About the Bdim chord
To play B diminished, use the first shape above. Place your index finger on the 1st fret of the E string, your middle finger on the 2nd fret of the C string, your ring finger on the 2nd fret of the A string, and your pinky finger on the 4th fret of the G string. Strum all four strings and check that each one rings cleanly.
Root
B
Quality
Diminished
Notes
B · D · F
How the Bdim chord works
B
Root(1)
The home note. It gives the chord its name.
D
Minor third(♭3)
The defining minor interval above the root.
F
Diminished fifth(♭5)
A lowered fifth that adds harmonic tension.