If the system is simply being broken into lows and highs, it is said to be bi-amped . If it is broken into low, mid and high, it is said to be tri-amped . The distinction is important. A tri-amped system requires an active crossover unit, three separate amplifiers, and speakers capable of having their drivers driven by separate inputs. Note the large number of controls on the unit, for controlling crossover frequency, slope, and volume levels.
Active crossovers have several controls for adjusting their operating parameters.
They provide a means to adjust the crossover frequencies - the frequency at which the sound will stop being reproduced by one driver and start being reproduced by the next. This transition is not instantaneous. In fact, it is modeled as two intersecting slopes. These slopes are adjustable on most active crossovers, allowing a very gradual change between two drivers to a farly steep change. Setting a crossover requires knowledge of where the individual drivers of a speaker system are designed to cross over.