Bb7sus4 keeps the flat 7th of , but puts where the major 3rd would be: Bb, Eb, F and Ab.
Let the 4th fall a half step and appears. Keep it held for a suspended dominant sound that does not need to resolve.
The 4th falls one fret to the major 3rd while the flat 7th stays put.
Also written Bb7sus or Bb dominant 7 sus 4.
Drop the third voice from the top an octave instead. The wider gap skips a string, so the muted string is part of the shape.
That result, 3–R–5–7, is the shape usually meant by drop 3. Named by its bass note, as the inversions are here, it is the 1st inversion.
More familiar jazz shapes are drop 3 than drop 2.
Bb7sus4 is a dominant with a fourth where the third would be. In older styles the fourth falls a half step and the chord becomes Bb7; in modern jazz it often stays, and the sus chord resolves to Ebmaj7 as it is.
Listen for: The fourth falls a half step to the third, which holds over the barline as the major seventh of the I.
Put Fm7 over the root of the V and you have Bb7sus4: a ii–V in a single chord. That’s why one sus chord can stand in for a bar of ii and a bar of V.
Listen for: The upper notes don’t change from the ii to the sus chord. Only the bass moves, to the root of the V.
A tune can be built from nothing but sus chords, with the fourth never resolving.
Heard in “Maiden Voyage”
In which keys. Every note of Bb7sus4 belongs to C minor, C# major, Eb major, Eb minor, F minor, F# major, Ab major and Bb minor.
Contains Bb7sus4 and adds minor third.
Contains Bb7sus4 and adds minor third and sharp eleventh.
Contains Bb7sus4 and adds second, major third and thirteenth.
Contains Bb7sus4 and adds second, minor third and flat thirteenth.
Contains Bb7sus4 and adds second, minor third and thirteenth.
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.