From Evans:
For over 60 years, Evans has been an innovator in drumhead manufacturing and design. As the creator of the first synthetic drumhead and other revolutionary products such as EMAD, Hydraulics, and the UV1 series, Evans drumheads are designed with the intent of solving problems for drummers. Regarded for high quality and consistency all Evans drumheads are made in the USA and feature Level 360 Technology.
Evans EMAD resonant series features an offset 4″ microphone port in a single ply of 10mil film. Similar to the EMAD batter a black, noise-free plastic sleeve holds a foam dampening ring around the edge of the micorphone port which controls overtones; enhancing pitch focus and attack.