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Amplitude and Frequency

Discussion in 'General Electronics Discussion' started by Electro132, Oct 21, 2013.

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  1. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I don't think he needs a coupling cap either. The PC's mic input is wired to take electret mics directly. If you couple an electret through a cap it won't work properly without providing battery power through a limiting resistor.

    Chris
     
  2. solo2racr

    solo2racr

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    Aug 21, 2013
    I built my test mic and used a Panasonic WM-61A electret cartridge. I tried it without power and promptly got no where. Added a bit 'o power and it was good to go. I mounted the cartridge at the end of an aluminum tube and held the battery in a PVC body on the base end.

    Attached are the datasheet for the WM-61A, it's response curve and the schematic I used.
     

    Attached Files:

  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I guess I should rephrase my statement. All my PCs employ phantom powered mic jacks to accept unpowered electret mics. The DC that the electret requires is derived from the PC mic jack. I've always assumed that all modern PCs are wired this way.

    So,.. if an external coupling cap is used between the electret mic and the PC mic jack you will be blocking the phantom DC that the PC provides and the electret mic needs to operate. After all, there's a JFET preamp in there. ;)

    Chris
     
  4. Electro132

    Electro132

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    Feb 12, 2013
    Just with your diagram of the mic, is the output connected to the end of the negative lead on the mic or does it go over?
     
  5. Electro132

    Electro132

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    Feb 12, 2013

    Do you mean something like this
     

    Attached Files:

  6. Electro132

    Electro132

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    Feb 12, 2013
    I have a honey jar to experiment on as well but i found out that it was either too damp or i was not reading the screen right when i hit it with a pen to get its resonance frequency. Would you be able to help out? I tried locating the top peak of the honey jar and db but didn't get it to work. What i got was between -30 to -36 db and a frequency of 940 - 970 hz.
     
    Last edited: Nov 15, 2013
  7. duke37

    duke37

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    The circuit in #45 is wrong, the capacitor will short out the signal, so did you get it to work?

    Chris suggests that the computer may provide some power to drive the microphone. You can check if this is present with a meter. If not then you will need some power supplied as in the earlier diagrams.

    A honey jar will be very thick and non uniform. To get a glass to ring you will need a thin glass on a thin stem.
     
  8. solo2racr

    solo2racr

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    Aug 21, 2013
    A dot will show a connection. Otherwise, it will "go over"
     
  9. Electro132

    Electro132

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    Feb 12, 2013
    Ok thanks.
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Duke previously explained how to resonate a glass in order to measure its resonant frequency. What you did here is not what he described. Frequency counters, whether real or PC based require a reasonably steady signal for at least a few seconds or it will return erroneous results... And yes, jars are a bad candidate.

    Chris
     
  11. Electro132

    Electro132

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    Feb 12, 2013

    I got hold of the resonating frequency of 880 hz for the red wine glass and 3200 - 3280 hz for the honey jar. The honey jar was hard to do and took me about an hour to get it to resonate so it is still unsure what the resonating frequency is exactly. But the good part is that i managed to narrow it down. I'm happy about that

    How i did it is that I actually kept going round the rim of both the Honey Jar and the red wine glass. I know an amp and speakers will break it for sure. Will need a schematic to build an amp with control pots so i can drive up the volume sound coming from the laptop. My laptop's sound level is already high and it still doesn't break it through a speaker.
     
  12. davenn

    davenn Moderator

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    if the homey jar of thicker glass and larger size than the wine glass ( most likely the case) then its resonant freq is going to be much lower than the 880Hz of the wineglass. NOT the many times higher frequency that you think you got

    Dave
     
    Last edited: Nov 21, 2013
  13. solo2racr

    solo2racr

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    Aug 21, 2013
    Thought this may help a bit....
     
  14. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Whoa, I missed that! ;)

    Chris
     
  15. BobK

    BobK

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    A jar or glass is going to have more than one resonant mode.

    Bob
     
  16. solo2racr

    solo2racr

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    Aug 21, 2013
    True. But only one fundamental frequency. All the rest are harmonics. That's not to say that it can't be broken at a harmonic. It would just take more energy input (more speaker volume) than what would be needed at the fundamental.
     
  17. BobK

    BobK

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    No, they are not harmonics. A two- or three dimensional object can vibrate in many different ways that are not harmonically related. These are called modes of vibration, and each mode will have a fundamental and harmonics. This is why bells, for instance do not produce a sound with only a single pitch.

    Bob
     
    Last edited: Nov 21, 2013
  18. solo2racr

    solo2racr

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    Aug 21, 2013
    I did some more research. You're right. I guess music theory really doesn't cover all the physics of vibration.
     
  19. duke37

    duke37

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    Bells used to be made to clang. Quite recently, perhaps 100 years ago, it was found how to tune the various vibrations to get a harmonic chord. A lot of church bells have been recast and tuned to make then sound sweeter.

    The Big Ben clock bell has a crack so will never sound sweet.
     
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