Bb Minor 9th (Bbm9)
Also written as A# Minor 9th (A# and Bb are the same key).
Notes in Bb Minor 9th
Inversions
Same notes as Bb Minor 9th, with a different chord tone as the lowest note. Useful for smoother movement between chords instead of jumping around the keyboard.
Root position
A# in the bass
1st inversion
C# in the bass (Bbm9/C#)
2nd inversion
E# in the bass (Bbm9/E#)
3rd inversion
G# in the bass (Bbm9/G#)
4th inversion
B# in the bass (Bbm9/B#)
Open voicings
A close-position chord like Bb Minor 9th can sound cluttered in the middle of the keyboard. Jazz players open it up by dropping one note down an octave, spreading the same notes wider without changing the chord.
Drop 2
G# on the bottom
Drop 3
E# on the bottom
Bb Minor 9th consists of A#, C#, E#, G# and B#, played at the same time.
A minor seventh chord with a ninth added softens the mood even further into something smooth and atmospheric. Jazz, R&B and lo-fi styles all reach for it whenever a minor chord needs to feel rich rather than sparse.