Why Do Rockets 'Crackle'? How Supersonic Jets Make This Distinctive Sound.

Rockets are some of the loudest things that humans can experience, the Saturn V generated more power than entire US electric grid and converted about 1% of that into sound! There's a very distinctive crackle in the sound of a rocket which is a result of turbulence in the shear layer between the exhaust and the external atmosphere. I try to explain and visualize this using recordings of rocket launches and CFD simulations of jets.
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[@CGDubz87]

I really really appreciate this video. "Why do rockets crackle?" Is one of those small, seemingly insignificant questions I've always had about launches but I'd always been too embarrassed to ask anyone. I can now cross it off my list of random space related curiosities, so thank you!

[@Capt.Turner]

My thoughts exactly. Awesome footage, too.

[@jeromethiel4323]

Never thought about it either. I knew about mach diamonds for a very long time. But i never thought about how that extremely hot and fast gas stream is going to interact with the mostly static air. And, while Scott admitted he might be wrong in the details, i'm betting he is more correct than he is incorrect.

[@Ron4885]

Me too. 👍 I love the sound too.

[@Fish-ub3wn]

me2

[@zam6877]

Me too! Me too!😲

[@jamesrussell7760]

Oh yes, for sure that "crackle" is very real. I was on vacation in Florida during late July 1971 and watched the launch of Apollo 15 from a distance of about 5 miles from the launch pad. Even at that distance, the crackling roar of the Saturn V first stage engines was overwhelming; the shock waves felt like a giant was pounding on my chest. You never forget an experience like that.

[@dmeemd7787]

One of those times where Nostalgia is definitely a good thing! I would have loved to have witnessed that! Thanks so much for sharing something so amazing!

[@jamesrussell7760]

@@dmeemd7787 😀😀

[@philgiglio7922]

Was 3 miles from the pad for a shuttle launch, distance confirmed from sound delay. What really struck me was the intensity of the subsonics... you can feel them in your chest and belly

[@fredfred2363]

Yeah, makes me wonder how significant the sound pressure waves are on a rocket structure. How do you even calculate for that?

[@jamesrussell7760]

@@fredfred2363 Astronaut Mike "Mass" Massimino wrote in his book, "Spaceman", about the day he and 6 other astronauts blasted off on the Shuttle flight, STS-109, to service the Hubble Space Telescope. "At six seconds [in the countdown] you feel the rumble of the main engines lighting. The whole stack lurches forward for a moment. Then at zero it tilts back upright again and that’s when the solid rocket boosters light and that’s when you go. There’s no question that you’re moving. It’s not like Oh, did we leave yet? No. It’s bang! and you’re gone. You’re going 100 miles an hour before you clear the tower. You accelerate from 0 to 17,500 miles an hour in eight and a half minutes. " The average rate of acceleration to go from zero to 17,500 mph in 8.5 minutes is 50.33 ft/sec/sec. So, the rocket would pass the speed of sound (1,100 ft/sec) in a little less than 22 seconds. My guess is that once the rocket goes supersonic, in the atmosphere, the "crackles" will be left behind and, of course, in the vacuum of space there is no sound. By the way, Mass' book, "Spaceman" is a great read.

[@JasonAchilles]

Hello all -- many thanks to Scott for including our Delta launch audio / video in this excellent compilation & explanatory video. For those that might be tech curious, audio capture was done at 32 bit / 192K at an approx. distance of about 600 feet from the rocket, co-located with Justin's camera setup. At that capture rate, theoretical headroom for distortion is exceeded by the recording medium, so the only possibility of distortion in the audio chain would be the SPL (Sound Pressure Level) limitations of the actual microphone(s). In this instance we have confidence that barrier was not exceeded, although a more recent recording (which will be public shortly) of a newer rocket almost certainly did --- as well as resulting in many destroyed camera lenses... and it's quite a thrill to hear. Any other audio tech questions please feel free to post below and will answer as best we can.

[@ke6gwf]

*raises hand What kind of microphones did you use, and what are their rated SPL specs? I will laugh if you used Sm57s... Lol

[@derrekvanee4567]

As someone who didn't understand much but loves 24 bit 192khz and higher audiophile recordings: Yes!

[@gert-janbonnema]

What's the "newer rocket" you're talking about?

