Extended Chords

Because they're above the octave. It's that simple
So if you bring a 2nd an octave up, you get 2nd+7 = 9th.

 

Yes.
You will notice that they don't quite sound the same, especially in arpeggios. Using a 9th rather than a 2nd brings a lot of room into a chord.

 

some people get very heated about wheter the same chord should be called sharp 4 or sharp 11. I've been told by different workshop teachers than each is the only possible accurate description!

 

I dunno.. I always favored #11.

 

That's only in an E-gads or a D-molished.

 

I'm pretty sure the C-section has a #7 in it.

 

that makes sense, I'd never thought of it that way...

 

My wife had two C-sections. One girl, one boy.

 

I was under the impression if a chord is called extended, it has to contain a seventh.

 

The real reason why they are called 9th's 11th's and 13th's isn't because they're voiced higher. They can be voiced below the octave and still be called 9th's 11th's and 13th's. The reason why they aren't called 2nd's and whatever is because of the principles of building chords. Chords are built by stacking 3rds. You start with the 1, stack a third on that and its 1 3. Stack another 3rd and you have a major triad. Stack another 3rd and you have 1 3 5 7 - some kind of seventh chord. You keep on stacking the thirds and you get the extensions.

 

While theoretically this does match up, IME 9/11/13 chords are put their specifically to have more colour on the top -- composer's intent and such. If you give a pianist a sheet with a sus2 chord in one place and a 9 chord in another, you're going to get a vastly different sound, because that piano player is (like any reasoning person) going to know the clear difference and voice them appropriately.

 

Your two examples will sound different not because of voicing but because those are two different chords. In a Csus2 the 3rd is replaced by the 2nd degree making it neither major or minor. A C9 is major in quality.

 

...touché!