All of my necks are reinforced with a double-action truss rod. The truss rod is used to stiffen the neck and can be adjusted to get the correct amount of relief in the neck. The proper amount of relief will allow the strings to be lowered without buzzing thus improving playability. When the truss rod is tightened it stiffens the neck which can improve sustain. The truss rod safeguards against warping of the neck due to humidity fluctuations. It is accessible through the sound hole of the instrument.