String Intonation

[J.T. Devine]

This is a question regarding intonation on a jazz hollow body archtop with a common rosewood, moveable bridge like that shown in Frank's Restringing Your Archtop page.

 

I recently replaced strings. With my old set of strings I could get perfect (to my taste) intonation across all the strings. With this new set, all strings are acceptable except the 3rd G, whose fretted 12th is @20 cents sharper than the harmonic.

 

The two sets of strings are similar weight, medium light, but the first set has a wound 3rd compared to the second's plain 3rd (.019" vs. .018"). Can this account for the difference?

 

As is apparently standard with theses bridges, the saddle point for the 3rd string produces the shortest length string. To make this new set work, however, the 3rd really wants to be longer, more like that of the 4th or 5th string.

What I need to do is replace the 3rd string with a wound one, but for knowledge's sake, is there a difference between wound and unwound strings of similar diameter? Are those bridges designed for wound 3rd's?  Are there any tricks one can use to adjust a single string?

[Grahame Myers]

This is a well-known "feature" of guitars with this kind of bridge: They were intonated for wound G's, (back then all G's were wound, plain G's are a relatively new invention), and if you use a plain G, the intonation is sharp. And of course, the only way to adjust the intonation is to file the G part of the bridge to effectively increase the length of the string, assuming there is enough wood to allow it without reducing the height.But then the change is permanent, and the intonation would then be flat with a wound G.

Another way would be to change the bridge for one with a wooden bottom half, and a tune-o-matic type top half, which allows adjustment of the string length. If the bridge you have now is in two parts anyway, with two knurled wheels to adjust the height, depending on the distance between the wheel posts, sometimes a tune-o-matic bridge fits without any modifications.

On the other hand, why re-invent the wheel? Just go back to a string set with a wound G and you're good to go :-) On a jazz archtop, string sets with wound G's sound better anyway, IMHO

 

Grahame

[J.T. Devine]

Thanks for the repy and explanation. I occasionally experiment with strings but I was not aware of the intonation issue with wound vs. unwound so this helps a lot.

[Russell Vance]

You got it, the wound and the plain 3rd have an entirely different intonation - the plain will be further away from the nut by a considerable distance (3 to 5 mm is common) when compared to the same wound string.  This was a big problem with LP Junior stoptail bridges which had a set intonation for a wound 3rd when everybody started using plains to play rock.

 

Either go back to using a wound or get a new compensated saddle made up (I don't know if they are available as an aftermarket item - haven't seen em, but I haven't been looking).  Anybody got anything on this?   Rusty.

 

P.S. just saw Grahames excellent post......I say what he says!

[J.T. Devine]

So,I'm trying to get my head around the physics.  The main lesson is that, for a given string diameter, a wound string wants to be shorter than a plain string. The difference must be in mass?  A wound string has more mass or do I have it backward?

[Gary Fried]

The intonation of the string has to do with the diameter of the core wire. The smaller the core wire the less compensation it needs.

[Pierre-Antoine Roiron]

Gary nailed it. The overall diamter is to the key, it's the core diameter.