Q: Finding resonant frequency

[Peter Lowrie]

Hello me again...Darn it.

This question is about finding the resonant frequency of a piece of
stainless steel. Wondering if there were formulae for this purpose I did
some searches in Yahoo and Google but, alas turned up nothing.

The piece of stainless is a 14swg perforated disc measuring 80mm in
diameter.

I hung it up by wire and recorded the sound it makes by tapping with another
piece of solid stainless, looped the sound file and attempted to measure it
with fft anaylsis but with disappointing results.

Who has bright ideas on methodology to accomplish a result?

Thank you for your indulgence.

PEL.

 

[CWatters]

You have the right idea but I would feed to output of the microphone into a
spectrum analyser. Look for peaks.

Another way might be to mount a small directional speaker next to the plate
and feed it with a sine wave. Bounce the sound off the steel into a
microphone. Ramp the frequency and look for the power _absorbed_ by the
steel plate. This should be a max at resonance..

 

[Watson A.Name - Watt Sun, Dark Remover]

Yep, did that.


Ooh, that's clever it like a grid dip meter in RF apps.


Hmmm. Situation Solved, as follows:

Who says the frequency has to me measured, it does not. The thing only has
to resonate.

Did it like this: Large air wound coil slipped ofer terminal with disk
attached, amplifier, sweep function generator...Viola, humming stainless
http://www.mit.edu/~jcb/jokes/viola.html

steel disk.

:-0 Peter Lowrie

PS: Thanks to those that helped.

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[DaveC]

Did it like this: Large air wound coil slipped ofer terminal with disk
attached, amplifier, sweep function generator...Viola, humming stainless
steel disk.

Peter,
I can't picture this. A coil attached to amplifier driven by sweep gen.
What's the "terminal"? How is it attached to the disc? Is this like a speaker
voice coil? You just drove a magnet or piece of metal attached to the disc?

More details, please.

Dave

 

[Spajky]

get a guitar, kick the disc with a stick & compare the sound, when you
find exact tone it matches to a guitar tone (or piano tone) - basic
tone, not harmonics! than go to my site to se a tone frequency chart
under electronics/fan stuff 3 second page ...

-- Regards, SPAJKY
& visit site - http://www.spajky.vze.com
Celly-III OC-ed,"Tualatin on BX-Slot1-MoBo!"
E-mail AntiSpam: remove ##

 

[Watson A.Name - Watt Sun, Dark Remover]

Peter,
I can't picture this. A coil attached to amplifier driven by sweep gen.
What's the "terminal"? How is it attached to the disc? Is this like a speaker
voice coil? You just drove a magnet or piece of metal attached to the disc?

More details, please.

If you drive an unmagnetized core coil with an AC current from an amp,
the lack of magnetization will cause it to put out a very non-linear
magnetic field. It would be better to superimpose the AC on a DC
current so that the DC current causes the coil to stay magnetized for
the full AC cycle.

I built one of these with the 'I' laminations removed from the core of
an audio output transformer. I turned the steel side of a washing
machine into a speaker.

Dave

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Don't be ripped off by the big book dealers. Go to the URL
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http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
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