[@TyMoore95503]

Wow, thanks for the technicals. I always knew the sample rates had to be way, way high to keep as much distortion out as possible. Thank you!

[@Tych333]

Awesome. Thanks for sharing!

[@MrPesht]

Amazing that for as loud as a rocket launch is, you're only getting 1% of the energy as sound. Really gives you a sense of the incredible forces involved.

[@lithostheory]

It's not a crackle, it just the rocket purring happily to finally be launched!

[@DarkSnideoftheRainbow]

The government doesn't want you to know this but rockets are actually powered by thousands of cats all purring at once

[@davisdf3064]

Rockets are cats?

[@lunantix]

@@davisdf3064 pretty much

[@Screamblade_]

@@davisdf3064 I mean…. Both can explode and rip you to shreds if they wish…

[@RechargeableLithium]

I guess SLS will never purr? 😂

[@Dauthdart]

That's it everyone, Scott Manley has descended from on high to make ASMR videos.

[@drunkpaulocosta]

Do you even know what an ASMR video is... its not an ASMR video just cause he has a deep voice. What about this is ASMR?

[@rogerrinkavage]

@@drunkpaulocosta I'm not an ASMR guy but between the exhaust noise and cfd I'd say it was pretty sweet

[@GoofyChristoffer]

I'm an acoustics engineer and I had no idea about this! This is instantly one of my favorite educational videos I've ever seen! Thank you!

[@anteshell]

I'm curious how's that possible. I'm sound engineer who has absolutely zero technical knowledge about acoustics in general (I do some but it's highly specific and completely irrelevant to this) and I still knew this. This question is genuine, but I have no damn idea how to ask it without sounding condescending. That is not my purpose.

[@SoumilSahu]

@@anteshell I'm even more surprised that you happened to learn about Kelvin-Helmholtz instability without any technical training. I only learnt about this stuff in a graduate course at uni.

[@anteshell]

@@SoumilSahu one does not need to have accurate minute level knowledge on the subject to understand how it works. I'm pretty positive you have no idea how carbon and oxygen reacts in subatomic level but still have at least general understanding on how internal combustion engines work.

[@AV036]

Silly questions aside, could someone please link an official launch video showing "Near Full Moon" some where in the background vicinity of launch pad 40 around 7:05pm EDT ? With a bit more triangulation it shouldn't be too hard to get some actual speed data, thus far I'm not seeing anything even remotely close to their telemetry of 700 kph.

[@Andrew-13579]

To you acoustic engineers, are the crackles possibly caused by constructive interference of sound waves from the exhaust's interaction with ambient air? I am not an engineer (but I did stay at a Holiday Inn Express).

[@scottmanley]

Trevor would like you to know you can buy his images here: www.tmahlmann.com/photos/Rockets/SpaceX/Galaxy-33-34/i-5Z5RTZc/ Jason, Benny and Taylor delivered the exquisite Delta IV audio kzbin.info/www/bejne/ZpfMY2V3d6-KZ9E A great article on the subject, including a couple of diagrams I borrowed: acousticstoday.org/the-sound-of-freedom-characterizing-jet-noise-from-high-performance-military-aircraft-kent-l-gee-tracianne-b-neilsen-and-alan-t-wall/

[@MonkeyJedi99]

Not only are you a better producer than most for crediting and sharing your sources, but you're also a bit of a demon for making me learn a bit more about fluid dynamics. I will need weeks of padded-room therapy to regain those sanity points.

[@havinganap]

I always thought of it as a "ripping" sound, also noticed this from military aircraft in AB at airshows, guess it's the same effect. Thanks Scott!

[@csn583]

Yes, ever since I went to the first Falcon Heavy launch I've called it "the gods tearing canvas".

[@forloop7713]

@@csn583 the firmament

[@Speeder84XL]

Yes - especially that "ripping" sound that often come from military aircraft really sound like it's induced by distortion/clipping on the recording rather than it being an actual sound. Since most people have shitty microphones and/or can't lower their gain enough for the sound to not clip, I expected that was the case without really questioning it - until I visited airshows my self. I have never seen a rocket launch in real life though - that would be fun. Seeing the explanation with exhaust moving much faster than the speed of sound also makes sense. Eddies will always form, where there is a boundary layer between air moving at different speeds (even at very low speeds actually - just an ordinary table fan will show this clearly at the edges of the air stream coming out) - but that also means the air surrounding those eddies have to be pushed out of the way (perpendicular to the boundary layer). So now, if the speed difference between gas layers is greater than the speed of sound, small shockwaves will form as the air don't have enough time to move out of the way (the almost vertical front and slower fade away, like we see at 5:23 was pretty much what I expected).

