These are normally circuit boards made up from different electrical components such as capacitors and coils. They don't have an external power supply and are usually wired in between the amp and speakers. They are usually designed by the manufacturer for a specific set of speakers, such as components.
A crossover with a power supply is 'active'. They can either be seperate units or in-built into an amplifier. They work by filtering through the correct frequencies before they get amplified and then passed on to the speakers.
Because active crossovers have their own power supply, they don't suffer from insertion loss. In fact, many add gain to the signal - improving sound quality and volume.
|An important feature to look at when buying a crossover is the 'slope'. We can measure the slope on a Real Time Analyser (RTA) - a device that uses a graphical display to show measurements of frequency in hertz (Hz).
If you imagine all the frequencies within the crossover's bandwidth as lines on a graph, you'd notice that as they got louder, the lines would slope upwards to one point - the cross over point (see diagram)
|Technical jargon explained|
There's no point in you system using power to play subsonic frequencies because you can't hear them. A subsonic filter actually helps to eliminate them and free-up power.
|Frequency||The number of identical sound waves arriving
at a point in one second. This measurement is expressed in
hertz (Hz) or kilohertz (1kHz = 1000Hz).
|Treble (highs)||: the top end frequencies, about 3kHz to 4kHz
|Midrange (mids)||: usually they key tones or vocal frequencies,
ordinarily 300Hz to 400Hz to 3kHz
|Bass (lows)||: the low stuff, around 20Hz to 400Hz
|Mid-bass||: mid-level bass, normally 100Hz to 400Hz
|Sub-bass||: the very low stuff, usually from 20Hz to
|Subsonic||: these are sound frequencies humans cannot
hear, generally outside of 20Hz and 20kHz