So you want to intonate a 12 string acoustic guitar

The problem with intonating a 12 string acoustic guitar is many. The biggest being that most of the pairs tuned to the same pitch are of a different gauge. This make the intonation or the pitch of the string as you move up the neck different for each gauge string. The pitch difference is compensated by changing the length of the string slightly at the saddle. On most electric guitars the saddle length is adjustable on most acoustic guitar you file the top of the saddle forward or backwards so the endpoint of the string, where it leaves the saddle is in the correct place. The problem with this is the saddle is often not wide enough to intonate the difference between strings and when it is often the b string or others is resting on a small point at the back of the saddle and that is not so great for the tone. Subtle but it makes a difference. Also, a wider saddle sounds much different than a thinner saddle. You can sometimes loose the nice ring and clarity of a guitar with a fatter saddle sometimes not. What to do....... We prefer a split saddle when appropriate. Here you see the saddle getting wider towords the lower strings. This is what was needed on this guitar to keep the pairs in tune. There are tricks to finding the intonation points. First we fill the saddle with matching wood, then we have small saddle pieces of different heights that we can rest the string on and move around while the guitar is strung up and playing. After we find the correct points then we come up with the best saddle to accomplish this. Sometimes a 3 piece saddle will do the job sometimes 1 or 2. Of course strings, nut placement, height and finger pressure are other issues.