The way you intonate an acoustic guitar is not as easy as how you do it in an electric guitar. The main difference is that in acoustic guitar, you have to replace or re-orient the saddle, while in an electric guitar, there’s no need to do it.
Before you proceed to intonate an acoustic guitar, you have to know what factors affect intonation such as string gauge, fret position, composition and age, nut or saddle compensation, and action at saddle as well as nut on the fingerboard.
Some people agree that if you intonate an acoustic guitar from string to string, the sound of the guitar is greatly affected by the tuning. When your guitar has already been set up and you put a new set of strings, there is the tendency that intonation might change.
Bear in mind that different brands of strings have their own corresponding set of gauges. This is a common case in brands of guitar or other musical instruments to indicate their uniqueness in style and brand reputation.
Therefore, it would be better for you to choose the kind of strings based on their gauges; not depending on whether they are Light or Extra Light. While the string composition affects its stiffness and density, the tension as well as the pitch are also affected that lead to intonation.
When you intonate an acoustic guitar, you have to fret the string and in doing so, the string is being stretched out; hence, length is added to the string that prevents note sharpening.
However if that happens, the open strings are also lengthened so, they don’t undergo fretting, and therefore, don’t need to undergo compensation. Some guitarists intonate an acoustic guitar by compensating the nut to produce a better sound.
Compensating the nut can be attained in various ways and one simple method is by shortening the length of the fingerboards at the end of the nut. You can modify the position of saddles and the length of the fingerboard depending on some factors like string gauge, action and scale length.
There are people who have the special ability to hear slight difference in sounds while others cannot. While some theories apply to nut compensation and appropriate saddle, there are also various ways to intonate an acoustic guitar.
Many guitarists believe that when the green light is activated, their guitars are already in tune. This may be true as a common method of intonating guitars; however, this is not the only technique that can be done to intonate an acoustic guitar.
Some people even use harmonics in tuning their guitars, others do the tuning of 2 particular chords to produce compatible sounds with one another, and there are others who devise charts in off-set tuning to indicate the number of flat or cents sharp each note should correspond to in tuning.
In whatever way you think is best suitable to intonate an acoustic guitar according to the sensitivity of your ears, just remember that there are different methods of tuning a guitar.