Exclusive to the Evans line, the Hydraulic Black Drum Heads have a layer of oil between the two plies to give you the fat, wet sound that was pioneered in the ‘70s. The oil acts as a natural muffler to decrease sustain and increase attack without affecting the feel of the head, as internal and external mufflers often do.
Evans Hydraulic's Incredible Percussive Sound
Hydraulics have a solid attack and a controlled, quick sustain, and are best suited for rock, and can be used both live and in studio.