The Evans EMAD Clear Batter Drumhead comes with 2 damping rings, each of which affects the head's sound and pedal response. EMAD stands for Externally Mounted Adjustable Damping and this external system maximizes natural attack characteristics. It offers tremendous dynamic range (even at low dynamic levels where other systems fall short). The Evans drumhead also allows quick, easy adjustments without having to remove the head from the drum-an especially valuable feature during recording sessions. Evans EMAD bass drumheads come in 18", 20", 22", and 24" sizes.