The Geometry of Intonation: A Guide

Intonation is the silent agreement between geometry and physics. When a string is fretted at the 12th fret, the resulting pitch should be exactly one octave higher than the open string — anything else, and chords up the neck begin to drift.

The usual culprit is bridge placement. A floating bridge on an archtop is held in place by string tension alone, which means a thousandth of an inch of movement can pull the entire instrument out of tune.

In the workshop, we set intonation with a strobe tuner, a sharp 6H pencil, and a great deal of patience. Slide, sound, slide, sound. The bridge moves backward to flatten, forward to sharpen.