The Open Perfect Fourths

Let's look at the tuning between the open strings A and D. We'll use this as an example of open perfect fourth tuning in general. Probably the most popular way of tuning the open perfect fourth string pairs by beats, is by using the harmonics over the 5th and 7th frets, (or 12th and 7th frets - see the end of this article) and tuning until beating disappears.

As we talk about in the book, this will result in a very wide open major third G - B, and numerous other tuning problems on the frets. This way of tuning isn't consistent with equal temperament. Guitarists who are more familiar with the principle of equal temperament leave these open string pairs beating wide, with a slow beat. In general, the usual technique is to pluck the harmonics over the 5th and 7th frets (or 12th and 7th frets), and tune to leave the beat present.

In the case of the A and D strings the harmonic plucking positions will be over the 5th fret of the A-string and the 7th fret of the D-string.

There is no reason why this cannot be achieved just as well simply by plucking the open string pair, without the need to pluck the harmonics. The harmonics are present in the sound of the open strings in any case. It's just a question of learning to hear them, which our ear and brain are very well equipped to do. All it requires is little practice, and a good deal less then it requires to learn to play the guitar well.

Here's the harmonics being plucked in the usual way, with the beating left in the tuning. The beat rate here is a little fast for this string pair, but that makes easier to hear in these short clips:
Now if you listen to the open strings, that beating harmonic is present in the sound of the strings, anyway. Remember to keep your ear focussed at the same musical pitch you were just listening to:
Here are the open strings again, this time with the rest of the sound suppressed a little, so that you can hear the harmonic in context, a little more easily:
What you are listening for is the same sound as in the first clip of the harmonics, after the initial plucks.

In tuning any open string perfect fourth, the pitch you are listening for is 2 octaves above the pitch of the lowest pitch open string. So in this case, it's an A.

Sometimes guitarists pluck the harmonics over the 12th fret of the lower string, and the 7th fret of the higher string, in an open string perfect fourth pair, as an alternative method.

That's because when you pluck over any fret position associated with a harmonic you'll also excite all the harmonics higher in pitch than that one. So plucking over the 12th fret also excites the harmonic that you would get by plucking over the 5th fret.

However you do it, the pitch of the main beating that you should be listening to, is always at the meeting of harmonics two octave above the lowest pitch open string.

There is more beating that happens another octave above this, but it's weaker, and around twice as fast. In general, you should ignore this.

We often want to tune open-string perfect fourths, for rough tuning, and when we are using them as the tuning intervals for getting checking intervals right.

Remember that tuning by open strings alone, even when tuning in theoretically correct beat rates, still will not generally address all the issues that need to be addressed in tuning the guitar.

Learning the method given in the book, will address the three main issues affecting guitar tuning - temperament, stopping sharp, and false beating - rather than merely attempting to apply the theory of temperament to the guitar without taking the other factors into account.

Equal temperament E Major:

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