A keyboard percussion instrument may include an improved dampening system that provides wave dampening or progressive dampening of the tone bars. A keyboard percussion instrument may also include a dampening system with a mechanism capable of retracting the damper without distorting the damper and capable of adjusting the leverage of the dampening system independently of the spring tension. A dampening system may further include an adjustable mounting for the damper that allows the dampening action to be adjusted at either end of the damper. A keyboard percussion instrument may further include an improved bar rail assembly that facilitates removability, adjustment of various dampening zones and/or vibration isolation.