Another approach to the quick and dirty intonation method.

[dshaker]

I finished up my first Gore and Gilet-style steel-string acoustic yesterday. My wife was out of town last week so I was able to work on it pretty much whenever I wasn't at my day job.

I spent much of the week at the dining room table, trying to get the intonation right. I tried using the Quick and Dirty method from The Book, but I got muddled far too frequently, so I backed off and rethought things. Here is the reasoning and the procedure I came up with.

The tools I used were (1) a Peterson Strobosoft iPhone app for a tuner, (2) "The Intonator" from Stew-MacDonald, (3) a stack of feeler gauges, (4) and an old NuBone saddle.

[Side note: The Intonator, as shipped, doesn't work all that well with the pins laid out in an arch as The Book's bridge design has them. The L-shaped components are too short. I made new ones by buying 3/32" brass rod, cutting and bending an appropriate length, then using a 4/40 thread die to put threads on them. They worked fine.]

Reasoning: The job of nut intonation is to take care of the difference in tension between open string notes and fretted note. Use the saddle to bring the fretted notes into proper intonation, then use the nut to make the open strings play in tune.

Procedure:

Saddle compensation-

1. Install all six strings, using The Intonator (or perhaps your homemade equivalent) as the saddle. For the nut, stack feeler gauges on the nut ledge until level with the fingerboard. Flip the NuBone saddle on its side and put it on top of the feeler gauges. That's your trial nut. Notch the nut for the strings as your level of industry dictates (Me= no notches).

2. Bring the strings up to pitch for the tuning you prefer.

3. Iterate on
a) Fret the target string at the fifth fret.
b) Tune the string to the proper note for the fifth fret.
b) Check to see if the note for the 12th fret is sharp or flat.
c) If 12th fret note plays sharp, move the Intonator saddle away from the soundhole. If flat, move it closer to the soundhole.
Continue until the two notes both in tune, or as close as your patience can get them.

4. Measure and record the distance of the top dead center of the saddle thing from the front of the bridge.

5. Repeat for the other five strings.

Nut compensation:
1. Leaving the Intonator saddle things where they are. Fret the string at the fifth fret and adjust the string tension until it plays in tune.

2. Move the NuBone nut substitute back and forth until the open string is also in tune. Moving the nut will move tension from one side of the nut to the other, so after you have moved it, be sure the fretted string is still in tune.

3. When the string fretted at the fifth fret and the open string are both in tune, measure the distance from the edge of the fretboard to the edge of the "nut" and record.

Helpful hints:
The StroboSoft tuner displays how far the sounded note is from target either in cents or tenths of a cent. I find it easier to read if it displays in whole cents, only.

If the cents are hard to read, I switch my focus to the striped display and try to find a string tension that makes it wobble up and down the least.

Adjustments to saddle position will proportionally effect the note with the shorter string length more than they will the note with the longer string length.

This isn't quite the procedure that The Book suggests, but it make sense to me and the result seems pretty good to me.

[Trevor Gore]

It took me a while but I finally got around to it...

I modeled your method Doug, and to all intents and purposes it come out identical to the full optimisation method (if I modeled your method correctly!)

Basically, the difference between the fully optimised book method and what you're doing is less than ~0.02mm on the nut and saddle off-sets. Well within manufacturing tolerances.

Well done!

[dshaker]

Trevor-

Wow! Thanks for the feedback! I had no idea anyone was paying attention and I had no idea I would be able to get so close! Woot!

I suspect my actual execution was done with less precision than your modeling, but my guitar still plays pretty darned nicely as far as intonation goes.

Thanks for taking the time to evaluate and thanks for the endorsement! Nice!

-Doug Shaker

[Trevor Gore]

Just to clarify what I actually modeled (seeing as I might reference this thread in the future), I ran a numerical optimisation technique that adjusted the nut and saddle compensation until the open string, fret five and fret 12 gave minimal error from Equal Temperament. So:

3. Iterate on
a) Fret the target string at the fifth fret.
b) Tune the string to the proper note for the fifth fret..... etc.

was iterated on a very large number of times until the difference between the nth result and the (n-1)the result was close to zero. In practical terms, doing it 3 or 4 times should get you to within manufacturing tolerances.

I'll also note that this method does not compensate for shifts in intonation due to coupling with body resonances (which should be primarily addressed by placement of the body resonances, anyway).

