This post is directed primarily at my lutherie brethren -- it's our culture as guitar makers to be generous with information and advice, so this is a bit of pay back for the tremendous help I've received from the community.
I'm currently building a fan-fret baritone guitar -- keep an eye out for further posts on that project as it progresses. One of the challenges is to address a design issue that is not generally transferable from standard 6-string guitars -- that being: "where to locate the compensated saddle?" While there are some online calculators for this purpose, those I found are not "transparent", so hard to know exactly how they work. There is the added complication that the scale-length for each string on a fan-fret instrument is different.
I decided to create a spreadsheet for these calculations, based on the article by materials engineer Saajk Elmendorp (2010: American Lutherie 104: 56-60). Elmendorp presented his calculations in metric units, but some of the string engineering data are readily available only in US units (e.g., D'Addario Strings). Some fiddling was necessary, as well as some supplementary calculations of tension based on unit weight and tuned frequency. In the end, I declared input in metric or US, depending on what was most readily available to me -- you may wish to revise the sheet to your preferred input units.
I'm making the spreadsheet available for anyone who may find it useful. The spreadsheet is available here: Download Steel string compensation calculator (you'll have to unzip the file once you've downloaded it to your computer). You simply replace the input data given in the yellow-highlighted cells, and the sheet will recalculate automatically. The saddle compensation required for each string is given in the last column.
Of course I make no guarantees, so you will have to accept the risk if you use it for your own instrument design work. Happy to get feedback on the calculator, so let me know your experiences and suggestions.
BTW: I notice that my post on my fret calculator has been corrupted by Typepad -- it seems they no longer like Excel files unless they are distributed as zip files. I'll make an edit to that post so that it will be available again for download.
