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 or more 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.  (It might help to tune the strings that are sharp on the lower frets a bit flat.)

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 shaping the saddle to improve intonation for some of the individual strings  

Subsequent improvements and adjustments can be made in the areas of neck relief, string height, and saddle compensation by luthiers and players, in order to increase playability, and adjust to individual player’s preferences.  

These efforts make most guitars sound fairly adequate, but, in my opinion, prevalent intonation methods are often rather crude, especially considering the high quality of modern instruments in most other respects.

Good intonation requires compensation at both ends of the strings!   The big advantage of the traditional mode of intonation is that it is quick and relatively inexpensive.  Though some players are satisfied with this, many are not.  The traditional method completely ignores the need for compensation at the nut, and then uses the open/strong> strings (which have not been intonated to the fretboard) for adjustment of the saddle.  The result is that only the open strings and the notes at the 12th fret are in good tune.  (but, after tweaking, even these will be compromised.)

The main reason that the open strings are not in tune with the fretboard is that the string tension is less for the open strings than when you pull the string to any fret.  The added tension causes the fretted notes to play sharp compared to open.   

The fretboard on a modern instrument is quite mathematically accurate.  When the saddle is properly adjusted, it will produce a wide range of notes in excellent tune.  The saddle is adjusted to a point where any two fretted notes (somewhat distant from each other) are in tune with each other.  (That is what fretboards are designed to do.) This will provide the best possible intonation of the fretboard.  You can however, choose which reference frets to use, so as to enhance accuracy in the area that you chose, ie open chords, closed chords, high leads.  

After he saddle is adjusted (compensated) on each string (or, on an acoustic, is delared to be satisfactory) then we can adjust (compensate) the leading edge of the nut to a point where the open string is in tune with the lower frets.

So to summarize, there are just three important elements for accurate guitar intonation that have been largely overlooked and resisted – and they are:   

1. We must let go of using open string pitch as a reference for adjusting the saddle.  The saddle is for adjusting fretboard pitch distribution. 

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

3. Adjust (compensate) 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 played on the lower frets will play sharp, and notes above the 12th fret will play flat. This is because the open strings have not been intonated to the fretboard (by compensating the nut).

Intonation error should be corrected at the nut, as well as the saddle.  It’s a blind spot in the industry – a deficiency, but it presents an opportunity - an opportunity for you to make you or your customer’s guitars sound a lot better!

Compensated Nut on Martin HD35Why has compensation at the nut been neglected?  Besides the power of tradition and and added cost, I would say that it's mainly due to lack of understanding - both of the nature of the problem, and of the variety of possible solutions. 

Nut compensation is generally more difficult than saddle compensation; more expensive in both time and $.  Some solutions are costly, but there are other, fairly simple methods that can produce improvements, without much effort or on-going expense.  Once a manufacturer, builder or luthier is properly set up, then nut compensation could become more routine, and far less costly.  

This is indeed a turning point, because awareness and desire is growing.  Luthiers, builders, and manufacturers  would 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.

The goal should be to better understand the causes of intonation problems, and to actually understand the solutions that are available.  With that understanding, one can creatively evaluate the most practical course of action for a guitar or for a building process.

In my own quest for knowledge (from the web and books) I found that there was great lack of knowledge of nut compensation – much confusion, and, unfortunately, even a lot of misinformation.  Web postings often fail to consider guitar intonation holistically.  There are a few sites with good information, though, and, combining that with some reasoning of my own (some understanding of geometry and physics helps) I came up with good answers, that I would like to share with you.  I was able to greatly improve the sound of several guitars of varying type and quality.

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 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.  Professional players, and the better recreational players, deserve to have accurate compensation at both the saddle and the nut.  

Although lowering the action at the 1st fret certainly helps a lot, if only the saddle is compensated, comparing open strings (or harmonics) with the fretted octaves, the result will be poor intonation over the fretboard.  (This might come as a shock to many, because this is the only method that they have heard of!)

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 wooden matchstick 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 most acoustic guitars!

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