[@mzaite]

Same. Never could look the mechanism up because of that. Now I know, it’s called Crackle.

[@Hansengineering]

having 'viewed' F16 launches from about 30' off the runway in Balad in 2004; it's because jet and rocket engines *tear open the universe* ! :V Also, the Starship belly flop flights are just barely barely safe at 2 miles away without hearing protection.

[@Marktec]

Living near Vandenberg SFB, I get to see these things launch all the time, including the Delta IV Heavy and one of the Falcon 9s featured in this video. I always described that crackle as more of tearing sound. Like the rocket is "tearing" or "ripping" the air. Also, the explanation of the sounds being emitted at different angles is excellent and can be observed during launches because the frequency of the crackle sound changes as it gains altitude. There's normally a point, right around (or at) max Q/dynamic pressure when the crackle really goes crazy and rattles everything in the house. You can actually see/hear the blinds and dishes and the like rattling to the frequency of the crackle sound!

[@devjaxvid]

One of my favorite sounds of all time! Now I know how it’s produced. Thanks Scott!

[@johnadler6987]

Oh god yes... that "crackle" sound of a rocket is so damn satisfying...

[@shermansherbert2570]

The crackle sound is one of my favorite sounds in all of life. Interestingly enough I always assumed the opposite, that the sound I heard on videos was indeed real.

[@CIinbox]

That crackle is an amazing sound even recorded. Now I want to experience this for real!

[@Carl_Aznable]

Do it. It's amazing. The engines ignite, silently from your perspective and as the rocket climbs into the sky, the sound washes over you and the vibration goes through your body and it rises into the sky and crackles above you as it goes up and "over the top" and then goes away from you as the sound very gradually diminishes to something like thunder, while the exhaust plume spreads out into the star shaped jellyfish and then, silence as it goes "down" toward the horizon and disappears from view

[@samsonsoturian6013]

Why would you want to be lit on fire by a rocket?

[@Aengus42]

I remember that crackle was something I loved as a kid when watching the Saturn V of the Apollo & Skylab missions. It's still something I find has a visceral, emotional impact on me even through the imperfect reproduction of TV & video. A fascinating video Scott! 😃🚀

[@ronjones-6977]

I honestly think it's a guy thing. There is that same visceral reaction when you're near a top-fuel dragster producing thousands of pounds of torque at close to 150db. You can actually FEEL the power in your chest. It just puts a smile on your face.

[@DeliveryMcGee]

@@ronjones-6977 Top Fuel dragsters and rocket launches are things everybody should experience at least once. It's not so much sound as ... well, basically only the God of the Jews made more of a spectacle. It really does feel like the world is ending when the tree goes green in a Top Fuel race or when a rocket launces. Fun fact: the fire shooting out of Top Fuel dragsters' exhaust pipes isn't unburned fuel -- the exhaust is so hot that it breaks the water vapor in the air into hydrogen and oxygen and then burns it again.

[@donjones4719]

Same here. Although some jet fighters have something like this, it’s briefly. Not in the same category as a large rocket, lol. A unique sound I’ve loved from Saturn V and earlier.

[@Aengus42]

@@ronjones-6977 I used to follow a Hawker Hunter called "Miss Demeanor" around the airshow circuit for exactly the same reason!

[@artvandelay4545]

A couple of good subwoofers will get you that visceral feeling you guys are looking for any time you want. Put in the 1812 Overture, sit back and enjoy.

[@StonedRedneckMarine]

never had the opportunity to be at a launch but I've heard this sound from military jets and HIMARS launches so I knew it wasn't an audio glitch. I did not know what caused it but I definitely have an appreciation for it now, thank you very much.

[@AV036]

Sounds very dramatic, shouldn't be too hard to compare some real aircraft transits of the moon to what ever that was.

