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Sound regeneration

  1. Jan 13, 2015 #1
    hello!

    can you explain me please in few simple words, how are we capable to produce sound?

    in nature, a great variety of different things produces different sounds

    from the wind on the leaves of the trees, to the huma larynx, a complex organ with numerous muscles

    yet, all of these sounds, can be produced from your speakers

    what exactly component is able to produce all these billions of sounds?

    is it a membrane that gets hitted with different areas of it? or specific properties electricity runs through it?

    but how can ALL sounds be produced from that single component?

    thanks!
     
  2. jcsd
  3. Jan 13, 2015 #2

    DaveC426913

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    Look at this diagram for a second.
    adding_sines_figure4.1.jpg
    Pretend the top left wave is a lion's roar, and the bottom left wave is a bird's chirp.

    These two waves add to each other, and are equivalent to the right wave.

    If a speaker can accurately reproduce the right wave, we will hear a lion's roar and a bird's chirp at the same time.
    You can add as many waves together as you want. (such as a 100 piece symphony)

    Here are some more examples of additive wave synthesis:
    Diag_AdditiveSynthesis.png

    additivesynthesis.jpg
     
  4. Jan 13, 2015 #3
    how can a speaker reproduce so many (billions) of different waves? (not at the same time)
     
  5. Jan 13, 2015 #4

    DaveC426913

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    As long as the speaker can vibrate at a frequency higher than the bird's chirp (maybe 5,000Hz), the speaker can represent that sound. (though if it needs to represent rich sounds faithfully, it will need to be able to vibrate higher)

    It simply vibrates to exactly match the waveform on the right. How it does so is directly a result of how much voltage it is given over time.
    So, that right waveform is an actual graph of the voltage passed to the speaker magnet over time.
    It also happens to be an actual graph of the position of the speaker diaphragm (in very small distance units) as it moves in and out, making sound.
     
    Last edited: Jan 13, 2015
  6. Jan 14, 2015 #5

    phinds

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    I think you are missing the point that the speaker doesn't vibrate at all those different frequencies, it vibrates at a COMPOSITE frequency and produces exactly the same thing that you ear gets when it is listening to all those things happening at the same time.

    To expand: The human ear hears a lion roar and a bird chirping at the same time. These events separately cause sound waves but when they impinge on the ear, what they create is a composite waveform. You only have one ear drum on each side after all. The speaker just produces that composite waveform from a single source rather than from multiple sources, but it is still one waveform, it just has the composite characteristics of multiple waveforms.

    When you study Fourier Analysis, you'll learn more about this.
     
  7. Jan 15, 2015 #6

    sophiecentaur

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    The sound that a microphone picks up is just a variation of pressure. This is a single quantity, varying in time which, to suit Engineers and Scientists, can be analysed in terms of the sum of many pure sinusoids at different frequencies. A loudspeaker, fed with exactly the same signal that the microphone picks up, will produce the identical sound by making the air move in exactly the same way. It is only necessary that the speaker cone can be made to move as required. It has to be light and rigid enough and to be driven with the appropriate force (from the coil and the magnet). It doesn't 'know' that it is emitting all those separate waves because that's just a way of looking at it.
    The Time Domain and the Frequency Domain are just two ways of describing the same complex signal.
     
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