by tzs | 2026-02-15 23:19:44+00:00
> The guitars were nearly impossible to play, with frets that could cut your hand and intonation that created sounds half and whole steps away from the intended tone

I'm curious about those intonation problems because a couple of years ago I wanted an inexpensive but decent acoustic guitar, and bought a Fender CC-140SCE acoustic guitar direct from Fender's online store.

It had frets that could cut your hand and a note that was off by a whole step. It also came with the truss rod way out of adjustment leading to lots of buzzing. I was able to get rid of most of the buzz by adjusting the truss rod, but I didn't want to deal with the rest of the problems and sent it back.

Only after it was on the FedEx truck on its way back to M̵o̵u̵n̵t̵ ̵D̵o̵o̵m̵Fender did I realize that I couldn't think of a way that the intonation error I saw was even theoretically possible. I wish I had realized that before sending it back so that I could have figured it out.

Maybe someone here has an idea?

Here's what I observed. This only happened on the first string. The others were fine.

To make this easier for people who don't know anything about music (because this is really a physics mystery, not a music mystery) I'm going to use numbers for the notes instead of names.

Let's call the note played when you pluck a guitar string without pressing any of the frets note 0. When you pluck while pressing the string down just behind the first fret, that is note 1. Frets are counted from the neck end of the guitar, and "behind" a fret means on the neck side. Second fret gives note 2, and so on.

Note n+1 is higher frequency than note n. The frequency ratio of adjacent notes is supposed to be 2^(1/12).

Playing up the fretboard, starting with plucking without pressing any frets should give this sequence of notes: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.

What actually happened was that note 13 was missing. It was replaced with 15. The sequence from 12 through 16 went 12, 15, 14, 15, 16.

A bad fret can easily case a wrong note, but there are limits. The way frets work is when you push the string down behind the fret, it changes the length of the vibrating portion. With no frets pressed the string vibrates between a support on the neck (called the "nut") and a support on other end (called the "saddle").

If you press down behind a fret, that pushes the string down enough that the portion between your finger and the saddle is suspended between the saddle and the metal of the fret. That's shorter than nut to saddle, so has a higher frequency.

The saddle is higher than the nut and the frets so that the string slopes up as you get closer to the saddle. Consider playing note 12 on mine. The string is then suspended between fret 12 and the saddle. It is sloped up enough from there the its up and down excursions from vibrating don't hit anything.

Now we play note 13, but what actually plays is 15. There is a straightforward way for that to happen: fret 15 can be slightly too tall. It is not tall enough to interfere when playing 0-12, but playing fret 13 pulls the string down farther than playing fret 12 does, and that is enough to reach fret 15 and so the string ends up actually suspended between 15 and the saddle instead of 13 and the saddle.

Can that explain what I observed? Nope! Because if 13 pulls down the string enough to run into 15, 14 will do also do so because 14 pulls down the string more than 13. The sequence would then be 12, 15, 15, 15, 16 not 12, 15, 14, 15, 16. It should not be possible to have fret n+1 play a lower note than fret n.