A diminished 7th chord ("dim7" or "°7") is known for its tense sound. They sound great as passing chords, creating tension. E.G. C Maj7 - C#Dim7 - Dm7 - EbDim7 - Em7 To construct a diminished 7th chord, you start with a root note and stack minor thirds on top of it. Begin with the root note, a minor third, a diminished fifth, and a diminished seventh. A diminished 7th is a double flattened 7th (7bb) which is enharmonically equal to a major 6th Since the interval between each note is a minor thir