If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Production of sound

Sound is vibrating air. But how does the air start vibrating? Created by David SantoPietro.

Want to join the conversation?

  • blobby green style avatar for user charlotte thomas
    i need this explained in spanish
    (13 votes)
    Default Khan Academy avatar avatar for user
    • leaf green style avatar for user Mark Zwald
      Las vibraciones hacen que las ondas de presión en el aire ( o cualquier otro medio de la materia) que propagar a la velocidad del sonido. Nuestros oídos detectan las ondas de presión y nuestro cerebro convierte las vibraciones detectadas en sonido.
      (62 votes)
  • duskpin seedling style avatar for user Vijeya Patel
    How can sound waves travel through our flesh?I mean why don't they get obstructed?Also,what is the criteria or the mechanism between sound proof rooms?How are the sound waves getting obstructed in this case?
    (9 votes)
    Default Khan Academy avatar avatar for user
    • old spice man green style avatar for user Matt B
      Sound is simply vibrations. Sound can travel through any medium where it can make neighboring particles vibrate to the same frequency, which is why sound can travel through any medium, including water and even our flesh. Sound proof rooms will have something on the walls, often some a soft and sponge, that will absorb the vibrations in the air and prevent it from passing through the room. Perfectly sound proof places might even be enclosed by a vacuum. (Note: there is no sound in space because there is no air for vibrations that cause sound)
      (29 votes)
  • leaf green style avatar for user Joel Peter Sony
    why does everyone sound different from each other ?
    (4 votes)
    Default Khan Academy avatar avatar for user
  • duskpin tree style avatar for user LaylaTheHowlingWolf
    At , he said that the air doesn't actually ever move away from the speaker, why does this happen?
    (4 votes)
    Default Khan Academy avatar avatar for user
    • stelly orange style avatar for user Krishna Phalgun
      When the diaphragm moves into the air, it pushes the air molecules into each other creating a region of higher pressure (more molecules per unit volume). When the diaphragm moves away it creates a region of low pressure. The oscillating diaphragm thus creates oscillations of pressure in the air which we perceive as sound. The diaphragm vibrates continuously. So the air molecules doesn't move away from speaker. Hope this is clear and helps you.
      CREDITS : Doublestack @Dirac76.
      (11 votes)
  • old spice man green style avatar for user Elijah Daniels
    How come if something is producing sound, it gets quieter when I'm further from it, and louder when I'm close to it?
    (4 votes)
    Default Khan Academy avatar avatar for user
    • male robot hal style avatar for user Andrew M
      For two reasons:
      1) The sound energy gets spread out over a bigger and bigger area as it moves away from the source
      2) The sound energy dissipates as it moves through the air, because of friction-like effects among the air molecules.
      (7 votes)
  • blobby green style avatar for user michaelchait0
    Why does the air oscillate? Why doesn't it just move forward?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user araana
    Could you please help me with this question.
    May we say that kinetic energy is the signature of sound?
    (3 votes)
    Default Khan Academy avatar avatar for user
  • blobby green style avatar for user kingfury27
    at , won't the particles of air collide(meaning touch each other) and transfer energy(sound energy) and also loose some energy during the collision?it means the particles wont come back to their initial position and hence travel some displacement?this means sound makes the particles cover some displacement and hence is not a wave. how is this possible?
    (3 votes)
    Default Khan Academy avatar avatar for user
  • mr pants teal style avatar for user bhashi2006
    do only vibrating object produce sound . is there any other way by which sound waves are produced ?
    (2 votes)
    Default Khan Academy avatar avatar for user
  • duskpin ultimate style avatar for user 🚀The knowledge Hunter🔭
    We have learnt that sound is a fast vibration. Isn't the amount of vibration same on all creatures? If so, Why does sound differ in creatures?
    (2 votes)
    Default Khan Academy avatar avatar for user
    • orange juice squid orange style avatar for user Squishy
      What do you mean by 'amount of vibration?' Are you talking about the frequency? Also, are you taking about the sound creatures make?
      If so, then no, different creatures make different sounds because the way they make sound differs in different creatures, changing the frequency and timbre, or the 'texture' of the sound.
      (2 votes)

Video transcript

- Check out this speaker. If we plug it in, it makes sound. (speaker hums) The way this speaker creates sound is by moving the front of the speaker, which is called the diaphragm, back and forth rapidly. Scientists often use the word oscillation to refer to the back and forth motion of an object. This speaker is oscillating too fast for the human eye to see, but if I put a piece of paper on the speaker, we see that because the diaphragm is oscillating, it's bumping into this piece of paper and causing it to dance. The oscillation of the diaphragm will also cause the air in front of the diaphragm to move back and forth, but here's the interesting thing. The air in front of the diaphragm doesn't actually travel away from the speaker. The air molecules in front of the speaker just oscillate back and forth. So, how can you hear the sound from a speaker if the air next to the speaker doesn't actually make it to your ear? Well, the reason is that the oscillating air in front of the speaker causes the air in front of it to also oscillate. This causes the air in front of that air to start oscillating, which causes the air in front of it to start to oscillate, until finally, the air that's actually next to your ear and your eardrum starts to oscillate back and forth. This oscillating air that's next to your ear is moving, so it has kinetic energy. So, it can transfer energy into your eardrum, which you can perceive as sound. So, this speaker was able to transport energy through the air, without actually having to transport the air itself. This is an important enough fact for me to state again. Energy is traveling across the room here, but air itself is not traveling across the room. Only the disturbance within the air is traveling across the room. If air were being transported across the room, it'd be better characterized not as sound but as wind. So, this is why we call sound a sound wave, because it shares the defining feature of waves, which is being able to transport energy through a medium without having to transport the medium itself. Medium is a fancy word for the material or substance through which a wave is traveling. Air is typically the medium for situations involving sound waves, but sound waves can travel through all kinds of different materials, like water, metal, or even human flesh and bone, and the fact that sound can travel through human flesh and bone explains something you might have always wondered about, which is, why do our voices sound (changes voice) so different on audio and video recordings? The reason for this is that when we're speaking to someone we actually hear two contributions from our voice. We hear the sound wave traveling out of our mouth, through the air, and into our ear, but we also hear the vibration of the sound wave traveling through our flesh and bone, through our skull, and into our eardrum. But on an audio or video recording, the only part that's recorded is the sound that travels through the air. So, when you hear your voice played back on an audio recording, you only hear what other people hear when they listen to you. So, the bad news is that, yes, what you hear on audio recordings is actually what you sound like to other people, but the good news is that most of your friends probably don't think it sounds weird, since that's the only voice they've ever heard you use, unless you do (changes voice) actually have a weird voice, in which case, I'll risk sounding pretentious by reminding you that you shouldn't waste a lot of time worrying about what other people think of you anyways. (techno music)