ACOUSTIC GUITAR SET UP

Let's begin by defining our terms. In the world of guitar repair, the adjustment of the string height on a guitar for optimal playability is called a "set-up". There are three steps in the basic set-up of any guitar. They must be followed, in the order I present them, to achieve optimum performance. In a basic set up we are assuming that structural or fret wear issues either do not exist (as, ideally, in most new guitars) or have already been resolved.

STEP 1 - CHECK AND ADJUST NECK

The first step in any guitar set-up is to check and adjust the curve of the neck. We refer to this curvature as the "neck relief".

Most modern guitars have an adjustable neck tension rod installed under the fretboard. Martin guitars made prior to 1985 do not have this feature, and affecting the curve of the neck in these guitars can only be done by a skilled guitar repair technician. For the purpose of this article we are only addressing those guitars with adjustable tension rods.

Here is an easy way to check the curve of the fretboard in the playing area: With the guitar tuned to pitch, hold the guitar in the playing position and depress the low E string at the 14th fret with the index finger of one hand. While keeping the string down on the 14th fret, depress the same string at the first fret with the index finger of your other hand. The bottom of the E string becomes a straight edge. Sight the area under the string around the 5th to 7th frets. If the neck is correctly tensioned there should be a hair breadth of space in the middle of this area between the bottom of the string and the top of the 6th or 7th frets.This gap gradually diminishes to zero as the string reaches the 1st and 14th frets. (I gauge this by eye, but if you were to measure this space it should be no more than 1/64th inch, maximum).You can evaluate the fretboard under each of the strings using this method. It is not unusual to get slightly different readings from string to string, though ideally they are all more or less the same.

On most guitars you can get away with a dead flat fretboard, but a back-bowed neck will surely cause fret rattle. For this reason, most repair techs will adjust for a slight forward bow.

Most guitar truss rods enable a lifting of the neck in the center of the playing area by tightening, or turning clockwise, the truss rod nut. Conversely, loosening the nut allows more flex in this area. "Double action" truss rods actually push in either direction depending on which way the nut is turned.

NOTE: Prerequisite to any neck adjustment, it must be confirmed that the frets are in good condition, seated firmly, and level.

The most misunderstood aspect of guitar set up is the neck adjustment. There is only one proper neck setting parameter - dead flat to slightly forward bowed. Too much forward bow causes excess height in the middle ( generally between frets 5 -9) of the playing area on a guitar with 14 frets to the body, and can also cause what's called "string rattle" or "fret buzz" from the middle frets up the neck. A back bow can cause fret buzz in the first five frets or so.

All too often, a guitar with high or low action has the neck adjusted by a well meaning person - to "adjust" the action - without paying any attention to the string height at the nut or the saddle. While it is true that adjusting the neck truss rod can affect the action, and sometimes this adjustment is all that is necessary, there is only one correct parameter for the neck setting.If the neck is flat to slightly forward bowed, you have to look elsewhere to affect the string height - the nut or the saddle.

NOTE: Adjusting the neck may need to be done periodically even after a basic set-up has been performed. The exposed wood of the fretboard absorbs and releases moisture as the relative humidity in the environment it is living in changes. 45 - 50 % relative humidity is considered ideal for guitars ( and people). A guitar neck which is dry tends to bow forward, raising the string height above the middle frets. Conversely, a neck which has been over humidified (for example, if the guitar is outside on a humid summer day), may tend to back bow. Ideally, a guitar is not subjected to these extremes of humidity, but in the real world it happens. Nevertheless, the setting of the neck is only done to place it within the aforementioned "correct parameter" - flat to slightly forward bowed - not to adjust the action.

STEP 2 - CHECK AND ADJUST NUT SLOT HEIGHT

Once the neck curvature is set, the string height at the nut is checked. With a correct neck curvature, there is one optimal setting for each nut slot. In theory each nut-slot should sit no higher than the preceding fret. Some builders use a "zero" fret, and a nut sits behind the "zero" fret only to guide each string on its path to the tuning peg. On most guitars the string is both guided and height adjusted at the nut. A string which sits too high at the nut can either feel too hard to push down, or even play sharp. At a minimum the string height should be lowered until it intones correctly, and ideally it should be lowered till it also feels comfortable to depress.

