An 8 Bar blues is the lesser-known little brother to a classic 12 bar blues, but just as important to any blues fan. The general chords used are basically the same as in the 12 bar blues (although we do alter that in this lesson), but the structure is different. As you may have guessed, you are playing 8 bars in your blues loop, rather than 12. Here is the structure (without the diminished chord) in the key of Bb:
Bb7 /// Bb7 /// Eb7 /// Eb7 /// Bb7 /// F7 / Eb7 / Bb7 / Eb7 / Bb7 / F7
Those last two bars are more typically known as the 'turnaround' section, and the 4th bar can be replaced with a diminished 7th chord (as in our track). Also, as always, you can interchange 7th chords with 9th chords and even 13th chords... Any extension you like to use.
Below are the full set of chords that we are using in the track, including that lovely diminished 7th chord. To get a more detailed view of how they are used, be sure to check out the guitar tab underneath as well.