A double action truss rod, as opposite to a single action truss rod, is capable to produce a neck up-bow or back-bow relief despite the tension of the strings.

Double action truss rod image
A double action truss rod.

The adjustment is identical to a single action truss rod i.e. by turning the nut clockwise you get an back-bow relief on the neck. By turning the nut counterclockwise you get a up-bow relief on the neck.

Both the material the truss rod is made of and the way it is installed into the neck play an important role on tone. Generally the more wood is removed to install the truss rod the more the tone will be affected. Another factor that the expert luthier should keep in mind the the relationship bewteen the truss rod adjustment and the neck setup when strings are in tension.

Correct installed truss rod should never move inside the neck to avoid dampening the strings with sympathetic vibrations and secondly should be always some way in tension when the guitars is tuned to pitch and neck relief is correct. This way the neck will be stiffer and sustain improved.

Modern double action truss rods requires a minimum removal of wood from the neck to be installed leaving more of the tone into the neck.

If you have never adjusted a truss rod please consider that, despite the common belief, this is a pretty simple thing to do and and unless you force it really a lot which rarely happens, this is something you can do in total relax. The whole operation is shown here.

Truss rod adjustment
Truss rod adjustment: adjusting the truss rod. In this video Galeazzo Frudua explains in details how to adjust the truss rod on your guitar or bass to achieve a comfortable action.

© 2018 Galeazzo Frudua. All rights reserved

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