Here are some thoughts from Al Carruth in a post on the UMGF:
http://theunofficialmartinguitarforum.y ... angle.html
As John says, the height of the strings off the top seems to be much more of a factor in the sound than the break angle. That's what I'm seeing an an experiment I've been working on for some time. Basically, the break angle seems to make a small difference in the static stress on the top, which, in turn, causes it to deform in a slightly different way. This can effect the way it vibrates, but it's not likly to be a huge change.
Altering the height of the strings off the top changes the balance betwqween the two main driving signals; the 'transverse' force signal that pushes the whole top in and out like a loudspeaker cone, and the 'tension change' signal that tries to tip the bridge forward twice for every cycle of the string's vibration. Generally speaking, it's the transverse signal that makes most of the sound, since it's stronger, more effective at driving the top, and more efficient at producing sound for a given strength of input. However, the tension change signal does produce some sound, particularly at higher frequencies. So raising the string height off the top will alter the timbre directly that way, even if it does not produce more power.
Also, you have to remember that raising the string height off the top puts a lot more static stress on it, and the resulting distortion can make the top harder to drive. What I'm seeing in my experiment is that raising the string height off the top yeilds a sound with less fundamental and more of the second partial. This change seems to be pretty easy to hear, if my listening tests are to be believed, wheras altering the break angle along does not make much difference, so far as we can tell from the data I've got. Of course, there's no such thing as a 'perfect' experiment, but IMO some data's better than no data.