Should My Subwoofer Phase 0 or 180?

Subwoofers / By Norvan Martin

So you have followed all the steps to setup your subwoofer, you’ve adjusted Hi/Lo Level (Gain or volume) and crossover. But what about the phase? Should your subwoofer phase be set to 0 or 180? How to know whether 0 or 180 is the proper setting for your subwoofer?

In this article, we will explain the difference between subwoofer phase 0 and 180 setting and which you should choose for your subwoofer. 

Subwoofer phase allows the user to add electrical delay to the incoming signal of the subwoofer. This delay can be over 0 to 180 degrees. Use the phase switch to match the phase of the sub to the main speakers. This is dependent on the positions of the mains and sub

You should set your subwoofer to 0 if you want your subwoofer and speakers to be in phase and if they are placed in the same area and pointing in the same direction. Set your subwoofer to 180 if you want the subwoofer and speakers to be out of phase if they are on opposite sides of the room and pointing at each other. 

For many people, selecting 0 or 180 degrees phase simply come down to choosing the option that sounds better and louder. This is fine as well. However if you are doing this, you need to continuously adjust the volume of the subwoofer until everything sounds good. 

Let’s discuss further. 

What Is Phase Control and What Phase Should You Set?

Subwoofer phase allows the user to add electrical delay to the incoming signal. This delay can be over 0 to 180 degrees. Some subwoofers only allow a phase switch of 0 or 180 degrees. These settings are also referred to as subwoofer phase normal and reverse.

Adding this delay can help the subwoofer to integrate better with the loudspeakers in the room. Here is the difference between subwoofer phase 0 and 180:

Phase 0 (Normal Phase): Phase 0 simply means there is no delay to the incoming signal and the speakers and sub are in phase.

You can do this when the speakers and sub are placed in a similar area and in the same direction. This causes constructive interference. This means,m the speaker and subwoofer waves add together to give an ever greater soundwave. 

Phase 180 (Reverse Phase): Setting the phase control to 180 degrees reverses the polarity of the subwoofer. This places the sub in the opposite polarity of the loudspeakers. This means that when the subwoofer’s driver moves inward, all other speaker drivers in the system move outward.

You would do this if you place the subwoofer on a wall opposite the speakers. This reduced destructive interference, meaning, the subwoofer, and speaker waves do not interfere with each other. 

The disadvantage of this however is that you will be canceling bass from your main speaker, thus reducing the overall output of bass which is counterproductive.

Variable Phase: Many subwoofers feature a continuously variable 0-180 phase control which allows you to adjust the phase of the sub in small increments from 0 to 180 degrees. Other subwoofers only offer a phase switch which is 0 or 180 degrees.

This means the sub and speakers are either in phase (0 degrees) or out of phase (180 degrees). Please note that setting the sub to some varying degree between 0 and 180 will cause some cancelation of the resultant total signal.

However, a subwoofer with a varying phase adjustment will allow you to more perfectly match phases between the speakers and sub. This will of course minimize losses due to cancellation which increases the overall efficiency of your sound system/

What Is the Subwoofer Phase Switch Used For?

A subwoofer phase switch is used to adjust the subwoofer phase between 0 and 180 degrees.

Some subwoofers have variable phase control that allows you to adjust this phase from 0 to 180 degrees. This means that you could change the phase to say 9 or 10 or 80 0r 100. 

You can check out this guide to learn more about what a subwoofer phase switch is for. 

Subwoofer Phase and Positioning

The phase switch is used to best match the phase of the sub to the main speakers. However, this is dependent on the positions of the main speakers and sub. Here is the rule of thumb:

If The Subwoofer and Speakers On On The Same Side of the Room: If the subwoofer and speakers are on the same side of the room and if they are pointed in the same direction, then you can set the phase of the subwoofer to 0.

If The Subwoofer and Speakers On On Different Sides of the Room: If the subwoofer and speakers are on the different sides of the room and if they are pointed towards each other, then you can set the phase of the subwoofer to 180.

Subwoofer Phase and AV Receivers Distance Setting

While subwoofer phase setting has always been used to align the subwoofers with the rest of the speaker system, modern AVRs (AV receivers) offer an additional setting.

Modern AVRS offers a subwoofer distance setting which offers a more precise and proper way to time-align the sub(s) with the mains. This means that if the AVR has a subwoofer distance setting, and if you only have a single subwoofer in the system, the phase should be set to 0 and the distance setting used.

What Is Receiver Distance Setting?

The distance setting on your AV receiver is actually time delays. The time delays allow the waves to constructively interfere or add up.

Let’s take an example. Let us say that you have surround speakers that are 4 ft from your head and your subwoofer is 12 ft away maybe in the corner. If the sound came out of all the speakers and sub at the same time you would hear the sound from the surrounds first then you would hear the sound from the subwoofer.

This delay would of course cause perceived distortion, inaccuracies, muddiness or echoes. So the AVR distance setting allows you to adjust the system so that all the sounds (both from the main speakers and the sub) reach your ear at the same time.

How To Set AV Receiver Distance – Measuring Time Dealy and Distances

To set the correct receiver distance setting, you can use any measuring equipment (e.g REW+UMIK-1) or at least an SPL meter. 

Assuming you don’t have any measuring equipment, you can simply use an SPL meter. There are even some phone apps that function as SPL meters.

You can find many smartphone SPL apps on your app store. In addition to using the SPL meter, you can get test tones downloadable from the internet. Some are even available on YouTube. 

