Spreadsheets and "Contemporary Acoustic Guitar"

[Greg Holmberg]

Over on anzlf.com, I've posted several spreadsheets in the past, implementing various formulas from the book "Contemporary Acoustic Guitar" by Trevor Gore and Gerard Gilet. 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

[John Parchem]

Thank You! These are great. I have started to go over you falcate classical sheets/

[Greg Holmberg]

Thank You! These are great. I have started to go over you falcate classical sheets/

OK, good. I'd love to work with you to make them better. Let me know what you find. My email is in the documentation if you prefer that to private messages.

Greg

[John Parchem]

I am using this for the nut and saddle and nut intonation. I finally found your documentation page:
Guitar Modeling Documentation. Really well done and useful. I had been working through the sheets previously. There is an amazing amount of work in the spread sheets.

[Greg Holmberg]

Thanks, John. I appreciate that.

Regarding the calculations for intonation compensation, there are several ways you can do it, so it's a little confusing, since the worksheet contains all of them. You can use Young's modulus for steel, which is fairly reliable (not so for Nylon). You can use the number published by the string manufacturer (D'Addario is the only one I know who does this). I had one luthier report good results from a guitar he built using this method.

But the only really accurate way is to build the string test rig as described in the book, page 4-107.

If you do this and test some strings, would you be so kind as to share these six values for each string? m_unfretted, L_unfretted, f_unfretted, L_fretted, f_fretted, d_fretted. Or, at least share the resulting values for k and μ.

I have been unable to find values from actually measured strings anywhere on the internet, and I don't trust D'Addario values for μ and tension. It would be so useful to have k and μ for some popular string products.

Thanks,

Greg

[John Parchem]

I use D'Addario strings and used their value. I have been planning to build a a tester. so I might fit that in. The nut compensation looked close to what I would have thought based on using the same strings on a longer scale on a different instrument. It is sort of easy to test on the guitar. I look for the nut compensation open to first fret. I will intonate the saddle as calculated but then see if I have to move it.