[@StonedRedneckMarine]

@@AV036 being less than half a mile from several HIMARS is more rattling than dramatic, I imagine the dramatic part is for those near the landing site lol

[@AV036]

​@@StonedRedneckMarine i.e RAAF dump and burn, or we could relate to airshows maybe, the engines fitted to WWl zeppelins where loud too. Your point, HIMARS are real rockets. The 'photographer' made two of these alleged 'live recording' transits, you should compare them on the basis of sound or reconsider how you just imagined noise to be a discerning link between real HIMARS and a Fall-Con launch 'vehicle' LOL.

[@butchs.4239]

I lived in Daytona in the early 70's, and my dad had a keen interest in things going on at KSC. As a result whenever possible he'd wake us up to go watch rocket launches. To this day the sound of a Saturn V liftoff is the loudest thing I've ever heard, and the crackle from them was something you felt as much as heard. Interesting to see the mechanics of it, I'd always assumed it was something akin to the way thunder is generated.

[@Lew114]

Fluid flow has always been a mystery to me. Thanks for explaining this so well.

[@frankgulla2335]

It still is for most, even those who study it. Trust me, I teach them all the time. It is not a simple subject and until recently very difficult to model in detail.

[@JonPMeyer]

What a great, understandable explanation of a hugely complex subject! You make it look so easy, but you must spend lots of time gathering the information and then finding good audio and video to go with. Thanks so much for the wonderful videos!

[@jeromethiel4323]

This video is a prime example of why i love this channel. You bring up something that everybody has experienced, but not really thought about. You did, and then not only brought it to our attention, you went a step further and tried to explain it! Marvelous! It just goes to show the amazing amount of science, engineering, and thought that goes into making these extreme machines. You have to account for everything you can think of, and then account for the things you find out you didn't think of the first time around. Rocketry is like all other branches of science, standing on the shoulders of those who came before.

[@jerrygrimes8813]

This is a terrific explanation and illustration of the phenomenon. Scott, I had the exact same realization when I watched the first space shuttle launch! I always had thought the crackle was microphone clipping, and was astounded that it was actually an audible phenomenon at my first live launch. Thanks for the validation. 😁 I really appreciate this, and all the videos you make!

[@TimLesher]

The adolescent version of me is in awe that you go to see this in person. One of my few lasting regrets is that I never got to see an STS launch.

[@milantrcka121]

@@TimLesher Understand. Had recording hardware on board. Never seen the launch in person.

[@jeffherald8542]

I remember watching STS-3 launch in 1982 from the KSC grounds (the only launch I've witnessed up close) and I recall that crackling sound and being pummeled by the noise in general from being so close. Videos don't do it justice; it's incredibly loud. Thank you for explaining this sound, I appreciate your effort here.

[@pseudononymouse]

Hey Jeff. I was there too and commented above about how omnidirectional the sound appeared to be. And yes, incredibly loud, and BIG too.

[@jeffherald8542]

@@pseudononymouse exactly, it was an all-consuming sound.

[@K31TH3R]

I have googled this numerous times and never actually landed on a satisfying answer, and it's great to finally have my curiosity satisfied, so thanks for this! Also, the capture at 2:12 is AMAZING. You can actually see the pulses affecting the surrounding air. I've never been to a launch before, and go figure that the first time I've realized just how violent the sound pulses are was not because of the audio from a video, but the video itself!

[@onomonopedia]

Thanks so much for this tutorial! I remember the crackle coming through the T.V. when the Saturn rockets launched and thought it might be coming from the boundary layer at the rocket nozzle. This was very helpful and detailed.

[@jjchouinard2327]

I wish I could give this video 2 thumbs up. So clearly presented to a subject I have never given any thought to. So cool Scott, so cool.

[@farklek]

This is amazing! I love when you are taught something your whole life and are left to use your imagination to visualize it, then technology advances and someone captures the phenomenon on video so you can now literally see something like sound waves with your own eyes. Thanks for putting this video together for us!

[@gymprofessor329]

I had the chance to see one of the transporter missions from a couple miles away and remember being surprised by how violent the crackle really is. Felt like gun shots. Super cool hearing the physics behind it.

[@bagel_deficient]

7:42 That's one of the coolest videos I've ever seen. Fantastic cinematography, rockets, weird physics, space. All it's missing is unnecessarily powerful lasers. Well done Trevor.

