If you wire your speakers backwards and listen to country music, the guy actually gets back his horse, his job and his wife

I learned about the importance of polarity when I was young. I received a ghetto blaster for xmas and I was shocked that AM radio sounded so much better than FM. AM was in mono and only came from the left speaker but FM being stereo came from both. My natural curiosity got the better of me and I opened it up 2 days after getting it. My mother was furious. I had no idea what I was doing or should be looking for but I knew the difference between positive and negative and colour coding. I saw the left speaker was wired white to + and black to - which seemed normal to me. But the right speaker was wired white to - and black to + which seemed wrong. I had already been soldering for a few years so I desoldered the wires from the right speaker, switched them and soldered them again. I put it on FM and was amazed at how good it sounded. My mother was so happy that it worked but still never gave me any credit for fixing/improving my gift. For years she would say "Do you remember that xmas you took apart your radio?" and I would always ask her if she remembered that not only did I put it back together but that it was better than when I had taken it apart. Never got any credit for that.

Having some education in electronics and a half century experience with home stereo, I can't say I learned from the video. But oh how I enjoyed seeing it explained so well. This young man has a gift for explanation.

When you listen to the initial hit of a kick drum there is a definite change of sound and feel with a single speaker wired with reverse polarity. Especially with a PA sub system that covers the 25Hz range. If everything is wired correctly you should feel the air hitting your chest. If the sub polarity is reversed then the kick drum completely loses it's impact. This because the first positive peak of the sine wave is the largest and sound pressure waves in compression have better projection than ratification of sound waves.

"Why are my speakers not speaking" "They don't agree with each other'

Years ago, I found I had accidentally wired one of my two subwoofers in reverse (in my mobile DJ rig). When I saw how I had screwed it up, I laughed so hard! I had been struggling for several months with my system - asking myself, "Why can I hear the base coming out of each sub when I stand right in front of it but when I move to the center of the dance floor, I don't hear or feel it?" No amount of EQing or compression made any difference. When I saw I had the cable to one sub wired backwards (positive to negative and negative to positive), man oh man, I was relieved. I still laugh today thinking about it.

i was taught this about 30yrs ago from some sound engineers for both studio and live situations. there's also been several articles in guitar magazine about this because especially important to the life of your gear and what's going to go on record. the last interview i read about this was from one of the sound engineers who worked on crew for Jimmy Hendrix on tour. it is as follows: when you wires your speakers backwards your cones hit in reverse. the initial blast from the speaker, i.e. that first vibration should always be the cone pushing outwards to deliver that first hit. when you wire them backwards the cones take a breath instead. i.e. pull in instead of pushing forward. that's going to affect the sound quality and volume of your session and speakers. if you got several amps going and one is in reverse, your phase is going to be messed up. it won't be something crazy like a full cancellation but your signals won't be balanced. over time, if the speakers are wired in reverse, the initial hit from your speakers will lead to damage from always sucking in at first instead of blowing outwards.

I knew this but this was the absolute best depiction of the principal I have ever seen. Well done!

This how noise cancelling systems work, listen to the unwanted sound and invert it add back to cancel the unwanted sound dynamically.

Fun fact: I once installed a dual subwoofer setup in my Nissan 100NX (yes it's been a while) .. After installation I played some subwoofer test music and was disapointed by the lack of bass from the subwoofers. I didn't understand, I had two subwoofers and still heard almost nothing. It was at this point I thought about polarity and I changed the phase setting (on one of the amplifiers). It was at this moment I learned that I should not have done that while the system was running a subwoofer bass test on 80% volume. The moment I flipped that switch I was scared to death, the system was playing so load suddenly. Learned some lessons that day!

I learned in the 1960's that wiring stereo speakers at opposite polarity diminishes the bass output of the woofer speakers. Because when one speaker is pushing air, the other speaker is pulling air. This cancels the bass sonic energy that gives music it's punch. My old tube stereo amplifier had a polarity switch that would switch the polarity of one of the speakers. I could really notice the difference!

