Description from Woodbrass :
Developed in conjunction with Dave Weckl the Active Snare Dampening System is a free floating adjustable dampening system that allows you to easily control the sustain time on your snare drum. Once fixed to your snare drum and properly adjusted to allow the plunger to rest level on the drumhead you can then adjust the millisecond ?gate time? by sliding the O-ring up or down and adjust the amount of dampening by moving the plunger assembly closer of further away from the counterhoop. These simple adjustments allow you to customize your snare sound for different playing situations.