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How can the vibrating disk of a speaker produce so many sounds at once

  1. Jul 18, 2011 #1
    When you listen to music, you hear the beat, the melody, and the vocals all at once... and they all emanate from the same disk. How does all the noise sound so separate and distinct from one another regardless of whether its a rumbly bass or a piercing pitch? This confusion comes from my understanding that waves superimpose upon each other (granted they are heading in the same direction), so I would guess that I should be hearing a jumbled mess of varying amplitude rather than clear distinct frequencies (like a drum beat wave combining with a syllable wave to add up to gibberish)

    How can one source generate different frequencies at the same time?
    Is it that there exists a unique wave-pattern for every concievable combination of sound?
  2. jcsd
  3. Jul 18, 2011 #2
    Hello strangeline,

    Yes that's a simple way of putting it but it's about the size of it.

    Consider this.

    Each ear has one vibrating membrane to hear the sound and it hears each sound combination quite well so why would you expect the source membrane to act differently?
  4. Jul 18, 2011 #3
    Think of it this way -- isn't it just as strange that all of those sounds at once are in each instantaneous needle position in the grooves on a record?

    I suppose you could imagine that on a CD it's different, but it's basically the same -- except really even more primitive, where it's basically broken down to 44100 distinct numbers a second (numbers that range from -32768 to 32767) -- you can imagine that each of these numbers corresponds to a particular position of the speakercone, and working backwards, a record is the same thing, except smoothed out.

    So yeah -- like the previous poster suggested, your hypothesis about there being a continuous waveform for each sound is correct. It's the principle of superposition -- any function, as complex as you want, can be made up of a sufficient number of sines and cosines.
  5. Jul 18, 2011 #4
    A speaker just creates one sound. Music can be complex but the speaker is recreating the sound of the music and not its individual components.
  6. Jul 18, 2011 #5
    Adding sines and cosines of different frequencies and amplitudes creates a unique waveform. This is why multi-track recording works. The speaker travel mimics this composite waveform. You can get a general idea of how what the waveform is (and how the speaker is traveling) by opening up an MP3 (or other audio file) in a program like Audacity.

    If you think about it, the speaker has no idea what sounds it's putting out. The human ear also doesn't distinguish between each sound. It's your brain that "separates" the components and recognizes the sounds as they come out.
  7. Jul 18, 2011 #6


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    The vibrations in the air are due to all the objects in the vicinity, all vibrating in their own particular way. There is just ONE value of air pressure at any one time, due to all these different sources. Your ear breaks down or 'analyses' this changing pressure (the sound) into the different frequencies But that's only a way of looking at it. A microphone reproduces (as well as the money will allow) the pressure variations and produces an electrical signal which varies in precisely the same way. The varying pressure is translated into a varying voltage. If you want to, you can digitise this as a stream of numbers which can be recorded on a CD or data-compressed into a mpeg file but that's not really relevant to the basic idea. A loudspeaker just has to vibrate in the same way that the microphone diaphragm did, to reproduce the sound.
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