Bb Dominant Sharp 9th

Fretboard

On the fretboard, Db represents C#.

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About

The B♭7♯9 (B♭–D–F–A♭–C♯) raises the ninth a half step, creating a striking enharmonic clash: the C♯ (sounding like a ♭3) sits against the major 3rd in the same chord. This makes the chord simultaneously major and minor in feeling — the D is in the bass of the voicing while the ♯9 rings on top like a minor color. The result is a harmonically ambiguous but intensely bluesy sound, which is why it is central to rock and blues-rock harmony — the "Hendrix chord". The 3rd and ♭7 are essential; the ♯9 is the defining alteration. Compared to B♭7♭9, 7♯9 feels more bluesy than classically tense.