In any case, there is the general process:

1. We will start with the center channel. For this channel, set your AVR to the Dolby PLII surround mode or Dolby Surround. In this case, you should be getting output from the center channel and sub(s) only
2. For the left and right channels (FL/FR), set your AVR to the Stereo surround mode. In this case, you should be getting output from the FL/FR + sub(s) only
3. Invert phase on your subwoofer(s)
4. Using your test tones, play a sine wave that corresponds to your crossover frequency (i.e. 80hz).
5. Measure the output with the SPL meter about a foot in front of your face at the main listening position
6. Gradually increase the sub distance setting in the AVR in 1′ increments.
7. Choose the sub distance setting that gives you the lowest SPL reading.
8. Invert the phase on your sub again.
9. Check if your wub is in phase. To learn more, check out our guide on how to test if a subwoofer is in phase.

Why do we invert the phase? Well simply because with an SPL meter, it is easier to find the lack of bass than it is to find the peak. 

Should I Set The Subwoofer Phase to 0 or 180?

The decision on whether to set your subwoofer phase to 0 or 180 degrees should be based on three factors – subwoofer vs speaker positioning, decibel reading and sound quality. However, the final decision should always come down to sound quality.

Subwoofer Phase and Positioning

The phase switch is used to best match the phase of the sub to the main speakers. However, this is dependent on the positions of the main speakers and sub. Her is the rule of thumb:

If The Subwoofer and Speakers On On The Same Side of the Room: If the subwoofer and speakers are on the same side of the room and if they are pointed in the same direction, then you can set the phase of the subwoofer to 0.

If The Subwoofer and Speakers On On Different Sides of the Room: If the subwoofer and speakers are on the different sides of the room and if they are pointed towards each other, then you can set the phase of the subwoofer to 180.

Use an SPL Meter (Test Tone)

You can use an SPL meter or SPL app to determine which phase (0 or 180) gave me more decibels on a given Hz. You would choose the setting that has the highest devicebls. 

By given Hz, we really mean the crossover region, water that is for your subwoofer. This is because you want the most output at the crossover region as that’s what is most audible when transitioning from the sub’s low pass filter(high cut)to the mains high pass(low cut) filter.

What If You Don’t Have An SPL Meter

As we mentioned, if you don’t have an SPL meter, you can use an SPL app. If you don’t have a smartphone, you can reverse polarity(swap + and – speaker wire) on your main speakers and listen for the most dropoff in bass.

You would then leave the phase adjustor at that phase setting and put the main speaker wires back the way they were originally(+ to+/ -to -) and the higher output will return. However, this will not work with a subwoofer that only has a 0/180 phase switch, you will need a variable phase knob. 

Sound Quality

At the end of the day, sound quality is the most important factor to consider when setting the subwoofer phase. Once you are getting the best sound quality, then nothing else matters. 

For example, in some cases, you may be getting a high decibel output, but the lower decibel output sounds better. Go with the lower decibel output in that instance. 

Adjust the phase of your subwoofer and keep whatever setting sounds better to you, it can really be that simple. 

What Should LPF of LFE Be Set To?

When setting the subwoofer phase, many people also ask about the correct settings for LPF of LFE. The LPF of LFE means subwoofer low pass filter of low frequency effects.

The setting applies to LFE content (low frequency effects or bass) that the sub handles by itself. In other words, it is a ceiling on the frequencies that the subwoofer will handle.

To put it simply, this setting is the upper frequency limit of the low pass filter of your subwoofer. 

In general, LPF of LFE should can usually be left at the default setting which is normally anywhere between 80Hz and 120hz. 80 Hz is to be used if you are not considering LFE and setting the LPF alone.

In some cases, if you have Audyssey set up (especially Audyssey MultEQ), it could set your LPF of LFE setting to say 100Hz. We still recommend 120Hz in any case. 

This is because there is content mixed into the LFE track up to 120hz. As such, if you have it set lower than that you may remove some audio content.

In some cases, however, people find that setting the LPF for LFE at 80hz sounds better. This is completely OK as well. Sound quality is the most important factor.

For more detailed information, please check our guide on what you should set your subwoofer low pass filter to as well as what is LFE+Main and when to use it.

Does Subwoofer Phase 180 Sound Muddy?

Setting your subwoofer to 180 degrees can sometimes cause your system to sound muddy. This is often due to destructive interference.

However, this is often due to a high crossover frequency. If you are having this issue, set your crossover frequency to about 80Hz.

Does Phase Matter To Subwoofer?

The phase of your subwoofer is very important, when your subwoofer and main speakers are out of phase, the woofer cones on the subwoofer and speakers will be out of sync, leading to distortion.

When your subwoofer and main speakers are in phase, the woofer cones on the subwoofer and the speakers will move forward and backward in sync at the subwoofer crossover frequency. This way they can boost each other’s output.

Subwoofer Crossover Frequency

The crossover frequency of your subwoofer is the frequency at which your speakers start to fade off and your subwoofer kicks in with LFEs and bass notes.

Nowadays AV receivers are designed with an auto EQ program that will automatically analyse and determine the appropriate crossover frequency based on the capabilities of your speakers.

How Do You Set The Phase On A Car Subwoofer?

• Play a track on the car stereo and turn up the volume more than halfway.

• Open the trunk.

• Observe the woofer cones.

• Check up on the car amplifier.

Flick the phase switch on the amp to either 0 or 180 degrees depending on how you have your subwoofer wiring setup.

What Does An Out Of Phase Sub Sound Like?

The most common determinant of a subwoofer that is out of phase is loss of bass. Listen to the bass, then change the balance to the opposite speaker. If your speakers are out of phase, you will notice more bass response from one speaker than the other one.