Spreadsheets

[GregHolmberg]

I have posted several spreadsheets here before. Panel thickness, fret positions, fretboard radius/width, neck shape, intonation compensation, 4DOF model, brace stress/sizing.

I decided to combine these into one big spreadsheet file with 20 worksheets, and create connections between them, so when you change one worksheet it affects others. In essence, I've tried to create a complete acoustic guitar model. How accurately this predicts acoustic function is yet to be seen.

I place them here for your use, in the hopes that they will be used to create better acoustic guitars. I feel that the necessity of creating ones own spreadsheets from the book is too high a hurdle for most people, and this has hindered the successful use of the wonderful information in the books. Yes, you can use the books to make a copy of a Medium Falcate steel-string, but I would like to see some new designs.

• Medium steel-string falcate with CF spreadsheet
• Medium steel-string falcate, no CF spreadsheet
• Classical nylon-string falcate with CF spreadsheet
• Wood Properties spreadsheet
• Guitar Modeling Documentation

You may copy and modify these spreadsheets for your own purposes, just always keep the copyright and the links to the original spreadsheet, and to the documentation.

You can work with these directly in Google Sheets (free to use, nothing to install) in your web browser, or can download an Excel or OpenDocument file to work on them offline. Use the File -> Download command in Google Sheets. For the OpenDocument files, I recommend the free LibreOffice software, available on all platforms.

Feedback, constructive or otherwise, is always appreciated.

I'm looking for people who would like to test the spreadsheets and work with me to find bugs. Please send me a PM if you're interested.

Greg

[kiwigeo]

Thanks Greg.....your efforts much appreciated.

[TomBeltran]

I decided to combine these into one big spreadsheet file with 20 worksheets, and create connections between them, so when you change one worksheet it affects others. In essence, I've tried to create a complete acoustic guitar model. How accurately this predicts acoustic function is yet to be seen.

I place them here for your use, in the hopes that they will be used to create better acoustic guitars. I feel that the necessity of creating ones own spreadsheets from the book is too high a hurdle for most people, and this has hindered the successful use of the wonderful information in the books. Yes, you can use the books make a copy of a Medium Falcate steel-string, but I would like to see some new designs.

Greg

Greg - thank you so much for putting these spreadsheets (and your earlier ones) up on the web. I definitively fall in the class of those for whom this would be "too high a hurdle." The thoroughness of you work is incredible. Tom

[joel]

Thanks Greg,

Gratefully nicked!

[edvinguitars.fi]

Thanks Greg

I tested the spreadsheet, made a new nut/saddle and got a big improvement from the values that were written in the Gore book.
I made the optimization for low action using the Libre office solver.

In my case, the problem was I originally made the saddle / nut by the book dimensions but then wanted to make a much lower setup to my guitar. I thought I was weird player preferring as low as 1.5mm/1.8mm action setup, but after quite a few professional Finnish guitar players liked the low action setup, I concluded maybe I'm not alone, it might be a northern preference to play acoustic on so low setup.

With my strings, nut compensation came out only 0.5 .. 1.1 mm, and saddle 0.22-1.06mm

Now, the new setup and compensation scheme is so accurate that I don't trust my tuners any more: some mobile app shows +4c on some fret while some other app show -3c. And my ears hear no difference. I do have a Peterson portable strobe tuner, which I think is the most accurate one I have. But the Peterson does not show how many cents the tuning is off.

Jani

[GregHolmberg]

That's great, Jani. It makes me happy that someone finds it useful.

I'm curious which method you used.

• Measure the action of every fret, every string
• Fit polynomials to the measured data
• Model the neck as a line + ellipse + circle
• Model the neck as a line + parabola

The spreadsheet is set up to do the last three, and by default, it selects the line + parabola method.

This method requires you to go to sheet 'intonation' and set the stiffness of the wood species used for the neck, and it also uses the thickness of the neck from sheet 'neck' and the force of the six strings, all to calculate the deflection of the neck under tension. This deflection is a parabola, according to beam theory.

In any case, glad to hear it worked!

