Does lowering the saddle affect intonation?

[imc2111]

If I sand down the saddle of my acoustic guitar, will the intonation be affected? So far I've heard mixed opinions regarding this topic without no clear answer apparently..

[Jim.S]

Intonation has a relationship to the action (that is fact not opinion), the higher the action the further you have to bend a string to get it to fret. So if you raise the action without any other alteration you make a fretted note slightly sharper.

So yes your intonation will be affected but depending on how your intonation is before you make the changes you may improve intonation or do the opposite.

Whether the slight change in intonation is a problem for you will depend on what you are used too in the way of accurate intonation in the first place.

Jim

[imc2111]

Originally Posted by Jim.S

Intonation has a relationship to the action (that is fact not opinion), the higher the action the further you have to bend a string to get it to fret. So if you raise the action without any other alteration you make a fretted note slightly sharper.

So yes your intonation will be affected but depending on how your intonation is before you make the changes you may improve intonation or do the opposite.

Whether the slight change in intonation is a problem for you will depend on what you are used too in the way of accurate intonation in the first place.

Jim

The action is a bit on the high side, so I would be sanding down the saddle a bit.

[redir]

Originally Posted by imc2111

The action is a bit on the high side, so I would be sanding down the saddle a bit.

If that is the case and the guitar was built properly then it may be the case that once you lower the action you will bring the guitar back into the proper intonation, is that why you are asking? Is the guitar out of intonation now?

[Jim.S]

Yes, so your fretted notes will be slightly flatter.

Jim

[imc2111]

Originally Posted by redir

If that is the case and the guitar was built properly then it may be the case that once you lower the action you will bring the guitar back into the proper intonation, is that why you are asking? Is the guitar out of intonation now?

No, it sounds fine, not out of intonation. I just thought that sanding the saddle down means also adjusting it for intonation.

[Ned Milburn]

There is such slight intonation change within normal usable action changes as to be insignificant in most cases. The biggest causal factor requiring intonation compensation is string stiffness, not string tension. (Before everyone jumps on me for this, because I know we have discussed it before, think of a classical guitar with concert action set up to 4.5mm on the low E, requiring very much less intonation compensation than a steel string. And look at the differences in string tension on certain standard guitar sets starting at .011 and .012. The regular intonation compensation on a compensated steel string saddle is not reflective of tension differences, rather, it correlates quite directly with the string stiffness - core + windings.) So, even across the regular usable range of action heights, the intonation compensation will not change significantly.

[Alan Carruth]

The difference in compensation required for steel and nylon strings is not directly related to string stiffness, but rather to the Young's modulus of the strings. I know it's a nit pick, but it does have some meaning. Good places to get more input on this would be Fletcher and Rossing's 'Physics of Musical Instruments', and Gore & Gilet's 'Contemporary Guitar: Design'.

[Ned Milburn]

Originally Posted by Alan Carruth

The difference in compensation required for steel and nylon strings is not directly related to string stiffness, but rather to the Young's modulus of the strings. I know it's a nit pick, but it does have some meaning. Good places to get more input on this would be Fletcher and Rossing's 'Physics of Musical Instruments', and Gore & Gilet's 'Contemporary Guitar: Design'.

From wikipedia (FWIW):

"Young's modulus, also known as the tensile modulus or elastic modulus, is a measure of the stiffness of an elastic material and is a quantity used to characterize materials."

Stiffness versus elasticity - how much force does it take to "push" an object away from its resting position, versus how much energy and how quick can the object return to its original resting position.

Many of us talk about "stiffness" in a soundboard, but in fact a more accurate discussion of soundboard qualities should likely state "elasticity". Indeed I often introduce the concept of "elasticity" to my clients when talking about soundboard design. Stiffness and elasticity are in one sense, opposite faces of the same coin. So in this sense they are very much inter-related.

For layman's discussions, I think it is safe to say "stiffness" in this instance. But you are quite right that a fully scientifically accurate description must go beyond "stiffness" alone.

[Rodger Knox]

Assuming a vertical saddle slot, changing action height does have some small effect on intonation.

Now if the saddle slot is angled back 8° to 10°, the intonation is adjusted as the action is changed.