The Complete Handbook of Crossovers

Chapter 1: Understanding Crossovers

At its most basic, an audio crossover is a filter or a group of filters. Its job is to take a single, full-bandwidth audio signal, which typically spans from around 20 Hz to 20 kHz, and split it into two or more distinct frequency bands. These bands are then sent to different drivers designed to reproduce them most efficiently - a tweeter for the highs, a mid-range driver for the presence band, and a woofer or subwoofer for the lows. Without this division, a single driver would be asked to reproduce the entire spectrum, resulting in poor sound and, more critically, damage to the driver itself.

Consider a standard 12-inch woofer. It has a large, relatively heavy cone that moves a lot of air to produce low bass. If you feed it the full signal, it will try to reproduce the 10 kHz sparkle of a hi-hat, a frequency it's physically too slow to handle. The dome tweeter, on the other hand, is lightweight and stiff, designed for rapid, tiny movements. If forced to attempt a 50 Hz bass note, the cone would likely rip apart or the voice coil would burn up from overheating, as it simply cannot displace enough air without extreme destructive excursion. The crossover prevents this by ensuring each driver only receives the frequencies it was designed for, protecting the hardware and ensuring a coherent, balanced sound output.

The principle of operation is rooted in electrical resistance and reactance. A filter uses