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  #16  
Old 11-22-2014, 05:05 AM
John Arnold John Arnold is offline
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If I put a capo on 3, retune everything dead on there and check the first frets then: same thing. They are sharp on the first three. Worse on fret one (4 in this case), getting better as you move toward 6...
This happens because fretting the string near the nut (or the capo) bends the string at a sharper angle, causing the tension to increase in a nonlinear fashion.
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  #17  
Old 11-22-2014, 08:15 AM
PhilQ PhilQ is offline
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Originally Posted by Ned Milburn View Post
Since doing the adjustment, did you try the intonation with a capo again??
I put a capo on the second fret and retuned to 0 with the capo in position. The open string and harmonic (14th fret) are the same. The fretted note on the 14th fret is pretty much the same. Ever so slightly sharp on the G and B strings, but not on the low E, A and D, which are the sharpest when fretted in the first position. It sounds like I'm making this up, doesn't it!

Quote:
Originally Posted by John Arnold View Post
This happens because fretting the string near the nut (or the capo) bends the string at a sharper angle, causing the tension to increase in a nonlinear fashion.
Is there a solution to that if I've already made sure the slots are filed back to leave the break point at the front?

Again, thanks so much!
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  #18  
Old 11-22-2014, 10:50 AM
Ned Milburn Ned Milburn is offline
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Originally Posted by PhilQ View Post
I put a capo on the second fret and retuned to 0 with the capo in position. The open string and harmonic (14th fret) are the same. The fretted note on the 14th fret is pretty much the same. Ever so slightly sharp on the G and B strings, but not on the low E, A and D, which are the sharpest when fretted in the first position. It sounds like I'm making this up, doesn't it!



Is there a solution to that if I've already made sure the slots are filed back to leave the break point at the front?

Again, thanks so much!
So, just to repeat to make certain we are talking apples and apples.

Your Low E, A, and D strings intonate correctly at the 12th fret, but in low positions (1-3rd frets), they intonate sharp...?

If your G and B strings are intonating slightly sharp at the 12th fret, you should move the saddle peak further back on the saddle (away from the sound-hole).

At least it sounds like you are finding improvement.

Another couple questions:

1) The nut: Are the nut slots cut angled towards the back so that the string is vibrating from the leading edge of the nut?

2) Frets - Did you dress the frets after installation? If yes, are the crowns dead center??
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  #19  
Old 11-22-2014, 12:02 PM
gtract gtract is offline
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Hi Phil. You might want to read this article. It explains nut compensation very well. Worked for me on quite a few guitars that were behaving the same way. Good luck.
http://www.mimf.com/nutcomp/

Dave.
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  #20  
Old 11-22-2014, 05:33 PM
Alan Carruth Alan Carruth is offline
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PhilQ wrote:
"I checked the intonation, and it is dead on for each string. The harmonic and fretted notes are the same."

Again, the harmonic can be off relative to the note fretted at the 12th fret: the harmonic doesn't know where the fret is. It's the fretted note that counts when checking the intonation, since what you're compensating for is the string stretch of fretting. It should be exactly an octave above the open note.

"The E, A and B string are sharp on frets 1, 2 and 3 (progressively less so as you move from fret 1 to 3)."

That's typical of a guitar that needs nut compensation. Try moving the contact point out away from the nut by wedging something under the string. you should find the fretted notes to be more in tune.

When you do that you'll also find the 12th fret intonation is out a little; typically I find that I need less saddle compensation when I use nut compensation. That's because compensating the nut makes all the notes on that string a little flat: in essence you've moved all the frets back a bit.

If you only compensate the saddle the notes will get flatter as you go up the neck. When you get the compensation right at the 12th fret the notes will probably go even flatter in the higher positions. Compensating the nut by moving it forward a bit throws everything a little flatter, so you need less saddle compensation. If you get the nut right, so that you get an exact semitone at the first fret, and then compensate the saddle to give an exact octave at the 12th, you'll be about as close to 'perfect' on the frets in between, and above the 12th fret, as it's possible to get on a guitar.
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  #21  
Old 11-23-2014, 01:47 AM
gpj1136 gpj1136 is offline
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Alan,
I'm confused a bit, how would this help when using the capo. I would be grateful for a little clarification

I have used your advise of compensating the nut with good results. So I do understand the mechanics of it.

With the same problem occurring with the capo installed leads me to believe it might be saddle related, or even frets that are taller than the OP is used to using giving more tension on the string near the leading edge.

If it were saddle related it would seem the intonation would be off at the twelfth fret, and have less effect near the 1st 2nd and 3rd frets.

Is he trying a heavier guage string ?

Alan,
I have reread your post, and now see that after nut compensation if he tunes the guitar before placing the capo it should remain in tune with proper intonation.

