Intonation — Lutherie Encyclopedia

IntonationType: techniqueAdjusting the effective vibrating length of each string so that fretted notes play in tune across the entire fretboard.## Overview Intonation refers to the accuracy of pitch at fretted positions across the neck. A guitar with good intonation plays in tune at every fret; one with poor intonation may be in tune at the open string but sharp or flat at the 12th fret and beyond. Intonation is set by adjusting the vibrating length of each string through saddle compensation—shifting the string's contact point on the saddle forward or backward. ## Process The basic principle is simple: if a fretted note at the 12th fret is sharp compared to the 12th-fret harmonic (or the open string an octave lower), the vibrating length is too short, and the saddle contact point must be moved back (toward the end pin), lengthening the string. If the fretted note is flat, the contact point is moved forward. On electric guitars with individually adjustable bridge saddles, this is straightforward: a screw moves each saddle forward or backward. On acoustic guitars, intonation is set by shaping the saddle crown—carving the peak of the saddle so each string's contact point is in the correct position. The luthier uses an accurate chromatic tuner, preferably a strobe tuner, to compare the open string (or harmonic) with the fretted 12th-fret note. Each string is checked and adjusted individually. Compensation requirements depend on string gauge, string type (plain vs. wound), action height, and the string's inherent stiffness. Heavier and stiffer strings require more compensation (a longer vibrating length). The wound G str…