Q: Finding resonant frequency

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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.

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..

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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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

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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 ... :-)

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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.

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