How to properly set sub-woofer crossover and phase settings

After setting up your sub-woofer, having the proper crossover settings will help you get a balanced bass. This also ensures that the sound from your speakers and sub-woofer work harmoniously improving your overall listening experience.

For starters, a crossover is an electronic filter that splits audio signals into 2 or more frequencies allowing each split signal to be sent to the respective speakers or group of speakers that will play the audio most effectively. On a sub-woofer, the crossover frequency is the frequency at which the speakers roll off letting the subwoofer play the bass and Low-Frequency Effects (LFE).

Phase, on the other hand, allows you to add an electrical signal delay for better integration between your speaker and your sub-woofer. The sub-woofer phase control ranges from 0 to 180 degrees with most subs having a phase control knob that allows you to switch between 0 or 180 degrees. Some sub may have knobs that allow you to make small increments of between 0 and 180 degrees.

Before installing your sub-woofer, you should be aware of how to properly set both the phase and crossover.

We are going to walk you through on how you can do exactly that, so, stick around.

What is Subwoofer crossover?

Sub-woofer frequency is the frequency at which the home theater speakers rattle down letting the sub play the Low-Frequency sounds. In other words, it is the frequency at which the speakers designate the bass notes and LFEs to the sub.

So, when the bass kicks in, the speakers tone down handing over most of the work to the sub. On the other hand, when the high frequencies kick in the sub rolls off, letting the speakers do most of the work.

The speakers and sub-woofers, therefore, work in harmony and seamlessly to give you that great sound experience that everyone craves.

Before we get into how you should set your cross over point, you need to familiarize yourself with some terminologies.

Sub-Woofer terminologies

  • Low-Frequency Effects (LFE)– These are low-pitched, deep sounds that range between 3 and 120 Hertz (Hertz is the unit for frequency or cycles/second).
  • Main + LFE– This is a crossover setting mode on your receiver where the bass or deep sounds are sent to both the speakers and the subwoofer. I would not recommend this setting and would recommend sticking to the manufacturer’s defaults.
  • Low Pass Filter (LPF)– This is an LFE channel setting that is usually included in the bass management crossover setting but is not associated with bass management allowing the frequencies above the chosen cut off to go to the speakers. In short, this is the point where the high frequencies are cut off for the Low-Frequency Effects or the .1 channel.
  • Low Pass crossover– This is the frequency below which the sub will be working to reach the deep bass notes that a speaker can’t. Ranges between 40 and 120 Hertz. Any frequency above the Low-pass Crossover is reproduced by the main speakers for anything sent to the sub channel.
  • High Pass Crossover– This is the crossover frequency above the Low Pass Crossover where the speakers take over from the Sub. If your subwoofer has a high pass crossover, you will not be able to change it.
  • Small speaker settings– A small speaker is a speaker that can only pass frequencies over a certain crossover point. These speakers do not have a full audio spectrum or only pass Mid and High frequencies. Setting the receiver to “Small” for the front, center, and surround speakers will help you take advantage of the receiver’s internal crossover regardless of the speakers’ capabilities. This is great if you have at least one sub and will help you have balanced sound experience.
  • Large speaker settings– A large speaker can pass a full audio spectrum or in other words, can pass the Lows, Mids, and Highs. If you are using a 2.1 channel set up or if you have front towers with internal subs, you can leave the front speakers to “Large” to take advantage of their full frequency range capabilities. If you do this you should also change the sub setting to (LFE + Main). This will distribute the LFE and bass to the Sub-Woofer pre-out and the Front channels.

How to properly set your Subwoofer’s crossover

You can use your subwoofer, receiver, preamp, or any audio processor to set the crossover frequency. But although most modern audio processors will have a way to automatically set the crossover point, it may be great to tweak the crossover to your likeness.

There are a few things that you should know before setting your crossover point;

  • The THX standard crossover frequency is 80 Hz. However, you are still free to alter the crossover to what fits you best.
  • Using the lower frequency response of your speakers, you can set the crossover point by adding about 10 Hz to it. You can use a subwoofer matching tool to check the speakers’ frequency, the speakers’ manual or you can also check the range online for the brand you are using.
  • With a proper crossover, the transition between your Sub-woofer and speakers should be seamless and you should not be able to pinpoint where the sub is by just listening. In short, the sub should not sound like a separate entity.
  • If you notice a peak at the crossover point, try adjusting your sub’s volume.

What does this mean for my system?

Let us take a center speaker with a frequency range of between 40 and 13000 Hz as an example. 40 Hz will be the lower frequency response of that speaker. In this case, we will want our crossover frequency to be above 50 Hz preferably 70 Hz.

So, if you set the low pass crossover point at 70 Hz, both the sub and the speaker will be producing the sound at 70 Hz. But as the frequency reduces, the sub slowly takes over, and the speakers roll-off. It is a matter of trial and error until you find that smooth transition between your sub and your speakers.

You can also use the chart below which give you general guidelines on sub/speaker crossover frequencies.

