Intonation question

[Stephen47]

I am new to guitar building and as I understand it intonation is basically having it play the same not an octave apart when fretted on the 12th fret.
My question is if the guitar is set up and has the usual 3/32" saddle, can the intonation be changed by adjusting where the string makes contact with the saddle?

[arie]

in answer to your question, yes. that is the prescribed method for adjusting intonation although it is a lot easier with a wider saddle. in fact, right off the bat your B string will have to be lengthened a certain amount if you are going to begin compensating the saddle. i have found the stew-mac online calculator to be a pretty good starting point (because i'm too lazy to make my own spread sheet). google "stew-mac fret position calculator" -i can't seem to link to it directly for some html/web reason. this will help you establish your saddle angle relative to the nut to start out with.

[badbazil]

Yes, you can change the intonation by contouring the saddle. Take a short section of a sewing needle or and put it under the string on top of the saddle. By moving it back toward the bottom of the guitar or toward the headstock you can fine the sweet spot where the string in in tune at the 12th fret. Then file the rest of the saddle away leaving the area you have marked with the needle.

[charles Tauber]

http://charlestauber.com/luthier/Bas...r_Setup_3.html

If you don't want the theory, skip to section 7, the how-to.

Generally, a 3/32" saddle is not wide enough to fully compensate all 6 strings fully.

[Ben-Had]

Originally Posted by charles Tauber

http://charlestauber.com/luthier/Bas...r_Setup_3.html

If you don't want the theory, skip to section 7, the how-to.

Generally, a 3/32" saddle is not wide enough to fully compensate all 6 strings fully.

I agree. I make my own bridges now and use a 1/8" saddle. Intonation is much better. But I think one can get real close with a 3/32" saddle.

[steveyam]

Originally Posted by Stephen47

.... as I understand it intonation is basically having it play the same not an octave apart when fretted on the 12th fret.

Simply, it is, yes. But, the intonation should be correct not just at the 12th, but - as far as possible - all along the neck. For example, you could have a guitar where the octave note at the 12th is correct, but the note at (say) the 1st or 2nd fret is out. Usually this points to nut slot depth issues or, less likely, nut placement errors. So, if you're trying to attain good intonation - as you seem to be, and that's good - then you must consider intonation accuracy at the first few frets in the way that I just mention.

[Alan Carruth]

Right.

'Intonation' is the degree to which the guitar makes the notes it's supposed to make, depending on the scheme of temperament you've chosen. The default is equal temperament, but it[s not without it's problems, and sometimes an issue that seems to be one of intonation has really to do with temperament.

No acoustic guitar can be made to play with perfect intonation if it has straight frets. Most of the crooked fret schemes I've seen are not methods of getting correct equal temperament, but rather are attempts to 'sweeten' the intervals in the usual guitar keys.

You can get very close to perfect intonation by compensating both the saddle and the nut. The reasoning behind this is covered in detail in the two volumes of 'The Contemporary Acoustic Guitar', 'Design' and 'Build', by Gore and Gilet. I don't agree with everything they say, but it's mostly quibbles about details, and when it comes to intonation, they're about as good as it gets.

[Stephen47]

Thanks for the responses. That is a very interesting article Charles, although some of it was Greek to me. I have a couple of questions. Did the guitar makers of the 19th century understand the 2 to the 1/12 power dynamics?
the other question I have is how does one play the 12th fret harmonic?

[donh]

Originally Posted by Stephen47

the other question I have is how does one play the 12th fret harmonic?

Really?

Answer one: count up twelve frets and play a harmonic
Answer tow: with your fingers, or perhaps a plectrum
Answer three: on a string
Answer four: very carefully

Really?

[Stephen47]

Sorry to seem dense but in Charles' article he refers to: "The two pitches - the 12th fret note and the 12th fret harmonic" I assumed these were two different notes.

[charles Tauber]

Originally Posted by Stephen47

Did the guitar makers of the 19th century understand the 2 to the 1/12 power dynamics?

I have every reason to believe that they did, though they would not likely have expressed it that way or worked with it that way. There are numerous geometric ways to work with irrational numbers, such as the twelfth root of two, and arrive at the same layout of frets. The ancient Egyptians, for example, had not conceived of irrational numbers, but worked with them indirectly, regularly, through geometric layout.

There is considerable literature on various approaches to intonation from lute makers of the 1600 and 1700's, predating the modern guitar. These were quite sophisticated and mathematically based. Equal temperament (twelfth root of two) has been around since at least the mid 1700's. An often-used approach was the "rule of 18", which gives a "close" approximation of the twelfth root of two.

the other question I have is how does one play the 12th fret harmonic?

Same as at any other fret. Place the tip of your finger against one of the strings directly over the 12th fret. Do not depress the string against the fret - just so that it contacts the string. Pluck the string. The pitch so produced will be one octave higher than the open, unfretted string. Touching the string in this way, divides the string in exactly half, producing two vibrating portions of the string, each exactly half as long as the open, undivided string.

In a similar fashion, one can force the vibrating string to be divided into any whole-number (i.e. 1, 2, 3, 4...) portions by touching the string at any place along the string that exactly divides the open string in a whole-number division. The 12th fret produces two portions that are half the open string length. The 7th fret produces three portions that are each exactly one third of the open vibrating string length. The 5th fret produces four portions that are each exactly one quarter of the open string length. And so on.

As an aside, you'll note that some of the harmonics are produced when they are not exactly above the frets - revealing the difference between Pythagorean (harmonics) and equal temperament (fretted) notes.

[charles Tauber]

Originally Posted by Stephen47

Sorry to seem dense but in Charles' article he refers to: "The two pitches - the 12th fret note and the 12th fret harmonic" I assumed these were two different notes.

Ideally, the pitch produced by plucking a string that is fretted at the 12th fret should be the same as the pitch produced by plucking a string that is touched - but not depressed against the 12th fret - at the 12th fret.

If the intonation is "out", or inaccurate, the two pitches will not be the same.

As steveyam points out, there is more to intonation than that, but that is a starting point.

[Stephen47]

Thanks for the clarification Charles

[Alan Carruth]

charles tauber wrote:
"Ideally, the pitch produced by plucking a string that is fretted at the 12th fret should be the same as the pitch produced by plucking a string that is touched - but not depressed against the 12th fret - at the 12th fret."

Close enough, anyway. In fact, string stiffness renders all the 'harmonics' a little sharp relative to the fundamental of the string IF the string is mounted on a rigid beam, so that the ends are 'fixed'. On a guitar motion of the top can drive any partial of the string off pitch, either sharp or flat, depending on the relationship between the pitches of the top resonances causing the motion and the partials of the string. In practice, the lower partials of the lower strings on acoustic guitars will often be shifted flat, and may, in fact, end up being 'harmonic', but you can't count on it.

Strings are not simple, even though they're the simplest part of the system.

[Stephen47]

After a day to think about it I feel I have to say something about the answer to the question I asked about harmonics.

I have only been a member of this forum for two years.

I have been building guitars for less than that and playing for less than that.

I thought I asked a legitimate question.

I have read a lot of threads on this forum and I have never seen such a condescending response as the one I received from donh.

So donh, Yes really.

By the way donh the number 2 is spelled two.