Subwoofers (and the air itself!) are NOT in-phase with your mixer and amplifier. 

You've gotta be one of the most passionate, most interested, most curious, and smartest people in audio on the Internet right now.

You are the only one in the web teaching actual science with audio engineering. Things most audio “engineers” have no clue about. Thank you

Two years studying audio engineering at Belmont and I hadn't heard 80% of the terms you've used today 😂

If you have a solid understanding of kinematics and fourier transforms it makes this stuff easier to grasp, but that is honestly more esoteric than what most people need to actually apply this in practice. This is BY FAR one of the best intuitive explanations of how phase works with sound reinforcement that I have ever come across. It's something I've understood but always had a hard time explaining in detail because it's such a math heavy topic to really get in to. Great job bridging that gap! Would love to see more.

This is now one of my favourite videos on tech. It's just... the applied sound engineering and exploration, I had to rewatch it to gain insight

For the first time ever, I finally understand the affects that phase response has on a system because of this demo. Thank you!

Most educational half hour I've spent in a long time. Awesome. Thanks!

Love it, this reminds me greatly of my electrical engineering classes at uni. You're like connecting all the dots when it comes to audio applications

I'm not sure I'll ever need any of this knowledge, but it was super interesting to watch. Your explanations are very detailed, yet easy to grasp.

Wish i’d found your channel earlier. I just finished my bachelor degree in music engineering and your videos would’ve made my time much much easier lol. your videos are so detailed and intuitive please keep making these.

Amazing! Amazing amazing. This is the kind of content I've always wished existed. Now we just need a pipeline for absolute beginners to get to this point

I believe there's a term called Jerk when decribes the rate of cahnge of acceleration. Also wonder how damping factor and power bandwidth comes into play. Awesome video, thanks!

I have to say that watching this video in the middle of the night accompanied by a glass of whiskey is a wonderful experience. Some parts you understand, while others seem familiar, just like the alcohol.

That was one of the best descriptions I've ever seen for the behaviors of the "signal, driver, soundwave, mic" relationship. It's a very complicated process, and this is a great way to break it down and understand each component. For your next challenge, you should try to do the same type of breakdown for a bass-reflex cabinet. That is one of the most important and least understood elements of speaker/cabinet design. I've been struggling to wrap my head around it for ages.

An insane amount of useful information and I’m all here for it! The visualizations are super helpful too, thank you so much for the effort!

Great video. I really like how you've taken something that can very dry, mathematical and abstract and make it understandable in an intuitive way

The phase relationship between the input signal and the output from the speakers is actually much more complicated in practice. The reason is that the equation m.a+c.v+k.x=F(x) applies to established sinusoidal stimuli. In practice, the musical signal is not like that. It is rather a transient process in which the behavior of the speaker is determined by an inhomogeneous system of differential equations, which makes the issue of instantaneous phase shift quite complicated. Thank a lot for video.

Hands down the best video I've seen describing audio phase relationships both in thoroughness and in critical thinking. I can only hope for more people to enjoy this!

In the near-field of a dipole, which is where you're measuring with your microphone, the pressure and the velocity are 180 degrees out of phase. The driver cone determines the air velocity and the microphone picks up the pressure field. That's where your phase shift at 14:00 comes from.

This must be one of the most beautiful videos I have seen. I watched it 3 times already and will keep doing it. It explains so much and rises so many new questions...

The animation 24 minutes in was such an awesome lightbulb moment, thank you!! Epically useful video!

nothing is in phase my friend

When i was at university we learned that particle velocity and sound pressure are out of phase in the nearfield and in phase in the far field. And considering that the Driver stimulate the particles directly, resulting in particle velocity and the microphone converting sound pressure to electrical current, your results would make sense (basically also what you explained at 23:55). It would be interesting to see the same measurements in the far field.

I totally love the detailed technical explanation. Fantastic video. Little brain numb (in a good way) after watching it with high focus. I learned quite a lot from this video. Thanks for the great work! I really didn't expect to get info on both the advanced electronics I expected, but on fluid dynamics as well. I never thought about that before, but it really does make sense having to factor air pressure, displacement etc. And that's all Fluid Dynamics/Mechanics. Totally awesome.

