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Why is Sound produced

  1. Nov 22, 2015 #1
    Why is sound produced?
    Say, for example, when a stone hits a tin box a sound is produced. Why is this sound produced?
    Even if the sound is produced in the ear, we generally say that the vibrations of the ear drum produces the sound, why is it produced. Why does vibrations produce sound.
    Even a mosquito's flapping of wings produces sound.
    Can any one please throw some light on this?
  2. jcsd
  3. Nov 22, 2015 #2
    Vibrations produce sound to animals due to the vibration caused in the air that passes through the ear. Thus molecules in the air vibrate when your examples occur and sound is the body's interpretation of these vibrations. The frequency of our ears must match that of the vibration. However, in a vacuum, vibrations don't 'produce sound' to be heard as there is no medium for the molecules to vibrate and to be passed through the ears. Remember, 'No one can hear you scream in space!' It can be concluded generally that movement makes vibrations and disturbs molecular movement, but sound is relative.

    https://www.quora.com/Why-do-vibrating-bodies-produce-sound-Do-all-vibrating-bodies-produce-sound [Broken]
    Last edited by a moderator: May 7, 2017
  4. Nov 22, 2015 #3
    yes, but what happens in a vibration, that makes it produce a sound.Why does our ears interpret that as a sound ?
  5. Nov 22, 2015 #4

    Vanadium 50

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    How else would our ears interpret it? As taste? Smells?

    It's clear you have one kind of answer in mind, and it's equally clear people are guessing as to what it is. Maybe you could describe the kind of asnwer you are looking for,
  6. Nov 22, 2015 #5
    I think your question is related about the biological part of the hearing. Each time two bodies collide, the move particles in the air. This way a mechanical wave is produced. The air particles collide with other air particles and so on until some air particles will collide with your ear drum. Through a complex system (see a course or something about the human ear) the moving of the drum is coded in an nervous influx which is transmitted to your brain through some nerves. The brain gets the code and then gives you the sensation of hearing a certain sound. I don't know exactly how you get that sensation from the brain, but I think it has to do with releasing some chemicals in the body or something.
  7. Nov 22, 2015 #6


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    That is a very Zen statement. If there are no ears to hear it then there is no sound? Hmmm.
    Try thinking about this topic the other way round. This thread could develop into a very pointless discussion until we define "sound" in another way. Sound is just vibration of anything at a frequency that's within the audible frequency range. Mostly, the sound we hear is transmitted through air but it can be through water or even just the bones of our head.
    We detect these 'sounds' and we become aware that something is vibrating. Our ears and brains analyse these vibrations and produce an awareness of what we call the sound of something happening. The signal processing that's involved is complicated and 'subjective'.
    Evolution produced this ability because it is such a good tool for living and communicating. The "why" part of that question has no end answer.
  8. Nov 22, 2015 #7
    This is actually explained fairly well by a comparison to the Fourier representation of a function. A Fourier series decomposes a repeating signal into a range of frequencies and can assign more linear values to them. If you google graphs of them, you can see what I mean. Sound is a repeating signal in short intervals. It changes because of interferences from other sources.

    When you hit a note on a keyboard, you are hitting a bar. You can think of that note as one of the bars in a transformed signal. Our ears interpret the bars as a sound rather than bothering with all the waves. More specifically, you can think of them as interpretting the bars within the range of frequencies that we can hear. Each bar is assigned a sound, and the more complex the signal, the more overlapping sounds we can hear at once... which produces the difference from striking a single key on a piano and multiple keys at once. In fact, some of the signals are stronger than others as well, which can explain why similar frequencies will sound different at different amplitudes (volume).

    Of course, it's just a metaphor. Your ears don't ACTUALLY perform transformations on the signals you hear, but they do simplify them a lot in order to interpret them. That's just because our brains register things on a different scale than that which is actually happening around us. Stuff that is happening slowly, we can process most of the information for. Stuff that happens very quickly (like the vibration of a sound wave) is mostly interpretted as an approximation so that we can keep up.

    Maybe that helped?

    PS: This is actually exactly how machines interpret sound. Have you ever seen these bars on a car's stereosystem bouncing with the beat? Lower frequencies are more dominant when the bass is turned up while higher frequencies can be better seen bouncing with the treble or singer.

    http://cdn.faveable.com/assets/articles/bring-your-tv-to-life-with-these-great-soundbars-1405609982.jpg [Broken]
    Last edited by a moderator: May 7, 2017
  9. Nov 22, 2015 #8


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    The structure of the cochlea would suggest that your ear actually does do a frequency analysis of the signals that go into it. In fact, both time and frequency domains are examined (the variation of the amplitudes in time). (Or at least that's one way of looking at it.) The large number of resonant hairs in the tapered cochlea allow it to determine frequency with a resolution of better than 1/12 of an Octave over many octaves And several different frequencies at the same time can be processed well. A bit better than the eye's frequency resolution of the light it receives.
  10. Nov 22, 2015 #9


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    Yes the human ear actually does do something quite similar to a Fourier transform biologically, as @sophiecentaur said. Each hair has a certain natural frequency and is sensitive primarily to frequencies very close to that. As you move inward, the hairs get sensitive to progressively higher frequencies (pretty sure I have that direction correct). So basically, the hairs being sensitive to specific frequencies breaks a sound wave down into frequency components and sends that information to your brain, which processes it as sound.
  11. Nov 22, 2015 #10
    Thanks to @Issy04, @Vanadium 50, @anachin6000, @sophiecentaur @Kori Smith , @boneh3ad for the wonderful insights into the thread.
    So, the hearing of sound is physics and the biologics . As I interpret it, vibrations are given a particular sound by our brains to identify the specific sound!!!
    Depending on how much our ear drums vibrate , our brain assigns that note to it and that produces sound.
    So, is it that, that whatever sound we hear is heard by every human, animals etc? So how is it possible that every brain of every organism( which has one) produces the same sound? ( I know Dogs can hear ultrasonic sounds, Bats can produce and hear Ultrasonic sounds) So are the brains of these better equipped to interpret these sounds or is it only the make of the ear which makes it vibrate at that high frequency and the brains just interprets it ? So the sound we hear is just vibrations + brain interpretations
  12. Nov 23, 2015 #11


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    There is no evidence that I am aware of that the sensation of sound (i.e. the "qualia" of sound) is identical in all humans and all animals. It is possible that the auditory sensations you feel from the first four notes of Beethoven's fifth symphony do not match the auditory sensations that I feel. It is possible that the sensations that my dog or cat feels are different as well. What we see experimentally is that both of us can recognize Beethoven's fifth and can usually point toward the speakers from which the sound emanates.

    The question of what auditory sensation we feel is not really a matter of physics. Depending on how it is made specific, it could be a question of neuroscience, of psychology or of philosophy. Not suitable subject material for discussion here.
  13. Nov 23, 2015 #12


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    Yeah, I would have gone in a different direction with this thread from the start: by definition, sound is vibrations (usually of air) that humans an animals detect. Sound is not "produced by the ear", it is only detected by the ear (and interpreted by the brain). There is no reason to bring philosophy into this.
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