[@qtrfull]

I was onsite for three Saturn V launches - one from only 3 1/2 miles away. I've always said the most impressive thing was the popping. But, I didn't just hear it, I felt it! Like someone slapping me on the chest. Thanks so much for the detailed, and very well produced explanation.

[@NickPoeschek]

I always wondered about that sound as well and (as someone who’s never been able to attend a launch) I also assumed it was an audio distortion on the microphone. Thanks for this!

[@quarter20everything]

Would love to hear this in person some day!!!

[@davidmccarter982]

Completely awesome Scott! Super glad for the detailed explanation.

[@julienbeck696]

For this kind of explaination, even if it might not be the 100% perfect one, we love you Scott. Thank you so much for the joy.

[@chrisglen-smith7662]

I have heard the same sort of crackle near or under a fighter jet doing aerobatics, always wondered what the mechanism of the crackles was. Thanks Scott. Never seen (or heard!) a rocket launch live - would really really like to!

[@jefffuller8386]

This is awesome. I’ve witnessed a number of launches myself and as an audio engineer always wondered what created the crackle. Thanks

[@jeffjeff4477]

I saw a F9 launch from the Gantry at KSC a couple months ago, 3.2 miles away from the pad. The crackling was completely different at that distance, more a rumble from further away. So incredible and loud

[@TomandSpace]

As an acoustic engineer who loves rockets, this may be my fav video ever. Love your work, Scott.

[@Dr_Kenneth_Noisewater]

Above and beyond with this video. Very interesting! Those crackles are so recognizable - even expected - as the sound of a rocket in flight. And I remember with the shuttles you’d hear the loud roar ‘fade’ (relatively) away such that the crackles became really distinct. I still hope to attend a live launch (all previous attemps ended in scrubs) so I can feel those pressure waves for myself.

[@christopherestrada8576]

A fantastic video! Thanks! I work on Santa Maria Tanker Base and we often have a great view of the launches from VBSF Base. I've always wondered about that "crackling" phenomenon but keep getting detoured by life on my way to investigate it. I also have to say those pictures and videos of the rockets passing in front of the moon and sun are insanely interesting! As always I appreciate your hard work and dedication, you are very much a light in dark places! Stay Safe and Stay Frosty!

[@mattcollins4550]

As a former audio engineer and now commercial pilot I have to say this is one of your best videos ever!

[@Michael-OBrien]

I was actually wondering about this phenomenon a couple days ago. Thanks for answering the question, Scott!

[@alexmhbr]

Can you imagine how cool one of this moon/sun transit videos with a SuperHeavy is going to be like? Great video Scott!

[@SkylersRants]

Thanks, Scott. You’re really good at explaining things.

[@7cle]

That’s something I love about your channel, about you in fact : you never loose an occasion to do good physics.

[@Rebar77_real]

The exact crackle. Scott there is a thing known as a "Cacklefest" where old nitromethane drag racing cars just idle around cackling at the crowd before or after their events. I think you'd love it. Cheer, sir!

[@skyhawk_4526]

I think the most mind blowing thing I learned in the video was that sound is not just audible, but also visible. Not only can you hear the sound of the rocket, you can also SEE the sound of the rocket!

[@crcpeart]

Magnificent. One of your best videos Scott, thank you 🚀🚀🔥🔥🙌🙌 And props to the photographers!!

[@79mini]

What always got me was the delay before it sounded like the rocket was ripping the atmosphere to be free. At least that's how it goes in my little head lol. Kinda cool to have a full understanding of the situation and know what I'm actually looking at now. Thanks Scott for the insight and explanation.

[@danoberste8146]

I've been asking this question every time I watch a launch. It's really there when you hear it in real life! Thanks Scott!!!

[@DeputatKaktus]

So I learned something new today! Thank you Scott!🙏🏻 ❤ I thought the exact same thing, that the crackle was from the mic just clipping. Never questioned it, which now I know was a mistake.

[@d.jensen5153]

If it hasn't already been noted, one doesn't have to go to Cape Canaveral or Vandenberg to hear this, either. At a local LDRS launch you can experience the same thing. The rockets aren't as big but you're a lot closer. And some of them create a dramatic ripping sound that is very satisfying and impressive.

