What Is a Subwoofer Filter?

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  • Written By: Troy Holmes
  • Edited By: W. Everett
  • Last Modified Date: 09 August 2019
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Stereo speakers are designed to optimally play at specific frequencies. Subwoofer speakers play extremely low frequencies, between 20hz and 200hz. A subwoofer filter is an electronic device that removes high frequencies from radio transmissions that are sent to subwoofer speakers. This filter is connected between the speaker and stereo receiver speaker wires.

Subwoofer speakers are large, thick speakers designed to play low-frequency bass. These speakers will become distorted and torn if high-frequency music is played through them. A subwoofer filter is special audio device that filters out high frequency sounds, which are above 200hz. This filter only passes low bass frequencies through the speaker wire.

Low-frequency bass is best heard through speakers that are designed to play loud low frequencies. A subwoofer filter is often built inside a subwoofer speaker box. This filter ensures high frequencies are blocked and not transmitted into the speaker.

Many modern stereo receivers have built-in subwoofer output channels. These audio receivers send only low-frequency signals to the subwoofer speaker. This ensures high-frequency tones are restricted from the speaker.

The subwoofer filter uses a crossover filter that detects high-frequency music. This type of filtering device is often used in music studios to make dynamic music sounds. The crossover filter is made with electric wire that can delete high or low notes as necessary.


It is important that a stereo only use one low-frequency filter. Most powered subwoofers have built-in subwoofer filters that can conflict with the crossover filter of a high-end receiver. A powered subwoofer configuration is best for cars and stereos that don't have subwoofer outputs. This ensures the stereo and speakers are not fighting over the crossover frequency.

A subwoofer filter is important because it keeps the speakers clean and clear. Speakers are basically dumb components that play all frequencies sent through the speaker wire. The filter protects the speaker by ensuring higher frequencies are blocked before they can damage the equipment.

There are several types of subwoofer filters available. These range from basic wire spools to more complex crossover switches. Switches typically cost more than standard filters but allow the stereo to be more precisely calibrated to match the attached speakers. Most high-end competition stereos use a crossover component configuration.


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