A crossover divides the audio frequency spectrum between different speaker drivers, directing each driver to reproduce only the frequencies it is best suited for. Tweeters, with their small, lightweight diaphragms, handle high frequencies but are damaged by low-frequency content they cannot efficiently reproduce. Woofers and subwoofers, with their large, heavy cones, reproduce low frequencies but become directional and inefficient at high frequencies. Crossovers ensure each driver works within its optimal range.
Crossover setup involves selecting appropriate crossover points and slopes for each driver in the system, and configuring the head unit, DSP, or active crossover to apply those settings. The correct crossover frequency for any driver is informed by its frequency response measurements, its power handling characteristics at the boundary frequency, and its physical size.
As a general framework, tweeters are typically high-pass filtered between 2.5 kHz and 5 kHz depending on their design, with a minimum slope of 12 dB per octave to protect them from low-frequency excursion. Midrange drivers are bandpass filtered — high-pass to avoid the woofer region, low-pass to hand off to the tweeter. Woofers in a two-way configuration are low-pass filtered at the tweeter’s crossover point. Subwoofers are low-pass filtered typically between 60 Hz and 120 Hz, with the exact frequency chosen to blend seamlessly with the lower extension of the door or dash speakers handling the midbass.
Filter slope selection affects both the degree of driver protection and the phase behaviour in the crossover region. Steeper slopes — 24 dB per octave or higher — provide better driver isolation but introduce more phase shift, which must be managed to maintain coherent summation at the crossover frequency. Shallower slopes produce gentler transitions with less phase shift but less isolation.
After setting crossover points mathematically, acoustic measurements at the listening position confirm whether the actual response is flat through the crossover region or whether adjustments to frequency, slope, or level are needed to correct for room interactions.