Open
More output / less volume. 
 ½ Open
When used with a floor monitor, you get an adjustible mix of your acoustic and electric sound. 
 Closed
More volume / less output.

Hear yourself better in any situation.
Improve intonation and tone quality.
Adjustable volume / output control.
Attaches easily to most microphones.
Folds in half for compact storage.
Stops annoying microphone feedback.
Cloth storage bag included.