Crossovers are devices that 'split' an audio signal into two or more frequency ranges so that they may be directed to loudspeakers most suited to produce each frequency range.

In the absence of a crossover, sending low frequencies to a Tweeter (high frequency speaker) can cause it damage. Sending high frequencies to a Woofer (low frequency speaker) are unlikely to damage the speaker, however having a large inertia it can't respond to the frequency fast enough and produces a 'coloured' (unpleasant) sound as a result.

Passive Crossovers

In low to mid power loudpeaker systems, the crossover is placed after the amplifier, usually inside the speaker cabinet itself, and requires no external power.

At it's simplest, a passive crossover is a capacitor and a coil (inductor).

• High frequencies see the coil as a large impedance and the capacitor as a small impedance (see High Pass Filter).
• Low frequencies see the coil as a small impedance and the capacitor as a large impedance (see Low Pass Filter).

Passive crossovers have a power rating just as speakers do, however they tend to survive transients above this power rating better than speakers do.

in many cases a passive crossover can make a system quite inefficient. Heat is generated which is power wasted and lost. It is therefore important that you do not use a passive crossover when there is no need to. In its simplest form a 2 way setupi using an active crossover may result in the bass speakers signal going through an inbuilt passive crossover aswell. Wherever possible, avoid this by disconnecting the internal crossover.

Active Crossovers

In high power loudspeaker systems, the crossover is placed before the amplifiers, and is usually a powered rackmount unit mounted in the amplifier rack. More amplifiers and cabling are thus required, but overall efficiency and system control is improved. There are both Analogue and Digital active crossovers available. Whilst the analogue ones are normally simple to use and cheaper, the digital ones tend to be much more flexible. With a digital active crossover you can adjust frequency and slopes, have each output as a bandpass filter (ie its own range that does not depend on other outputs). There is often adjustable delay on each output and input, additional features such as EQ and dynamics are sometimes available along with the facility to save presets and recall them as necessary. One other advantage to these is the ability to lock them and password protect them to save unauthorized editing. Digital crossovers can be bought for under £200 such as the Behringer DCX2496, they can also cost several times more such as the offerings from BSS and XTA. Generally a noticeable increase in features and quality is noticed here. Active crossovers are sometimes built into amplifiers, in simple forms such as a analogue rotary dial or in much more complicated forms such as the D&B D12, this amongst other things allows sensing of the amplifier outputs to protect from short circuits, clipping and overload in the same way that some normal amplifiers use sense circuits to help protect the speakers, Again, D&B Audiotechnik is an example of this.

See Also

• Active/Passive

External Links

• Rane Notes (scroll down a bit)