Evans improved EC2 drumheads contain Evans" exclusive and patented Sound Shaping Technology (SST). Sound Shaping Technology allows the drumheads to be fully optimized for each individual size by varying the thickness and density of the damping material, ensuring greatly improved performance and tone across the entire kit. Unlike other heads that lack SST, Evans EC2s contain the ability to balance attack and tone for each size. The result is a drumhead series fine-tuned for attack, tone, length of sustain, and ease of tuning. Packed with a more balanced and pre-EQ"d sound across the full kit, the Evans EC2 with SST will make your toms sound better than you ever thought possible.