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[Herman]

John, you are so into this guitar resonance material, I'm not. Here are two audiospectrums of tapping my latest top and back. Body completly built, but no neck attached. Can you relate this to the tings you wrote above?

[John Parchem]

What is you setup, when taking those spectrum samples. There are too many peaks between 100 - 200, I have seen this in two cases. The first was when I had the gain too high on my microphone input, causing a distorted input, the second I saw when someone accidentally had a distortion filter on (like used when recording an electric guitar).

Trying to read through the distortion I think I see, it look like the Air resonance is around 95, the top is somewhere around 200. The back looks to be around 240. All of these numbers will go down once the guitar is strung up. The top could come down close to 190, 180 something if the bridge still needs to be glued on. If my reading is correct those would be pretty typical of a small to medium sized guitar. If you look for the back peak, that you see in the back sample, in the top graph you see that there is not much there, so my guess is the back was made to be reflective and is not coupled very strongly with the top.

Here is an example of my last classical tap before I put the strings on. The first thing to note is to see the clarity of the graph between up to 250. I had a graph nearly like yours and I turned down the gain on my microphone. Also look at how strong the 237 Hz back resonant peak is when tapping the front. This guitar was built with an active back.


Here is the same guitar after I put on strings and tuned the back. You can see how the first two peaks lowered. The back moved quite a bit cause I shave the lower transverse brace on the back.

[Herman]

Thanks John, I think I'm about to getting the idea.

The body, not a small guitar actualy, a HD28 with smaller bodydepth has large volume, but little "poiiiing".
I followed your advise and took some wood of the lower braces of the back. (Small/high braces).
Now the body begins to develop some sustain in the tappitones.
After taking off about 1/8" of the braces, this is the spectrum of the toptapping.
I think, now the back is reacting with a 230 HZ respons.

[John Parchem]

Yes it appears that way to me, it looks like the top frequency also came down a bit as now you are getting some coupling to the back. I would wait to do more until you can do a tap strung up as it that will bring the resonance down a bit. You can hold the strings on the neck and tap.

[Herman]

I'll do John, Thanks