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You will see a double peak like that when the main top and main back tap tones are close in pitch, but any resonance that couples well with the top can do that to some extent. You could try mass loading the back and run another spectrum on it, to see if the double goes away.

Thanks Hesh

I'll check it out. I have been using REW (Room EQ Wizard) it a pretty neat software package and its free online but its geared more towards equalizing the sound Acoustic of a room or space for audio quality adjustments so its not so much geared specifically to Acoustic guitars.

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Ron Riggs

I have been Bitten....by the Guitar building bug!
Not sure there is any cure for my condition
at least I hope not!

That is the same software I use. I think it has a unique ability to show the spectrum in real time. No other software does that.

Just stick an FFT app on your phone…

Phone app is the way to go. Zero setup to measure a guitar meant I measured a lot more of the guitars I encountered out in the wild and collected more data.

Yep…did you also find the better sounding ones closely matching the numbers in the books?

In many but not all cases. In particular, I found some great sounding dreads with higher resonances than “ideal”, north of 100hz.

What I also found, in measuring some mediocre lguitars, was that occasionally some were pretty “good” by the numbers despite being poor sounding instruments.

Yeah there’s def a lot of combos that work, and differing ways to get there.

Oops. Late and sleepy. This has been a fascinating conversation!

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Peter Havriluk

The advantage that I have found with using windows based software and a laptop at least for me is the ease of taking a screen shot of all of the graphs and pasting into a word document for archiving along with measurements and pictures of the guitar at various stages so if I need to refer back to them everything is in a single location.

But I get it!, that may be more than some people want to do since it is more work documenting as you go. For me I want to be able to pull up every piece of information about a particular guitar with a simple click to open a file.

By the way has anyone used the "Visual Analyser" software. I read an article by Trevor Gore and he recommended it. The only problem is all of the documentation as far as user manuals are in Italian and I haven't found any videos specific to it being used for analysing a guitar.

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Ron Riggs

I have been Bitten....by the Guitar building bug!
Not sure there is any cure for my condition
at least I hope not!

Hey! Barry Daniels

Maybe you know the answer to this. In REW when you look at the graph at some of the peaks it has a number above it usually 1 through 9.
Have you figured out what those numbers mean. Are they the numbers of the harmonics ?

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Ron Riggs

I have been Bitten....by the Guitar building bug!
Not sure there is any cure for my condition
at least I hope not!

Once you get the books from Gore / Gilet you’ll get a deep dive on using VA or you can use the video that Trevor produced for Robbie O’Briens luthier academy - https://lutherieacademy.com/courses/analysis


Also take a look at Luthier Spectrum Analyzer. I have been using this for the last couple builds and it’s great. A simplified interface specific for what we’re trying to do - viewtopic.php?t=52566


Sent from my iPhone using Tapatalk Pro

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I am not sure. Do you have a screen shot of that? I only use the RTA (real time analysis) module.

A friend of mine who is a retired software developer worked up an Android app (along with his wife; another software type) he calls 'Luthier Lab'. When they got it done they figured that there would be no profit in trying to sell it, so they put it out for free. It's aimed at builders, so it has a lot of modules for laying out shapes, bracing, fretboards, and arches if you want to make an archtop. There's a signal generator for those of us who play with glitter patterns, and it will save photos of the patterns (or anything else) in a file for that project. It also has a nice little spectrum analyzer that allows you to pick out and label peaks in the spectrum and zoom in. Check it out; the price is right, and he does support it.

Here is the link to the graph of my first guitar that shows the numbers I'm referring to just above each peak.

https://drive.google.com/file/d/1gK1-C88NXFebG-yABoGMZ6YVae1ej1VR/view?usp=sharing

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Ron Riggs

I have been Bitten....by the Guitar building bug!
Not sure there is any cure for my condition
at least I hope not!

I don't know what those numbers mean.

Too many numbers confuses me after a while, and I have trouble keeping everything sorted out. I've always believed there are three kinds of people in this world, those who are good with numbers and those that aren't.

I’m not certain what that graph represents either…

Ron, here is my best guess; those numbers correspond to the list in the legend that seem to show a decreasing rate of percentages of peak resonances..

Ed, it is a frequency strength plot aka histogram, spectrogram.

Pardon, I do know what the graph represents, I don’t understand what the numbers in the boxes represent, nor do I understand why it’s labeled at 173hz. I’m more accustomed to an FFT scan that shows the freqs of the peaks…

Sorry Ed. I mis-understood your question.

I think the 171.73 is the 1st major peak above somewhere around 150 hz. You can see that the legend's list starts with item 2.

Oh, I think I see what’s happening. I think the box on the left indicates that he’s got the back resonance selected…he did mention his back peak was in that neighborhood…

Hutch, I'm in the same place as you. I've tap-tuned the soundboards after they were joined and sanded to suit. And then stopped. Just last week i visited a luthier (same person who exposed me to tap-tuning) and got some instruction and experience in tap-tuning a braced soundboard. The changes were dramatic but I had a tin ear trying to see if the soundboard needed its bracing loosened and when to stop trimming. We'll see how this one performs and try to apply something to the next one.

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Peter Havriluk

This is why I like measuring stuff. It’s objective, not subjective…