That's an incredibly inciteful tutorial. I had no idea how much went in in the journey of music through my sound system! Terrific demonstration!

I look at those Yamaha Dante interfaces everyday,This a great video. Great channel

Fascinating. You were able to come up with great ways to show what I have suspected for years.

In a car, what pushes you (pressure) back in the seat? Acceleration. Not speed and not position. Similarly the air in front of the speaker cone becomes pressurised by the acceleration of the cone, not the speed or the position. This should also explain why high frequencies have more acoustic power thab lows at the same driver displacment - acceleration is higher. EDIT: In hindsight I misspoke. Pressure is not created by acceleration, but sound (modulation of pressure) is. Thus g-force felt in a car is analogous to sound energy.

Love it when i can feel like i understand a complex subject without actually understanding the any of it 😅. But in all honesty, you did an excellent job of explaining things i know little about without losing me and the length of the video perfectly pushed my brain all the way out to its limits!

Love it, appreciate your curiousity and determination to understand things. Some nuggets of gold in here for those into audio system measurements

21:00 This was the most interesting part for me! Great work explaining the microphone behavior.

This changed my life

Immediately subscribed! The fact YT just recommended your video to me tells me its algorithm isn't as good as it should be. Awesome work! This must have taken a lot of time!

Wow this all makes sooo much sense. Wish I found your channel sooner. This has answered alot of questions I've had when figuring out phase relationships between multiple driver setups. I can actually hear phase differences in drivers after some listening. I went and bought rta mics to see if I could see what I was hearing. Turns out I was right. This video puts everything in perspective for me fromy own experience. It all makes perfect sense. Finally a channel that makes my brain tingle! I love it. ❤

Thank you for this excellent presentation of complex topic!

AC coupling is just a lower cutoff frequency low cut filter... oh hey you said it yourself. I better stop commenting. Oh yeah by the way, absolute phase does not matter as much (no human can hear absolute phase differences from a single source). Of course group delay is more important (yes they are related by frequency), but even then up until a certain point mostly unnoticable in a PA kind of situation (room modes and accoustics in general will make sure of that). I still respect this kind of research and compilation of knowledge.

Wow This was so much fun stepping this out the way you have.. Learning tons.. Love it...

Regarding the 180 phase shift between the laser sensor and the microphone at 13.30. The first is a position sensor, the second a pressure sensor. The pressure at the speakers is proportional and in phase with the acceleration of the membrane. There is a mathematical relationship between position, velocity and acceleration of a quantity varying according to the sin law. relationship position - velocity d(t)sin(x)=cos(x) - they are 90 degrees apart. velocity - acceleration d(t)cos(x)= - sin(x) - they are again at 90 degrees. Position-acceleration relationship d(t)d(t)sin(x)= - sin(x) - they are 180 degrees out of phase.

Congrats on the bump in views. Great content.

This content was very nice and blissfully pleasant to watch! Thanks

Absolutely INCREDIBLE content and presentation - lifetime producer and audio & physics enthusiast here. You are one of the top RU-vidr's I've come across mate

I all my life play Viola in symphony orchestras, really good ones. I sit where Bach, Mozart and Beethoven sat in the middle voices and directly in front of the conductor. I sit where the listener sits and I worked in public radio as a classical music host and announcer. I could hear what a lot pretended to hear.

This video is brilliant. Taking advantage of the fact that your branch is also music and not just a sound scientist, make experiences with real music (even if you don't have the ability to explain what you see, and therefore it would be much more fragile conjectures). They are all individual or isolated signals, when in reality we work with complex signals. It is true that pink noise is a complex signal, but it still lacks the transient component, which is a key attribute in music.

Anyone else find interlaced video to be distracting for some reason? This is super interesting.. I wonder how hard it would be to create a frequency based delay filter that would compensate for the delay, and how that would sound Thanks for making this! I'm gunna have to look at your other videos, Subscribed!

