Big Intonation Problem

[Craig Bumgarner]

As in major difference in the string lengths needed to get this guitar to intonate even close. Guitar is a French manouche style guitar built by Claude Patenotte. It is not dated, but probably no more than 10 years old. Not a high end guitar, but built by a small factory in France by a well establish builder, has very authentic tone, plays and sounds good except...... The intonation is WAY off. Scale is a 640mm and I would expect ~ 3mm offset in string length between the high and low E strings. The bridge on these guitars float, so they can be moved for intonation. A mm or two from the original placement over time is not unusual, but this one needED 13mm offset to get even close. See Pic:

• No obvious structural problems inside or out
• Neck is straight, action is reasonable at 3mm
• Frets look okay, basically straight, of adequate height and properly spaced. Some minor fret wear.
• Strings are standard 11 gauge Saverz Argentines, 3 months old, but owner says changing strings does not make a difference. This guitar was probably built with 10 gauge strings in mind and that might make a little difference, but not this much, eh?
• With bridge set as per the picture, it intonates more or less correctly, +/- 10 cents, over all the frets.
• The little trim pieces either side of the bridge, known as mustaches, where located by the builder where he thought the bridge should go for proper intonation. What could have changed?

I've never seen anything like this, any ideas?

[Doug Shaker]

Perhaps there was nut-intonation to start with and the nut was replaced by someone who didn't understand it?

In any case, the amount of bridge intonation needed after nut intonation is much less and might allow you to place the bridge where it doesn't look like it was placed by a drunken luthier.

[Craig Bumgarner]

Thanks for the reply. The guitar uses a zero fret as a nut. What appears to be a nut is just a string spacer. The zero fret looks fine and the strings are all bent over the zero fret as they should be. Here is a pick of the entire guitar, maybe you'll see something I don't.

[Peter Wilcox]

What is the distance from the 0 fret to the 12th fret, and what is the length of each string as you have the bridge set now? It doesn't make sense to me that to intonate you have to move the saddle closer to the nut from its original position, rather than farther away. Do the rest of the frets play in tune?

[Craig Bumgarner]

What is the distance from the 0 fret to the 12th fret,

320mm.

and what is the length of each string as you have the bridge set now?

1st string is 631mm 6th string is 643mm

It doesn't make sense to me that to intonate you have to move the saddle closer to the nut from its original position, rather than farther away.

Doesn't make sense to me either.

Do the rest of the frets play in tune?

Yes, with the way I have it set up in the picture, all the frets play reasonably well in tune. With bridge set between the mustaches, the intonation is unbearable and I'm not very picky about intonation in general.

[Peter Wilcox]

So just to be clear, the octave harmonic frequency of each string is the same as the 12th fretted note for the same string, the way it is set up now?

[Barry Daniels]

Have you tried new strings?

[Craig Bumgarner]

So just to be clear, the octave harmonic frequency of each string is the same as the 12th fretted note for the same string, the way it is set up now?

Yes. And I see what you are getting at. The harmonic should be half the string length and over the 12th fret. And it is, the way it is set up now, in the picture. And, the string length measurement from the 0 to 12 is 12mm more than the length from the 12th to the bridge, the way it is set up now. This can't be.

Have you tried new strings?

No, because the owner said changing strings did not make a difference and the ones on the guitar now look to be in good condition. Also, it is not just one string, it appears to be all of them in a progressive manner. The way the bridge is setup now, the notes are reasonably true throughout and the guitar actually plays pretty well.
But strings seem like the obvious thing to try. I wonder if the fact that the strings on the guitar now are heavier that usual could make this kind of difference. I've witched between 10s and 11s a number of times and never seen anything like this.

PUZZLER!

[Peter Wilcox]

This can't be.

Yes, to me this flies in the face of classical physics and Euclidian geometry. For this to be so, fretting (stretching) the string would lower its tension. Maybe someone with knowledge of relativity theory can figure this out.

[Bill Raymond]

I think this goes beyond relativity theory; perhaps "string theory"?

[Rodger Knox]

I think this goes beyond relativity theory; perhaps "string theory"?

Al Carruth wrote that. I've read it.
http://www.alcarruthluthier.com/Downloa ... Theory.pdf

[Doug Shaker]

Try damping the entire guitar system, except the strings, by stuffing a couple of sweaters inside the body and see if the intonation is still strange.

[Craig Bumgarner]

Yep, it was the strings, put on new strings, same brand and gauge, and intonation is now right where it should be. Hard to believe old strings could cause the intonation to be as much as half a fret off at the 12th, but that is what it was.

I found in pursuing this that much of what we think we know about the behavior of a guitar string assumes uniform wire size and density to pretty close tolerances. Over time, the wire can stretch in unequal ways, changing the wire size slightly in place and this change in uniformity will change the harmonic behavior of the string. The string wear at the frets can cause lack of uniformity too. And, I noticed a lot of corrosion on the under side of the strings when I took them off and this corrosion was not uniform either, mostly below the 12th fret. I would guess the corrosion changes the mass of the string, locally in this case.

Thanks for helping me brain storm this one.

[Peter Wilcox]

It was an interesting problem - guitar strings like tapered fly line, I guess. Thanks for the answer - a little more knowledge added to the brain (as more slips out.)

Don't charge the owner more than $100 for the repair.

[Alan Carruth]

I wonder if one culprit might have been gunk in the windings of the bass strings. That would tend to add more load at the nut end, I'd think. It can also make the strings stiffer. Anyway, strings are the simplest part of the system, but they sure are not 'simple'.

[Trevor Gore]

Some players have rather bad habits in the way they change strings. Strings are put on, then brought to tension, then stretched by pulling them upwards to "settle" them. Problem is that if the strings are pulled too hard they can yield and stretch locally so giving a non-uniform string mass per unit length. If the user always goes through the same routine he would perpetually have the same problem which would not change with different strings.

[Ryan Mazzocco]

Some players have rather bad habits in the way they change strings. Strings are put on, then brought to tension, then stretched by pulling them upwards to "settle" them.

Guilty! I never knew this was bad.

edit: now that I think about it, I'm not sure I'm understanding this correctly. when you say pull them up do you mean pulling them out from the guitar's body, or bending them on the fretboard, like a sharp bend?

[Michael Lewis]

Modern strings are designed to operate near but below their permanent deformation point, where they take a "set" from stretching too much. General rule is to not apply more tension to strings than what brings them to their appointed pitch. Before deformation takes place the strings are springy and 'alive', after deformation they are less springy and less lively.

[Trevor Gore]

Some players have rather bad habits in the way they change strings. Strings are put on, then brought to tension, then stretched by pulling them upwards to "settle" them.

Guilty! I never knew this was bad.

edit: now that I think about it, I'm not sure I'm understanding this correctly. when you say pull them up do you mean pulling them out from the guitar's body, or bending them on the fretboard, like a sharp bend?

Pulling them out, away from the guitar body. Go at this too vigorously and you'll definitely plastically (permanently) deform the string, making it non-uniform along its length with attendant intonation problems.

However, whenever I break strings on my Strat, it is nearly always over a fret, due to bending. So that's another method of plastically deforming strings to failure!

[Jason Rodgers]

When I change strings, which is not often, I will simply string it up and let it be. The next day I'll tune it up and play it hard across all strings, then set it aside again. With heavier strings, this only takes a couple days. When I've seen folks give a string a yank, as described above, I've always whinced.

A few times, I've tuned it up a semitone initially, then brought it back to standard the next day. Not sure if that really speeds things up that much, but as a side observation, it's amazing how much more strident a guitar can sound when simply tuned up a semitone.