Amplifiers have two settings for speaker output, positive and negative. If the sub is wired with one polarity, then the amplifier’s sub out the terminal will push or pull with that polarity. This is because the subwoofer cone moves back and forth to create bass sound waves that either push the cone forward or pull it backward.
When powered by an amplifier hooked up in parallel (both amp terminals connected), both cones will move together when pushed, but only one will move when pulled. This difference between these movements causes uneven low-frequency noise due to standing waves inside the box cavity/port/speaker enclosure.
The solution to this problem is taking the subwoofer and inverting either the positive or negative terminal. When pushed, it moves as expected, and when pulled, it moves as expected. This can be done on some amps with a switch for the sub out polarity settings, but others require an actual electrical process of swapping terminals (called bi-amping) which will be covered in another article.
Some brands call this “out of phase,” and others call it “inverted polarity.” You may also hear these terms referred to as “+” and “-,” but that terminology is incorrect; while technically correct, we should not use such reference points because there are other electrical conventions for speaker wiring like “+/-,” “+v/-,” and “+/v.” So for this article, I will use “in-phase” and “out-of-phase” or “normal” and “inverted.”
The stereo amplifier you hook up your subwoofer to typically has only one set of speaker terminals, so if the polarity is incorrect, you cannot fix it without disconnecting wires from each other. Some receivers may have a separate non-fading (fixed level) sub-pre-out, which does not require awkward connections.
Check with your receiver’s manual to know what type of output it uses and how to change the phase setting. If your receiver does not allow changing the phase at the speaker level outputs, there are ways around it, such as bi-wiring or using an outboard electronic crossover.
You will want to check the polarity on either your receiver’s speaker-level output terminals (sub) or the dedicated subwoofer pre-outs (sub). If you are connecting multiple subs, make sure they all have their phase set the same way. If you only use one at a time, it is unnecessary to set them all identically.
However, if different amps power them, you should follow the above guidelines. Some models have built-in switches on the back of the sub, which allow for easy change between settings without opening it up. This can be very useful since once you have changed this setting on one sub unless it has a switch, the only way to return is to open up the enclosure and change it again.
So as a simple check, put your ear near the cone of one speaker and have someone start/stop the music while you flip polarity. It should sound about as loud as before, but there may be some cancellation in the bass since they are pushing/pulling in different directions; with normal polarity, both cones push which makes more bass than pulling. If you do not hear any difference (and it does not matter if you do), then set all subs to out-of-phase (inverted polarity). Again, there is no need for an in-depth explanation of what will happen; listen for yourself, or ask someone who knows acoustics.
However, if you hear a difference – one sounds more pronounced than the other or something like that – check which terminals are inverted on your receiver and set all subs to that setting (assuming they are powered by the same amp). For example, if only the left-hand terminals were inverted, set all subs’ right-hand terminals to out-of-phase and see what happens: more bass on L+R than R+L will happen.
If this does not sound correct or makes it, so one is louder than the other, switch polarity back and forth between minus plus until you get an orientation where both subs seem equally loud on their respective speaker wires.
If you watch movies with out-of-phase subwoofers, any bass effects will seem like they are happening behind you where the subwoofer is not. However, if you are listening to music, you may still be able to pick up the location of the other sub depending on how close it is, or it may just sound like there is more bass everywhere. It depends on the song itself and your preferences.
Let’s say that speakers A and B have their terminals swapped in polarity compared to speaker C. This means that when speaker A plays inside cone moves forward while the outer cone moves backward, which cancels some bass notes out; the same thing happens at speaker B but now with speaker C, so there will be no cancellation – all bass will be reproduced.
Then again, depending on the orientation of the sub’s driver concerning the listening position, it may cancel or emphasize some sounds even if they are correctly connected since not all drivers work well in a push/pull configuration.
There is no real difference between pushing and pulling on the subwoofers, so you should test both orientations and see what works best for your particular setup, but it would probably be easier to switch polarity by swapping speaker wire terminals on the receiver.
If this does not work, try inverting each speaker’s polarity (that is, connect + with – and vice versa) one at a time to see which orientation results in more bass; then switch all speakers in that group together to that setting.
