How To Tell If Your Subwoofer Is Out of Phase?

Norvan Martin
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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 Subwoofer 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 peaks and troughs.

how to tell if subwoofer is out of phase

How To Tell If Your Subwoofer Is Out of Phase?

1. Listen For Thin Bass

First, 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.

The easiest way to tell if your subwoofer is out of phase is to listen for thin audio because phase cancellation is most apparent in low-frequency sounds. If the subwoofer is out of phase, you will hear a thin-sounding signal with little or no bass sound. In addition, certain instrument sounds such as bass guitars or drums will sound as if they are moved around the mix instead of coming from one spot.

As you will learn, the 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 an 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. Pink noise is any sound that contains a random assortment of all the audible frequencies, meaning low, mid, and high. However, you will find more power in the lower frequencies 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.

Once you have determined that your subwoofer is out of phase, there is a step-by-step procedure that you can use to set your subwoofer phase.

What Happens When Your Surboower Is Out of Phase

On the other hand, if two signals are not timed the same when they combine, there will be some destructive interference occurring because the 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, you must 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 are normally very hard to detect.

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

What Happens When Your Subwoofer Is In Phase?

If two waves are timed 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 Is Phase Control On A Subwoofer?

Now that you know what phase is, what is the phase control on your subwoofer 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. Some subwoofers have a phase switch which allows 0 or 180 degrees phase.

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 theater system, adding the correct delay to your subwoofer signal 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.

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 80 Hz 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.

FAQs

How Do I Get The Most Out Of My Subwoofer Phase And Positioning?

A great way to get optimal function from your subwoofer is to crank the volume of your subwoofer to its maximum setting, then toggle the sound levels till you find your preferred settings.

Why Would A Subwoofer Be Out Of Phase?

Subwoofers operate on a push-and-pull principle directly controlled by the polarity of signals they receive. When a positive signal goes to the speaker, it pushes the woofer forward. When the signal sent is negative, the woofer pulls itself backward. Too many negative/inverted signals will put the woofer out of phase

Should The Subwoofer Phase Be Normal Or Reverse?

This is dependent on how many subwoofers you are using. If you’re working with one single subwoofer, your phase settings should be set to Normal.
The phase should be set to Normal if you are running just one subwoofer. When dealing with two subwoofers, one should be set to normal and the other one set to reverse.

Why Are My Subwoofers Pulsing?

This is usually a problem between the amplifier and your woofer. You have to make sure your speaker wires aren’t shorting, especially at their point of connection.

What Is Polarity On A Subwoofer?

Polarity is a term used to show whether a signal is positive or negative. Inverting polarity means that what was positive is now negative and vice versa.
This implies that reversing the connection of your speaker wires will reverse its polarity.

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 use an SPL meter and check out if the sub’s 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!

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Norvan Martin is the founder of BoomSpeaker.com. He is a professional Electronics Engineer and is passionate about home theater systems and AV electronics. BoomSpeaker was created as an online hub to share his knowledge and experiences as it relates to home theaters and home audio electronics. My email: [email protected]  Connect on Pinterest and Linkedin