Whether you are designing your own stereo system or purchasing components for a personal audio system, you should have a basic understanding of how an amplifier sorts the audio signal and delivers it to your speakers. Part of the sorting and filtering of a multi-component audio system includes crossovers, of which there are three basic types and further differentiation within those types.
Crossover Fundamentals
A loudspeaker may have both a mid-range and tweeter (high range) speaker within it. The amplifier that generates power to those speakers needs to be able to differentiate between what signals it should deliver to each speaker, including the subwoofer.
A crossover divides the audio frequencies, whether they are high, low, mid-range, or sub to ensure that each speaker is playing the exact frequency it is designed to play. You must also keep in mind that each crossover has a filtering slope. Crossovers do not perfectly filter frequencies, so the frequencies attenuate as the crossover filters out the desired frequency.
Three Types of Crossover Filtering
There are three different types of crossovers based on the type of audio frequency filter they use: high pass, low pass, and band pass. Understandably, high pass crossovers filter out everything but high frequencies; low pass crossovers filter out everything but low frequencies; and band pass crossovers filter out both low and high frequencies based on established crossover points. Band pass crossovers can be thought of as filtering everything but "mid-range" frequencies.
Active Crossovers
Also known as equalizers, active crossovers require external power to function. These crossovers use low signal voltage levels, and split the signals from the head unit (for instance a CD player) at low, mid, and high frequencies. It then sends the signal to the amplifier. The advantage of an active crossover is that it does not have much effect on the main signal because it uses a low signal voltage and external power. Also, you can adjust the levels without having to replace the crossovers.
Passive Crossovers
These crossovers are often internal and work "after" the amplification occurs. Passive crossovers receive high-level signals. They allow you to attach more speakers to a single amplifier channel. Passive crossovers are more flexible and can be purchased separately from your amplifier and they can be mixed and matched to produce the desired filtering of your system.
Inductors and Capacitors
Passive crossovers are further divided into inductors and capacitors. Inductors function as a low-pass filter and are simply a coil of wire wound around an iron core. Capacitors are used in high-pass filters and are made of special material like polypropylene or mylar. They are layered rather than coiled. Each inductor or capacitor has a "resistance value," which is the effect on amplification as it filters out high and low frequencies. You should keep this in mind as you purchase crossovers and attempt to power your speakers, because each speaker requires a minimum amount of amplified power.
Tags: high frequencies, pass crossovers, crossovers filter, each speaker, pass crossovers filter, audio system, band pass
