If I take a standard A minor chord as a barre chord on the 5th fret of a guitar and play it but move my pinky from the root note A on the 7th fret and move it to the 8th fret, I get a dominant chord sounding chord. Essentially it is an Aminor with a min9th... is this called a minor 9th chord? and why does it sound like a dominant chord?
I would call it Am b9 (A minor flat nine), it sounds like a dominant, because it has the notes of a C dominant chord, something like "C7 add 6 omit 5 / A" and it resolves to an F chord. If you leave out the bottom A note, it's a nice dominant for F.
Edit. At least in some kind of theoretical thinking, a "b9" chord tension means that "there is a ninth", and because there is a ninth, there should also be a seventh, because chords are - in theory - built from stacks of thirds. To explicitly state that one of the notes in the stack are missing, words "add" and "omit" can be used. For example "C add 9" would mean that there's a root, third and fifth, but no seventh. Or "C9 omit 3" would mean that there's the root, fifth, (flat) seventh and ninth, but no third. In practice however, some chord notes are routinely omitted. In 11 chords the third is omitted so systematically that it's even "officially" stated in some theory material, and the chord is in practice used as a jazzier sus4 chord. In 13 chords, the 5h, 9th and 11th might be left out either because they add too much mud or because e.g. the guitar simply doesn't have enough strings and guitarists don't have enough fingers to play theoretical 13 chords.
For "b9" and "#9" ... is there a 7th in the chord? In the Hendrix chord E7#9, it is explicitly stated that there is a 7th in addition to a 9th. So if you leave out the 7, "E#9", then wouldn't it be reasonable to assume that there is no seventh?
From your description, the chord is based on the A minor triad (A, C, E), with an added Bb, the minor ninth. The correct label for the chord would be Am (add b9). It is probably better to call it "add b9", instead of simply "b9", since that may be taken to imply the presence of a flat seventh, which you don't have. That said, since this chord is not used as often, you'll find that some people notate it one way, and others the other way.
Why does it sound like a dominant chord? Most importantly, there is a tritone between E and Bb. The tritone is the characteristic (tense) interval of dominant chords (at least if you use the word "dominant" mostly in a jazz sense).
As in one of the other answers, you should compare your chord with C7. C7 contains C, E, G, and Bb. Your chord contains C, E, A, and Bb. So the fifth of C7 (a G) has been swapped for an A. Overall, this is not that big a difference, since the two chords have roughly the same intervals:
Am (add b9) has:
- 1 semitone interval (A - Bb)
- 1 whole tone interval (Bb - C)
- 1 minor third interval (A - C)
- 1 major third interval (C - E)
- 1 tritone (E - Bb)
- 1 fourth/fifth (A - E)
This pattern is also referred to as the all-interval tetrachord. "All-interval" because it contains each interval type exactly once, "tetrachord" because its a chord with four (tetra-) notes.
C7 has the following intervals:
- 1 whole tone interval (Bb - C)
- 2 minor thirds (E - G and G - Bb)
- 1 major third (C - E)
- 1 Fourth/fifth C - G)
- 1 Tritone (E - Bb)
So these chords have a lot in common, which is why they sound alike. That said, using different root notes and inversions can make a big difference to the ear. Using A minor and then sneaking in the minor ninth as a color note is a more subtle way to evoke a tritone dominant than simply going for C7. Good luck with your discovery process!
If I'm understanding correctly, the notes, from 5th string up, are E B♭ C E A, making a kind of dominant 13th chord. C13. Oft-times, a 13th chord needs only the m7 (B♭) and the 13th (A, aka 6) to be a 13th chord. 9th and 11th are routinely omitted. Also the 5 (G) is often left out.
I feel it's a red herring to say there's a m9 in the chord - unless you still want it to be A based. But then the dominant sound won't emanate from it having root A. And, that apart, Am9 is a completely different animal.
I think your question is really about jazz chord nomenclature.
"Minor nine chord" in jazz would be a minor triad with a major ninth, ex.
Am9 called "A minor nine."
"Minor flat nine chord" in jazz would be a minor triad with a minor ninth, ex.
Em♭9 called "E minor flat nine."
In Roman numeral, functional analysis the wording can be different.
C: V9 tones
G B D F A and
Cm: V9 tones
G B D F A♭ can be called "dominant ninth chords." The particulars of the major or minor ninth will be understood in the context of the key. Likewise if you have
C: vi9 or
C: iii9 they both might be called simply "ninth chords" or "submediant ninth" or "mediant ninth" or "A minor ninth" or "E minor ninth." Various wordings like that might be used. Again, the ninth would be understood in the context of the key.
Aminor with a min9th... and why does it sound like a dominant chord?
A dominant should be a dominant to something. I'm not sure how your hearing it as a dominant. It could go two ways...
C# then it's a dominant to
Dm. If you move the
A to some tone of a
C dominant seventh chord, it's a dominant to
F. Without knowing where you would move the dominant sound you hear the generic explanation is it differs from some potential dominants by only one tone.