Actually, engineer here, speaker does not have positive and negative terminals. As you said it is just a coil, which is an inductor wound to a circle. Some electronic components and machines does have polarity because it is important where does the current flow and in which direction. That is why you must put DC voltage in correct polarity on input. But as you connect coil to an AC power source you can imagine it not just changing the ammount of current/voltage but also its polarity (sine wave). That means it does not matter which way you plug it in. What were you talking about in video (the speaker muting while "reversed") is phase shift. You phase shifted the signal on one speaker so when the signal on number one is in top + section, the signal on second one is in top - section and then they indeed disturb each other.

Very simply, when one speaker is out of phase (wired backwards) in a stereo system, they cancel each other out. Mainly heard in the lower frequencies, but also affecting image and sound staging.

If you have two stereo speakers wired with opposite polarity (a.k.a half a cycle out of phase), you get an interesting effect because the signals cancel each other out in a fringe pattern which generally makes it feel like the sound is coming from around or behind you, because it will bounce off the room walls before it reaches your ears. This effect is used in legend of zelda ocarina of time for the sound of the townspeople in the castle town courtyard, and in the movie twelve monkeys for the mystery voice he hears in his head Flipping the polarity of one of the channels in a pop song can also work as a useful hack to get something approximating an instrumental version of the track, because generally the vocal is dead centre but the backing is not so the vocal gets cancelled out

This just happened to of popped up on my KZfaq. I spent many years in the automotive stereo industry, starting out very young. I could never hear the difference AS long as everything was wired the same. But wire one speaker wrong in a stereo system and you most assuredly can and will hear it. That was almost 40 years when I started, and nothing much has changed. Very important to get it right and right the first time. Nothing worse than having that person coming back because you got it wrong.

In a world of misinformation, particularly on audio, this channel is such a breath of fresh air! Superbly explained too.

You should take a pair of those linear transducers and have them agitate a shallow pool of ~dyed water. In theory, we should be able to see how the delay required to propagate the signals through the media affect constructive and destructive interference at different frequencies, distances, polarities, etc.

On a side note, the term phase and polarity are often used to describe the same thing but are actually different. Polarity inversion (flip or swap)is what is described in this video and is a 180 degree phase inversion. It is possible to have phase discrepancies that are not a full 180 degrees.

Really interesting to see how little most people (including myself) actually know about these simple concepts. I was taught I could blow up or short circuit speakers when I connected them wrongly

We used a battery to figure out the polarity of the speakers;when trouble shooting a previous installation. A dead give away is solid bass when turned to one channel or the other, but when balanced no bass out of either indicates inverted polarity on one or more speakers depending upon setup. Our shop used to troubleshoot a lot of other shops work. Motor noise used to be a huge issue for some shops.

It's actually fun to experiment with out of phase speakers and placement. If they are directly facing each other with the listener in between, you get a push-pull effect that's pretty cool. It depends on the spacing and frequencies as well.

This is the best audio engineering channel on KZfaq.

When I worked on cars as a Auto Electrician in late 80’s. So many cars had owner installed stereo’s with no regard to polarity! I could hear the dullness and fixed many.

At live events you'll often see arrays or fills aimed backstage and wired out of phase. This cancels the sound from monitors and main PA. While the crowd is getting blasted. The crew backstage can speak normally and often don't need ear pro while working. They do the same thing to create "dead zones" in large clubs - areas like the lounge or the bar. Those speakers over the bar that don't appear to be on are actually doing a big job. Theme parks even use phase cancellation to kill mechanical noise.

Back in the mid 1970's I worked installing PA systems in a grocery store chain, the system was a 70 volt system that was used to play mono background music when it was not being use for announcements. The speakers were mounted in the ceiling of the stores and to keep the speakers from canceling one another out we had to space the speaker properly to take in account the delay of the audio from each of the speakers and we had to switch the polarity of each of the speakers because of that delay to keep them in phase with one another. This was to minimize the locations in the shopping aisle that presented cancellation zones. It worked very good.

Coincidentally last week I was installing an home theater in my room (the old style one, not a sound bar) and I was wondering why the speakers had polarity and I was very afraid of inverting wires. Now everything is very clear. Thanks for the video!

While teaching physics I did a little experiment involving these waves. Take a simple minded tone generator and using a relatively low (ie slow) wave put it through both speakers. and you will find that the wave cancels in certain locations in the room. Of course this problem is nearly undetectable with actualy music since actual is changing all the time.

