If you’re into home theater and audio equipment, you will frequently hear the term crossover. What exactly is a crossover?

I will talk about the crossover in the home theater sense since it is what I know more about, but a crossover practically does the same thing whether it is used in car audio, home theater, internal speaker applications.

Speakers commonly have crossovers inside their cabinets, a 2-way speaker has one crossover, a 3-way speaker has two crossovers. Know why?

A 2-way speaker has two drivers, the tweeter which takes care of the high frequencies and the midrange/woofer which takes care of the lower frequencies. The crossover in a 2-way speaker is responsible for routing which frequencies (in this case, high frequencies) goes to the tweeter, and which frequencies (in this case, low frequencies) goes to the mid/woofer.

The same concept is applied for 3-way speakers, a 3-way speaker has four or more drivers. These are grouped into the tweeter, the midrange and woofers. The woofers are typically more in quantity if the 3-way speaker has 4 or more drivers. Manufacturers clearly indicate how many drivers of each type are in a speaker. Take a look here, and you will see that Polk Audio indicates that the RTi A9 below has one tweeter, tw0 5.25-inch midranges and triple 7-inch woofers.

Getting back to crossovers, the RTi A9 above has two crossovers with the specifications below.

A low pass, will allow frequencies below the mentioned point to pass. A high pass, will allow frequencies above the mentioned point to pass. So for the mid-high array, the 2.7kHz high pass routes frequencies to the tweeter while the 2.7kHz low pass and the 125Hz high pass are responsible for routing frequencies to the midrange. Using hard values, 2.7kHz and above goes to the tweeter, while 125Hz to 2.7kHz goes to the midrange. Lastly, for the woofer, the 125Hz low pass only lets 125Hz and below go to the woofers.

More information elsewhere:

• How Speakers Work (HowStuffWorks)
• Audio crossover (Wikipedia)