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Growing up I always thought a sonic boom was something that happened once when you broke the speed of sound. I now understand that's not the case, but still do

Growing up I always thought a sonic boom was something that happened once when you broke the speed of sound. I now understand that's not the case, but still don't quite know what it is. I think a supersonic aircraft is constantly "dragging" a boom behind it. So when it passes overhead sometime later you'll hear a boom. Is that right? Does that mean you'll see a plane flying overhead, hear the normal drone associated with it, but at one particular moment here a distinctly louder but shorter noise? And is this a real thing that can be done? How do you make the sonic boom go away? As someone who lives where planes are flying overhead constantly, can it be used to make non-supersonic planes quieter, too?

freeone3000 1y ago
When a boat goes faster than water, it makes water waves. When a plane goes faster than air, it makes air-waves. When a plane goes faster than sound, it makes sound-waves. It’s lightning/thunder: you will be able to see the plane, and then after a bit, hear the boom. You won’t be able to hear other plane noise, all of the combined noise from turbulence and engines is forced back into the boom. It is shorter duration, yes, but MUCH louder: F-18s at 5000 feet can rattle windows on the ground! Usually not a good trade-off.
- zigzag312 1y ago
  You're mixing apples and oranges. Air and water are matter, sound is not. Any sound-producing plane generates sound waves, not just a plane that goes faster than sound.
  - freeone3000 1y ago
    Sound is the vibration of matter. Waves do not move matter! Like, look at a leaf on a lake. The leaf moves up and down with the ripples, but does not move back and forth. The water isn’t moving, the wavefront is. Sonic booms are nothing more than a collapsed wavefront of that wavefront. The speed of sound, definitionally, is the maximal speed at which any physical wavefront can propagate through a medium. (We hear it in air as sound, but no wave can be propagated through the medium any faster than this. You cannot move air any faster than the speed of sound in air.) This causes all of the disturbances from the aircraft moving through the air to be compressed into a single, maximal wave that itself moves at the speed of sound, since it can’t move any faster. Thus the boom. (You can see a similar cool thing with Cherenkov radiation, where neutrons moving faster than light in water produce a bright blue glow — or, waves of light!)
    - zigzag312 1y ago
      I was referring to your explanation "When a plane goes faster than air, it makes air-waves. When a plane goes faster than sound, it makes sound-waves." In physics, an air wave typically refers to a sound wave. While both of your statements are true (plane makes sound-waves at both speeds), they didn't explain the sonic boom, like you did now. > You cannot move air any faster than the speed of sound in air. Minor nitpick, doesn't a plane traveling above Mach 1 displace (i.e. move) air faster than the speed of sound in air? :)
      - freeone3000 1y ago
        Right, sorry. The wave can't propagate any faster than the speed of sound -- the air itself be moved faster, but you have to do so by physically displacing it.
winkywooster 1y ago
growing up i remember experiencing sonic booms a handful of times. i never heard or saw the plane, it would just be the sound and feeling of the boom.
firejake308 1y ago
The latest generation of supersonic aircraft does still generate a sonic boom, but the key innovation seems to be to fly at an altitude where the sound wave will mostly be reflected. Source: this picture from the Boom XB-1 website, which was originally made by Pennsylvania State University: https://boomsupersonic.com/wp-content/uploads/2025/02/xb-1-boomless-cruise-1440x1080.jpg https://boomsupersonic.com/wp-content/uploads/2025/02/xb-1-b...
Majromax 1y ago
> And is this a real thing that can be done? How do you make the sonic boom go away? You can't completely make the sonic boom go away, but you can change how it's experienced on the ground through careful design of the airplane shape. The X-59 Quesst (https://en.wikipedia.org/wiki/Lockheed_Martin_X-59_Quesst#Design https://en.wikipedia.org/wiki/Lockheed_Martin_X-59_Quesst#De...) is an experimental supersonic aircraft that reportedly reduces the sound of the sonic boom to something comparable to a 'car door closing', mostly by ensuring that different shockwaves created by different parts of the plane don't combine into a single, stronger boom. > can it be used to make non-supersonic planes quieter, too? Sadly no; the principles of design are very different for sonic booms and ordinary plane noise. For ordinary aircraft, the big causes of noise are the engines themselves and turbulence over the airframe. That being said, the problem of ordinary aircraft noise is usually limited to the areas near an airport. Sonic booms are noticed underneath the entire flight path of a supersonic aircraft, even when it's flying at altitude.
echoangle 1y ago
Because the plane is supersonic, you don’t hear the drone. The first thing you hear is the boom, which is basically the front of the drone which accumulates because the plane is always at the edge of its sound. After the boom, you hear the normal decaying drone as the plane moves away.
krisoft 1y ago
> Does that mean you'll see a plane flying overhead, hear the normal drone associated with it, but at one particular moment here a distinctly louder but shorter noise? Not really. Supersonic means faster than sound. Meaning that the plane flies faster than the sound. Even its own sound. So you would hear nothing before the sonic boom reaches you. Because the sound didn't have time to get to your ears yet. > I think a supersonic aircraft is constantly "dragging" a boom behind it. What was really revealing to me is to look at shadowgraph images of supersonic wind tunnel test. Like this one: https://media.sciencephoto.com/image/s3300054/800wm/S3300054-X-15_aircraft_shadowgraph.jpg https://media.sciencephoto.com/image/s3300054/800wm/S3300054... You can see the dark airplane looking shape. That's the model of the airplane in the wind tunnel. And then you can see that V shaped shadow edge starting from the tip of the nose. That's the sonic boom. It is a sudden step change in pressure. In this visualisation it appears as two lines, but in reality it is a cone centered on the tip of the nose (or other protrusions.) Where and when your ear crosses that cone surface that's where you experience a sonic boom. > How do you make the sonic boom go away? If I understand it correctly their plan is not to make it not happen, but to fly such that the pressure wave is bent upwards away from the ground. Which sounds like a weather dependent trick. I recommend the video in the article which shows the idea.
Kim_Bruning 1y ago
https://www.youtube.com/watch?v=r9MzxSfA0R0 https://www.youtube.com/watch?v=r9MzxSfA0R0 So this happens to be rockets. In most plane videos you have sound of other aircraft in the video. This is because people are usually recording at air-shows. It's really hard to find a clean version!
zigzag312 1y ago
> How do you make the sonic boom go away? You can't, but you can prevent it from reaching the ground. https://www.youtube.com/watch?v=NdJWIkwxjcA https://www.youtube.com/watch?v=NdJWIkwxjcA

