How To Tell If Your Subwoofer Is Out of Phase
(Last Updated On: September 27, 2020)

Many people get confused when trying to determine what phase to set their subwoofer to as well as how to tell if their subwoofer is in or out of phase.

In this article, we will simplify the idea of audio phase as well as explain how to tell if your subwoofer is out of phase.

 

What Is Subwoofwer Phase?

Simply put, audio phase refers to the timing of the audio waveform or audio signal. Audio signals travel as what we call sine waves which comprise of peaks and troughs.

how to tell if subwoofer is out of phase

What Happens When Your Subwoofer Is In Phase

If two waves are timed exactly the same, their peaks and troughs will match up and the waves are said to be in phase.

Since the waves are in phase and the peaks and troughs match up, the signals with add up. This is what we call constructive interference which will result in a stronger overall signal.

Check out the illustration below.

constructive interference waves in phaseAs far as the subwoofers and main speakers in your home theater system are concerned, this physically means that the cones on the subwoofer and the speakers will move forward and backward in sync at the subwoofer crossover frequency.setting subwoofer crossover

The crossover frequency is the point at which the subwoofer frequency cuts out and the speaker frequency cuts in. In other words, it’s the highest subwoofer frequency and lowest main speaker frequency.

In the end, they’ll reinforce each other’s output. Check out the following link to learn more about setting subwoofer crossover frequency.

 

What Happens When Your Surboower Is Out or Phase

On the other hand, if two signals are not timed exactly the same, when they combine, there will be some destructive interference occurring because they signal peaks and troughs won’t match up exactly.

The more out of phase your signals are, the more destructive interference will occur. If the signals are fully out of phase, there will be complete destructive interference or signal cancellation.

subwoofer destructive interference

Physically, this means that the cones on the main speakers will move backward while the subwoofer cone moves forward, and vice-versa. They won’t move in sync.

In this case, they will degrade or cancel each other’s output.

This means the resulting signal will be weaker and not as clear.

For this reason, it is very important that you set the correct phase on your subwoofer in your home theater system to ensure that the sub is in phase with the rest of your system (main speakers, center speaker, etc.)

Phase is important in sound systems because this setting can have audible implications on the elements in a song, on sound effects, or any audio for that matter.

Despite this fact, in most cases, audio out of phase issues will manifest only very subtly and is normally very hard to detect.

Suffice it to say that when the system is in phase, the audio will be stronger and crisper.

 

What Is Phase Control On A Subwoofer?

Now that you know what phase is, what is the phase control on your subooffer and how does it work?

how to tell if your subwoofer is out of phase setting 0 to 180

Simply put, the phase control on your subwoofer will allow you to add an electrical timing delay to the incoming signal. In general, phase control operates over a range of 0 to 180 degrees.

Most subwoofers have this continuously variable 0 -180 phase control knob which allows the most complete range of adjustment in small phase increments to achieve the best sound possible.

Depending on the phase of your speakers in your home tehter system, adding the correct delay to your subwoofer siglal will help you better integrate the loudspeakers.

So what does the 0 to 180 degree setting mean?

Well think about it this way, this value determines the degree to which the wave is shifted which determines the timing of the wave. The higher this number, the more the wave is shifted or the more delayed the wave is.

 

How To Tell If Your Subwoofer Is Out Of Phase?

The use of the phase switch is to help with integrating the sub with the rest of the speakers in terms of setting the proper phase and ensuring that the sub and main speakers are in phase.

However, it is important to realize that there is no hard and fast rule as it related to setting your subwoofer phase.

This is because finding the best subwoofer phase will largely depend on the placement of the other speakers relative to the subwoofer and room acoustics.

However, there is a step by step procedure that you can use to set your subwoofer phase.

So how do you tell if your subwoofer is out of phase? 

1. Listen For Thin Bass: Firstly, phase cancellation is most apparent in low-frequency sounds, especially at or below the crossover frequency.

This is because the out-of-phase effect will be stronger at lower frequencies and so will result in a loss of bass and may even distort the stereo imaging.

You need to listen carefully when trying to detect phase issues. When your subwoofer is out of phase, the audible result will normally be a thin sounding signal with little or no bass sound.

Another common problem that is harder to detect is the bass moving around the mix rather than coming from a single spot.

As you will learn, phase is difficult to determine by listening alone. You need to listen carefully and have some understanding of how music sounds over low and high frequencies.

To make this process easier, set your system at a higher frequency range and listen for phase issues.

You can do this because it is easier to hear phase changes when the crossover is more gentle and higher up the frequency range.

2. Vary and Listen: Another simple method is to have someone vary the phase of the sub while you listen from the main listening position. The best phase setting will be at the point where the bass is most intense.

3. Use a SPL or dB Meter: This method is for persons who aren’t very familiar with sound frequencies. You can use an SPL meter (Sound Pressure Level meter) to see how it affects the sub’s output with pink noise.

It is usually recommended to use the setting that yields the highest pink noise output when the sub’s + main channels are playing at the same time. You don’t even need to purchase an expensive meter to do this. There are many SPL or dB meter apps out there.

 

Subwoofer Phase and Frequency

While you will be able to detect phase issues easier at higher frequency ranges, it is important to realize that setting phase is always dependent on frequency.

As such, subwoofers and speakers are said to be in or out of phase at a particular frequency.

In other words, the phase of both devices changes with frequency. This means that if you get your speakers and sub in phase at 80 Hz, they might not be at 100 Hz.

So, even if you get your system in phase at 100 Hz, you still need to recalibrate and get it in phase at 80Hz if that is your normal operating frequency.

 

Normal and Reverse Subwoofer Phase

While many subwoofers have a 0 to 180 phase dial, other subwoofers may have a simple 0/180 phase switch which allows you to change the polarity of the subwoofer. Normal and Reverse Subwoofer Phase

Setting the phase to 0 is known as the normal phase while setting the phase control to 180 degrees reverses the polarity of the subwoofer. Here’s a quick overview:

  • Normal: keeps the polarity (+/-) of the Sub the same relative to the rest of your speakers.
  • Reverse: flips the polarity (-/+) of the Sub relative to the rest of your speakers. This means that the sub will be 180 degrees out of phase.

When you reverse the polarity of a subwoofer, the subwoofer’s driver moves inward while all other speaker drivers in the system are moving outward.

subwoofer phase switch

Of course, this is not as useful as a true variable phase control. However, it is actually useful in some applications.

Take for example, if the subwoofer is placed on a wall opposite from the speakers, reversing the subwoofer polarity can improve the sub’s response.

 

Conclusion

There are many ways to determine if your subwoofer is out of phase. One way is to listen for thin bass just below the crossover frequency, another way is to vary the phase and listen at the main listening position in the room or us an SPL meter and check out the subs pink noise output is affected.

In general, you will get the best bass out of your subwoofer by varying settings such as amp gain and crossover frequency. However, you need to consider your subwoofer placement in the room as well as overall room acoustics to get the best bass. All the best!