John O’s explanation of compensation

Compensation allows the string to play in tune when the string is fretted. As a player frets the string it will be stretched a small amount which is dependent on the action (height of the string above the fingerboard.) This stretching will make the non-compensated string play the particular note sharp. To deal with this, builders compensate the scale length moving the whole saddle back toward the pins a small amount, but this is further complicated by the string diameters. Larger string diameter require more compensation, therefore the saddle needs to be brought back even more on Bass strings, but this is even further complicated by the fact that the center solid core of the string  is what is stretching so the compensation is really based on the diameter of this solid core. For example the core diameter of a set of light strings might measure something like this:

6^th = .0175” (wound string core only)

5^th = .016” (wound string core only)

4^th = .015” (wound string core only)

3^rd = .013” (wound string core only)

2^nd = .016”

1^st = .012”

So the 6^th string with the largest core needs the most compensation and thus the saddle is moved back the most for this string. Now we need to move the saddle less and less back until we get to the 2^nd (B) string. Notice that being a non wound string has a larger center core then the 3^rd string . This string wants to be back further again similar and is often why we see the shelf cut into the saddle on the second string bringing that back more.  During the build process this needs to be factored in to getting the saddle slot of the bridge in close vicinity to where the compensation will work. There are other factors involved including the overall scale length, alternate tunings that will impact all these things.

Small adjustments can be made once the guitar is strung –up  When I set up guitars I use a strobe tuner to get the intonation set by adjusting the saddle. It can be done by moving  tangent point (with a file) of the saddle where the string  breaks over the top  back or forward a small amount.

If is saddle is tilting forward in the slot, (with respect to the soundboard) this is usually a bad sign. It could be from a couple of factors but is usually due to a poorly fitting saddle. I actually mill my saddle slots back toward the pins a few degrees so my saddles tilt toward the pins  with respect to the soundboard but I will leave that reasoning for another discussion.

Compensation is important to get a guitar to play in tune. There are some compromises that we have to make because of the factors involved. Since action, string gauge, scale length, tunings all play a part in this, it is really tough to get a guitar set just right for every situation. As a builder, I shoot for the middle during the build and then adjust the saddle with a strobe tuner for the player’s needs.