Bb Minor 9b5 (Bbm9b5)
Also written as A# Minor 9b5 (A# and Bb are the same key).
Notes in Bb Minor 9b5
Inversions
Same notes as Bb Minor 9b5, 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 (Bbm9b5/C#)
2nd inversion
E in the bass (Bbm9b5/E)
3rd inversion
G# in the bass (Bbm9b5/G#)
4th inversion
B# in the bass (Bbm9b5/B#)
Open voicings
A close-position chord like Bb Minor 9b5 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 9b5 is built from A#, C#, E, G# and B#.
A half diminished seventh with a ninth added. It softens the searching quality of m7b5 into something smoother and more modern, and it works well as the ii chord in a minor key ii-V-i when you want a fuller sound than the plain seventh.