Guitar chords in the key of A# or Bb:
Chord Bb7 (4th fret) notes: Bb, D, F and Ab. You must leave out the 6th and 5th strings.
Bb(A#) dominant 7th chord's alternative names: Bbdom7, (Bb septim).
1(A#/Bb), 3(D), 5(F), b7(G#/Ab).