How to Choose the Right Crossover Frequency

By David Lipscomb

Updated September 28, 2017

Items you will need

A/V receiver
Receiver owner's manual
Speakers
Speaker specification sheet
Personal computer with access to the Internet

With speakers of all sizes deployed in home theaters of all varieties, the question of what crossover frequency to use for those speakers is a legitimate one. Home-theater receivers offer options of "large" or "small," with further adjustments of specific crossover points available as well. Many speakers can handle nearly full-range bass, but not enough to avoid the use of a sub-woofer for the lowest bass notes. Additionally, many rooms reinforce certain frequencies, leading to boominess at one end the spectrum and a tinny sound from tweeters at the other that is annoying and hard to overcome. Choosing the right crossover frequencies to blend from the satellite speakers to the sub-woofer is therefore extremely important.

By the Numbers

Consult the speaker specification sheet online. Search for the specification that details frequency response. This will look like "40-20,000Hz" or a similar set of numbers.

Enter the receiver's set-up menu with the receiver's remote. Access the area of the menu that addresses speaker size and crossover point. Consult the owner's manual for procedural specifics.

Look at the speaker's specification sheet while in the receiver's menu. Make note of the lowest frequency listed in the "response" section. This is typically 32, 40 or 55Hz.

Observe the options available in the receiver's crossover adjustment menu. Take the lowest frequency listed in the speaker's specification sheet and double the value. If the value is 40Hz, the crossover point should be 80Hz in the receiver's menu. This will account for the typical behavior of a 12db/octave high-pass crossover, found in nearly all receivers. High-pass crossover points mark the frequency where, if we assume the use of a bookshelf speaker and sub-woofer, the bookshelf speaker begins to taper off. The low-pass crossover point is where the subwoofer begins to taper in the opposite direction, so that it does not play much mid-range. As a result, response will be flat from the crossover point down to the speaker's natural roll-off. The "roll-off" is the point slightly below the speaker's published lowest frequency where the speaker ceases to produce sound. For example, if a speaker's lowest frequency rating is 40Hz, most likely the roll-off is around 32Hz. This works for tweeters as well. Most speakers roll off at the top end around 22kHz, beyond the point most humans can hear.

Tips

Set the sub-woofer's low-pass crossover to the same figure as the satellite speakers' high-pass. Most low-pass filters on receivers use a 24db/octave crossover, a steep slope that means the response above the chosen point will rapidly roll off. Avoiding too much of a gap between the high-pass and low-pass crossover points will help ensure no gap in response.

Note that dedicated low-frequency effect (LFE) content is mastered at 120Hz. This is a filter, not a crossover in the traditional sense. If the vast majority of content viewed is 5.1, this should be the LFE setting in the receiver's menu.

References

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