Compensation 101 the basics

[tippie53]

I want to offer up what I have learned about compensation and intonation.

The basics of this is that we want to match the working length of a string to the scale length , the best we can.
We all have seen the compensated saddle angle and compensated saddle were the saddle has material removed to increase the working length.

So with this one fact in mind
A string with a certain diameter , when under a specific tension will vibrate to a specific fundamental frequency. Here is a good read
( http://www.noyceguitars.com/Technotes/Articles/T3.html )

So as you increase the length you will lower the frequency and therefore shorten the length it you will increase the frequency so longer length is lower note shorter is a higher note

OK so how can you use this information ?

Lets look at the basics of a guitar.
A :scale length or the placement of the frets (http://www.liutaiomottola.com/formulae/fret.htm)

When the guitar is ready for set up what does this information do for me ?

Well lets add one more ingredient to this The variables
The variables are just that , things that may be different from one guitar to another and things that can change the end result.
B: string height
the higher the action the more you will bend the string ( increase tension raising frequency )
Tops stiffness ( this is hard to determine) but over time the bridge will rotate shortening the string length
Playing style Some people fret cleaner than others but when it comes down to it , you tend to play sharper than you may tune
Neck relief
Higher neck relief will influence the action height and it can cause you to stretch he string

Ok so with this information how do I go about setting the bridge and saddle ?

I use the nut to 12th fret times 2 then to that following the line of the #1 and #6 string I will set the saddle position I add 1/10 of an in on a 3/32 saddle to the front of the saddle and 1/8 on a thicker saddle but locate that just inside the saddle slot. This locates my bridge to a point on the top.

So why do I it this way ?
What I have learned over the years is that the guitar will change shape. As it does the bridge will tend to rotate and this will slide the saddle forward , and I can then adjust the saddle as it changes. The heavier saddle can allow more adjustment but the key to know is the front of the saddle will move eventually.
I like to set my guitar up on the initial set up to be about 2 cents flat based off the 1 and 6 string. I don't do much adjusting on the guitar for about a month. Allow a settle in period , but you can do some adjustments.

The ABCs are
Neck relief first
adjust the new nut slot and I shoot for about a .007 nut slot height off the fret plane. This is my starting point
I then set a straight edge on the 1st fret and set it on the saddle , with about 10 lb on the body and the neck supported I can take a measurement of expected action height and make my saddle.
My starting point is 4/64 on the 1st and 6/64 on the 6th.

once strung up I will again check the basics this is based on the assumption the frets are leveled and dressed.
A relief Check this by fretting the 1 and the 13th fret this gives you a line off the 1 and 12th fret. At the 6th fret you want to see .004 to .008 in off the 6th fret to the bottom of the 6 string.
B 12 th fret height ( action height )
C check nut While I set this last , having roughed the nuts slots in you are only a few thousandths off if any.

So now lets see what we have.

I check the 1st and 12th fret. Be careful as you don't want to over adjust.

I like to check the harmonic positions also . I do let the strings settle in for about an hour or 2 first.

In this state I want to see the intonation a touch flat or on the mark. If you have sharp ( usually the B ) you can adjust that by filing a small step out of the saddle. This is all done after you have the string action height adjusted.

Now if you want to get to the next level we can go and compensate the nut. I do this when I make my fretboard and I will taper the nut or Zero fret location but .030 from the high side to the bass side. This sets the nut down the string and affords you a 2nd point to work the string length.

it is worth a note that as you go up the neck , the shorter the string length ( fret to saddle ) becomes, the more critical the saddle position. So plan to make the adjustments to fit the players style.

So with the nut we can afford compensation to the 1st position. At this point the string is at the longest so we have more room for error but this still effects the higher register. When you adjust the nut you can file a steep ramp off the front of the nut , this will lengthen the string and platen the note.

So lets say your 12th fret harmonic is good. but your intonation on the first 5 frets are sharp you can take some material off the nut in effect lengthening the point from the nut to the 1st fret. This will flatten the string helping intonation in the 1st position.
I find that the bass E and the G usually need the adjustment.

It may take a few attempts to master this but it is well worth the time investment.
I hope this helps you understand the basics of the intonation and compensation .

[Danl8]

Great information, John, if not somewhat intimidating. I think I will need to cook this into a process SOP in order to take full advantage.
-d.

Non nobis solum

[tippie53]

To really get this down what I did was glued a neck on a piece of wood. I had my bridge mounted on a board that was rabbited into that board that allowed me to move the bridge and I could use a clamp to hold it. I could shim it up and down. The truss rod was able to be adjusted from the headstock.
now you can play with the positioning of relieve saddle and nut and learn the cause and effect relationship on all the variable.

[Diane Kauffmds]

This is really excellent information John. Intonation can be a funny thing, esp. with a short scale guitar, and since I play a piece that is tuned extremely low, it becomes even more critical.

Even though the 00 that I just finished, seemed to be "perfectly" intonated by harmonics and between open and 12th fret, I noticed that it sounded flat on some notes. Apparently my problem is keeping the fret file perfectly perpendicular to the fretboard. I spent a solid 3 days adjusting the intonation on each string, fret by fret, with the fret crown file, to ensure that the crown was as perfect as I could get it. Of course, I wasted a day and a half, until I realized the problem. Live and learn; it's a mistake I'm not likely to make again.

Intonation is critical and seems really intimidating, yet when you finally work with it, it's very intuitive.

[tippie53]

when in doubt play louder

[Diane Kauffmds]

when in doubt play louder

If I did that, every cat in Parkersburg would scream!