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Thread: bell made from compressed gas cylinder - harmonic content?

  1. #1
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    Default bell made from compressed gas cylinder - harmonic content?

    I cut the bottom off an old cylinder and hung it up and banged on it. It was plenty loud but what impressed me about it was that it seemed to my ears to have a lot of sonic energy at many frequencies.

    I don't own a machine that can do an FFT on a signal coming from a microphone.

    I'm curious, though, about the harmonic content of such a bell tone. If it has enough high-frequency components (relative to human hearing) then one should have hearing protection when ringing the bell.

    Ideas?

    metalmagpie

  2. #2
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    May 2015
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    Stick a lump of bubble gum inside the rim.

  3. #3
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    Quote Originally Posted by metalmagpie View Post
    ... I don't own a machine that can do an FFT on a signal coming from a microphone. ...
    Yeah, it's too bad no one offers FFT software fore a PC or a cell phone.

  4. #4
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    I have done a number of these. I see a large difference between the steel and the aluminum (diver's tank) cylinders. I don't have any special equipment to measure, although I suppose it might be interesting to run it through the oscilloscope just for laughs. Some have a very impressive persistence - the sound takes several minutes to die out.
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

  5. #5
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    If you really want to know, download a copy of Daquarta here:

    http://www.daqarta.com

    Quite sophisticated audio analysis software thatís free to use in the basic version and super cheap for a non commercial use if you want some of the more fancy functions. Does spectrum analysis and all sorts of other cool stuff.

    Plenty of other such stuff around as well as smartphone apps that do similar.


    Sent from my iPhone using Tapatalk

  6. #6
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    Punch in FFT in the play store on Android. You may be surprised.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  7. #7
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    Quote Originally Posted by Bob La Londe View Post
    Punch in FFT in the play store on Android. You may be surprised.
    Well, that unleashed a flood!
    Which would you recommend?
    Len

  8. #8
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    Aug 2016
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    Quote Originally Posted by Bob La Londe View Post
    Punch in FFT in the play store on Android. You may be surprised.
    I have a lot of fun with the spectrum analyzer on my phone.

    I took a flight recently and analyzed the noise. I found definite peaks at 400 Hz, 6400 Hz, and the engine running between 12,000 to 14,000 RPM. I talked to the pilot after we landed and showed him some stored traces and he thought it was great.

    I also got bored as a passenger in a car and looked at the noise. I could spot the engines RPM, the RPM of the tires, and when I asked the driver to drift over and hit the rumble strip by the side of the road I could make a good estimate of the distance between the grooves in the rumble strip.

    I played with it once in the shop to see if it would be a decent tachometer. I have an optical tach so I compared the two results on the lathe. To get the audible I put a metal finger" that barely touched the outer edge of the jaws of the chuck... thick of a card and bicycle spokes. I listened to the noise and got the frequency, and divided by 4 (4 jaw chuck) to get RPM. The optical and the audible were in close agreement.

    Note that you can get a visual strobe for your android phone that you can use to do optical tachometer, too.

  9. #9
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    Quote Originally Posted by QSIMDO View Post
    Which would you recommend?
    Ummm? Solly to be a boar, well?

    Please answer the Q? I am curious. JR
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

  10. #10
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    Aug 2010
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    card and bicycle spokes.
    Well, that brings me back. The 7 year old's Harley!
    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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