A lot of people like to number the strings of a twelve-string guitar from one (high E) to twelve, but it also works to number them as a six-string guitar, that is one through six, adding the designation “a” or “b” to each string. “A” means closer to the floor (as viewed when I am sitting with the guitar) and “b” is closer to the ceiling. The main reason for this is readily apparent when all the “a” strings are tuned just like those of a regular guitar in standard tuning. So if you ignore the “b” strings for the moment, you'll see that the two guitars compare like this:
| 12 String guitar | 6 String equivalent | ||
|---|---|---|---|
| 1a | E | 1 | E |
| 1b | |||
| 2a | B | 2 | B |
| 2b | |||
| 3a | G | 3 | G |
| 3b | |||
| 4a | D | 4 | D |
| 4b | |||
| 5a | A | 5 | A |
| 5b | |||
| 6a | E | 6 | E |
| 6b | |||
The first two sets of strings, the high E (1a and 1b) and the B strings (2a and 2b), are unison pairs. When struck, they sound the same note and this is the same note as on the first and second string of a normal guitar. So let's add them to our chart:
| 12 String guitar | 6 String equivalent | ||
|---|---|---|---|
| 1a | E | 1 | E |
| 1b | E | 1 | E |
| 2a | B | 2 | B |
| 2b | B | 2 | B |
| 3a | G | 3 | G |
| 3b | |||
| 4a | D | 4 | D |
| 4b | |||
| 5a | A | 5 | A |
| 5b | |||
| 6a | E | 6 | E |
| 6b | |||
And now the fun begins. The next four pairs of strings are tuned in octaves. This means that, although they are the same note in name - like the “do's” in “do, re, mi, fa, sol, la, ti, do” - they will be two different notes. String “3a,” we already know is the same as the G string on regular guitar. String “3b” is tuned to the G note that its an octave higher. The simplest way to think about it, if you're a linear person, is to think that it's the note at the twelfth fret of the G string. But it's just as easy to find these notes in first position. The G an octave higher than the open third string is at the third fret of the first string. Let's go on and find the rest of the notes:
| 12 String guitar | 6 String equivalent | ||
|---|---|---|---|
| 1a | E | 1 | E |
| 1b | E | 1 | E |
| 2a | B | 2 | B |
| 2b | B | 2 | B |
| 3a | G | 3 | G |
| 3b | G (octave higher) | same as third fret on 1st string | |
| 4a | D | 4 | D |
| 4b | D (octave higher) | same as the third fret on the 2nd string | |
| 5a | A | 5 | A |
| 5b | A (octave higher) | same as the second fret of the 3rd string | |
| 6a | E | 6 | E |
| 6b | E (octave higher) | same as the second fret of the 4th string | |
These six “b” strings give the twelve-string guitar its fullness of sound. Whenever you play a string, you are playing an additional note.
A 12 string guitar doesn't have to be tuned to standard tuning. There are many alternate tunings for twelve string guitar that sound great.
Tuning Down A Step
There is (was and probably will always be) discussion on whether or not one should keep his or her twelve string tuned down a step or so because of the extra tension on the neck caused by having twice as many strings as a regular guitar.
With most twelve strings made in the past twenty years or so, this isn't really much of a problem. You should be able to keep your twelve string tuned to standard without worries.
Still, if you're truly worried about it, check with your guitar's manufacturer. Or simply keep it slightly detuned when you know it won't be played for some time.
(By the way - there are people who like having their guitars (twelve string or regular) tuned down a step or so. There are no hard and fast rules for tuning, so feel free to do what you like best.)