Dividing the Sound: Speaker Crossovers
A single speaker driver cannot efficiently reproduce the entire range of human hearing (20Hz to 20,000Hz). High-fidelity audio systems use multiple drivers: Tweeters for high frequencies and Woofers for low frequencies. A Crossover is a circuit that acts as a traffic controller, ensuring that each driver only receives the frequencies it was designed to handle.
Passive Crossovers and Capacitors
The simplest crossover is a High-Pass Filter—a single capacitor placed in series with a tweeter. Capacitors have a property called 'Capacitive Reactance,' which means they resist low-frequency signals while allowing high-frequency signals to pass through.
The Formula
The 'Cutoff Frequency' (where the filter begins to reduce the signal) is determined by the capacitance of the component and the electrical impedance (resistance) of the speaker.
f = 1 / (2 * π * R * C)
First-Order vs. Second-Order
- First-Order (6dB/octave): Uses a single capacitor or inductor. It is the simplest and most phase-coherent but provides a very 'gentle' slope, meaning some unwanted frequencies still reach the driver.
- Second-Order (12dB/octave): Uses both a capacitor and an inductor. It provides a much steeper cutoff, protecting delicate tweeters from power-hungry low frequencies more effectively.