A crossover network, also called a dividing network, is the component of a loudspeaker that divides the audio signal between the drivers. Most speakers must use more than one size of driver because it is extremely difficult for one driver to accurately reproduce sound waves over the entire 20 Hz to 20 kHz frequency range of human hearing. The most common multi-way speakers use two drivers, a tweeter and a woofer. This requires the electrical audio signal to be divided into a high-frequency part and a low-frequency part before the signals reach the drivers. This is very important because most tweeters will be damaged if they are driven with a low-frequency signal. The illustration below shows the sound being divided between the tweeter and the woofer:

 

The frequency where the sound is divided is called the crossover frequency. Ideally, a crossover frequency is chosen which protects the tweeter, allowing it to produce only those frequencies that it can reproduce the best, and allows both the response and coverage pattern of the woofer to blend well with the tweeter. The coverage pattern is the shape of the listening area where a driver will provide a relatively uniform direct sound pressure level.

 

If the speaker has more than two sizes of drivers the crossover network also divide the audio signal into one or more additional midrange frequency bands.

 

There are two places where a crossover network can be placed in the audio system: after the amplifier or before the amplifier. Here are some points about each location:

 

After the amplifier

 

Generally the most common and least expensive location for a crossover network.

 

Uses passive components that do not require an external power supply so they are referred to as passive crossover networks.

 

Uses large components that can handle the full power delivered to the speaker.

 

Is very sensitive to the impedance response of the drivers.

 

Can be mounted inside or outside of the speaker box. When a crossover network is mounted in or on the speaker box, it is considered a part of the speaker.

 

Only one amplifier channel is required per speaker because the audio signal is divided after it has been amplified.

 

Are often easier for the hobbyist to construct at home because a printed circuit board and power supply are not required.

 

Before the amplifier

 

Generally a more expensive location for a crossover network but it can produce higher fidelity and offer more adjustability.

 

Is usually constructed with active components that require an external power supply so they are referred to as active crossover networks. Passive crossover networks can also be used before the amplifier but they are uncommon.

 

Uses smaller components since they are located "upstream" of the amplifier outputs and handle much less power.

 

Is not affected by the impedance response of the drivers.

 

Must be located between the preamplifier and power amplifier(s), usually in an equipment rack or cabinet. Because it is not located with the speaker, it is usually considered a separate component and not a part of the speaker.

 

Requires a separate amplifier channel for each driver or crossover network filter and thereby raises the overall cost of the audio system.

 

Are usually more difficult to construct because a printed circuit board and case (chassis) are often desired and an external power source is required.

 

The important point to remember about crossover networks is that they divide the audio signal so that each driver in a multi-way speaker will receive only frequencies that it can handle and reproduce well.