B♭ Dominant 9th
9
0 - 4 - 7 - 10 - 14Dom7 + major 9th
About B♭ Dominant 9th
B♭9 is the funk grip at the first fret, and it is where that shape is least comfortable. The same fingering that falls easily at the fifth or eighth has to work here against the stiffest strings on the neck — which is why most players take the chord up an octave and leave the low register to the bass.
The notes
B♭, D, F, A♭, C. The A♭ is the flat seventh, the C the ninth, and the F is normally dropped. Nothing here is available open, so the chord sounds identical wherever it is played.
Against plain B♭7 the ninth adds warmth without changing direction. Both resolve toward E♭; the ninth simply makes the journey sound arranged rather than raw.
The shape
Root on the A string at the first fret, or on the low E at the sixth. The second is easier in every respect and is what recordings actually use.
Because no string rings freely, the character comes entirely from the right hand. Damped it is rhythm; sustained it is harmony, and funk arrangements use both within a single bar.
The first-fret position does have one use: when the chord must be the lowest thing in the arrangement, nothing higher will substitute. Outside that case the sixth fret wins on every count.
Where it shows up
As the V of E♭ major and as the IV in a blues in F — both horn keys, which is where this chord belongs. Soul and funk inherited those keys from the sections that recorded them.
It also appears at the end of a jazz blues in B♭, where the final chord takes a ninth rather than a plain seventh to soften the stop.