EVANS Hydraulic bass drumheads give you the fat, deep, short sound pioneered by rock and roll drummers in the 1970s. Made with a thin layer of oil between two plies of 7 mil film (6.5mil & 7.5mil for Hydraulic Black), these heads not only suppress unwanted overtones, but are also famously easy to tune. Hydraulics have a defined attack, short sustain, and dark tonal character. This bass drumhead also features Level 360 Technology and is available in clear, red, blue, and black.