The cancelling out of of opposing signals is why XLR cables don't reproduce induced noise, and can therefore use long runs in noisy environments. The signal is sent down two wires, but opposing each other (with a common ground being the third wire). Any signals that are induced become opposing when one of the signals is inverted at the end and cancel out just the noise. (This is a rather simplified explanation just to get the concept across) 🙂

Right foot first or left it doesn't matter unless you want to coordinate with another. Just like dancing.

I don’t think it was mentioned in the video, so I just wanted to add that the common naming when speakers are wired the same is “in phase” and when they are wired with different polarities is “out of phase”. There are some interesting acoustic characteristics when speakers are wired out of phase in a home listening environment where the sound seems to appear diffuse and almost like it’s “floating around your head” with no distinct source. There are some fun examples elsewhere on KZfaq where you can listen to in-phase and out-of-phase white noise that demonstrate this.

That's how noise cancelling headphones work, a mic on the outside picks up the ambient noise, flips the phase and feeds it into the headphones. That's why noise cancelling can feel a bit queasy sometimes

I paused the video to write what will happen when you attach a speaker to a battery. The cone will either go forward or backward and stay there, as long as it is connected to the battery or until the battery goes dead.. if you do not know which terminal is positive, this is a way to find out, with a battery terminal marked positive connected to a speaker terminal, the wiring that makes the cone come forward away from the magnet is the identifying telltale sign. Which ever terminal you have connected to the battery when the speaker cone moves forward, Then the terminal on the speaker that you have the positive wire from the battery connected to is the positive wire on the speaker.. Being in rock bands through the 70s 80s and 90s, I have fried my share of speakers and a few amplifiers

I noticed a difference in sound decades ago on my Dad's stereo. Maybe it's not noticeable on headphones, but if the speakers are far enough apart, the inverted wiring caused it to sound very hollow.

It's possible to isolate the voice in all songs that have a similar instrumental version by inverting one of the two audio files. It doesn't work perfectly because of audio compression and sometimes the original song includes more or less sounds than the instrumental. But with a bit of luck you can get pretty good results.

Waaaay back in the mid 70s we had a stereo console with turntable that wasn't working. I was 14 and I started messing around with the player and all that. Just tinkering I got my hands on Quadrophenia. I had heard it was supposed to be in quadrophonic. Somehow by playing with the speakers and crappy old equalizer, I managed to isolate the whole drum track to Love Reign O'er Me; albeit, I could still hear echoes of vocals and other instruments. It was so good, that before the final drumming piece, I could hear one of the band members either sniffle or cough. I'll have to try it again with my gold cd I have of that album.

A little known thing about 2-channel automotive amplifiers that are bridgeable: One channel has it's terminals labeled backwards from what it really is. That channel also has it's RCA input reversed. The input signal is being sent into the amp out of phase, but since you are actually wiring that channel backwards, it all comes out correctly and in phase. This is done to make bridging the amp easier.

I saw a perfect example of this in application - there’s a documentary on making of Metallica’s Black Album where the sound engineers had James Hetfield sing in a booth with two monitors wired in opposite phase so that the mic would only pick up his voice. He was having trouble wearing headphones for some reason. It was truly mind blowing how this worked.

Many, many years ago (like 1970s), I installed 2 speakers in my car's front doors for my Pioneer Super Tuner stereo system. Somewhere, I saw an article about adding a 3rd speaker and mounting it on the rear deck of the car. I took a positive lead from the left and right channels and connected them to the 3rd speaker. Whether or not or was good for the electronics, I don't know, but it made for an interesting effect since the only sound coming from the 3rd speaker was the difference between the 2 channels. Like sounds were filtered out.

I've been doing sound in many forms professionally for over 40 years. A lot of crazy things can happen with sound. Let me first say that with a really good and highly tuned stereo system you not only get right to left imaging, (like you can here the saxophone mainly coming from the left speaker and the guitar coming from the right) , you can also get front to rear imaging. So if your listening to a well recorded symphony recording, especially with eyes closed, you can hear the violins at the front and kettle drums in the rear. If you wire both speakers backwards (both speakers are - black wire to red terminal and red wire to black terminal), at first listen they will sound normal. But if you listen more closely, you will hear the kettle drums at the front and the violins at the rear.

