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Measuring distance a sound wave travels

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  1. May 7, 2015 #1
    I would like to be able to measure the distance a sound wave travels. This is for a violin bridge and what I would like to do is apply a frequency corresponding to the frequency the string (196 hz for the g string) and determine the distance the wave traveled to get to the foot of the bridge. Is there a method to do this?
     
  2. jcsd
  3. May 7, 2015 #2
    How are you generating this frequency?
     
  4. May 7, 2015 #3

    sophiecentaur

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    The answer to your question is: 'with a ruler' between the bridge and the nut or, possibly from the bow to the bridge. But I don't think that's what you actually want to know. Could you elaborate?
     
  5. May 7, 2015 #4
    No it is not. I want to know how far the vibration travels from the G string ,for example, to the bass foot of the bridge and how far the same vibration travels to the treble foot. it is not as simple as using a ruler as there are incisions and holes in the bridge that are there to slow the vibrations down. The goal here is to get the vibration to the feet at the same time from all strings being played.
     
  6. May 7, 2015 #5
    paisiello2,
    Not sure at this point. Thought that would be the easier of the two problems to solve. Thinking electronic generation, but open to suggestions
     
  7. May 7, 2015 #6
    It may be that you mean "how fast" and not how far? It seems that you know both where the wave starts and where it ends. So if you really want to know how far, sophiecentaur's answer is it. No holes or incisions matter.
     
  8. May 7, 2015 #7

    sophiecentaur

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    I think I get what you need. You are not so much interested in distance as time* this can be found in terms of the phase of the waves as they travel / spread out across the table (?) of the instrument. Put a vibrating source at a particular point on the surface and a microphone at various other points on the surface and you can plot the locus of points on the surface that have equal delays over the path.
    I am not quite sure why you would want the same delay in the paths from all four strings because the sources are at different frequencies and the start times of the notes (when you double stop) are not likely to be the same in any case. It sounds reasonable that you may need the waves from one side (foot) of the bridge (for each string separately) to get focussed so that they arrive at the same time at the sound post as from the other foot. Iirc, there are rules of thumb for placing the sound post in the optimum position. I guess, with this phase method, you could help to identify the point better. It strikes me that it may be best to use the sound post as the source of the vibrations and then look at the phases (dual trace scope?) of what arrives at the two feet of the bridge or anywhere on the table. Reversing the signal direction would be perfectly valid.
    *The thickness of the wood will vary over the table and so will the speed of transmission so distance will not actually tell you reliably about the delay (which is what counts, I think).
     
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