The Bow Stroke Variables
The bow stroke has several variables. An easy way to remember them is to say WASP:
Angle - parallel to the bridge produces the fullest tone
Placement - distance of the bow from the bridge
It is the sophisticated technical control of these variables in combination that results in the highest levels of artistic expression. Learning to control these variables while maintaining the bow parallel to the bridge and executing the movements of the left hand is the ultimate technical challenge that is presented to the string player.
All problems with tone can be analyzed by examining these factors:
1) The bow is not moving parallel to the bridge.
2) The bow is too close to the fingerboard, or too close to the bridge.
3) The bow is moving too fast, or too slow.
4) There is too much bow pressure (weight), or too little.
5) There is too much hair contacting the string, or too little.
It seems pretty straightforward, but as students advance and start playing more and more challenging repertoire, if the bow stroke basics are not under the student's control, playing with a poor tone can become an almost irreversible habit.