[@steveknight9254]

It’s the same thing with old school low bypass jet engines, especially in winter. I used to love the sound of a big jet taking off in winter Becuase of the crackle of that high velocity air when it mixes.

[@danielmoser1012]

Wow, that video of the acoustic waves from the exhaust refracting the moonlight is amazing. Thanks for sharing.

[@evanmills8559]

I finally got to hear this for the first time in person at KSC during the launch of SpaceX Crew-5 last week and boy was it impressive. Thank you Scott for making this great video!

[@sc07tie]

I also wonder if waves of sound also tend to merge to increase the peak of some sound waves over a given distance? The same phenomenon that causes rogue waves in the ocean, as many little waves merge with slightly different speeds, they combine to create a large wave from seemingly nowhere. Great video, thanks Scott!

[@kauffmanba]

I'd give this one several thumbs up, if possible. Love the premium photographic demonstrations of sonic phenomena.

[@Sinned1208]

To be honest, I absolutely took it for granted that this sound phenomenon is just the microphones not being able to capture the enormous loudness of a starting rocket and never questioned it 😂 Thanks for this video!

[@yahccs1]

Thanks for these ways sound waves can be visualised. The fluid dynamics simulation with rows of eddys reminds me of the eddys they get (on sea surface temperature maps) with warm and cool water around the Cape of Good Hope from the Agulhas current and the colder Atlantic water. It also reminds me of several fluid dynamics demonstrations with denisty currents, and some spiral patterns that look like Roman mosaics from a book on geometrical patterns! Awesome images and videos going across the sun and moon creating mirage-type effects. I expect the air density is varying by a massive factor around that hot exhaust.

[@Danger_mouse]

Thanks Scott, I'm so glad you did this video and also that it confirmed my simple explanation that I gave my adult sons recently in regards to the noise 👍 I said that I assumed it was due to the exhaust gasses breaking the sound barrier as they exit and mix with the surrounding air.

[@MaxAviationVideos]

This is actually the BEST scientific video and possibly the ONLY one ever created handling this exact subject. Thank you so much for this

[@peetiegonzalez1845]

Those turbulence photos and videos with the sun and moon are absolutely amazing.

[@pseudononymouse]

WONDERFUL treatment on this cool effect. BTW, I'm curious why that sound is so omnidirectional. I was at the press stand watching STS-3 and after a few seconds when the sound arrived I was astonished by how that crackle seemed to come from all directions (but mostly from the sky, of course). Thanks for your postings. I watch every one and love to be reminded to fly safe.

[@kedrednael]

My guess is that the sound is reflecting off quite distant objects. With usual volume when the sound source is near you, sound reflections will be way less loud than the original source, because the sound level quickly falls of to where you cannot hear it. But because a rocket is so loud, and so far away already, the difference in volume between the origin and the reflections are more negligible.

[@pseudononymouse]

@@kedrednael Thanks. That must be a lot of the answer. I was close to the VAB which was clearly a sound reflector. But in the opposite direction the sound was seemingly coming from the clouds. Maybe water vapor, on a large enough scale, creates a sound reflection too?

[@kedrednael]

​@@pseudononymouse I don't think water vapor could reflect sound like that. When a solid large object (VAB is the perfect object indeed) reflects the sound, the sound wave immediately turns around completely, so it keeps being the crackle wave of similar intensity. But if it reflected on droplets/ vapor, it wouldn't reflect at the same time(location), it would kinda break the soundwave up, each part of the soundwave reflecting at different locations. That is actually how the deluge sound suppression system works. Perhaps the different air density changes the soundwave direction. It's actually interesting that wind (which has lower speed near the ground), can cause soundwaves to change direction up or down. Maybe we're just quite bad at guessing the direction such a sound comes from. Especially if it is coming from several locations. (I'm having fun thinking of possibilities, I thought of two bonkers ideas) (low) Clouds form because moist air has risen there from the ground, this must be because it heated up (thus became lower density). Speed of sound is dependent on density, so perhaps the clouds can act as lenses for the soundwave. Perhaps the clouds are something for your brain to latch onto as a possible sound source, and thus your sense of sound got influenced by your vision. This adjustment of what you see and what you hear through the other sense happens for instance, in the double flash illusion, or with ventriloquists.

