Understanding Guitar Setup

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Understanding Guitar Intonation

These pages will enable you to understand how guitar setup and guitar intonation work.  The principles of compensated nut and compensated saddle will flow easily from that understanding, enabling you to do a better guitar setup, or to better work with your luthier.


A few summers ago, I was admiring a friend’s beautiful J-45 sunburst.  He said: “it’s amazing that people who make such fine and expensive guitars, don’t make them so that the open strings are in tune with the fretted notes”.  I had been thinking the same thing myself for years!  Most  acoustic guitars are sharp about 10 cents on the lower frets of the sixth string.  Unwound 3rd strings on electric and classical guitars also typically play quite sharp. All of the other strings are off too, but not as much.

That's why people are discouraged when they tune with an electronic tuner, and then have to re-tune, until their favorite chords sound OK - then they have to tune again when they change keys.

Compensated Nut on BridgeAcoustic guitar builders and manufactures routinely provide just OK compensation (by bridge placement, slanting the saddle for more length on the lower strings, and sometimes compensating the saddle to improve intonation for individual strings).  

Subsequent adjustments can increase playability and make most guitars sound fairly adequate, but, in my opinion, prevalent intonation methods are inadequate, considering the high quality of modern instruments in most other respects.

Excellent intonation requires compensation at both ends of the strings, however, standard intonation omits nut compensation!   

The big advantage of the standard intonation is that it is quick and somewhat inexpensive.  Though some players are satisfied with this, many are not!  

Nut compensation is  more more expensive in both time and $.  Although some solutions are costly, there are other, fairly simple methods that can produce improvements without much effort or on-going expense.  For instance, once a manufacturer, builder or luthier is properly set up, then nut compensation could become more routine, and far less costly.

The fundamental cause of difficulty with guitar intonation is that fretting a note creates more tension in the strings, increasing pitch, making fretted notes sharp compared to the open strings.  Standard intonation matches the pitch at the 12th fret to the open, but leaves the lower fretted notes sharp!  

The degree of sharpness of each string depends on the size of the string (mainly of its core) which effect its resistance to stretching and also resistance to bending.   

With nut compensation, you first adjust the saddle to make all of the fretted notes as accurately in tune as possible (ignoring open string pitch) and then adjust the nut to make the opens in tune with the fretboard.  (This is done by adding material to shorten the distance from the nut string release point closer to the first fret.)  Finally, after these things are done, the open strings along withe the fretted notes are all in good tune.

These are the important elements of accurate guitar intonation that, have been overlooked:

1. Adjusting the saddle for intonation, comparing two notes on the fretboard, and not to the open strings.

2. Compensating the nut so that the open strings are then in tune with the lower frets.

Traditional compensation at the bridge intonates notes at the 12th fret to play in tune with the open strings, however, after doing this, lacking nut compensation, notes on the lower frets will play sharp, and notes above the 12th fret may play flat. This is because the open strings have not been intonated to the fretboard (by compensating the nut).

Compensated Nut on Martin HD35

The main impediment to understanding (the blind spot) is the great reluctance of people to give up the open-string pitch as the key point of reference in intonation work.  This leads to much confusion regarding the effects of nut versus saddle adjustments.  

The fact is that, the mathematically spaced fret layout, along with individual string saddle adjustment,  can produce near-perfect intonation over a large part of the fretboard.  It is the open strings that are out of tune with the fretboard!  Grasping this leads a person to a clear understanding of intonation in which fretboard intonation is done independendently of nut intcompensation, and vice-versa. This leads to practical and accurate solutions.

This may be a turning point, because awareness and desire is growing.  Luthiers, builders, and manufacturers  could benefit by becoming knowledgeable sooner, rather than later, and be able to provide better intonation to those willing to pay for it.  This site is not only to inform luthiers, but also do-it-your-selfers, and players who rely upon luthiers - anyone who desires better intonation.

Although I only mention guitars, these principles are relevant, to varying extent, to all fretted musical instruments, and especially to fretted bases.

Summary of the Problem and Solution

Open strings are out of tune with fretted notes because all fretted notes are sharped by the increased tension caused by the fretting action, while the open strings are not.

Compensation at both ends of the strings can and do solve intonation problems, so that the instrument will play in tune, with equal temperament.    

Fretted notes can be made to play in tune with each-other by adjusting the saddle for each string.  When 2 notes, about an octave apart on the fretboard - not open - are in tune with each other, then all of the notes on the fretboard will be in very good (though not absolutely perfect) tune with each-other.  

After the fretboard is intonated in this manner, via the saddle(s), then the nut can be compensated to make the open strings play in tune with the fretted notes.  This is done by effectively moving the nut forward (toward the bridge) in the correct amount for each string.

Many acoustic players (and some electric players) play mainly at the lower end of the fretboard.  For them, accurate compensation at the nut is much more important than improving compensation at the saddle, so if saddle intonation is at least fair, and is not adjustable, you may decide to go directly to nut compensation.  Professional players, and the better recreational players, deserve to have accurate compensation at both the saddle and the nut.  

Lowering the action at the nut will certainly help a lot, but if only the saddle is compensated, in the standard method, the result will be poor intonation over the fretboard.  


Diagram of intonation error with traditional guitar setup

The above diagram shows the poor intonation pattern of a guitar set up in the traditional manor, and open strings tuned.  See this and additional diagrams on a subsequent page.

P.S:  My friend with the J-45 improved his guitar's intonation by placing a piece of a toothpick against the nut under the 6th string.  Although I chuckled, I could not criticize this method, because it does effect an improvement for the worst intonation problem on acoustic guitars!

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