Great. That was nicely done. Thank you.

Years ago when speakers didn't give polarity we used to put them face to face about a half inch apart and reverse the wires on one. Which ever way sounded better is the way you would leave it. We called it putting them in the same phase.

There is one case in which connecting stereo speakers in reverse polarity is a GOOD thing. The best imaging and sound stage is acquired by placing a twin set of tweeters and midrange drivers on the outside of your main speakers and wiring them to the opposite channel in reverse polarity to cancel crosstalk. That's how the Polk Audio SDA's work.

On a side note - you *_can_* wire the speakers in the reverse polarity _(positive to negative, and negative to positive),_ and in some cases _(especially for subwoofers)_ you *must* do it _(because of the phase shift due to passive filters)_ - just be sure to wire *all* the speakers the *same way,* be it either the "regular" polarity or the reverse, because all speakers should be *in phase.*

The inverse wiring can be tailored to a room. If you hold dinner parties and want background music, but not so that it overcomes conversation, then put your stereo speakers behind the furniture, but wire one backwards. The people seated can hear the music, but the people standing cannot (or significantly reduced). Also, putting a microphone in your car, and playing the inverse wave back over the speakers will soften the road noise. Great video.

Listen to the stereo copy of the debut album by Moby grape. The producer, David Rubinson, put a lot of the backing vocals (and sometimes the main vocals) out if phase; left channel vocals were positive red and right channel was negative red. If you play the stereo copy on a mono player which were prevalent in 1967, the backing vocals and sometimes lead vocals disappear. The producer also did this on a few songs on their second album called ‘Wow’.

This is true that there should be no audible difference when your DAC, amp, and speaker are all operating linearly. However, in practice there are nonlinearities and biases in all these systems. I would imagine it would be easier to A/B test polarity inversion on cheaper systems or at very high sound pressure levels.

Extremely clear and methodical explanation. Well done.

Apropos of near nothing, way back afore most of you were born, AR LST was a happening speaker. It was said to be able to handle the output of the Crown DC-300 and SAE amplifiers. They did a multi speaker test using a steady tone to see which speaker could handle how much power. The LST's voicecoil lit up like a lightbulb at 8w and smoked at 12w... but today we have 200 watt speakers - progress!

I've said it before but I'll say it again: you are an incredible teacher!

An excellent, illustrated, detailed, demonstration of speaker polarity, an important factor one that I have been promoting for over 50 years!

When I was in school, this was one of the reasons I loved physics class. It's kinda insane to me to realize that speakers can in fact cancel each other out, but in the real world, such things don't happen that often or not as badly. The reason, as stated at the end of the video, is that the sound waves do not travel only directly into your ears from the speakers, but are also being reflected by walls, for example, thus coming into your ear just a little later than a second speaker might and the waves overlap diffently. So if you position two speakers with opposite polarities at the same distance from you, you might actually hear the sound less loud because the opposite polarities end up canceling each other out when they hit you or just before that.

Fantastic explanation ❤

From a guy who got his MECP back in the early 90s, which is pretty much being a professional in creating and building high-end stereo systems in automotive and also in homes. And I have to say this may be one of the best breakdowns in the simplest forms to make sense of this. If you are a beginner, this I think is a great example to get the basic idea. I think he did a great job at this, and realistically that is what a teacher should do Now on a little side note, when I first started out, I had two 12-in subwoofers side by side in a hatchback, 3rd gen Camaro, and I wired the subwoofers positive to negative positive to negative, remember mono amps and dual voice coil subwoofers we're not as accessible as they are now. Regardless, this does help simplify my example. So I'm testing & tuning my sound, & when i had one sub connected it would always be louder & deeper than when adding the 2nd. It was technically wired correctly. And I just couldn't figure out how this was possible. Long story short, eventually I learned how the Box the subs are in are built, the environment they're in, and other factors can actually affect phasing. Somebody told me to reverse the positive and negative on one of the subs, negative to positive and positive to negative, and I heard the immediate difference. So if you are putting together either a home and or car audio system, be mindful that this could happen. And you may want to try something like this. Obviously when you get into much higher end audio systems there are a lot of equipment to help you through this.. some of the tuning equipment can pick up this type of issue and where it possibly is coming from, all types of crossovers, equalizers and amplifiers that can adjust phasing for individual channels, etc etc, and sometimes still you have to do it the old-fashioned way

