B Dominant 9th
9
0 - 4 - 7 - 10 - 14Dom7 + major 9th
About B Dominant 9th
B9 is the movable ninth grip at the seventh fret — B, D♯, F♯, A, C♯ — and it is where that shape finally becomes comfortable. The frets are close, the strings are slack enough to bend, and the chord that is nearly unplayable as a first-position barre becomes routine.
The notes
B, D♯, F♯, A, C♯. The A is the flat seventh, the C♯ the ninth; the F♯ is normally dropped. Five sharps in the key signature and none of them a problem, because nothing here is open.
Against plain B7 the ninth softens the chord without weakening its pull. In the key of E both resolve the same way, and the choice between them is a matter of idiom.
The shape
Root on the A string at the second fret, or on the low E at the seventh. The second position is the one players use, for the same reason B major is played there rather than at the second fret.
Damped between strums the chord becomes a rhythm part; sustained it becomes harmony. Funk uses the first, soul ballads the second, and the grip is identical.
Where it shows up
As the V of E major in soul and gospel, and as the turnaround of a blues in E. In the second role it replaces B7 whenever the arrangement wants polish.
It also appears in jazz as the dominant of a ii–V–I in E — a key guitarists reach more often than horn players, which makes this one of the few ninth chords that belongs to the instrument.
The seventh-fret position is also where the chord stops being an exercise. Played at the second fret it fights the hand; seven frets up the same notes fall out easily, and that single fact decides where most players use it.