Here's how you play a half-diminished chord, also known as a minor 7th chord with a flat 5th. The half-diminished chord is a diminished triad with a regular minor 7th. If we use "G" as our example, we play our "G" diminished triad which is "G" with a flat 3rd, B-Flat. And a flat 5th, D-Flat. Now we're gonna play our "F" which is our minor 7th. And then "G" again. This is the "G" half-diminished chord in two octaves. And that's how you play a half-diminished chord or a minor 7th chord with a flat 5th on the bass guitar.