Subwoofer/speakers crossover frequency guidelines chart

Speaker type Crossover frequency
Tower speakers (with 4 to 6 inches woofers) 60 Hz
Tower speakers (with 8 to 10 inches woofers) Full-band/Large or 40 Hz
 Small-sized center, surround, bookshelf 100 to 120 Hz
Mid-sized center, surround, bookshelf 80 to 100 Hz
Large-sized center, surround, bookshelf 60 to 80 Hz
Extra-large-sized center, surround, bookshelf 40 to 60 Hz
Tiny, on-wall speakers 150 to 200 Hz

With that said, a crossover of above 100 Hz can put out a lot of muffled sound regardless of how powerful or large your speakers are. The last thing we want is unnatural bass or excessively boomy bass.

How to adjust the gain(volume) and phase settings

Gain/volume

The gain control allows you to calibrate the bass level on your subwoofer making sure it matches the speakers in your home theater. This will ensure that you get the most out of your subwoofer and speakers for the optimal listening experience.

Gain control is different from volume control although increasing your sub’s gain can increase or decrease the volume. The difference between the volume and gain is that gain controls how loud the input of the amp or sub channel is while volume controls how loud the output is the subwoofer is. Put simply, gain controls the tone relative to the input levels but not the loudness.

There is no correct setting for the gain control but correct adjustments will ensure that you are getting the proper bass level.

For the gain, I would recommend playing a track that you love and know very well. Turn down the sub to the point where you can’t hear the sub anymore then turn the gain up until you hear the subwoofer start to fill in the bass. At that point stop.

Phase setting

In a subwoofer, the phase control allows home theater owners to add an electrical delay to an audio signal and ranges between 0 and 180 degrees. This electrical delay helps the speakers and subs having a better integration.

Some subs will have a knob control to vary the phase from 0 to 180 by making small adjustments while others will have a switch (polarity switch) to toggle between 0 or 180.

If the subwoofer is out of phase with the speaker woofers, the output gets canceled out as the subwoofer drivers move forward while the speaker woofers move backward and vice versa. When they are in phase both the speaker and sub drivers will move in sync.

The phase will vary with the crossover frequency. Therefore, your sub may be in phase at 70 Hz but out of phase at 90 Hz.

Depending on the distance between your listening position and the main speakers, the sub, the amp’s, and speakers’ absolute phase, the bass may be smoother if you reverse the sub’s phase. However, in most cases, leaving the phase at 0 degrees works great.

What is a reverse-phase on a subwoofer?

Reverse phase on a sub is the polarity at 180 degrees out of phase flipping the polarity relative to the other speakers. A normal phase keeps the polarity between the subwoofer and the speakers the same.

How to test the crossover on your Subwoofer

After setting your crossover point, you should test the settings to see if the transitions are smooth and seamless.

You will need to play a song that you are well conversant with, then listen carefully. If you notice a peak at the crossover frequency, reduce the overlap until the transition is unnoticeable and as smooth as possible. In case you notice a dip, increase the overlap for a more seamless transition.

Sometimes, the output volume may cause transitions that are not smooth. Therefore, you should make sure that the volume on your Subwoofer matches the speakers’ volume.

Another option is to use a bass frequency sweep. A bass frequency sweep is a tone that will show you how your speakers and subs are handling the crossover transition starting from a high frequency as it drops down.

You can find a bass frequency sweep online or in any THX certified movies as an app and this will help you determine when your system has a peak or a deep. If there is a peak or dip, reconfigure your crossover accordingly.

Frequently asked questions

What is the recommended crossover point for a subwoofer?

80 Hertz is the standard THX-certified crossover frequency. However, you can tweak and play around with the crossover for your Subwoofer until you find the sweet spot.

What is the LFE setting on a Subwoofer?

LFE means Low-Frequency Effect. These Low-Frequency Effects are sent to a subwoofer from a system with the .1 channel (2.1, 5.1, 7.1, and so on). The .1 stands for the LFE channel.

Does a crossover improve sound quality?

Crossovers definitely improve sound quality in any sound system be it a home theater sound system or car sound system. The crossover will set up a path for which sound signals will be sent to which speaker. This helps make sure that the sub does not play a frequency that is supposed to be played by the speaker or a surround speaker playing the front speakers’ frequencies and so on.

What should I set my low pass filter to?

Typically, you want to set a low pass filter at slightly below 70% of the speaker’s lowest frequency or equal to 70%. If your speaker has a lower frequency of 40 Hz, 70% of 40 Hz is 28 Hz, therefore, you should set the sub’s low pass filter at around 28 Hz or slightly lower, let’s say a low pass filter value of 27.8 Hz.

Is LFE the same as a subwoofer out?

The LFE channel is used to carry additional bass information to supplement the bass in the main speakers removing some of the strain from the main channels. On the other hand, the subwoofer out carries the bass information from the other channels and reproduces it in the subwoofer. The subwoofer output bass information will be determined by the bass management settings for the playback system.

Final take on crossover, phase, and gain settings

Having the correct settings for your sound system will help you optimize their performance and get the most out of your system.

This can be a complex process, that will require a lot of experimenting. Also, if you are not too keen on the audio output, you can let your audio processor be it a receiver or a preamp do all the work for you.

But all in all, having the proper settings will make a huge difference in the audio experience that you get.

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