This is good content. Thanks for the effort!

Great work! This is the level of detail I would love to see from all audio hardware testing. The only mistake I noticed is that you didn't deinterlace the video around 16:30 which results in horizontal comb artefacts in video. Another example of missing deinterlacing can be seen around 18:22. I'd recommend using ffmpeg for deinterlacing because it has resulted in best quality for me but other options do exist, too.

There's a small mistake on the "AC coupled" waveform drawing (graph on the right) at 1:55 , after the "DC" portion of the signal, the AC coupled signal should not have any positive slope since there is no positive slope in the original signal. (like when the DC battery is released at 2:12) Thanks for the nice thorough video again :)

Thanks for this insight! Exactly the content for my morning coffee (and then I have to watch it another 5 times to somehow comprehend 😅)

A great explanation of the phase changes of the subwoofer, understanding it won’t get you a hit record but it an interesting curiosity.

While nothing new to the folks designing such hardware, this is an awesome first dive into this topic. Great work! Interesting things I've noticed: - As pointed out in 2:30 1st order HPF will create a 90° phase shift. A 2nd order filter will create a 180° phase shift. - In 17:10 you can see the driver reach 180° phase shift. At 180° the speakers output becomes pretty useless. This seems very similar in behavior to the Gain Bandwidth Limit(GBW) of an OpAmp. (The GBW basically dictates how much of your maximum amplification you can use for a certain frequency). When driving the speaker at a higher volume, I would expect the amplitude to drop even quicker, but the phase behavior to remain the same. - I would love to see a plot of actual time delay instead of phase

Amazingly well presented explanation of the very interesting behaviour! 5/5 will view again 'cuz I'm not entierly sure I got it nailed down on first attempt.

one thing I can add , as I know a sound person or two, is that delay lines are often used with big systems to ensure all drivers are in phase with each other. And if any are at a different distance either ahead or behind the main drivers, then the sound from them is phase corrected with what is comming from ahead or behind them

The current lags behind the voltage in an inductive AC line. Since speaker lines are more or less varied-voltage AC, and you're coiling it around that ferrite ring, you're creating inductance. That inductance will affect the phase and frequency of the output. This is why we use coil inductors to make low-pass circuits. And that's not to mention all the other interference from various amp stages and whatever else. So long as the delay is no more than ~2ms it's fine, humans generally can't hear intervals that small anyway.

This is excellent! Learning so much here!

Have you thought about the mic being too close to the coil and reading magnetic force instead of air pressure?

god damn, it took me years to understand but this video helped ma A LOT!

First time viewer. Awesome stuff. Would love to see a part ii of what this means in practice

Crazy setup. Put a lot of effort into this !

yup. particle velocities ... pressure ... reactive near-field acoustic energy (air) flowa ... mechanical impedances. great video.

Very good content, nicely explained! 💪

I'm only partway through the video, but I gotta say I'm impressed by this video a lot. I'm an electronics engineer and took a course on audio engineering in college (the kind where we talk about speaker low frequency dynamics, Thiel-Small models, psychoacoustics, etc) and seeing the same content from an actual audio engineer's perspective is really fresh and interesting. 13:29 -- There is a phase shift between the position and pressure waveform because of several factors actually; I believe because the acceleration of the movement of the speaker cone and therefore the air molecules it is pushing against is the 2nd derivative of the position, and since one derivative imparts 90 degree of phase advance (think about the derivative of sin(x) being cos(x), which is 90 degrees up), you will immediately see a 180 degree phase advance of the acceleration. Roughly speaking force = acceleration, and force is pressure * area, so pressure (that's SPL) and acceleration is in-phase. In the Thiel-Small model it talks about volume velocity; the relationship between volume velocity and particle velocity is analogous to pressure and force.

Fascinating.. as well as a sound guy and electronics engineer..😊

Excellent video! Loved the bit about sound wave trough created at speaker movement crest (sound crest 180° out of phase with speaker movement crest). And how for 30 Hz and 200 Hz, speaker movement crest is 90°-180° out of phase with the driving electrical crest (although I'm not sure I grasped why for that part).