[Deems Davis]

I was OK with the compensation formulas and Excel, BUT,I've had zero success in wrapping my brain cells around mathematical optimization techniques so, I thought I'd give this method a shot. I made a new neck for my 1st build after detecting an error in the CNC cut fret slots) I fashioned my own 'intonator' and set about the process Dave outlines. Everything was going smoothly for the 2-3 lower strings (6,5,4), but when I moved to the higher pitched strings 3,2,1 When fretting the 12th fret, I'd see 25-35 cents flat with the intonator saddle in the mid-position of the saddle slot. In order to eliminate the flat cents errors I would have to run the saddle so much closer to the soundhole that it literally drops off the front edge of the bridge.
It's been bugging me all day as to why this is. Obviously something amiss somewhere. So.. tonite I went back through the design book, and reread 4.7 and particularly 4.7.2.1 where it discussed body resonance induced errors. The guitar that I'm attempting this on has a low Main Top of 163hz.
Is it possible that the misplaced body resonances can make that much of a difference? Or do I need to look elsewhere? 4.7.2.3 ii suggests that 3mm delta at the saddle can be 20 cents so if I'm starting off 25-35 cents flat that would account for why the 'saddle' drops off the front, so I just need to verify that the problem is with the coupled freqs. (tomorrows exercise)

Your comments greatly appreciated/welcomed

Deems

[Trevor Gore]

Table 2.5-1 shows some fairly large intonation errors due to over-coupling with the body. I've seen larger than that, but 25-35 cents on the high strings is excessive. The large errors tend to occur on the lower strings around the main top resonant frequency. If you check out Table 4.7-4, even with no compensation anywhere, the high E will only have ~ 4 cents error on the 12th fret if the fretboard and saddle are in the correct relative positions.

I'm assuming you're attempting nut and saddle compensation and that this fretboard (at least) has the frets in the right places. First, check that the saddle and fretboard are in the right relative positions in that for the high E string, nut to 12th fret and 12th to saddle should be approximately the same distance. That should show up any major positioning errors if they're there. After that, I'd start looking at your frequency meter/tuner and calibrate it. After that I'd start looking at resonances, but not initially in the guitar structure. Check out your "intonator" and see if any part of that is coupling in. After that, try some different strings. You should already have a tap response for the box, but I'd be very surprised to see resonances responsible for 25-35 cents flattening at three different frequencies.

Good luck!

[Deems Davis]

Thanks for the feedback Trevor. I will re-recheck the nut -12th-saddle-distances to eliminate that possibility. The initial problem was the CNC machine was out of calibration when the fretboard was cut, it is now producing resuls +/- .00x ". I'm using the iStrobosoft tuner on an ipad. I haven't calibrated that but I'll check it using VA.
How could the "intonator" be coupling? I made the 'body' of it from acrylic as I didn't have a piece of brass avail. I also made it to match the arc of the bridge pins. picture attached.

[Trevor Gore]

How could the "intonator" be coupling?

You have a collection of masses (the adjusters) on the end of a set of cantilever springs (the brass "control rods"). They will have a resonant frequency and are in direct contact with the strings. That doesn't mean that they will couple in, but best to check. Drop in a temporary saddle and see what happens.

One more thought....

When laying out, it is possible to confuse front of bridge with front of saddle. That would account for ~5mm.

[Deems Davis]

The mystery is solved!

The short answer is that the temperament setting is iStrobosoft was set to Just (JMI). Equal temperament is NOT listed when you click on temperaments icon ???? you get to it via a separate CLEAR icon which clears everything else out and resets the tuner to EQUAL temperament !!!!

After re-re-re-remeasuring scale length, fret distances, nut ledge offset, bridge/saddle offset, I tried going through the process with my Android free "Pro Guitar Tuner" and what do you know, but everything was bang on the money! So that got me looking at the iStrobosoft app and ultimately led me to discover that the temperament was set to JUST!

What a relief! I've waisted 2 day's on this: moral of the story:

1. When using new software/tools for the 1st time, don't assume anything, take the time to walk thru the setup and read the instructions.

2. It turns out that my free Android Pro Guitar Tuner is as accurate as iStrobosoft, The Peterson tuners have an excellent reputation and I ASSUMED were better, I could/should have saved myself $10 and 2 days by using what I already had!

Deems (boy do I feel dumb!)

[Trevor Gore]

Well, at least it's all over now!

[Dave M]

I don't think you should feel too bad Deems. That seems a pretty obscure thing for the software tuner to do.

What I do like the look of is your version of the intonator. I didn't like the price from (was it ) LMI and your version looks relatively easy to build. Also a good fit to the curved string pins of Trevor's design. So thanks for the photo.

Dave

[Deems Davis]

. So thanks for the photo.

Dave

I should thank you, it was your comment about the 3/32" rod and the 4-40 threads that got me on to building my own. I've since replaced the Acrylic with 6061 Aluminum, I was worried the Acrylic might pick up it's own vibrations too easy, I replace the original nuts with nylon safety nuts as the vibrations kept loosening them, I cut the length of the alum standoffs by 1/2 and I also found it necessary to weave a rubberband between the adjusting rods as they would also vibrate. I had to drill the holes in the alum block 1/64 over to allow for the threads to pass through and that allowed for some vibration. A piece of felt glued to the front of the block where it mates with the bridge pins also dampens any transmitted vibrations, I think I spent $6-7 for the hardware bits, and a few minutes on the CNC. All in all a bargain.

Deems