i "hear" the difference in the snare, but honestly i think it's more about feeling it. the pressure difference in a speaker pushing the note vs pulling the note into existence. sound waves are just a transfer of energy from one object to your eardrum. under normal conditions, the eardrum is pushed first, then pulled by the sound made by the speaker, where as with inverted phase the eardrum is being pulled first, then pushed by the soundwave produced by the speaker, and i think that subtle difference is what people are noticing.

I think the hearing of the snare differently does happen but only when the speakers are a distance away from your ears. With your headphones on, they are right next to each other thus any air pressure difference is directly picked up. With speakers a distance away, however, the following effect gets more pronounced - how blowing (outward movements) go forward strongly like a laser and sucking (inward movements) suck from all around. This is why your speaker playing a sine wave can actually blow a net force of air forward and blow out a candle -- and means that the initial spike of the snare will be stronger if it starts in the positive and you are a distance from your speakers - as the air pressure will travel further if the cone moves outwards

This isn't about polarity but it is about speaker output: A friend had just set up a new stereo in his living room and was getting a hum from the speakers whenever he played a vinyl record. Knowing that I was an electronics technician, he asked me over to take a look at it. After listening for a minute I asked him to bring me a clean bath towel, which he did. I folded the towel and placed it under the turntable. The hum went away. My friend was baffled until I explained to him that the top of the floor speaker cabinet wasn't the best place to put the turntable. He was still baffled until I pointed out the needle picked up the speaker vibrations and set up a feedback loop. He still calls me a genius. And he still has that towel under the turntable! 😂

Very professional as a teacher for the audience. Great speaker-tone, good info. You have a gift to teach

They start speaking Spanish

Just stumbled across this video. I've always heard about this and always made sure to wire correctly, but now I feel like I need to experiment and actually listen to this cancelling effect.

reversing one speaker on a stereo will cancel a lot of bass. And the stereo effect sounds like it's coming from one side of the room

Man spent 7 minutes explaining ANC

Every time I wired up my speakers backward's,, They wouldn't play but only listened.

4:42 actually the only difference I hear is that the audio sorta pans from left to right in one and right to left in the other. I mean the snare sounds heavier in one ear than the other and the heaviness gets reversed for each audio.

I once accidentally inverted one of the rear speakers in my car. At first, everything seemed fine. But when I listened from my front seat, I noticed there's much less sound and especially bass coming from behind. The center (mono) waves are mirrored and cancel each other out when they meet in the air. Stereo waves are different from eachother anyway so they're not affected. But in music, usually instuments like bass and kick, are mixed in mono. L & R waves are equal, so if you invert one, you'll hear less of those instruments.

WAOW... the quality of your content is impressive 😄 So sharp and clear, I love it !

2024 and most of us are still listening to mono audio😂

It's worth noting that destructive interference can happen even if all the speakers are wired correctly. It's especially annoying when just the acoustics of the room can make the sound unbalanced depending on exactly where your head is.

Audio signals, as you correctly point out, are oscillating polarity (AC) so there is no "backwards" or "forwards" in wiring up a speaker -- as long as all your drivers are wired with the same polarity. The phenomenon you're describing is called "absolute polarity" and it posits that, with a "correct" wiring, the attack of a drum hit will drive the cone forwards into the room first, the same as the skin of the drum. However, as the drum skin quickly bounces back in the other direction, the wiring of the speaker becomes a non-issue. The ears aren't capable of hearing the difference. It DOES make a difference that all your speaker cones be time-aligned, so all your drum hits occur in unison instead of canceling each other out, but that's kind of a separate issue.

they do sound different - but it is very subtle...one sounds 'softer' and the other 'sounds annoying' ever so slightly haha great educational video on this. phase inversion is great for filtering/accenting or isolating. keep it up!

Great explanation thanks

years ago having noticed polarity markings, i experimented. When one channel was wired reversed, the audible difference was loss of the 'center' of the stereo. It sounded scattered.

