A Rough Guide For Adjusting The Playability Of Your Acoustic Guitar - Action and Truss Rod Adjustmen

Published: 30th September 2011
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Guitar "action" just signifies how high the strings are above the twelfth fret, and a reasonably low action is important for any acoustic blues guitarists. If you like to perform several styles, then a medium action should be aimed for. Too low and the strings will make a buzzing sound - if they are too high it will be hard to fret the strings. On the other hand, certain players may prefer a significantly higher action, for example if you play blues guitar and use the guitar mostly for playing slide.

The action can be set by adjusting the saddle height, which of course changes the gap between the strings and frets along the length of the neck. First of all, measure the distance of the low E and high E strings from the 12th fret. For a medium playing action well suited to finger picking and strumming styles of playing, the action at the 12th fret should be a tad under three millimetres for the bass E, and around two millimetres for the high E string.

As the 12th fret is exactly half the distance along the string, you should write down the amounts by which the action should be adjusted higher or lower for the 1st and 6th strings, and adjust the saddle by double that distance. Most blues guitar players need a medium action.

If the saddle needs to be lowered, this can be done by filing material away from the base of the saddle. If it needs to be a little higher, a hardwood shim of the required thickness should be attached to the base. You must also ensure that the base of the saddle is perfectly flat, particularly if the guitar is an electro acoustic model, because an uneven saddle can lead to problems with the pickup response.

Neck Adjustment

Many acoustic instruments are fitted with a truss rod, which adjusts either at the heel of the neck inside the sound box, or at the headstock. The rod balances concave bend, by exerting a force in the neck which opposes that caused by the tension in the strings. The strings attempt to pull the neck into a curve. We want some curve, in order the strings don't hit the frets when vibrating after being hit hard.

Remove the cover of the truss rod end, if your guitar has one, and fit a capo at the first. Fret the bass E string at the 14th fret with one hand. Using a feeler gauge, measure the distance from the top of the fifth fret and the bottom of the bass E string. There should be a little gap, between 0.15 and 0.05 mm. If you are experiencing string buzz, the rod could be adjusted too tight, flattening the neck too much. Loosen the rod a bit, measure again and play some. If there is too much curvature, then tighten the rod. On Martin acoustics, use a 5mm allen key to turn the truss rod adjusting nut clockwise to straighten the neck and counter-clockwise to add some curvature.

Medium gauge strings (.013"-.056") exert more force, and so need more truss rod tension to oppose the tension produced by thicker strings. This results in more volume, sustain and more rounded guitar tone. One final word, if you meet excessive resistance, or you're not comfortable carrying out these adjustments, take your guitar to your Service Center.


Jim Bruce is a working blues man making a living playing blues guitar. His acoustic blues guitar lessons are fast becoming the standard to reach for acoustic blues guitar picking lessons.

Main site: www.play-blues-guitar.eu
Youtube: www.youtube.com/user/acoustictravellersl

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