If the height of the 1st fret above the fret board is known, a metal gauge ( such as an auto mechanics "feeler" gauge - a strip of metal of a known thickness) of the same height as the existing frets , laid in front of the nut can be used as a guide. With a file of appropriate width, the nut slot is lowered until the file touches the gauge.

Without a gauge, the setting is done by eye. To calculate the appropriate height, depress the string in question between the second and third frets with your middle finger and sight back to the first fret. If the string rises above the first fret more than the thickness of a piece of paper (just a hair) the slot should be lowered until just this amount of gap is apparent. While holding the string down between the second and third frets with the middle finger, the index finger can be used to depress the string at the first fret to discern this gap.

If the string sits on the first fret, while the position between the second and third frets is being held down, the slot is probably too low and the string will probably buzz if plucked "open."

STEP 3 - CHECK AND ADJUST SADDLE HEIGHT

Once the neck curvature is correct, and the height at the nut is set, ( and never before these steps are taken) the height of the bridge saddle can be set. This adjustment is made by filing or sanding the saddle piece to give the desired height for each string. There is no "correct" height of the strings over the fretboard. Playing style determines the appropriate setting. A light finger-stylist can get away with very low action, whereas a blue grass flat-picker will prefer it quite a bit higher. My "shop setup" for acoustic guitar is generally acceptable for both moderate flat-picking and finger-picking, but favoring neither. As measured at the 12th fret I look for 3/32" between the top of the 12th fret and the bottom of the low E, A, D, &G strings, 2.5/32" at the B and 2/32" at the high E string. Bluegrass players would find this too low, pure finger-pickers would want this dropped a hair. Variables besides style also include the size of the players hands, the right hand picking attack of the player, and their level of experience. New players often want a lower string height to make it easier on their undeveloped fingers, whereas more experienced players may prefer a slightly higher string height.

IMPORTANT NOTE : Even assuming that the mechanical elements of the guitar are correct - the frets are firmly seated and level, the neck is correctly adjusted to near flat and under tension from the truss rod reinforcement, the string slots at the nut are at an acceptable height, the box of the guitar is stable ( no loose bracing), bridge and saddle are stable and correctly fitted - there is still no guarantee that a guitar can be made not to buzz at a given string height over the frets, ( I suppose you could set the strings extremely high over the fretboard by raising the saddle way up). Playing style is the key. Ultimately, how you pluck/drive/attack the strings is the biggest determining factor in whether a given guitar will buzz ( once again assuming correct settings of the neck and nut slots, and level frets). The fact that a particular guitar can be made to buzz reflects nothing about the quality of the guitar or of the set up. If I drive my car such that the tachometer is "redlining" ( reflecting overly high engine rpm's) for a long enough period of time, the engine will likely fail. But this is not a reflection of the quality of the engine or it's adjustment, it is a reflection of my driving style. And remember - a quality guitar can be adjusted to fit many playing styles. Also, sometimes, for a given string height, setting a guitar up for slightly heavier strings can make the difference. And when all else fails, if you are getting string rattle and can't abide by it, just keep raising the string height at the saddle. Eventually, it will go away. Whether the guitar will still be comfortable to play is another story. Ultimately, as with many things in life, compromises must sometimes be made.

Which reminds me of the time renowned Telecaster playing guitar-genius Bill Kirchen came to have his instrument refretted at my shop. This guy can really get around on a guitar, and he uses every note. I looked at his guitar, aghast. Every fret was worn and pitted to what had finally reached ( beyond) a critical stage. When I asked why he hadn't had the refret done five years ago ( when it surely would have been justified) he just said - "Well I just kept working around all the wear" Just goes to show you that ones attitude has a lot to do with what is or is not acceptable in a guitar.

CONCLUSION

That's it. Three basic steps in the set-up of an acoustic guitar. They must be done in this order: neck then nut then saddle. If the neck curvature is off, it won't help to adjust the saddle or the nut slot heights. If the strings are high at the nut, lowering the saddle will never get you where you want to be. Neck, nut, saddle. Neck, nut, saddle. Neck, nut, saddle...