Some manufacturers recommend in-phase with their speakers no matter what. It probably depends on the design of their drivers (i.e., how much sound they emit when pushing/pulling). However, most people use out-of-phase settings, so you should not have problems here unless something is drastically wrong with your setup or you are using an early 90s model without controls for phase.
A typical customer question about subwoofer wiring: “If I set all subs out-of-phase, will they cancel each other?”
No. All speakers in your A/V receiver or amplifier work together to create the net effect you hear from all of them. This is called summed acoustical output. When you flip two subwoofers’ polarity (or either one’s), then that subwoofer emits sound waves 180 degrees out of phase concerning its driver, which has the effect of canceling some bass notes out since those particular air pressure points happen at the same time.
However, any sound waves produced by other drivers will not be affected by this, so there should be no cancellation where woofers are playing simultaneously. So you could say that they counteract each other, but not entirely.
For example, if your receiver’s polarity is positive for Speaker A and negative for Speaker B, they will sound louder together than if both were set to the same polarity. With out-of-phase wiring, they would cancel some bass notes out from reproducing simultaneously.
Speakers do not have a built-in phase switch, so you can only control it on your amplifier – this means all of them at once with one switch position (minus or plus). Reaching around back to flip a tiny switch on each speaker is annoying, so most people leave them as they are unless there is a compelling reason to change their polarity.
The correct way to connect speakers: Speakers positive (+) to amplifier’s positive (+) and negative (-) to negative (-).
What does phase 180 mean on a subwoofer?
A phase 180 is a setting that can be adjusted on some subwoofers in which the polarity of the driver is reversed, meaning that when the cone moves forward, it moves backward. While this does not change any frequencies for better or worse, it does affect how the subwoofer sounds, depending on its location in your room.
If you are using multiple subwoofers in your audio system, it is essential to set phase 180 on each subwoofer to ensure optimal performance.
Subwoofer placement can have an effect on how much bass energy you perceive from one subwoofer versus another. The sub’s location has a lot to do with whether or not specific frequencies will be enhanced or canceled out due to interference or resonance based on room characteristics and the location of your ears.
For instance, placing a subwoofer close to walls that support low-frequency waves can cause cancellations at different points around the room, creating dips in response at those locations. Phase 180 tells the subwoofer which direction it should move based upon where it is placed in the room.
When a subwoofer is placed close to walls or corners, it can “see” those same surfaces as if they were an extension of the cabinet. Unfortunately, that can cause some frequencies to arrive at your ears out-of-phase, creating cancellations instead of reinforcement.
The phase 180 switch helps correct this problem by reversing the driver’s direction inside the enclosure. When it sees a wall or corner, it moves away from it instead of towards it, effectively canceling any interfering waves and allowing all harmonics to remain intact.
As opposed to moving towards a wall that would cause destructive interference similar to sound-canceling headphones, correcting polarity with phase 180 allows for constructive interference, which reinforces bass frequencies along the entire wall length instead of just a tiny strip.
That is because sound waves move in both directions from the source and do not simply cancel each other out when you have subs placed at opposite ends of a room or facing different walls. If you have subs set to phase 0 (standard) and place them on opposing sides of a room, it can cause subtle but noticeable cancellations along the entire length of the wall, which could be perceived as boomy bass that lacks detail.
Phase 180 equalizes these effects by changing the direction the driver moves so that no out-of-phase splashing occurs when it faces a boundary, resulting in a cleaner response in your listening area with increased definition at any listening position.
While this does not affect the frequencies played in any way, it does affect how your subwoofer sounds depending upon where it is placed relative to room boundaries. If you want an optimal bass response, phase 180 should be set on both the powered subwoofer and all of the active or pass-through speakers that are crossed over to that subwoofer.
In some cases, this could mean more than two subs, so if you have a larger area you’re trying to cover with multiple seating locations, then more than one single driver cabinet could be needed for accurate bass reinforcement. On the other hand, a single cabinet placed near a wall would likely suffice in a more modestly sized room, assuming the phase 180 switch was appropriately used to reduce cancellations – but even smaller rooms can have complex acoustics.
In some cases, it might be challenging to find just the right spot for your subwoofer that provides a flawless frequency response, but with patience, you should be able to get it right on at least one position, if not several. Phase 180 is an excellent tool for increasing the accuracy of any subwoofer, so knowing how and when to use it will significantly benefit your listening experience.