Haven’t posted here for a while, every time I come around here I want to buy some thing I don’t really need 
Been watching u tube videos just because and on 12 string tips and came across this one mentioning to tune down one full step ,and they say to put a capo on the 2nd fret and carry on in normal tuning .For kicks and giggles I tried that and especially the D cord just doesn’t sound right ,so I checked rechecked to make sure it was in tune and it was but my12 just didn’t sound in tune .So I said, heck with this put it back up to regular tuning and it sounds way better, can’t help but ask - is it me or any one else come across this ?
Louis,
My short answer is yes, I agree, but it's not quite that simple. I find that using a capo on either a six string or a twelve string can change the pitch a little bit. If the frets are positioned correctly, that probably shouldn't be too noticeable, especially if all strings are off by about the same amount using a capo.
Specifically for a 12 string, in the example you gave about the D chord using the capo at 2d fret (even if the frets are correctly positioned), the chord might sound a teeny bit sharp to your ear if you are used to playing in normal tuning. In an open position, I will presume that the all the strings lie across the nut at the same height. So when a given pair of strings is fretted, the strings are stretched about the same amount against the fret. When using a capo, the octave string is stretched a tad less, since behind the capo it's smaller diameter is pressed up (not down) against the capo where its companion string is maybe pressed further down (maybe a tad sharper) to fit under the capo. Thus when you fret your D chord, the strings as a pair may not be exactly in tune with each other. This may depend on how good or bad your musical hearing is, or exactly where you place the capo behind the fret. Or I may be way off base (bass) with this.
Getting back to the D chord, what happens if you fret it without a capo? Given what you said, it must sound different, maybe more correct or at least more what you are used to. In addition, let's say the D chord is normally fretted. I will also assume that you are not wrapping your thumb around to fret the bass on F#. So if you strum your chord on 4 strings, you are still playing an open pair of D strings whether or not one of the fretted pairs is slightly off-pitch. So your D string is correct, your D on the second string might be a little off and maybe not much noticed due to the effect of the D string, and the fretted A and F# might also be a little off, but not that noticeable because they are not D notes. If you are playing the A string open along with the open D string, the overall effect should be lessened also. Once again I may be off base with this, but some experiments with a chromatic tuner might be enlightening. Bottom line is that I would agree that something isn't quite right to my ears using a capo.
At this point, some background so you can better understand where I'm coming from. First, I've owned and played a 12 string (not the same one) since the late sixties. As such, I still tune my Taylor 355 down a full step if only because that is what I'm used to, and now also because it's easier to play (fret) as I get older. And second, I never capo my 12 string anymore. And I only capo a six to play one or two songs, specifically "Here Comes the Sun" and "That'll Be the Day". (Capo on 7th fret and 5th fret respectively.) I just like open strings.
And a quick note about tuning a 12 string. I always had issues with tuning one and suspected for a long time that the extra tension played silly buggers while the tuning was actually in progress. When I got my first chromatic tuner, I found that if I started tuning on the bass strings, by the time I got to the treble strings, the bass strings were off pitch a bit. So it requires 2 passes to get it in tune. Back in the day, I remember seeing a folk singer, Michael Cooney, who is a guitar-centric multi-instrumentalist. He liked to play 12 string, and he would open tune and re-tune between songs. Always admired him for that talent. Anyway, he would talk to the audience while tuning, and once mentioned that 'tuning a 12 string was like tuning a centipede'. Still like that phrase.
Don
Oh yeah, I use Elixir '12 string light' strings on my 12.
For extra credit, what is the plural of capo (somehow capos looks bad to me)? Past tense? Participle?
