Setting the Intonation
Intonation is adjustment of the string length at the bridge for different string gauges so that the notes played are as “in tune” as possible. With the string height set, and the relief set (truss-rod adjustment), the instrument is ready for Intonation adjustments. It’s important to set the intonation last because the string height and truss-rod adjustments both, minutely, effect the string length and thus the intonation.
Intonation De mystified
The guitar is an imperfect instrument. The mathematical calculations that define where the frets are placed is perfect on paper, but on the actual guitar other factors come into play.
Different string gauges are needed, along with intonation adjustments, to have the strings play relatively in tune with each other. The guitar is never really in perfect tune, rather it is balanced to sound as good as possible for chords and playing with other instruments.
Buzz Feiten has developed a method to compensate the strings length to provide a hybrid intonation setting. Other companies have developed compensated nuts, and even spanned fretting systems with the intention of solving the intonation problem. This article focuses on setting the intonation on a standard guitar that does not have any special enhancements.
Measuring and Setting The Intonation
For this tutorial we are using a standard sets of strings (either nine or ten gauge) tuned to EADGBE standard. The image below is a good starting point for setting your intonation – but there is a little secret trick that we have found that makes it work better.
Notice the stair-step pattern the saddles are in. The Fender style bridge (on the left) has more adjustment travel forward and back than the Gibson bridge’s saddles (on the right). The Gibson style bridge is installed at a slight angle (indicated by the arrows).
The ModGuitar Intonation Trick
To get a head-start on getting the intonation set, and to double check the intonation as it is currently set, use a ruler to precisely measure the length of string between the center of the 12th fret and the point where the string passes over the bridge saddle.
The 4th string tends to be the most balanced between gauge and tension, which results in the bridge saddle being intonated at exactly half the scale length.
For other scale lengths divide the total scale length by 2 and use this as your anchor point of the 4th string bridge saddle.
Check this measurement on the instrument, manufacturers occasionally alter the exact placement of frets and use slight variations on standard scale lengths. What we are measuring is the exact middle point of our scale length.
Intonation Trick, step-by-step
- First, using a precision ruler, measure and set the bridge saddle for the 4th (D) string. This will be our anchor point for positioning the other saddles.
- For 25.5″ scale length guitars set the 4th string bridge saddle at 12.75″/32.35cm.
- For 24.75″ scale length guitars set the 4th string bridge saddle at 12.375″/31.45cm.
- Once the 4th string bridge position is set, match the placement of the rest of the saddles to the above illustration. Each saddle will be offset roughly 1/16th of an inch, with the third unwound G string set back further.
This is a quick trick to get the bridge saddles close to the correct intonated position. Fine tuning will still be advisable for the best sound.
Fine Tuning Intonation Using An Electronic Tuner.
Fine tuning the intonation is done by comparing the twelfth fret note, with the open string note. We use the twelfth fret harmonic as a tuning reference because the harmonic is unaffected by fretting, and is the pitch of exactly the mid point of the guitar’s scale length.
- The open note and the twelfth fret harmonic are relative to each other. The twelfth fret harmonic is an octave above the open string pitch.
- The fretted notes are compensated by adjusting the bridge saddle so that the fretted notes match as closely as possible the open string pitch (or the 12th fret harmonic).
- Finger pressure, variance in scale length, fret size, and string gauge effect intonation.
Now that we’ve explained a little of the theory behind the method let’s take a look at how fine intonation adjustments are made.
If you’ve used our Intonation trick above, now you are ready for fine tuning the intonation.
For Fine Tuning Intonation:
- Play the 12th fret harmonic, adjust the tuning until this pitch reads true.
- Play the note at the 12th fret. Observe the tuning. Is the string exactly in tune, sharp, or flat?
- Adjust the string saddle to compensate for the difference between the 12th fret harmonic note, and the open string note in small increments.
- Re-tune the string using the 12th fret harmonic – then compare again to the note at the 12th fret, continue adjustments until the pith matches.
- This technique is then repeated for all the strings to complete the intonation fine tuning. Note that the saddles should not require more than 1/8″ or so forward or backward travel to fine tune the string from the ‘land marked’ measured position. Strings that are dented, grimy, or just very old may not play true and be very hard to make accurate intonation adjustments.
When setting the intonation on electric guitars using the bridge pick-up position tends to work better with electronic tuners.
If the string played at the 12th fret is observed to be flat compared to the 12th fret harmonic then we know that the string length is too long, and the string saddle needs to be adjusted forward.
If the 12th fret note is shown to be sharp relative to the 12th fret harmonic, that indicates that the string’s actual length is too short, so the string saddle is adjusted back.
The above illustration shows the 12th fret harmonic matching the 12 fret pitch. This string is correctly intonated.
Common Intonation Problems and Solutions
Question: A string can’t seem to get set correctly no matter how far I turn the intonation screws. It just won’t go sharp or flat the way it needs to. What is wrong? Answer: You can set the intonation so far off that it cannot be adjusted properly, though it will seem to be close. This is because the range of adjustment of the bridge saddles is very fine. A common problem is to have the saddle set too far forward or back to begin with. Solution: Use our ‘land marking’ trick (as described in this article) to get your saddles back within the proper range relative to your guitar’s scale length – then fine tune.
Question: Changing string gauge (from 9s to 10s, etc), do I need to adjust intonation?
Answer: A change of string gauge up or down one gauge may require fine intonation adjustment. A good rule of thumb is that the heavier the gauge of string the more the bridge saddle will need to be adjusted back.
Setting up the guitar is a process in several steps, each of them necessary to create a balanced state for optimal playability. By following the methods described in this article, you can effectively adjust and maintain the playability of guitars and bass instruments. With practice, these adjustments will become second nature, and are valuable skills in assessing new and used instruments for purchase or sale, as well as keeping your own instruments ready to play at their best.