Evans '56 Calftone EQ4 Bass Drumheads are made with a 12mil film base and blended with unique materials these heads are thicker than our tom/snare 56' Calftone heads to help optimize the sound for larger drums, lower tunings, and greater tonal response. The approach is identical to how natural skins are used across a drum set in which thinner skins are used up top and thicker skins are used down low for increased bass response. As an EQ4, a fixed internal overtone control ring helps focus the tonal response of the drum. Can be be used as both a batter and resonant head. As a throwback to the year Evans was founded, Evans '56 calftone drumheads are for drummers looking for a vintage look and sound. These drumheads are a synthetic alternative to traditional calfskin and embody the calfskin look and sound but with the consistency, fit, and tuning range made standard with Level 360 Technology.