[@penaschmidt]

Maybe ... the sound front wave passes by you and keep irradiating backwards thus creating this 360 field.

[@SirCharles12357]

Your videos are never a waste of my time. Always learn something and in this case a lot! Thanks for making them!

[@davidcarter8861]

I remember my first space shuttle launch and my surprise at the crackle sound (and the volume!). Hearing that distinctive rocket crackle still, to this day, gives me goose bumps and feels inspirational.

[@rocketmentor]

"Clipping" Finally, someone address this phenomena, having tested rocket engines all of my life I asked this question decades ago and what I was told you said briefly, Scott, but in a different context, "clipping", the air which has a finite mass/pressure can only transmit sound energy at a limited quantity above which it 'clips' just like an over driven speaker or, as you said Scott, a "microphone clipping". Additionally, on the ground below rocket engine I've tested (horizontally) were standing shock wave in the loose soil/gravel. Always been intrigued by rocket noise so much so I devoted my life to building the devises that generate this noise. Thank you, Scott, Ken M.

[@MarcelHuguenin]

Thanks Scott for making this unique video that explains what we always wanted to know!

[@MikkoKalavainen]

Is the “pulsing” that we can see in the cloud on liftoff in launches also a function of this crackle? I thought it was just a mic-issue too tbh.

[@scottmanley]

Yes, same effect

[@Midcon77]

LOVE THIS! I was actually thinking about this the other day and wondering what caused it. Thanks for the timely answer!

[@Grant5321]

It’s pretty cool to hear and feel the power of the rockets in person.

[@RyanDCH]

So basically, the turbulence itself is breaking the sound barrier? That's pretty dope. Thank you Scott!

[@AstroDragon33]

Fantastic Scott. The rocket engine crackle is my favorite sound ever. I was going to research it and write a paper, but now I'm somewhat satisfied. Seriously, fly safe.

[@sixstringsimpleton]

Having never experienced a launch in person, I was wondering. Now I'm even more excited to see one!

[@notgryphon5155]

Thank you for the explanation! I only found out earlier this year when watching an F-22 display that the crackle was a real sound, and not just in recordings. Really fascinating stuff!

[@mikea5067]

It's like you read my mind! I was confused by the distortion in all the moon crossing pics from that last launch. I just assumed it was some kind of artistic effect. This was an awesome video explainer for me. Thanks Scott!

[@Gary.Holmes]

What an astonishing and well researched video. Like many others, I'd just assumed it was an overloaded audio chain doing the crackling. Never thought to ask somebody who'd seen a launch what they actually heard! Thank you Scott. Fly safe!

[@witchdoctor6502]

Thanks, I assumed it was just audio recording, but now I want to see&hear a rocket launch evem more. The video from Trevor Mahlmann is absolutely incredible.

[@TrevorMahlmann]

thanks very much!

[@davidboyle1902]

Can’t wait to hear the crackle from Super Heavy! Gonna be some serious decibels that day. Great video, Scott.

[@BLKBRDD]

Those moon and sunshots are incredible. Hats off to the photographers and videographers for capturing it so clearly.❤

[@captainobvious9188]

The rocket in front of the moon footage is fan-freaking-tastic. Like, some of the coolest footage ever.

[@nohphd]

When a child I went on a couple of field trips to watch the various Saturn rockets being tested, mostly the second stage, at the Mississippi Test Facility, now the Stennis something or other. Along with the stupendous crackle of the engines, there was a giant banging sound. I explain it sounding a 55 gallon drum being hit by a sledge hammer, except the 55 gallon drum has a steel thickness of about an inch. Sound was every few seconds, didn’t seem to be periodic. What was interesting was that every time there was the banging sound, you could see a very distinct shockwave pass through the engine exhaust steam cloud. Nobody has ever explained that sound to me satisfactorily. (Hint, hint Scott!)

[@TyMoore95503]

Thank you, Scott for this video. I am reminded of a project I attempted about two decades ago: I realized that the crackle in rocket exhaust, each individual impulse was very, very close to the sound made by a large 12-16" ballon exploding in like an auditorium. The choice of acoustics of venue is important as the impulse has to have just the right amount of echo and fall off. Once sampled at high definition, a computer program could be written to create an audiostream of sampled ballon explosion and string the impulses together with the right frequency shifts and pulse times to simulate in high definition an authentic rocket launch sound. The mathematics involved with Doppler shift are solid and well known, but acoustic ray tracing was beyond my programming abilities. I still believe that such a path exists to simulate a pretty authentic rocket skund that could be used in games, movies, or simulations using such a method. Anyways, great presentation as always, Scott. And Fly Safe!