Greg

[JRCros]

Thanks a lot GregHolmberg for your work with these spreadsheets, it is an amazing work that you've done. I'm starting to use them.

[oliver]

Thank you for your work and for sharing the Excel tables. I am trying to understand how it is structured and what the values refer to. I am working with "Classical nylon falcate noCF V3.xlsx"
During the construction is grateful for some values here some questions:
-In the sheet model in the cell Side density I find the value =0.8/110 what does it mean?
- What does the value "Side mass" mean? Is it with linings and blocks or just the mass of the side?
-Further down is the value for "Uncoupled top" is this theoretical or should it be measurable during the build?
Finally, something small.
Shouldn't the length "Depth, tail block" in the "body" sheet be less than "Thickness, top and back"?
Many thanks if you have time for an answer. Oliver

[GregHolmberg]

Hi Oliver--

You're welcome. I hope it's helpful.

Good questions. I'm going to assume you've read the book and also my documentation for the spreadsheets.

1. sheet 'model'
9 | Side density | side_density | kg/mm | Mass of sides per mm of height.
39 | Side mass | ms_bare | kg | Without added mass.

side_density is there to help you estimate the side mass. In the book, side mass is referred to as Ms, first seen in Equ. AII 2-8 (page AII-6). And yes, it's not exactly clear what parts of the guitar qualify as "sides".

Trevor says he fit the model to a guitar he had, and came up with a mass for the "sides" of 1.4 kg (Table 2.4-1, page 2-37). I think by "fit" he means he played with the values until the model produced a frequency response that matched the guitar. So it's hard to say exactly which parts it is that weigh 1.4 kg.

If you read the book carefully, it becomes clear that the "sides" are everything outside the Chladni lines of the back and top, including the sides (and linings, splints, etc). I think of it as "outer" not "sides". It's not easy to estimate that. You could get it from a CAD model (I'm working on it), but short of that the best you can do is make a guess.

side_density was my attempt to make guessing easier. ms_bare = d_average * side_density, so the deeper your body (body!d_average), the more side mass. The value for side_density=0.8/110 kg/mm is just the side mass of a typical guitar (0.8 kg) divided by the depth of the body (110 mm). The guitar in the spreadsheet is 120 mm, so its side mass came out to 0.87 kg. But this is just a wild guess. If you have a better guess for the guitar you're designing, go with that.

There are several other similar parameters under "factors for estimating" that are my attempt to make guessing easier, but may or may not produce good guesses. They're just meant to be more convenient "dials and knobs" to fit the model to a guitar.

Maybe Trevor can explain more about how he fits a 4DOF model to a guitar.

2. Uncoupled top
Is it measurable during the build? Not sure. I know that the Build volume shows how the frequency changes as various steps are completed (thinning the outer top, gluing the bridge, finishing, stringing up, etc.) I think you should be able to see the uncoupled frequency in the completed guitar when you disable the coupling by plugging the sound hole (appendix AI 3, page AI-7). I guess one uses a piece of styro-foam or a plastic yogurt cup?

3. sheet 'body'
Thickness, top (t_top) is the thickness of the top panel, 2.49 mm.
Depth, tail block (d_tb) is the block of wood inside the body, as shown in the Build volume, page 10-3. It's 50 x 20 x 121 mm.

The reason d_tb is in the spreadsheet is to calculate the internal air volume of the body (the "cavity"). One has to subtract all the internal parts to get the air space.

But perhaps instead of t_top you meant "depth at tail" d_tail=121mm, and are asking why they are both 121? Sure, I suppose d_tb should be less, since it's inside. So subtract the panel thicknesses: 121-(2.49+2.08) = 116.43

At some point I just figured the air volume calculation was close enough, and I should put my effort into the CAD model to get better estimates of mass and volume. I'm working on it.

Hope this helps.

Greg

[oliver]

Thanks for the quick and competent answers.

Yes, I have read the books and the documentation.
Sometimes there are uncertainties in understanding English (deepl helps me).
Now I can see where the =0.8/110 comes from and I am happy to know that it is an estimate.
I had doubts if I could understand it.