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Recently I was playing a buddy's Martin 12-string.
I have not picked one up in years...
After about an hour of tuning I got it somewhat playable.
In the process i got to wondering about saddle compensation.
On 6-string guitars we spend a lot of time getting the saddle compensation set to an acceptable degree such that the inherent tuning errors are not noticeable and the guitar plays reasonably in tune.
Especially when going, for instance, from an E chord to a D chord.

On a 12-sting however, for instance when looking a the low E with the huge difference in string diameters, you would think that the low and high octave strings would have to be way offset at the saddle to equalize the compensation - but they are not....
I certainly noticed this when tuning - where when the open note and 12th fret was close for the wound string, off on the octave string.

Is this just inherent to a 12-string?

Rob

Yup. Part of the 12 string sound.
Some custom builders do try to compensate the strings individually, but I don't know of any factory guitars that do.

If you are talking about chords in the first position, then saddle comp wont help all that much .... the percent change of a note at the third fret from adjusting saddle comp is almost negligible, especially if the 12th fret note is close. My guess is that the nut is not comp'd (something I do on all my guitars) or possibly even in the wrong place, and that has much more effect.

If the open strings and the 12th fret are good, and the seventh is off that much .. something else could be off on the fretwork and/or placement. how do the 3rd and 5th fret read on a tuner ???

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Well, it is part of the 12 string sound but there are some things that can be done about it. First, as Tony says, you don't notice it very much in the first few frets and many twelve string player only strum cowboy chords on them. As you go up the neck the first two pairs of string will have the same compensation and will be in tune, with the others the octave will be slightly flatter than the primaries but usually that isn't objectionable.

It is possible to compensate each string of each courses but usually the saddle isn't wide enough. When I build a 12 string I like to make the saddle extra thick and use a little piece of wire to find the break points that are more or less in tune at the 12th fret - the saddle ends up looking a little bit like a rip saw blade LOL.

I think Taylor now does this on their 12's, at least on the T5-12

Freeman, you nailed it - that is exactly what I was hearing.
Buddy is a cowboy chorder, no worries...
But I was thinking, if I made one for myself, how would I deal with this compensation vexation...
Your resolution is precisely what I envisioned...

I built one a couple of years ago for somebody who does play up the neck, and did the full nut and saddle compensation on it. I've actually been doing the saddle comp for a long time, but adding in the nut work made it 'way better. I was a little worried that it lacked the usual 12-string 'crunch', but the owner loves it: now he doesn't have to retune in between the A and B parts when he makes a recording.

I developed the nut compensation distances using a string rig: a beam with a movable first fret, nut, and saddle that I can put a string on. It has a pickup in the saddle, so I can plug it into a tuner. I set it up with the first fret, nut, and saddle at the correct distances from the 12th fret (having a movable first fret allows for checking different scale lengths), and the action height where I want it. I then move the saddle back to produce an exact octave between the open string and the string fretted at the 12th fret (NOT the 12th fret 'harmonic', which can be sharp due to string stiffness). When that's correct I move the nut toward the first fret to get an exact semitone. This messes up the saddle intonation, so I re-adjust that. Then it's back to the nut. After going around a few times I get to the point where things are as close as I can make them, and I note down the offsets. Then I go to the next string. To be really careful, I do each string three times, and use the average of the readings.

In practice, it seems to me that top motion is more likely to mess up the saddle intonation than the nut, so I just make the nut by the numbers. Then I use the old 'wire-under-the-string' trick, with a flat topped saddle and a short length of wire, to find the correct break point on top of the saddle. This is usually pretty close to the numbers from the rig (as it should be if you don't have a strong resonance near an open string note), but I like to be sure.

What you usually see on the saddle is that the high E and B strings have normal sorts of offsets, while the offsets for the others fall on two lines, more or less. The octave G will require the least compensation of all; less than the high E, and the other octave strings run back from there as a shallow angle. The low strings require more compensation, of course, so there's a line for those behind the octave string line, at more of an angle. I find the saddle has to be at least 3/16" wide, BTW.

When I've got the lines, I take the saddle out, and file the front and back edges up to the lines, with the front edge giving a sharp break, and the back edge rounded. This leaves a flat on the top between the lines. I use a three-square (triangular) file to cut that flat down from the bass end, so that the saddle has two ridges at the lines. I then file a notch into each ridge where I don't want the string to contact it: the octave strings get notches in the back ridge, and the regular strings are notched out in front. This produces a neat looking saddle that doesn't take too long to make.

On that last one each course sounded like a Wes Montgomery solo, with the octaves right in tune all the way up. A tuner showed that none of the notes up the neck was off by more than three cents, which is pretty close. As Trevor Gore says; once you've played one that's in tune, it's hard to go back.

Alan, I want to live I your shop for a few months. Every time you post a response there is so much to digest. Thank you!

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This was exactly what I found when I intonated my 12-string build (pictured earlier in this thread). As I described, I wanted to "fix" the things that annoyed me about my (former) Martin D12-28. With that ridiculously skinny saddle, there was no way to have the Martin sound like it was "in tune" in ANY key. The 3.5 mm saddle was a big improvement -- so much so that I feel it explains the smile that a lot of players have on their face when they try it -- it sounds so much different from their memory of 12-strings, and they like it a lot, although they usually can't put their finger on what's different. I agree that a 12 string saddle really needs to be at least 3/16" (wide. In fact, that's what I now put on ALL of my guitars, just to facilitate intonation, and think I should go back and cut a new slot on the 12 string to really nail it. Heck, maybe I'll go the whole 9 yards and follow your technique to do the nut as well -- thanks for the detailed and clear description!

Alan:

I was following right along with your description until I got to this part:



I can't tell what you're saying here. Maybe it's just me.

Also, is your 3/16"-thick saddle at an angle or can all the compensation needed be gotten from a straight slot?

Thanks for all the info you provide online. It's very generous.

A section through the saddle looking at the end looks like:

/\/\
|__|
(hope the ASCII art comes through!)

The 3/16" saddle still need to be angled down toward the bass side. Note that compensating the nut reduces the compensation needed at the saddle, so the angle is less than you'd normally use. I also use a back tilt of 9 degrees, which helps reduce the tipping force that breaks out the front of the slot.

Okay I think I see now. You actually file a trough into the length of the saddle to split it into the 2 ridges you need---from low E to G. Then you lower the ridges in front of the main strings, and lower the ridges behind the octave strings.

I think.

I think that is correct Dennis - pretty clever - I knew there had to be a way to get these to play more in tune.
The 9 degree tilt is pretty cool as well!
The Martin I was fooling with had a narrow saddle, so it is destined to be forever out of tune...
Now the one I eventually make for myself will be another story with these tricks in hand....

Agreed, if we recognize that the fundamental of the open string doesn't define its "pitch". This opens another can of worm holes (super glue and saw dust won't fill these). How do we define and measure "pitch"? I'll start another thread.

Hey, it's a Martin; the only maker I know who put the bridge in the wrong place for a decade and even had people copy them...

(...but that simple fact was responsible for at least one career in guitar building...)

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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

Ric does make bridges with 12 adjustable saddles, but that's not an acoustic. Not all the Ric 12s have 12 adjustable saddles, my '98 360-12 does not.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon