Q: Finding resonant frequency

Dec 07, 2003 7 Replies
P

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.


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R

another

it

Why can't you just measure the distance between a couple of good-looking waveforms and calculate the frequency? Shouldn't need to use FFT for something that simple.

Is the frequency of the "tink" sound different when you "hang" it through different holes (in the perforation)? It may have more than one mode of resonance.

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C

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..

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P

a

Yep, did that.

plate

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 steel disk.

:-0 Peter Lowrie

PS: Thanks to those that helped.

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@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/electronics/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). 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@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
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On Thu, 11 Dec 2003 3:29:34 -0800, Peter Lowrie wrote (in message ):

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

DaveC me@privacy.net This is an invalid return address Please reply in the news group
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S

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 -

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In article , snipped-for-privacy@privacy.net mentioned...

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.

@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/electronics/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). 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@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
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