Alain, that's great! I wish I was more fluent with even programs so basic as
Excel. I'll definitely save that one for the shop computer (whenever I actually
get one over there
).
Thanks
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| Author: | David Collins [ Sat Dec 02, 2006 9:49 am ] |
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In another intonation thread I mentioned my use of calculators for quick figuring of compensation, and after some inquiries thought it may be worth it's own topic. My calculator is such an everyday tool it my shop that I may take it for granted that many don't realize how much time and headache some simple button pushing can save you. In the intonation example specifically, this is a brief summary of my procedure. For routing a saddle slot for a typical scale length I don't usually go too wild for specific intonation. I use a piece of 1/8" brazing rod as a dummy saddle. It is slightly flattened on the bottom and bent to match the radius of the bridge to set the initial line. At this point I generally nudge it around to set the high E slightly flat and the low E slightly sharp (The brazing rod is of course round on top, so the string's end is at the center – on actual saddles the high E will normally be shaped forward and the low E set back). In doing this I know that I can shape the saddle to bring the high E forward while making sure that I will have enough room to move the B back to where it needs to be. The same idea for the bass side, as the low E typically needs to be further back than a straight line from the G, D, and A would point to. This typically gives a line at roughly .075" back at the high E and .125" at the low E when measured from the actual scale length. If I were building guitars using the same scale length, fret board, etc., I would just be using a template to set the line. For fine tuning the saddle after the slot is cut I keep some bone dummy saddles around, with the peak beveled to the front (all the strings will be a little sharp) and shim it to the correct height. Of course all this is done after the nut height and truss rod adjustment are good. Then I use my Peterson VSAM to check how far out each string is. Tune the open string or octave harmonic, then as you play the fretted 12th you can dial in the tuner until it is stable. That will tell you how many cents sharp that note is. Jot it down, and check the others and it goes quite quickly. To figure out how much compensation you need, all you need is a calculator that can figure specific roots and powers. I use the TI 35XII, because it's under $20 and does everything I need. You don't need a $100 fancy graphing calculator for any of this. The numbers that I keep stored in my memory are the 12th root of 2, the 1200th root of 2, and (12th root of 2) / ((12 root of 2) -1). This last one is the 17.81715.... that’s where the actual number used for the "rule of eighteen" comes from, and is actually the one I use least. The 1200th root of 2 is the one used for calculating cents. So now let’s say you have a 25.34” scale guitar, and the E reads 3 cents sharp fretted at the 12th. Raise the 1200th root of 2 to the 3rd power and multiply that by 1/2 the scale length – 12.67 in this case. Then subtract that 12.67 from the answer, and there you have how far back from the front edge of the saddle it needs to be compensated. 3 cents would come out to just under .022”. Perhaps the B reads 11 cents sharp. 1200th root of two, to the 11th power, multiplied by 12.67, minus 12.67 comes out to just under .081” set back from the front of the saddle. It may sound complicated at first, but I in practice it probably takes me as much time to lay out compensation for all the strings as it’s taken you to read this posting. If you didn’t want to deal with the calculator at all you could even make a quick chart to keep handy for compensation needed per cent. I think it pays to become fluent with your calculator though. I’m sure some may have noticed a flaw in my numbers above. Rather use half the scale length for my calculations it would be correct to use the actual measurement. Since the saddle slot is already set back at an angle I should be using 12.745 for the high E down to 12.795 at the low E. I usually do add a rounded .1” to the half scale length for my calculations, but it really isn’t enough to make a difference in the real world results. For example the difference between calculating 6 cents compensation using ? scale length vs. the actual measurement of .1” greater would be a whopping .000347”. If you can control your file well enough to reach those tolerances then great for you, but for the rest of us it won’t really matter. I didn’t throw it in to the formula above because it could probably be seen as intimidating enough already for many. Like I said before though, it’s really quite simple. My personal methods for adjusting intonation vary in little details from what I described above in method and philosophy I guess, but that’s another topic all together and the math is all the same. You can also use this for figuring out nut compensation just as quickly if you juggle the numbers around a little. The same idea covers fret placement or compensating frets if you prefer to do that. There are certainly other methods that work quicker or better for others as well. Some prefer tools, some numbers, and some just trained listening or even intuition. I myself like to keep a healthy mix of all of the above. |
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| Author: | Shane Neifer [ Sat Dec 02, 2006 12:14 pm ] |
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Thanks David! I appreciate you taking the time to explain and I will be adding this to my note book! Shane |
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| Author: | Joe Beaver [ Sat Dec 02, 2006 12:57 pm ] |
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Thank you David, that is really good stuff!!! I'll have study it a little to get a firm grip of it but it doesn't look to difficult thanks to your great explaination!! |
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| Author: | Alain Lambert [ Sat Dec 02, 2006 1:53 pm ] |
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Here is a small spreadsheet to calculate what David has explained. Thanks much David Oops where did the file go? 2006-12-02_215519_Intonation_Calculator.xls Ok second try |
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| Author: | David Collins [ Sat Dec 02, 2006 7:37 pm ] |
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Alain, that's great! I wish I was more fluent with even programs so basic as Excel. I'll definitely save that one for the shop computer (whenever I actually get one over there ).
Thanks |
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| Author: | Serge Poirier [ Sun Dec 03, 2006 1:27 am ] |
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Thanks to David and Alain, great thread, info saved to file! 
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| Author: | Andy Zimmerman [ Sun Dec 03, 2006 1:36 am ] |
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Alain Thanks for the Excel file. Are the results in mm or inches. Also I tried to change the scale length but it wouldn't work Any suggestions. |
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| Author: | Andy Zimmerman [ Sun Dec 03, 2006 1:45 am ] |
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Alain I saved the file and then worked with a new version and it allowed me to change the scale length. Thanks This is awesome. I will use it forever!!!!!! Andy |
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| Author: | Alain Lambert [ Sun Dec 03, 2006 2:37 am ] |
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The scale length can be changed in the yellow cell. It is just then repeating for the six strings. I would think this would work in any system (mm or inches). Right David? If you put the scale in mm the result will be mm. if you input the scale in inches then it would be decimal inches. I have protected the sheet so that formula are not erased by accident. However there is no password and you can unprotect in Tools, Protection, Unprotect the worksheet. |
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