Bb7 is Bb, D, F and Ab — with the flat seventh added on top.
It sounds restless and pointed at something. The V of a key, and the whole vocabulary of the blues, where even the tonic is one of these.
Dominant — it points a fifth down.
Play it instead of a maj7 or a m7 on the same root, you are comping or blowing over it and want more to play on.
Also written Bbdom7 or Bb dominant 7.
Bb7 is the V of E♭ major. Its third and seventh are a tritone apart, the most unstable interval there is, and each resolves by a half step into the I. The dominant a tritone away shares those two notes, so it resolves the same way.
Listen for: The dominant’s seventh falls a half step to the third of the I. Under the tritone substitute it is the same note.
In a blues, Bb7 is the home chord rather than a V: it moves to Eb7 and back without resolving. Its third and seventh each slide down a half step to become the seventh and third of Eb7, so the shape stays the same, one fret lower.
Listen for: Both notes above the bass drop one fret into the IV and come back: the third becomes the IV’s seventh.
In the turnaround in D♭ major, jazz players usually replace the vi chord with Bb7, and usually alter it.
Replace the VI7, II7 and V7 of a turnaround with their tritone substitutes and you get Amaj7, C7, F7, Bb7. Bb7 is the last, a half step above the I.
In which keys. Every note of Bb7 belongs to C minor and Eb major.
Every note of Bb7 is in Bb mixolydian, Bb lydian dominant and Bb half-whole diminished.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where Bb7 sits in it. Every scale.
Change one note of Bb7 and you have (drop the flat seventh), (the flat seventh becomes the major seventh), (the major third becomes the minor third), (the flat seventh becomes the ninth), (the flat seventh becomes the sixth) or (the major third becomes the fourth).
Bb7 is a dominant chord — root, major third, fifth, minor seventh. Dominant seventh chords on every root.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.