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Two-Way Speaker Crossover

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Recipe #43 — two-way speaker crossover

Capacitors and inductors can divide audio by frequency. A first-order two-way crossover sends high frequencies toward a tweeter and low frequencies toward a woofer.

FIRST-ORDER TWO-WAY SPEAKER CROSSOVER AMPLIFIER C1TWEETERhigh-pass path L1WOOFERlow-pass path C1 increasingly blocks lows from the tweeter; L1 increasingly blocks highs from the woofer.
High-frequency branch: C1 is in series with the tweeter, so low frequencies are increasingly blocked. Low-frequency branch: L1 is in series with the woofer, so high frequencies are increasingly opposed.

Why protect the drivers?

A tweeter is designed for high frequencies and can be damaged by excessive low-frequency energy. A woofer becomes inefficient and directional at high frequencies. The crossover divides the spectrum so each driver works mainly where it is useful.

First-order approximations

For a speaker treated approximately as resistance R:

Tweeter: fC ≈ 1/(2πRC)     Woofer: fC ≈ R/(2πL)

Real loudspeaker impedance varies strongly with frequency, so practical crossover design uses measured driver impedance and acoustic response rather than a single nominal resistance.

Electrical crossover is only part of the story

Driver sensitivity, physical spacing, acoustic phase, enclosure response, impedance peaks, and desired crossover slope all matter. Real designs may use second-, third-, or fourth-order networks and additional equalization components.

Try these yourself

What component is placed in series with the tweeter in this first-order crossover?
The series capacitor forms a high-pass path to the tweeter.
What component is placed in series with the woofer?
The series inductor increasingly opposes high-frequency current to the woofer.
Why are nominal speaker ohms only an approximation for crossover calculations?
A loudspeaker is electromechanical and its impedance varies with frequency, especially near resonances.
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