I teach a three hour workshop called Music Theory for Bluegrass which is most of the theory a person needs to know for bluegrass and nothing more. When I studied theory in college, I found most of what I learned didn't apply to the bluegrass world since it was based on classical music. It was a very inefficient wayfor me to learn what I wanted to know, so I ended up taking private lessons on music theory. So when I put this class together, I was careful to only include things that applied directly to bluegrass. Here is handouts from the class.
Music Theory Handout
Here is an interesting look at the physics of pitch and western scales.
Physics of Pitch