How to accurately drop-tune an acoustic guitar?

Question

I like to play in drop-D, for a variety of reasons mostly involving the use of a low drone string, simplicity of fingering certain chord-shapes quickly, and I like some of the interesting possibilities with regard to open strings and minimal fingering, especially high up the neck. I play largely by ear, and like to improvise a lot, so it's really important the intonation is very accurate. Even though other people might not hear the difference, a little bit off and it gets confusing as to where to go next, and isn't pleasing when you go to let something really stand out and it's just wrong to my ears.

On my electric I have adjusters for intonation, it's 24 frets, easy to play, and sounds great. But it's not always convenient, or easily portable, and it's precious to me. My acoustics are, well, cheap. I've tried lots of things, but always seem to be a few cents sharp at the 7th fret on a drop-D 6th string when tuned accurately with open strings. Or tuned accurately at the 7th fret, flattish when open.

I've tried modelling a saddle that mimicks the positioning on my electric, adjusting the nut, even using screws, toothpicks, or anything about the right size and shape to wedge in there, on either end, to get the intonation right. I've come a lot closer, but still a bit off, which drives me nuts.

Anyone out there with experience adjusting intonation on an acoustic guitar for drop-D tuning who might have a word of advice that doesn't involve spending a bunch of money?

Answer 1

The problem is that if your bottom string is in tune on the frets when tuned to E, it's simply going to play sharp when tuned down. Unfortunately, you either need a D-string which is a bit more elastic (so it goes up less when stretched) than your E-string, or you need to compensate the nut and/or the bridge-shortening the string length at the nut, or lengthening it at the bridge, or both. Or you could lower the string in the nut and/or bridge. All of this will of course adversely affect the intonation of the string when tuned back up to E, and lowering may cause buzzing.

If you have a guitar you want permanently for drop tuning, you could conceivably do the compensation yourself: shortening the mensur (the acoustic length) of the bottom string a couple of millimeters at the nut and lengthening it at the bridge (assuming you have enough material there) should do the trick. You have to be pretty good with a file, though. Don't try it on an expensive instrument.

Good luck.

edited for accuracy. Sorry, must have been half asleep: you of course need to shorten the string length at the nut if you want it to not play so sharp on the frets.