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Question about the book, for Trevor or anyone who has built enough nut compensated guitars to know for sure...

Are bridge compensation values measured relative to the theoretical zero fret location, or relative to the compensated nut location for each string?

What got me confused is that in the "nut compensation without the math" section, it says to apply half the total compensation to the nut and half to the bridge. Which means that if the bridge is measured relative to the compensated nut, then you just leave the bridge where it would normally be without nut compensation.

But, if bridge compensation is measured relative to the theoretical zero fret position like I think it is, then you have to move the bridge up a little bit compared to normal. And that would affect capoed playing, because a capo always creates a non-compensated zero fret. So maybe that isn't always the best thing for every player. Or is it? Capos do always seem to cause intonation trouble for me, so it's not like the usual bridge location is necessarily the best for it either.

Interesting question and thought about producing less saddle compensation for fretted notes. I have also gone round and round with these type of questions. My understanding is that intonation of a typical guitar is just putting the open and 12 fret in tune with each other, just two points. The fretted notes going toward the nut have an increasingly greater error. The half and half way is looking to even out the error. Basically distributed the error inherent in the design of most fretted instruments across the first 12 fretted locations instead of fixing just one location.

I am just doing a new guitar now and did all of my compensation off of the zero nut and the scale length for the saddle. String length is shown in the charts in the book where an example of a calculated steel string and a calculated classical compensation is shown. The lengths work out if the compensations are from the zero position and the saddle at the scale length from the zero slot. So on my classical the leading edge of my saddle is about .8 mm toward the neck than I would normally have it. My saddle is a bit wider than I normally had a classical so I could still compensate a bit more than 4 mm total on the saddle.

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http://www.Harvestmoonguitars.com

I don't think you're correct about the capo idea. A capo is just an artificial fretter, like an extra finger. If you made a barre chord, would you expect it to be out of tune? So why would it be out of tune with a cap instead of your finger? Asides from the usual capo quirks...

I routinely compensate the nut on my guitars. As you move the break point over the nut closer to the saddle, you will also need to move the saddle closer to the nut to keep the 12th fret intonated properly. I use a 1/8" saddle and need to move the bridge closer to the nut as 1/8" is not enough. My numbers match Trevor's numbers for that scale length. I built an intonation rig to get close for the different scale lengths that I typically use. Here are a pictures of the rig, you will notice that everything is adjustable,

Chuck

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Thanks Chuck! That pretty much answers it: The bridge does move.


Umm, yes? I'll have to ponder more on this... why is nut compensation ever necessary, if stretching the string down to one fret, and then stretching it down to another doesn't cause a double tension rise? Is it because with the capo, the after-length between the capo and the string post is longer than the after-length between the nut and string post, so the stretch has proportionally less effect on pitch?

Do you find that playing with a capo throws off intonation? I don't, but I don't use one much. Though we have lots of house jams where capos are widely used and I never notice a problem...

Nut compensation continues to make a difference when you fret a string or use a capo. It has to do with how you have to tune the open string in the first place. I am sort of capable of understanding how this works but I doubt my ability to explain it clearly. Perhaps someone better at these sorts of things will weigh in.

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Tim Allen
"Never hurry, never rest."

Capos that clamp all the way to the finger board can pull your strings sharp. If you use one like a Shubb capo then you only clamp down as much as is needed to fret the strings - makes a big difference in my opinion.

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Steve Smith
"Music is what feelings sound like"

Page 4-102. Life starts with a string of specified scale length, with the 12th fret bisecting the string length. Positive nut compensation measures from the string end (theoretical zero fret position) toward the tail end of the guitar. Positive saddle compensation measures from the other string end toward the tail of the guitar.
...so the string length doesn't change, but the whole string effectively moves down toward the tail of the guitar (e.g 2mm compensation toward the tail at the nut and 2mm toward the tail at the saddle, or whatever the number you derived for each string).

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Hmm, I still don't see it stated explicitly anywhere on that page, though the math does make more sense this way. My question is answered


Yeah, this is the other thing that made me second guess myself. With the traditional compensation style, the open low E is almost 1/4" longer than the scale length. Amazing that both systems end up sounding so similar!

Because fretting near the nut bends the string at a sharper angle. That is why a guitar can intonate perfectly at the 12th fret, but be sharp when fretted near the nut.

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John

One of our clients was complaining that his guitar was 7 cents sharp on some of the notes in the first couple of positions. We checked it on a strobe, sure enough 7 cents or so sharp and then we cut his nut slots properly and saw 7 cents reduced to a bit over 2 cents..... Client was happy as a clam.

And that's the point, nut slots matter!

It's probably stone age thinking but I just cut a fret slot for the nut which shortens the nut-first fret distance around .012" and then take a good straight edge, butt it against the nut and mark the center of the 12th fret and then use that distance plus compensation for the saddle position. 1/8" set back angle on the saddle and 1/8"thick. Intonate the strings individually at the saddle.

Oh yeah, get the nut slots right.

Seems to work.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

That is a detail that is often overlooked. The frets are located on the center of the slots, while the cut on the nut end of the fingerboard shortens the nut to first fret distance by half the slot width.
Most references indicate that about 0.030" is the amount to trim off the fingerboard, but since this method already trims 0.012", only 0.018" additional is necessary.
In most cases, intonation that is noticeably sharp near the nut can be traced to badly-cut slots.

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John