freeone3000 1y ago

When a boat goes faster than water, it makes water waves. When a plane goes faster than air, it makes air-waves. When a plane goes faster than sound, it makes sound-waves. It’s lightning/thunder: you will be able to see the plane, and then after a bit, hear the boom. You won’t be able to hear other plane noise, all of the combined noise from turbulence and engines is forced back into the boom. It is shorter duration, yes, but MUCH louder: F-18s at 5000 feet can rattle windows on the ground! Usually not a good trade-off.

zigzag312 1y ago
You're mixing apples and oranges. Air and water are matter, sound is not. Any sound-producing plane generates sound waves, not just a plane that goes faster than sound.
- freeone3000 1y ago
  Sound is the vibration of matter. Waves do not move matter! Like, look at a leaf on a lake. The leaf moves up and down with the ripples, but does not move back and forth. The water isn’t moving, the wavefront is. Sonic booms are nothing more than a collapsed wavefront of that wavefront. The speed of sound, definitionally, is the maximal speed at which any physical wavefront can propagate through a medium. (We hear it in air as sound, but no wave can be propagated through the medium any faster than this. You cannot move air any faster than the speed of sound in air.) This causes all of the disturbances from the aircraft moving through the air to be compressed into a single, maximal wave that itself moves at the speed of sound, since it can’t move any faster. Thus the boom. (You can see a similar cool thing with Cherenkov radiation, where neutrons moving faster than light in water produce a bright blue glow — or, waves of light!)
  - zigzag312 1y ago
    I was referring to your explanation "When a plane goes faster than air, it makes air-waves. When a plane goes faster than sound, it makes sound-waves." In physics, an air wave typically refers to a sound wave. While both of your statements are true (plane makes sound-waves at both speeds), they didn't explain the sonic boom, like you did now. > You cannot move air any faster than the speed of sound in air. Minor nitpick, doesn't a plane traveling above Mach 1 displace (i.e. move) air faster than the speed of sound in air? :)
    - freeone3000 1y ago
      Right, sorry. The wave can't propagate any faster than the speed of sound -- the air itself be moved faster, but you have to do so by physically displacing it.

