The core of the ProLite series is the sound spectrum provided by the Vintage Maple shells with reinforcement rings. These provide an unmistakably open sound and an enormously wide tuning range for practically all styles of music. Optimum Shell Measurement (O.S.M.): SONOR implements a slightly narrow outside shell measurement for optimized head contact. This is a SONOR specialty, resulting in excellent tone, better sustain and controlled decay. SONOR ProLite shell design: SONOR cross-laminates shells for superior stability, sonically enhanced resonance and spectacular tone. SONOR ProLite shell thickness: 9 plies for tom toms, floor toms and snare drums = 4 mm + 2 mm Dynamic Edge reinforcement rings at the edges. 12 plies for bass drums = 6 mm + 2 mm Dynamic Edge reinforcement rings at the edges.