Bb Minor 7th (Bbm7)
Also written as A# Minor 7th (A# and Bb are the same key).
Notes in Bb Minor 7th
Inversions
Same notes as Bb Minor 7th, 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 (Bbm7/C#)
2nd inversion
E# in the bass (Bbm7/E#)
3rd inversion
G# in the bass (Bbm7/G#)
Open voicings
A close-position chord like Bb Minor 7th 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
E# on the bottom
Drop 3
C# on the bottom
Bb Minor 7th consists of A#, C#, E# and G#, played at the same time.
Add a minor seventh to a minor triad and the chord's sharper edges soften. It reads as less dramatic than a plain minor chord but more colorful, and it's the backbone of the jazz ii chord in a huge number of ii-V-I progressions, along with most of soul and funk's chord vocabulary.