Last edited by gpj1136; 11-23-2014 at 01:57 AM.
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  #22  
Old 11-23-2014, 01:58 AM
gpj1136 gpj1136 is offline
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Alan,
I'm confused a bit, how would this help when using the capo. I would be grateful for a little clarification

I have used your advise of compensating the nut with good results. So I do understand the mechanics of it.

With the same problem occurring with the capo installed leads me to believe it might be saddle related, or even frets that are taller than the OP is used to using giving more tension on the string near the leading edge.

If it were saddle related it would seem the intonation would be off at the twelfth fret, and have less effect near the 1st 2nd and 3rd frets.

Is he trying a heavier guage string ?
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  #23  
Old 11-23-2014, 08:37 AM
PhilQ PhilQ is offline
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There's some info in here that is a bit above my level at this point and I will need to re-read a few times to digest. It is much appreciated.

I spent some time with the guitar and a Peterson strobe tuner this morning. Intonation-wise, the open string and fretted note are the same. Whatever difference there is one way or the other is inconsistent and extremely small.

The fretted note goes sharp on fret one, but I just realized that it is less sharp on 2, flat even on a couple strings, then again much sharper on 3. This alternating pattern happens a few times on the neck. Seemingly randomly.

SO... would this point to a crowning issue?

Thanks so much for your input everyone. It's prettty incredible to get advice from such knowledgeable people!

Phil
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  #24  
Old 11-23-2014, 08:47 AM
Ned Milburn Ned Milburn is offline
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Quote:
Originally Posted by PhilQ View Post
There's some info in here that is a bit above my level at this point and I will need to re-read a few times to digest. It is much appreciated.

I spent some time with the guitar and a Peterson strobe tuner this morning. Intonation-wise, the open string and fretted note are the same. Whatever difference there is one way or the other is inconsistent and extremely small.

The fretted note goes sharp on fret one, but I just realized that it is less sharp on 2, flat even on a couple strings, then again much sharper on 3. This alternating pattern happens a few times on the neck. Seemingly randomly.

SO... would this point to a crowning issue?
Crowning and/or slightly misplaced frets OR bad strings. Trying a fresh set of strings might be very worthwhile.
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  #25  
Old 11-23-2014, 01:33 PM
Alan Carruth Alan Carruth is offline
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Again, there's no way to get an acoustic guitar to play perfectly in tune on every note, and the capo can't help. In theory, if you get the nut and saddle intonation right any note you play will be somewhere near 'perfect' in intonation. Resonances of the top can shift individual notes up or down a bit due to the motion of the bridge.

All of that assumes that you're pushing the strings down on one fret. With a capo you're pushing them down on two frets. That has to make some difference. I suppose you could set the intonation up with a capo, but then it would probably not play in tune without one.

In practice what I find is that getting the nut and saddle compensation right helps, period. The compensated nut works better with a capo than an uncompensated one.

Finally, 'intonation' really only has a meaning in reference to some standard. In the case of the guitar, that's equal temperament, and that always sounds a little off anyway for the simple reason that it is. The fact is that it's mathematically impossible to set up a tuning scheme that has both the fifths and octaves 'pure'; without beats. Any scheme of temperament is a compromise chosen for any number of reasons. In the case of the guitar we use equal temperament because it allows us to modulate freely between keys, and use straight frets. At some point you just have to get used to it...
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  #26  
Old 11-23-2014, 05:23 PM
PhilQ PhilQ is offline
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Thank you, Alan. Wow. So much to learn.
I'm intimidated/afraid to screw up the nut compensation...
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  #27  
Old 11-25-2014, 02:41 PM
Alan Carruth Alan Carruth is offline
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Just when you think you've got it figured out....

Several years ago I was doing some 'string' experiments, and I wanted to see how bridge movement affected intonation. I put an A string on a rigid beam, and plotted out the pitches of the partials, which went progressively sharp as you went up. That's what you'd expect, due to string stiffness.

The same string on a guitar showed something interesting. When I tuned it to A using a tuner the two or three partials above the fundamental were actually flat. Not only that, but the fretted note on the first fret was also flat. Checking the resonant modes of the guitar gave the explanation.

The 'main air' mode on that instrument was slightly flat from the pitch of the open A string. Coupling between the string and the top motion shifted the string pitch up a little bit. In order to get the open string to show up as 'in tune' on the tuner you had to leave it a little slacker than it 'should' have been. The partials, of course, were too far from the 'air' mode pitch to be affected, so they came in flat, mirroring the real tension of the string. Similarly the first couple of fretted notes were flat, since they were not influenced by the top motion, rather than sharp as they would normally have been on a guitar without a compensated nut. The trend was for the notes to go progressively sharper as you went up the neck, they just started out a bit flat.

Switching the string back to the beam showed that the problem was not in the string: it worked just the same way the second time there as it did the first time.

This is why it's just about impossible to get an acoustic guitar to play in tune on every note.
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