David's Tip of the Day: Beginner Tips #11 - Cupping, Part 2

The fully-closed cup, when playing acoustic, should only be used the moment before a "Wa" affect (closed, then open = Wa). Your cup should then remain open so that we can hear you play. The more open your cup, the less coloration from your hands. The more you close your cup (still leaving a little bit of room for sound to escape), the more hand muting you achieve, thus the more your hands color the sound. Experiment with this to hear the differences in color. How open or closed should you be?... this is personal preference.

In regards to a bullet mic... staying fully-closed is the default... opening every now and again for affect.