Intonation on the Classical Guitar
Intonation is a very complex subject and I am only going to give a very brief intoduction here to one or two practical issues that affect the beginner/internmediate player.
Because the guitar is fretted, the spacing of the frets by the builder determines the pitch at which each string will sound. So you might ask what else is there to do?
Well, the fact is that many guitars - even quite good ones - do not play "in tune" on every fret on every string. You can test this for yourself: using a good quality digital tuning meter, tune the open strings as accurately as you can in the normal way.
TEST 1: go to the 12th fret on the 1st string and play a harmonic there - the meter should show exacly the same as it did on the open tuning (only an octaver higher). Now stop the string behind the 12th fret and play again. You must be as accurate as you can in stopping the string - finger right behind the fret, no pushing or pulling the string. What does the meter say - does it still give the same reading - neither a cent too high or too low? Repeat the test on each of the other strings. It is not at all uncommon to find that the note sounding when stopped at the 12th fret is not exactly 1 octave above the open note. It may be sharp or flat - the most common fault is sharp I have found.
TEST 2: tune the open strings as above and stop each string in tune behind the 7th fret. Are you getting an "exact" B? Repeat the test on each string - if you want you can repeat on each of the frets on each of the strings - and see if you are getting "exact" notes.
Quite often the tests above reveal a number of places where the guitar's intonation is less than perfect. Most often the G string is the most troublesome, and most often it goes sharp from the 7th fret upwards. There are thousands of exceptions and this is not meant to apply to all guitars.
What causes the problem? As implied at the start, the problem is a complex one. However the following can all contribute to the problem -
- Old strings
- A poor batch of strings
- Strings other than those for which the maker designed the guitar
- Very high tension strings which are thick and stiff and seem not to respond as they should when fretted
- A guitar which has had the saddle raised or lowered to change the action
What can you do about it? Well, if you only perceive the problem when using a meter and don't notice it when playing then best just to live with things as they are. If your ears are troubled by intonation issues and the tests with the meter have only served to confirm what you felt anyway, then the best and cheapest first steps are to experiment with different strings. Put on new strings. Put on strings by different makers. Try alternative tensions. If the G string is the only problem then try using a wound G rather than the typical unwound G.
Some players - having settled the string issue - then adapt their approach to tuning to "average out" the intonation problem. Instead of tuning the open string, try tuining each string to a meter at its 5th fret. Repeat the tests above and see if the problem has been reduced. You may well find that if it has, a slight problem has been introduced on some open strings, but it may be that the new compromise is an improvement.
If neither of the above does enough to reduce the problem, then you need to delve into the subject more deeply and/or consult a very good luthier. It is possible to modify nuts and saddles and this can reduce the problem significantly.
If you want some background to the issue of intonation look up "equal temperament" and intonation in Google. There are many articles to be found by guitar specialists who have gone to great lengths - much further than touched on here - to address this issue. An introductory article of moderate complexity on the subject has been written by the German guitar maker Sebastian Stemzel.
See also this article on the NOWO scale by Wolf & Lehaman [use an on-line translation service if you do not read German].
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