Crossover Frequency
Definition
A crossover divides the audio signal into frequency bands sent to different drivers or loudspeakers, and the crossover frequency is the point where two adjacent bands meet. An active crossover filters the line-level signal, usually in a DSP, ahead of separate amplifier channels. A passive crossover, built from capacitors, inductors and resistors, sits between the amplifier and the drivers and dissipates part of the power as heat. The crossover between subwoofers and full-range loudspeakers is commonly set around 80 to 120 Hz, and between mid and high drivers around 1.5 to 3 kHz, depending on the drivers. Linkwitz-Riley filters, widely used in sound reinforcement, sum to a flat amplitude response at the crossover point when both outputs are in phase.
In the field
The crossover point between subwoofers and main loudspeakers is usually chosen from the manufacturer's presets and from on-site measurement, because the result depends on the natural roll-off and the phase of each box as well as on the filter frequency. When the two bands overlap in phase, the level rises around the crossover; when they are out of phase or leave a gap, the level drops.
Sources
- Audio crossover (Wikipedia) : filtres actifs et passifs, pertes du passif · en.wikipedia.org
- Linkwitz–Riley filter (Wikipedia) : somme d'amplitude plate au point de coupure · en.wikipedia.org
- Ballou, Handbook for Sound Engineers : filtres de répartition et alignement des bandes