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Does anyone know a device that reads the frequency of objects?

  1. Jul 14, 2010 #1
    Does anyone know a device that reads the frequency of objects?

    I want to be able to read the frequency of a glass plate and a
    sheet of aluminum.

    What is it called?
     
  2. jcsd
  3. Jul 14, 2010 #2
    Hello mapa.A "stroboscope" might be suitable.Try googling.
     
  4. Jul 14, 2010 #3

    russ_watters

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    What frequency? Resonant frequency? Reflected light frequency? Radiated heat frequency? How often it gets stepped on frequency?
     
  5. Jul 14, 2010 #4
    Well, to put it to the basics, I am attempting to break glass with sound using a frequency generator I have on my laptop. I want to determine the frequency the object is vibrating.
     
  6. Jul 14, 2010 #5
    I think you can just hit your glass and detect the generated tone, you can then analyze it using a computer program and regenerate it. it's not an easy task though.
     
  7. Jul 14, 2010 #6
    I think this means you want the "resonant frequency".

    If you want to hit a glass and determine the frequency of the tone which results, the computer program you want is called a "spectogram". If you have a Macintosh I recommend Martin Hairer's "Amadeus" program, it has several utilities you might find useful. I think Audacity, which is free on all operating systems, also has a spectogram tool.
     
  8. Jul 15, 2010 #7

    alxm

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    Sounds like a nice suggestion for a school lab that could be done with an ordinary pc. Record the sound, analyze the spectrogram to determine the resonant frequency, and use the tone-generation features to make it resonate again, verifying your result. Nifty!
     
  9. Jul 15, 2010 #8

    russ_watters

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    You could also go the other way and get a tone generator for your computer, hook it up to an amp, and watch it resonate.....carefully.
     
  10. Jul 19, 2010 #9
    I tried both suggestions. From what understand is that the computer automatically sets a frequency called the "sampling rate", in which there is a set rate at which the speaker will vibrate at. Does anyone have any other solutions?
     
  11. Jul 19, 2010 #10

    russ_watters

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    The sampling rate is the rate at which it gets data samples from a sound - it is not the frequency at which the speaker vibrates. The sampling rate is well above the maximum audible frequency (otherwise it wouldn't be able to reproduce high frequencies).

    You didn't provide any description of what you did: how exactly did you attempt to use the two methods described?
     
  12. Jul 19, 2010 #11
    Russ_waters, the way you recommended, I actually tried performing a few months ago, and it was very difficult to find the glasses resonant frequency. I spent several hours traversing slowly through different frequencies ranging from 0-20000hz. I concluded that my speakers were not loud enough to break the wine glass(I reached about 110-120 dB).

    The second way I tried was by pinging the glass with a butter knife. I recodered the sound and put the file on my computer. I used the software "Audacity" to analyze the waves. I also used the "NCH" tone generator to get a more precise frequency that the wave resonates at. After doing a little math I figured that the waves per second was about 43,800Hz. That number did not seem right to me. Then I started look at the sampling rate which was bout 41000Hz. So I naturally assumed that the frequency I was looking at was incorrect. It is not that this method does not work, I should accurately say that I was unable to receive any real data. Theoretically it should work, but I keep getting a frequency of 41000 regardless of the sound that is being played(pinging glass, or my voice).
     
  13. Jul 19, 2010 #12

    russ_watters

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    Hmm.....Are you sure you were actually recording? Could you play back the sound? Perhaps it wasn't loud enough and you were just reading the static?

    I just tried the method you suggested and got a good result. I used a headset mic, and a 1/4 full wineglass (with water) and did the rub your finger around the rim trick to make it resonate. Frequency of the first/largest peak: 568 hz. See attached screen cap.
     

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    • Tone.jpg
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  14. Jul 19, 2010 #13
    What you are looking for is an oscilloscope. You may already have but just in case, do some research on Nikola Tesla and his earthquake machine. He determined that everything vibrates at a certain fequency and if you mimic this frequency you can destroy that object. Which is exactly what you are trying to do. Check out this vid:
     
    Last edited by a moderator: Sep 25, 2014
  15. Jul 19, 2010 #14
    Russ Watters. I think my confusion is how to get the frequency from the software. I do not know where you got 568Hz from. I did the trick your recommended right now and got results, but I do not know where to read the frequency?
     
  16. Jul 20, 2010 #15
    So basically your computer reads the vibrational data in some time domain. For example you could record the glass vibrating in seconds from 10:15 and 0 seconds to 10:15 and 36 seconds. This is the first graph in Russ's post (it's not the right timescale or time, but you get the picture!)

    From there we can do this absolutely amazing technique called a Fourier Transform which takes the data we collected in the time domain and can give us a reading of frequencies. This frequency reading can tell how "strong" each frequency is from your vibrating object.

    You see most everyday objects do not just vibrate at exactly 1 frequency. Objects will have a main resonate frequency but in addition you will also get harmonics which are small added amounts of additional frequencies that give an object it's distinct sound.

    Anyways, we reading a fourier transform you are looking at the frequency with the largest amplitude is probably your resonate frequency.
     
  17. Jul 20, 2010 #16
    Interesting project.

    I think the easiest way is here:
    http://www.physlink.com/education/askexperts/ae698.cfm

    About frequency analysis with Audacity:
    https://pantherfile.uwm.edu/type/www/420_Field_Audio/FrequencyAnalysis/FrequencyAnalysisAudacity.htm [Broken]

    Good luck.
     
    Last edited by a moderator: May 4, 2017
  18. Jul 20, 2010 #17

    russ_watters

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    Well, if you had it give you some frequency, I assume you've already selected "plot spectrum" from the "analyze" menu. then you just hover your cursor over the largest peak and read what it says.
     
  19. Jul 20, 2010 #18
    Try putting something like a drinking straw in the glass and driving your oscillator through the frequency range when the straw starts to move about you've found the resonant frequency of the glass, then build up the volume.
     
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