winkywooster 1y ago

growing up i remember experiencing sonic booms a handful of times. i never heard or saw the plane, it would just be the sound and feeling of the boom.

firejake308 1y ago

The latest generation of supersonic aircraft does still generate a sonic boom, but the key innovation seems to be to fly at an altitude where the sound wave will mostly be reflected. Source: this picture from the Boom XB-1 website, which was originally made by Pennsylvania State University: https://boomsupersonic.com/wp-content/uploads/2025/02/xb-1-boomless-cruise-1440x1080.jpg https://boomsupersonic.com/wp-content/uploads/2025/02/xb-1-b...

Majromax 1y ago

> And is this a real thing that can be done? How do you make the sonic boom go away? You can't completely make the sonic boom go away, but you can change how it's experienced on the ground through careful design of the airplane shape. The X-59 Quesst (https://en.wikipedia.org/wiki/Lockheed_Martin_X-59_Quesst#Design https://en.wikipedia.org/wiki/Lockheed_Martin_X-59_Quesst#De...) is an experimental supersonic aircraft that reportedly reduces the sound of the sonic boom to something comparable to a 'car door closing', mostly by ensuring that different shockwaves created by different parts of the plane don't combine into a single, stronger boom. > can it be used to make non-supersonic planes quieter, too? Sadly no; the principles of design are very different for sonic booms and ordinary plane noise. For ordinary aircraft, the big causes of noise are the engines themselves and turbulence over the airframe. That being said, the problem of ordinary aircraft noise is usually limited to the areas near an airport. Sonic booms are noticed underneath the entire flight path of a supersonic aircraft, even when it's flying at altitude.

echoangle 1y ago

Because the plane is supersonic, you don’t hear the drone. The first thing you hear is the boom, which is basically the front of the drone which accumulates because the plane is always at the edge of its sound. After the boom, you hear the normal decaying drone as the plane moves away.

krisoft 1y ago

> Does that mean you'll see a plane flying overhead, hear the normal drone associated with it, but at one particular moment here a distinctly louder but shorter noise? Not really. Supersonic means faster than sound. Meaning that the plane flies faster than the sound. Even its own sound. So you would hear nothing before the sonic boom reaches you. Because the sound didn't have time to get to your ears yet. > I think a supersonic aircraft is constantly "dragging" a boom behind it. What was really revealing to me is to look at shadowgraph images of supersonic wind tunnel test. Like this one: https://media.sciencephoto.com/image/s3300054/800wm/S3300054-X-15_aircraft_shadowgraph.jpg https://media.sciencephoto.com/image/s3300054/800wm/S3300054... You can see the dark airplane looking shape. That's the model of the airplane in the wind tunnel. And then you can see that V shaped shadow edge starting from the tip of the nose. That's the sonic boom. It is a sudden step change in pressure. In this visualisation it appears as two lines, but in reality it is a cone centered on the tip of the nose (or other protrusions.) Where and when your ear crosses that cone surface that's where you experience a sonic boom. > How do you make the sonic boom go away? If I understand it correctly their plan is not to make it not happen, but to fly such that the pressure wave is bent upwards away from the ground. Which sounds like a weather dependent trick. I recommend the video in the article which shows the idea.

Kim_Bruning 1y ago

https://www.youtube.com/watch?v=r9MzxSfA0R0 https://www.youtube.com/watch?v=r9MzxSfA0R0 So this happens to be rockets. In most plane videos you have sound of other aircraft in the video. This is because people are usually recording at air-shows. It's really hard to find a clean version!

zigzag312 1y ago

> How do you make the sonic boom go away? You can't, but you can prevent it from reaching the ground. https://www.youtube.com/watch?v=NdJWIkwxjcA https://www.youtube.com/watch?v=NdJWIkwxjcA