What is the difference between a low-pass filter and high-pass filter for home subwoofers?

A low pass removes frequencies ABOVE a set level.

A high pass removes frequencies BELOW a set level.

A separate high pass filter can be used to route only frequencies over, say, 80 Hz to your main speakers (if your receiver/processor did not have this function). Then you would set the low pass filter on the subwoofer to 80 Hz to reject signal above that level. First of all, there is no high pass filter for subwoofers. They only use low pass filters.

Here's what normally happens in a complete system. The audio is passed through a crossover which contains both a high pass filter, low pass filter, and some controls to adjust levels. The highs (frequencies above 100 to 150 hertz) are sent to the midrange/treble speakers. The lows (below 100 to 150 hertz) are sent to the subwoofer. There are many configurations using different amplifiers and so forth, but this is the most basic set up I could illustrate effectively.

'Nuff said? not much Technically, the first guy's answer isn't entirely accurate. Filters (high or low) may be used for any type of audio signal, regardless of speakers.

If you're speaking about a home theatre set-up, or perhaps car audio, then a high pass filter is what allows high frequencies to "pass" and directs them to an appropriate speaker (usually a tweeter) while blocking low frequencies. A low-pass filter does the opposite.

However, you CAN use a HIGH pass filter for low frequencies to attenuate (alter) the overall sound quality.