For a single frequency of sound, when two speakers are separated in space, there are positions in the room where the sound waves constructively interfere (such as the point exactly between them) and places where they destructively interfere (such as a point between them that is a bit closer to one speaker than the other (the "bit" being exactly one quarter of a wavelength). If you plot out these points of constructive and destructive interference, you get lines of constructive and destructive interference that are separated by distances in the range of 1/4 of the wavelength. Even when the speakers are wired "correctly", you STILL get spots that have destructive interference, but where the spots are depends on the frequency/wavelength of the sound. Flipping the polarity of one of the speakers should just move the various quiet and loud spots around the room. If one speaker is flipped, the position half-way between the speakers is one of those destructive interference spots. Importantly, this spot has destructive interference for EVERY frequency of sound. Middle C is around 256 Hz, so about 78 cm of wavelength, with higher frequencies having shorter wavelengths. For the very low frequency sounds (60Hz has a wavelength of around 5.3 metres (18.3 feet), the destructive interference zone would be a large part of the room. Thus you probably would be unable to notice a reversed polarity speaker for any of the high frequencies, but could for the lowest frequencies. Thus, if you have mismatched polarity on your pair of speakers in two corners of the room - the centre line of the room will be quiet for all frequencies, and for the lowest frequencies, the quiet area will extend well beyond this centre line. For higher frequencies, even a little distance from the room's centre line, all other places in the room will sound pretty much the same as if the speakers were "properly" hooked up.

This is largely the case of making sure the stereo speakers are properly phased (positive to positive, negative to negative). With surround sound (five channels plus subwoofer), its even more important.

And this is exactly how noise cancellation works The microphone on the outside hears the incoming audio and plays a "flipped" version in the earpiece, the sound from outside and the sound from the earpiece cancel eachother and you don't hear outside interference

Just to clear some things up here. If the driver is wired to move outwards at DC, this does not mean that it moves outwards for a positive voltage across the entire frequency range. Below its fundamental resonance frequency, it does move outwards for a positive voltage (assuming one polarity of the two choices). However, then it moves INWARDS for a positive voltage at higher frequencies well above it fundamental frequency. This is typically also what you want, because the inwards movement will result in a positive pressure when the driver is loaded with a free-field-ish condition, which a room pretty much is at higher frequencies (excluding at lot of details here). This goes against most acoustical engineer's intution, but the theory as well as simulations will reveal this. So the battery test is merely a proxy for what is actually going in the frequency range of interest; the pass-band of the driver.

great videos!! - easy to follow and to the point!........keep them coming! 👍

Excellent lesson!

in fact this was the topic of my Master study in Physics. I discovered that the non-linearity of our hearing system can make polarity differences audible. This was the case with headphones and in the anechoic room with signals with distinct higher harmonics. In a "normal" room, the reflections mess up the phases of a the frequency components (Fourier) and there is no more interference with the auditory distortion products. Therefore, in a normal room you cannot hear the effect of polarity.

Excellent information

Well explained! It's about adding waves. Thanks!

Thank you very much for taking the time making this video….it is appreciated

Beautifully explained.

There are times when reversing polarity is a good thing. I have an SQ build in my car right now with a 3 way set up up front and my midrange are reversed polarity compared to my mid bass and tweeters. It helped me achieve a brighter “center stage” .

As long as everything is wired backwards it doesn't matter, it's all relative. For instance wiring a subwoofer backwards can cause issues at the crossover frequency but can sometimes actually do the opposite and fix those issues, this helps if you don't have a variable phase knob and you can only invert polarity

As a Retired Disc Jock, I have seen and heard a reversed speaker under heavy Audio Load give out what is called "Baffling." This occurs when the backside of the Coil recoils against the rear of the Magnet Enclosure Housing. This can also result in structural deformity of the said Coil. MJ. in B'dos.😢

I feel like the snare drum test, if i close my eyes the inverted sound might sound very very slightly more duller. But I think human inner ears just turn analogue sound into a Fourier transform which it sends to the brain, which I'm 99% sure shouldn't be able to tell phase information like that... So i'm probably imagining it. 6:50 what you'll end up getting is an interference pattern. If you're in a room and you're standing N wavelengths from speaker 1 but N+0.5 wavelengths from the speaker 2. The speakers will destructively interfere with each other. Of course that's only really a problem if you're playing a single tone... Edit: at least that's what i thought until I saw your comb filter video...

