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Trying to measure the cross grain frequency using Trevor's method to get the get the cross grain modulus. My question is on holding the top. It appears that the top is held in the same place for the long grain frequency, but tapped in a different location, is this correct?
I was just checking a Lutz top and had a long grain frequency of 73 hz and a cross grain frequency of 146 hz. 2 x the long grain frequency, it seemed possible but maybe a bit too convenient being a perfect harmonic and all. I tried holding it in slightly different spots consistently got the 146 hz, just varying amplitudes of the various frequencies.
It also seems to be the second peak on the long grain top.
Do you think this is right?
Thanks

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Jim Watts
http://jameswattsguitars.com

Check pages 4-57 (Design) and 6-7 (Build) which explains about where to hold the panel to suppress the modes you don't want to see whilst not damping the modes you're trying to measure. The hold point is different for long and cross grain and needs to be on the node line for the mode you want to measure.

Your numbers look about right, Jim. The factor of two is just coincidental. The partials of vibrating plates are not harmonic unless by some happy coincidence, or are made so, as in the tuning of marimba bars.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks Trevor.
I'll try rechecking again just to be sure and re-reference the sections.

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Jim Watts
http://jameswattsguitars.com