This is like music to my ears after taking Magu's Meyer Fundamentals training :-) ty

Informative video! Thank you.

Wow, someone who actually knows the science behind audio instead of endlessly buying stuff and comparing everything by ear.

Amazing video, really helps understand all those microphone measurements! Would be interesting to see how a cardiod condenser microphone(capsule with 2 exposed capacitive membranes) would measure, instead of an omnidirectional one, because it would capture a difference in pressure between two sides of the capsule, and not average pressure around it.

Even for a layman like myself this was incredibly insightful!

Great Video, The laser measures position of the speaker membrane. But position is not what's making sound, that's probably speed or even acceleration. Which is why the Freq. Response of the laser position took a nose dive. Because position is the integral of speed, and speed is the integral of acceleration. And an integration is actually a low pass filter operation. So, you have 1 or 2 low pass filters to compare against sound measurement.

Only five minutes in but this is sick! Love it!

Curiosity, realworld orginal tests, weird data that makes it more interesting. very very informative.. thanks man, I was full today too...

Brilliant stuff. I'd love to see the comparisson between the laser and the mic with a complex wave, to see if the various consituent frequencies all track at 180 degrees to each other, or if there's a compounding effect.

Thank you very much! You put so much passion and work in your investigations and the video. Awesome setup, respect! All of your argumentations sound logic to me. The only thing I need to think about again in detail is what happens here with the acoustic nearfield/farfield with the longitudinal waves we produce. With the mic distance we should be in nearfield with 90 degrees phaseshift between pressure and velocity but with 200Hz not. I wonder if it matters, because what sensor is capturing what? Mic: captures pressure Laser: captures excursion and translate it to voltage, what represents pressure at the source without nearfield/farfield acoustic effects…good reference btw! …so it is possible, that we also see some of these acoustic effects, what you mentioned and explained with the mic excursion.

Brilliant! Very well explained xx

Hi, first of all, amazing video, thank you! question: why are you using interlaced video in 2024? I can see the interlaced artifact in several parts of the video.

My god, this is the most physically correct description I have ever seen of the microphone - speaker interaction. Do you plan on solving the differential equations for the speaker-air-microphone-system? This should give a nice analytical solution, where the theoretical phase should be easy to calculate. (Because if you ain't going to do so, I feel like I want to do it ^^)

Awesome explanation, thankyou

Phase shift does not alter how we hear a single frequency per se... It alters the relationship between two or more frequencies. Thus, while it alters the timing of peaks at one frequency, this is of little consequence. What is of significant consequence is that phase shifting alters the timing of two or more frequencies differently. It mis-aligns their timing in relation to each other. This alters how you hear the combination. Because remember that our ear only hears one change in air pressure at any given moment. That one change in air pressure is the combination of all the frequencies it can hear. We can't hear 4 separate keys on a piano; we hear the combination of those 4 vibrating strings. All the rest is an illusion of pure brain processing. The more steep the phase shift, the more this relationship is altered, and the more you can hear it compared to the reference sound. And like the microphone, we cannot hear the absolute pressure of one singular moment. We can only hear the change in air pressure between two or more moments. I think I've belabored the point too much already. Phase shift is inevitable. It's nearly impossible to eliminate without major compromises elsewhere. But we can try to make it as gradual as we can. The point is to maintain the relationship between frequencies across the entire audio spectrum. The human ear hears just like the microphone. It's a change in air pressure that creates an electrical signal that goes to the brain; not a measurement of absolute pressure. So the microphone is actually a good representation of the human ear. Eardrum and diaphragm alike, must be in motion to produce a signal. Perhaps someday, we will figure out how to bypass the eardrum entirely and induce electrical signals directly to the brain - producing the absolute perfect recreation. No more speaker design compromises, no more air pressure delays or external noise, no more hearing deficiencies.... just pure sound exactly as the artist intended.

