The synch and asynch 4 balls fountain patterns are two of the very basic four balls juggling patterns. In the four ball fountain pattern, two one-handed patterns are done at the same time, with each hand juggling two balls, so the balls never cross from one hand to the other. Each ball is thrown at a slight angle away from the center of the body to the same height. In the 4 balls synch fountain, both hands throw at the same time; in the 4 ball asynch fountain, the hands throw one at a time, make a throw from one hand and immediately make a throw from the other hand before the first ball peaks. Before learning a 4 ball fountain, you should already be good at juggling 2 balls in one hand, both your left and right hands.
Four Ball Synchronous Fountain
I personally find synchronous patterns easier to begin with than asynchronous ones. You have more time between the throws. No need to alternate our hands or throws. You can start by just doing 2 throws and count aloud when learning, “1-2 catch.” Then add an extra throw until you can get it solid, 1-2-3 catch. Add 1 throw at a time until you feel comfortable. The difficulty would be you have little room to avoid collisions since both hands throw at the same time. It makes it harder to keep the two columns in shape without collisions.