Intonation VIII

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My Weirdest Intonation Horror Story

I have a client whose ears are a phenomenon of nature. She can hear intonation discrepancies that I have to strain to discern. This remarkable ability is both a blessing and a curse: she sings absolutely perfectly in tune, and tunes her guitars perfectly by ear, but little intonation discrepancies in her guitars drive her nuts! Having her as a client has motivated much of my investigations into guitar intonation. I'm happy to say that she's more satisfied with the intonation of her Doolin Guitar than any other she owns, and believe me, I had to work pretty hard to achieve that distinction.

She brought me a very nice Martin "M" model which she had played for years. She had taken it to a good repairman who had trued the fretboard, refretted the neck, and compensated the saddle, but it still sounded wrong to her so she brought it to me to see if I could do any better. I agreed that it wasn't playing in tune, so I did a detailed intonation study of every fret on every string.

What I found surprised me so much that I borrowed another Martin (a dreadnought) and did the same intonation study, with the same results:

  1. All the strings were in tune at the 12th fret, and reasonably close at every other fret, except
  2. at the 2nd, 3rd and 4th frets, the low E was quite sharp and
  3. at the very same frets, the A was quite flat!

This completely blew my mind. I checked the fret placement, and it matched my precision fretting template perfectly. There was no excessive fret wear or neck warpage since the guitar was newly refretted. I tried several brand-new sets of strings and got the same results, from both guitars. How could different strings be out of tune in opposite directions at the same few frets, when they were both in tune above and below those frets? I would have thought that the fret would have to be slanted or staggered to accomplish that.

I did the same detailed intonation study of one of my guitars, and every fret played in tune, no exceptions. I'm not saying this to prove that I make a better guitar than Martin, I only mean to say that something I was doing saved my guitar from this anomaly that was common to both of the Martins I studied. So what was I doing different?

All I can do is speculate, but I believe that the problem was resonances in the necks of those two Martins. I inlay two strips of graphite in my necks, one on either side of the truss rod. Graphite is about 15 times stiffer than wood for the same amount of material, and stiffer means higher frequency. I speculate that the Martin necks had resonances close to the notes that were playing out of tune, and that those resonances were pulling those notes sharp or flat. I knew that graphite would make my necks more resistant to warpage, and had noticed that it prevented "dead spots" as well - every note on my guitars has about the same tone color and sustain. I think that the graphite also raises the resonant frequencies of my necks above the fundamental frequencies of the notes on the neck. Since the neck doesn't sympathetically resonate with any note more than any other, it doesn't sap away any energy, and it doesn't drag the pitch of any note away from where it should be.

At least, that's my theory. The use of graphite as neck reinforcement has become pretty commonplace, and I was happy with the results even before this weird intonation experience. Now I'm even more sold on it.

That's all, folks!

I really think I've dredged up every bit of intonation information I know at this point, and I hope I've entertained and interested you more than annoyed and bored you with this long series of articles. But I never say never: if anyone has questions or if I haven't been clear about something, please write me at:

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