[@davidca96]

I always wondered about this but never looked it up, appreciate the explaination and visuals that make it easier to understand.

[@mikebridges20]

Scott Manley: the man who can make some of the most esoteric science downright entertaining! Those videos were not only amazing (thanks to the photographers), but I actually learned something!

[@MEisLOLtoday]

I've been mind blown, Scott. Thanks for that really. Golden content.

[@dontwanttobeforcedtogoogle6636]

Excellent clear, concise, and intuitive explanation around the three minute mark. Recordings are one thing but hearing it in person is pretty special. I first experienced this at an air show with an F18 effectively hovering. Ive always described the sound as tearing air, like tearing paper but more energy.

[@georgeneitzjr2772]

Working at the Crystal River Energy Complex on the west coast of Florida, when we still had five operational steam generating power plants, I have been unlucky enough to be within 150 feet of the emergency steam blow off pipes when there was a turbine trip on startup. The sound of all that high pressure steam unexpectedly venting is the same as the that of a large rocket launching. We also had a great location on top of our control complex to watch the space shuttle launch on multiple occasions and while faint we could still hear the crackle of the rocket exhaust.

[@RCAvhstape]

I had commented on that short video that I always thought the crackle was from rough-burning solid rocket propellant and that I was surprised that the all-liquid rockets do it, too. Very cool that you made this video so soon after that.

[@bruceschoenberger7975]

Scott, when I watched the first shuttle launch on TV and heard that crackle, I too thought it was the microphone's diaphragm being overdriven and hitting its endstop, but after numerous launches the sound remained and my opinion gravitated toward the 'many sonic booms' theory. When I saw a shuttle launch in person some years later, I was amazed at the sound level of the crackling, even at a distance of 5 miles from the pad, and it seemed to be omnidirectional. I was convinced that it was indeed, numerous sonic booms. Your excellent video has justified my armchair theory after all these years! I appreciate the thoughtfulness and the quality you put into this channel.

[@ShorelineThomas]

So: rocket exhaust -> supersonic turbulence -> series of sharp pressure waves that sound like crackling. Cool!

[@weschilton]

Wow, GREAT video Scott! And those visuals at the end were both spectacular and incredibly educational!

[@gregcollins3404]

Kudos to your very fine description and analysis of something few know about. I appreciate your precise and accurate terminology.

[@kkloikok]

Scott you do such a great job with these videos. If you ever become an Aerospace professor I'd watch all your lectures for fun... mostly because literally everything is more entertaining with a Scottish accent

[@FU2Max]

What a marvellous and spot on explanation. Thanks Scott.

[@thomaskennings]

Might be one of Scott's best videos ever, and I've been watching since 2014!

[@DeWessel97]

Those images and footage of the moon "melting" is one of the gnarliest space related things I've seen

[@crashovride02]

This is amazing! Ironically, I was asking myself about that crackle watching your previous video and here you are reading my mind. Thank you!

[@kdub6593]

The crackle is endearing and explains part of the reason we love big rockets.

[@DavesRocketShop]

I've never been to an orbital rocket launch, but even with amateur rockets I've found that recordings never truly capture the sound. It's so much more impressive in person

[@zam6877]

Scott! Brilliant! Especially finding the clip of the pressure waves shown as the rocket passed by moon I was always in awe of sense of violent hardness of the jet plume manifested from the sound I so want to see a rocket launch in person some day

[@peterh5165]

Excellent video! I remember when I was stationed overseas many many years ago, hearing exhaust crackle from SR-71As taking off in full afterburner: that sound reminded me of the Saturn V rockets I heard on TV. I will never forget those SR-71As.

[@noeldavis618]

Gosh, what a great explanation with AMAZING imagery to support it. I have always wondered about the "crackle" sound of rockets and I assumed they were artifacts from old Apollo-era recordings, but now I realize they're still there with modern rocket launches. Thank you!