• Question: why don't all the sound waves get mixed up to produce one big sound wave? (since sound travels via particles vibrating, and the same particles seem to be used to carry many sounds at once, how do different sounds still manage to remain distinct?)

    Asked by kaurprincess to James, Marcus, Martin, Rob, Suzanne on 19 Mar 2012.
    • Photo: Martin Zaltz Austwick

      Martin Zaltz Austwick answered on 19 Mar 2012:

      Well, that is what happens in a crowded place! Lots of people talking and cars going past just sounds like “noise”. Our brains aren’t able to pick out all of the information and work out what everyone is saying, but it’s all there in the sound wave. But if you’re indoors you’re shielded from a lot of outdoor noise – and sound gets quieter further away, so both of those things mean we don’t just hear a load of noise all the time!

    • Photo: James Boone

      James Boone answered on 19 Mar 2012:

      Also, waves can travel through one another without being destroyed. For example if you drop two stones in a pond near to each other, the circular emanating waves from each stone cross over one another but after crossing still remain circular and travelling in the same direction. When waves travel through one another, a process called “superposition” occurs where amplitudes of waves add together according to their phase. Then when they pass each other, the wave looks the same as they did initially.

    • Photo: Marcus Gallagher-Jones

      Marcus Gallagher-Jones answered on 19 Mar 2012:

      I think it also has something to do with frequency. If the frequencies of the sound waves aren’t well matched then you should be able to hear them independently. This is why it’s possible to tune into a friend talking to you in a busy high street. It’s not quite that discrete though.

    • Photo: Robert Thompson

      Robert Thompson answered on 20 Mar 2012:

      I guess there is not much I can add to this. I beleive humans are very good at patern recognition aswell which allows you to filter known sounds from unknown sounds. Also you can get wayve adding up to nothing. If one sound wave is on an up bit when another is on a down bit then you get nothing at that point.

    • Photo: Suzanne McEndoo

      Suzanne McEndoo answered on 22 Mar 2012:

      A part of it is the physics, so sound waves have different physical properties like frequency that our ear can tell the difference between.

      A huge part of it, though, is the processing our brain has to do. If you record all the sounds in the room around you, you’d be surprised how much noise there is, and yet you can still hear your teacher. Some people can’t do this as well as others (sometimes known as auditory processing disorder), which means that while they physically receive the same sound information as everybody else, their brain doesn’t separate things out and prioritise things as easily. For example, I have very hard time hearing voices in a noisy place, like a school canteen, where other people don’t have a problem. On the other side, I’m always the first to hear a phone ring because I’m listening to all the background noises. 🙂