A Rough Guide For Adjusting The Settings Of An Acoustic Guitar - Action And Neck Straightness

Guitar "action" simply means how high the strings are above the twelfth fret, and a playable action is a must for any acoustic blues guitarists. If you like to play a variety of styles, then you should aim for a medium action. If it's not high enough the strings will buzz - too high and it will be hard to hold them down. On the other hand, certain players might prefer a slightly higher action, for example if you play blues guitar and use the guitar mostly for playing bottleneck.

The action can be set by adjusting the height of the saddle, which of course sets the distance between the strings and frets along the length of the neck. To do this you need to measure the distance of the low E and treble E strings from the twelfth. For a medium playing action that suits finger picking and strumming styles of playing, the distance at the 12th fret should be a bit less than 3mm for the bass E, and about two millimetres for the high E string.

As the 12th fret is exactly half the distance along the string, you should write down the distances by which the action needs to be adjusted higher or lower for both E strings, and adjust the saddle by double that amount. Most blues guitar players need a medium action.

If you need to lower the saddle, this can be done by filing material away from the base of the saddle. If the saddle needs to be raised, a hardwood shim of the right thickness should be inserted under the base. You must also ensure that the bottom of the saddle is perfectly flat, which is very important if the guitar is an electro acoustic model, as an uneven saddle can lead to problems with the pickup response.

Check And Adjust The Neck For Straightness

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

Remove the truss rod cover, if your guitar is so equipped, and fit a capo at the first. Fret the bass E string at the 14th fret with your right hand. Using a feeler gauge, measure the distance between the top of the fifth fret and the bottom of the sixth string. There should be a little gap, between 0.15 and 0.05 mm. If you are experiencing string buzz, the rod could be too tight, flattening the neck too much. Loosen the rod a bit, check the measurement again and try it out. If the neck has too much bend, then tighten the rod. On Martin guitars, use a five millimetre allen key to turn the truss rod adjusting nut clockwise to straighten the neck or to the left to add some curvature.

Medium gauge strings (.013"-.056") have higher tension, and so require more truss rod tension to oppose the tension produced by thicker strings. This results in bigger volume, sustain and more rounded guitar tone. One final word, if you meet excessive resistance, or you're not happy with this adjustment, take your guitar to your Service Center.