Reading a Long Grain frequency spectrum graph.

[johnparchem]

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

panamarosewoodFL.jpg (37.65 KiB) Viewed 7184 times

thickness33.jpg (147.55 KiB) Viewed 7184 times

thickness54.jpg (147.46 KiB) Viewed 7184 times

[DarwinStrings]

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.

[johnparchem]

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.

[Trevor Gore]

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]

Thank you Trevor,

Unfortunately my only set.