B 13th Chord

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Formula R – 3 – 5 – 13 – ♭7

Summary

B 13th is built from the notes B, E♭, G♭, A♭, A. The interval from B to E♭ is a major 3rd (4 semitones), from B to G♭ is a perfect 5th (7 semitones), from B to A♭ is a major 6th (9 semitones), from B to A is a minor 7th (10 semitones). This chord contains 3 flatted notes.

The maj9♯11 is a major 9th with a raised 11th that gives it an ethereal, floating, wide-open sound. It's one of the most beautiful chords in modern harmony — dreamy and expansive.

Theory

Built from R, 3, 5, 7, 9, ♯11, this chord captures the complete Lydian mode sound. The ♯11 avoids the clash that a natural 11th would create with the major 3rd, instead producing a bright, expansive quality. It naturally appears as the 4th chord when you use the Lydian mode, which is why it sounds both familiar and magical.

On the guitar

Drop the 5th and voice it as root, 3rd, 7th, 9th, ♯11. The ♯11 sits 6 frets above the root. Some of the most beautiful voicings use open strings to let the ♯11 ring against the major 7th. Works wonderfully on strings 1-4 with the root on the 5th or 6th string.

Advanced

Use maj9♯11 as the 4th chord in a major key for an instantly beautiful sound. Try Cmaj9 → Fmaj9♯11 for one of the most gorgeous two-chord progressions in modern harmony. This chord appears frequently in Pat Metheny, Steely Dan, and modern jazz guitar.

Piano