Watch the Fifths online guitar lesson by Robben Ford from Chord Revolution: Foundations
Let's talk about fifths now. We talked about thirds a little bit and some of their applications. It sounds lovely just to play the thirds in the major scale, up and down the major scale. Fifths have a really different sound, and therefore, a different application. If you play fifths in the major scale, harmonized in the major scale, it doesn't have the same musicality that you find with the thirds. That's like a little song. When you play fifths it has slightly empty, hollow sound to it. It's used in Gregorian chants. It was the first harmony that ever existed, beyond just the melody. Very different sound to it than you'll find with any of the other harmonizations. It is very popular in heavy metal music.
Power chords are called power chords because that's what they got. Generally they'll be used in a pentatonic scale motion. You don't really hear them like that. It's pentatonic. People use power chords basically in the shape of a pentatonic scale. That's where they really apply very well. I use them very rarely, and it's always for impact. Therefore, not a lot of dynamic range necessarily within the fifth spectrum. Little less musical, a little bit more for impact, for power, for punchiness. It's an effect and works very well for a lot of people.