calculator

A tweeter's voice coil is tiny — typically 0.25–1 cm of aluminum wire — so it cannot pass low frequencies without overheating. A series capacitor blocks DC and rolls off bass below its cutoff frequency. 99% of tweeter failures come from low-frequency excursions, not power handling. Even a 1st-order high-pass series cap will double tweeter life by keeping the cone from bottoming out on sub-bass.

1st-order = one component (one capacitor for HPF, one inductor for LPF) rolling off at 6 dB/oct. Cheap, but has a phase shift of 90° at crossover frequency. 2nd-order Butterworth uses two components (C + L), rolls off at 12 dB/oct and has maximally flat response in the passband. Most commercial speakers use 2nd-order or steeper; 1st-order is common for DIY 'bass blocker' upgrades on old tweeters.

The math is identical — the only difference is which component goes where. Use the same calculator with your midrange impedance and crossover frequency (e.g. 1200 Hz for midrange, 80 Hz for woofer). For a full-range speaker you might put a bass-blocker cap in series at 60 Hz. Subwoofers often use active crossovers with digital filtering instead of passive C/L networks, but the formula is still right for passive designs.

Film capacitors rated ≥ 2× the peak amplifier output voltage across the tweeter branch. For a 100 W RMS amplifier into 8 Ω, peak voltage is √(2 × 100 × 8) ≈ 40 V, so 50 V minimum, preferably 100 V. Never use an electrolytic or tantalum — both are polarized and will fail if audio waveform reverses.

A tone pot and tone cap in series form a low-pass RC filter that rolls off high frequencies when you turn the tone knob down. Typical values: 0.01 µF for bright/warm midrange, 0.022 µF for thicker tone, 0.047 µF for dark/rounded Les Paul-style tone. Use the RC calculator on our RC page with R = 250 kΩ (pot wiper to tone cap), C = your tone cap, and fc = 1/(2π × R × C).

Moving-coil and moving-magnet phono cartridges expect a specific load capacitance — typically 47 pF + cable capacitance. The turntable preamp usually provides this, but external preamps sometimes let you adjust it. Too much or too little load capacitance rolls off the high end and causes resonant peaks. Typical values: MM cart 100–200 pF total, MC cart 100–500 pF.