How to adjust your guitar
intonation
In this article you will find instructions and tips about the intonation setting of electric guitars (on acoustic guitars it is factory compensated). This is part of the general setup of the guitar, that involves topics covered on the Soundsation blog, as neck truss-rod and action adjustments.
Before continuing with intonation
setup you should have:
All that verified, we can talk
about self-adjusting the intonation by acting on bridge saddles.
Foreword
Many people could ask why it is necessary to adjust
their guitar intonation. Isn't it already in tune when the strings have been
tuned? Actually, guitar (as bass) is not a perfect instrument from this point
of view, and will never be. In fact, it reveals an intonation mistake
due to fret positions, fixed and equal for all strings though they have
different gauge, tension and manufacture. This mistake is spread through
the fretboard so as to optimize a correct intonation feeling, approximating the
so called equal temperament, without being perfectly in tune in all
positions.
We are just tuning plucked
open strings; afterwards it is necessary to compensate the differing
lengths of six or more strings when we press them on different frets. In this
matter are involved: fret installation and finishing, action, quality of strings, gauge, pull and build, all topics you can find on our blog.
A hint about scales
Let's say some words about an
instrument scale (not the neck or fretboard scale, as
someone often says): it is the distance from the nut (or zero-fret) to the 12th
fret multiplied by 2. In theory this calculation should give us the precise
length of the string from the nut to the bridge saddle centre.
Actually this is not true. In fact, given the variable position of the bridge
and its saddles, each tuned string has its own length on that
instrument, the one that allows a production of notes as accurate as possible
on any fret. You can take as a reference the B or second string, ensuring that
the scale is nominally exact for it and gradually adapted to the other strings.
For example this is useful to find the right position of a jazz guitar moveable
bridge.
The most popular scales
are:
Let's cite some more examples
among diverse scales:
Obviously the number of frets has
nothing to do with an instrument scale, but the longer the scale, the more the
same number of frets are spaced.
In recent years, manufacturers use to indicate the scale length with mixed inch and decimal values, thus adding further confusion between millimetre and inch sizes. For example, the above mentioned Gretsch Country Gentleman scale is now officially specified with 24.6”.
A little geometry
Let's imagine a scalene
right-angle triangle, the hypotenuse of which is represented by a string
stretched from nut to bridge (instrument mathematical scale), the
shorter cathetus by the bridge height and the longer one by the string pressed
on the fretboard (instrument actual scale). It's clear that the
hypotenuse and the longer cathetus don't have the very same length, with all
the consequences on the string segments determined by any single fret, for
instance when you are playing open and fretted note mixed chords. When you are
adjusting a guitar intonation all you are doing is trying to compensate for
the gap between mathematical scale and actual scale, that is between the
hypotenuse-string and the cathetus-string. I like to use the definition of
authors Franz Jahnel and Dan Erlewine (*) calling them respectively true
scale and singing scale.Fixed bridge guitars
Intonation compensation it is not necessary on electric instruments that are equipped with a fixed wrap-around bridge without individual saddles, though it sometimes can show a set compensation. Modern versions often feature two Allen screws for horizontal shift.
In the same way, intonation
setting it is not necessary on most acoustic instruments, both folk and classical having a bone or plastic fixed saddle. They are almost
always very well built instruments, intonation is ensured by a perfect
bridge/saddle placement and possible fixed compensations for one or more
strings, usually the B (second) string.
Anyway, it should be specified
that fixed bridge and saddle drop or raising – both on electric and
acoustic guitars – can slightly affect factory set intonation. Replacement
of strings with others of different gauge and tension can also cause
intonation differences.
In any case intonation adjusting
of an acoustic guitar is possible, but it has to be entrusted to the
craftsmanship of a luthier.
You can turn to a luthier for
fixed bridge electrics too or think about replacing the bridge with an individually adjustable saddle replacement.
Let's go ahead!
It's time to go ahead with
your guitar intonation. Once the guitar has been tuned, check by means of
an electronic chromatic tuner if the notes you get pressing the strings on the 12th fret are
equivalent to the octaves of the open strings.
For example, if you are tuning
the B string, you should get an octave up B at the 12th fret, well tuned,
neither sharp nor flat.
In case of a 12th
fretted flat or sharp note, you have to act with a screwdriver (sometimes
with an Allen wrench) on the screw that makes the B string saddle move:
When you shorten and lengthen the
string, general tuning will change, so you'll have to patiently retune any time
you evaluate the octaves.
This applies both to tune-o-matic style bridges and vibrato (or vibrato (or tremolo) bridges) bridges.
Do not be tempted to make this
operation with the guitar laying horizontally on a work bench. You must compensate keeping the guitar as if you were
playing. Gravity has been performing its force for 13,8 billion years, on
guitar strings too.
Special cases
A few tips
In order to taste the effect of
your work, play some chords with fretted notes and open strings around the 12th
fret: if the guitar resonance is good, the more the chord is full, pleasing, euphonic,
the more the intonation is accurate.
Keep in mind that intonation
is steadier and easier to compensate on guitars with:
On the other hand intonation
is more difficult to compensate on guitars with:
It's easy to understand the
reason why '50s, '40s and previous decades guitar manufacturers paid
little attention to intonation adjustment possibilities: today's popular light string sets, such as .010-.046 and .009-.042, were yet to come.
Intonation improvement efforts
I'd like to mention few
interesting solutions – though partially successful: the Buzz Feiten Tuning
System and the Earvana Compensated Tuning System, that fundamentally
are nut modifications aimed at improving the instrument general intonation, but
have to be considered while tuning.
Finally, in order to make your lives easier, do not modify your guitar setup too frequently. Once you have found the right strings for you, try to change them regularly using the same kind and brand: a quality new set is always the first step towards a better intonation!
Fabrizio Dadò
(*) F.Jahnel, Manual of Guitar Technology: The History and Technology of Plucked String Instruments - Bold Strummer Ltd, 1981
D.Erlewine, Guitar Player Repair Guide - Miller Freeman Books, 1990.