I did this experiment a few years ago and found that if you connect all speakers the wrong way, that is all negative are connected to positive and all positive to negative, the system plays excellent. Once one speaker is connected differently, the cancellation starts.

*BEAUTIFUL EXPLANATION*

The algorithm was strong with this one. Very cool!

1) The stereo is the lab equipment. So your lab equipment needs to be of a quality that can reveal the audible differences. 2) The song you are playing for the test matters. Most songs have sub-par sound quality. In such cases, it is difficult to hear which one is right, even on a highly revealing system. Although, on such a system, you will hear a difference. However, if you walked in to the room, and someone asked you "Which one is in phase, and which one is out of phase?", you would not be able to tell -- even though you will hear ever so slight differences. Again, that is with a so-so sounding song. The vast majority of songs are so-so (sound quality wise). With a properly mixed and mastered recording, it becomes more obvious which one is in phase, and which one is out of phase.

I built a speaker box years ago where they were bolted face to face with one inside a sealed box and the other outside the box. Inside the box was wired normal and the outside speaker wired backward. It worked great.

I learned this a long time ago before even viewing this video. The speaker will work either way but if you connect them backwards, they will be "out of phase", the cone of the speaker moves in the opposite direction as it should which affects it's performance.

Phase is shifted 180 degress. Thank you. This was my ted talk.

Back when I was building and tuning subwoofer enclosures, and learned all about proper tuning for clipping avoidance, I accidentally mis-wired the internals of one enclosure. (Lousy blue/blue stripe wiring convention!) Anyway, had it all nicely tuned for max wattage at 60hz and I could hear "bass" but it was like weirdly quiet. No boom. No SPL compression on my chest. Yeah. . .a quick recheck of everything, discovering my mistake, fixing it, and retry almost left my ears bleeding. 😂 First hand experience in cancelling sound waves! Thanks for the vid too! Excellent scientific description of my "oops!"

Had this happen in a hilarious way once.. We were installing a subwoofer and the L/R channels went into the back through the crossover and back to the L/R speakers. When they plugged one, the subwoofer was loud.. When both it was quiet. I kept trying to tell then what I thought was going on but the older guys all knew better than me since they are all 20 years older and have experience as musicians but I am a self taught sound guy. I gave up trying to get them to listen to me so I wandered off until they gave up in frustration then unplugged their 1/4 inch to XLR cables and replaced them with 2 adapters. When I put them into my cable tester I could see the XLR cables each were wired differently. The more experienced guys came back to find everything working.

This makes it a lot easier for me to understand noise cancelling speakers because they would be actually be pushing the opposite direction from usual even though the signal is so similar

4:48. I noticed a difference when the music was playing at the start, but that singular sound was the same. With more context, you definitely noticed something weird, but it’s almost like it had some weird effect turned to 2% opacity, and if it was 100% it wouldn’t even be listenable.

The sounds cancelling out like that is the basic principal behind Active Noise Cancellation headphones. Though it does make me curious if you could design a room that ends up having noise cancellation zones with this technique and an oval shaped room.

This is why bass traps are a good idea. Bass reflections are out of phase with the sound coming from the speaker, causing cancellation. Bass traps swallow the reflections.

Reverse wiring does have an effect depending on the type of sub, enclosure and power. A sub designed for outward throw if wired backwards can cause bottoming out and or reduced sound at higher power input. A backwards design is usually one for mostly enclosure tuned ported, so backwards throw can cause over heating of the coil from travel outside the magnet. And neutral throw, same in as out isn't effected as much by reversal input. The signals are ac current, but just like ac house current, one direction is longer than the other. Your primary signals is for sound, the reverse helps with return and dampening. A forward throwing sub in a sealed enclosure will have reduced sound, where as a forward throw in a ported enclosure can have increased tuned volume but greatly reduced outside of the bandwidth. At low volumes especially with computer or TV speakers which are normally neutral throw for best SQ and don't need high outputs, of course you won't hear a sound difference