Reading a Long Grain frequency spectrum graph.

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johnparchem
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Reading a Long Grain frequency spectrum graph.

Post by johnparchem » Fri Apr 17, 2015 8:54 am

I was doing some tap testing on a Panama Rosewood plate to thickness for a classical. After my first pass I had some eyepopping numbers, So I went back and looked at the graphs. Here are my results for the long grain frequency. I originally picked the 54 Hz, but I do see a small peak at 33.7 Hz that gives me results closer to what I was expecting. The plate does have a really good sounding and sustaining tap tone.

The 54 Hz gave a GPa of 19 where the 33. Hz results in a GPa at 7.7. Is the low first peak the one to pick
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thickness33.jpg
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thickness54.jpg
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DarwinStrings
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Re: Reading a Long Grain frequency spectrum graph.

Post by DarwinStrings » Fri Apr 17, 2015 1:16 pm

If you are tapping it right for the Elong and have your mic in the right position then it should be that peak of greater amplitude.
Life is good when you are amongst the wood.
Jim Schofield

johnparchem
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Re: Reading a Long Grain frequency spectrum graph.

Post by johnparchem » Fri Apr 17, 2015 2:03 pm

DarwinStrings wrote:If you are tapping it right for the Elong and have your mic in the right position then it should be that peak of greater amplitude.
Thanks, I am holding the node tapping at the anti-node, I have the mic at the anti node. I have done it a bunch of times and always looks the same.

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Trevor Gore
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Re: Reading a Long Grain frequency spectrum graph.

Post by Trevor Gore » Fri Apr 17, 2015 3:40 pm

I've had Bloodwood (Brosimum Rubescens) come in with similar figures, but at a density of over 1000kg/m^3. I suspect the ~33Hz figure could be a heavily damped diagonal mode. Panama rosewood has a reputation for being "glassy", but I've never built with it.

If you have any more, I'd recommend you send it to me so I can verify your results!

johnparchem
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Re: Reading a Long Grain frequency spectrum graph.

Post by johnparchem » Sat Apr 18, 2015 1:07 am

Thank you Trevor,

Unfortunately my only set.

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