Evans EQ4 series features a single ply of 10mil film. A fixed internal overtone control ring focuses the tonal response of the drum. The frosted surface provides a warmer tone. Evans EQ4 series features a special, single ply of 10mil film that provides durability and a woody attack that speaks live and in the studio.. The fixed internal ring is proportional to the head size, optimizing control from 18" to 26"., 24" drum head with fixed internal overtone control ring proportional to the size of the head, An internal overtone control ring and a removable muffle ring coupled with dry-vents work extremely well with and without a microphone, Single ply of 10mil film offers full, wide-open tone, Also available in a clear version, All Evans drum heads are designed, engineered and manufactured in the USA