Guitar Shop with Guitar ER
Now the Doc is in:
This month we are going to talk about the part of a set-up that is a very
important aspect if you want your axe to play in tune (not sharp or flat)
this is called:
INTONATION
We will start out by talking about scale length. A guitar's scale
length refers to the theoretical distance of the vibrating or "speaking
length" of the string. In reality the actual string length is slightly
longer to compensate for the fact that to vibrate properly the string
must sit above the fingerboard and frets. The distance from the underside
of the string to the top of the fret is called the string height or (action),
and the higher the string the more the string sharpens in pitch as it
is pushed down to the fretboard. So this brings us to the beginning that
we must accept the fact that fretted string instruments are accurate to
a point, but they are not perfect and never will be. With the guitars
fixed frets it is known as an even-tempered instrument. The fret scales
are compromised so that a guitar plays closely in tune in all keys but
never perfectly in any. Many players can hear the out-of -tune notes in
the even-tempered scale, and it does drive them crazy. I have many people
that come to my shop and want to know why their guitar sounds out of tune
when playing up the neck and this is the reason why.
So to make a guitar sound better at best, proper intonation is a compromise
among many different factors. Then at a certain point guitarists must
accept some degree of being out of tune or give up the guitar. Even though
on some of today's saddle systems you can get very close. Understanding
compensation factors that determine the need for intonation adjustment
is tricky, and experience is the best teacher for this. When a repairman
sets up a guitar he is doing a lot more than just setting the intonation
and turning a couple of screws, he is checking the action, the neck (and
in relation to the saddle) frets, nut, saddle and saddle shape, string
gauge and much more and all of that is before you set the intonation.
Now back to scale length, the scale length remains the fundamental dimension
around which all guitars are designed. Apart from determining the nut
and bridge positions, the scale length is the critical dimension, with
which the fret positions are calculated. This is why the 12th fret is
exactly half of the quoted theoretical scale length. Fender's primary
scale length is (25 1/2"). Gibson says their scale length is (24
3/4") even though it actually measures closer to 24.6 than 24.75.
The scale length along with the distance and angle of the string behind
the nut to the tuners, and the distance behind the bridge saddles to the
strings anchor point or tailpiece, affects the tension and perceived feel
of the strings when you are fretting and bending. In theory, with all
the factors identical and the same string gauge a 25 3/4" scale length
will have a tighter feel and a 24 3/4" scale length will have a slightly
slacker feel. Tonally the scale length plays a part. Many designers and
players feel a longer scale emphasizes string definition. So obviously
the smaller the scale length a guitar has the closer together the frets
will be, which may make a guitar with such a scale less desirable if you
play primarily in the upper areas of the neck and like big and wide frets.
Now when we discuss a string length or scale we are referring to the distance
from the nut to the center of the saddle, measured in a direct line down
the center of the fretboard and body. So a Strat scale length is 25 1/2,
but the bridge saddles may actually measure as much as 1/8" to 3/16"
more than that depending on string height, string gauge etc.. This addition
to the strings length at the saddle is known as compensation. A basic
understanding of compensation is needed before a guitars intonation can
be set. Compensation is the adjustment that changes the mathematical scale
of a guitar by altering the string length, almost always at the bridge
saddles. This procedure sets the intonation, and is important for proper
noting. Compensation has been accounted for at factory on most non-adjustable
saddles on acoustic guitars and is seldom a serious problem. Most acoustic
guitars with problems suffer from string sharpness and need to be compensated
by adding to the string length. Occasionally though flatness caused by
overcompensation is found on acoustics where the bridge has been installed
out of position. Although acoustic guitars are compensated at the factory,
do not expect them to play in perfect tune, intonation wise. This job
must be completed after the sale to suit the individual players needs,
and is governed by many factors.
When setting intonation, we try to get a string to play the same note
when fretted at the 12th fret as when played as an open string, only an
octave higher. In theory, the distance from the nut to the 12th fret is
the same as the 12th fret to the saddle, since the 12th fret is the octav
and the halfway point of the scale length. The string length must be increased
to offset the sharpness that results when the string is pressed down during
playing. The string however runs up and away at an angle from the nut
to the saddle. So when played or pressed down during playing the string
becomes stretched which causes it to go sharp. This is the basic and most
easily understood explanation of the need for compensation I can give
you. Add to it the other factors involved and the simple job of setting
your intonation can cause you to go crazy or at least think you are before
you finally take it to a good repair shop so we can go crazy (as if we
already aren't).
Just a few more words INTONATION
Setting the intonation guitars with an adjustable bridge (which some acoustics
have) is simple. All that is needed is a small Phillips or flat head screwdriver
or an Allen wrench. If a string sounds sharp at the 12th fret move the
saddle back away from the nut to increase the string length if
it is flat move the saddle forward toward the nut. I find it easy to use
a electric tuner I first tune up my guitar then check intonation by lightly
fretting at the 12th fret if you have to change any of the saddles return
(all the strings) before moving on to the next saddle.
BASIC RULE: If the string note is sharp moving the saddle back
increases the strings length. If the string note is flat, moving the saddle
forward shortens the string length.
One final note, acoustic guitars tend to shrink over the years, add to
this the effects of string pressure pulling the nut towards the saddle
and you lose a bit which can be measured in thousands of an inch. Now
the factory installed your saddle at a slant, which usually is enough
for compensation to please most players. The saddle slants approx. 1/8"
from high E to Low E on a 3" saddle. If the intonation still does
not please you ask your repairman about a compensated saddle (a saddle
blank which is wider, a wider slot is needed and then filed to staggered
peaks under the different strings). This job takes time so expect to PAY
for it.
Finally all the above factors when setting your guitars intonation by
compensation do work. Their interrelation is complete and the slightest
change in any factor (especially string height) can throw the whole deal
out of adjustment. Be sure that the important adjustments described earlier
have been made before setting intonation.
Thanks Again
Greg/Doc
P.S. Keep your fingers dancin and your toes tappin
Until next time: Keep the toes tappin and the fingers dancin.
Doc/Greg
The Guitar ER
515-707-4878
www.greg@theguitarer.com
e-mail: Greg@theguitarer.com
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