18:50 I think the delay is caused by the inertia of the moving parts of the speaker. And that cannot get worse than 180 degrees because if it were delayed more, it would catch the next incoming electrical wave and that would result in effective speed-up of the movement reducing the delay to less than 180 degrees again. If you have constant latency, it's caused by some kind of processing, not by physical movement of the speaker.

Amazing video! Finaly understood deeply this topic.

YT needs you. Salute...

This video is a treasure!

0:54 Keyence on the job! 💜

Nice job. 👍🏻

OMG It's a pretty amazing experiment, I'm shocked.

Wow that was an excellent presentation! I have one question. How did account for amplifier damping factor influence on the speaker?

Right on. Thanks for sharing.

man your research is underrated, this must be put on papers❤

I think it would be nice to watch more of these in action. How would it be form the floor? how woul it be from above? Beautiful, I was thinking abount these set up for a while and here we are! Cheers, Congratulations for your knowledge and imagination and dedication and sharing!!!

This is amazing!

great video. Let me make a wee observation. ALL microphones have HPF. They need to equalise the pressure or they would break in a plane or with changes of atmospheric pressure. Typically this is tuned around 1-3 Hz in lab mics

Dang, very interesting to see. I've spent years with these as mental exercises. I came from the side of why do certain very simple tube amps have so much more detail in the mid ranges. Most simply say it's "just tube amps add distortion" but often not in the levels detectable by the human ear. I know that muddy bass they can produce, some might like it, I don't, and that's not what many people are talking about. I have future plans ( I have a workshop clean full of projects, and I"m prone to severe sidetracking) to use a laser or capacitive sensor to resolve speaker position. Nothing was off the shelf, or within budget, last time I looked. So a DIY project planned. But needs to get into the mid ranges as well. But my interest is that single ended tube amps have great highs and mids that I love, but bass is muddy. I believe that is due to the fact that they are more like current sources than voltage sources. I got a book on current source driving loudspeakers, they math is above my skill level, but comes to the conclusion that trying to control a large bass speaker with current control is nearly a lost cause, but very effective at frequencies above that. I believe the author to be correct in his conclusions. One issue is that testing with sine waves only doesn't catch the complex interactions of actual music. Between the forces of the surround and the velocity of the cone what happens when you try to impose a second signal. Instruments(snares come to mind) that have frequencies across the spectrum also seem to sound very good on low or no feedback tube amps. I once heard a wise old HiFi guy say if you see the speaker move it's no longer HiFi, I laughed, then slowly I've started to agree. Started to think that's why I like ESL panels so much. But being unwealthy I have some ugly home built speakers with a couple 6" woofers and AMT tweeters on a simple crossover to avoid phasing issues with a equally ugly hacked together amplifier. People say it sounds great, or I have nice friends, IDK. Sometime soon I'm building another amp to biamp the speakers with a digital crossover. Anyway, great video and very educational, I have nothing to disagree with.

Great video!

thank you so much for this!!!

Great explanation

Interesting insight, this raises many questions in what is the objective of sound reproduction, and what matters and what does not. The basis of sound reproduction is for our ears to hear the same sound i.e. original sound versus sampling the original sound and attempting to reproduce the same experience of the listener at a later time. Do the very low frequencies matter and if so is phase significant or how much is the question.

Makes sense since the transfer function of a speaker can be modelled as resistor, inductor and capacitor. To counter this, you'd need use an amplifier with the inverse transfer function like that used in Yamaha's servo technology. Cheers

This is awesome!!!

Amazing video

Is the « slowness » of the system at 200hz due to the resistance of the surround and the weight of the moving parts or does back emf go up with frequency. I’m not sure but faradays law states that back emf is given by the rate of change of the magnetic flux (Wikipedia). At a higher frequency I would say that the rate of change of magnetic flux is higher since the coil is moving in and out of the magnet faster to try and match the input signal. I’m sure the answer is somewhere in the middle, the mechanical resistance and inertia of the moving parts will impead the movement of the cone at higher frequency’s, but I would also guess emf has something to do with it. Lovely video though, it’s so nice to have people to break down the fundamental phenomena at play in speakers, thank you and well done 😊