Is there a tool to measure resonant frequency?

michiru

For a science investigation, I want to investigate how different factors affect the resonant frequency of wineglasses, however, I need some way to measure the frequency quantitatively. Is there some kind of computer program that can do so through the computer microphone? And if so, would the microphone be sensitive enough to detect such a sound and give an accurate reading of the frequency?

russ_watters

Welcome to PF...

Yes, yes. See this thread: http://www.physicsforums.com/showthr...light=audacity

Studiot

Speak to your art and drama department. There are several sound analyser on the market to do just that. These instruments were originally designed for stage use, so they may have one.

http://www.soundonsound.com/sos/feb0...les/phonic.htm

nasu

You can download some simple, free, programs to use with the audio card.
For example:
http://www.electronics-lab.com/downl...001/index.html

HallsofIvy

Dang! I was going to suggest a set of tuning forks! I'm getting too old!

jambaugh

Another "old school" approach is to set the wine glass by a (tuned) piano, put your ear next to the opening and listen for resonance as you compare it to the piano notes. (Lightly tap the glass with a pencil to hear its resonant freq.)

Look up the frequencies and you should be able to get pretty good measurements. Even if the wine glass frequency exceeds the high note on your piano you should be able to pick out the note compared to one or two octaves below. And you should be able to interpolate between keys to a half note by ear.

The human ear is a pretty darned good frequency analyzer all by itself.

michiru

Hi everyone, I like the idea of using Audacity and the free computer programs, but I am worried that the computer microphone will not be sensitive enough to detect the sound of the wineglass? Would this be a problem?

russ_watters

Please check the link I posted, michiru: that is exactly what I did!

I used the trick where you wet your finger and rub it around the rim of the glass and held the mic next to it.

michiru

Hi, I did a test, with audacity and a computer oscilloscope and got some nice waveforms, but I am not sure how to analyze these waveforms to determine what the resonant frequency is? I tapped an empty wineglass with a spoon near the microphone and got these:

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jambaugh

The second image looks useless. Either it is saturating (signal is actually too loud) or it is not sampling fast enough or both. The first image looks like it might be good but you need to zoom into a small segment.

You should see a decaying sinusoidal waveform. You should be able to then determine the period of one cycle.

Zoom in, measure the distance between 10 peaks of the waveform and divide by 10 to get an average period. The frequency is then 1 over the period.

Can you post a zoomed in image from the audacity sample?

michiru

I do see part of a sinusoidal waveform. As seen in the last recording in the screenshot.

Don't I need to do a spectral analysis or something?

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russ_watters

Analyze -> plot spectrum

michiru

Is the value of the first peak the resonant frequency then?