A mounting assembly includes first and second brackets. The inventive device is of the type that comprises a panel formed by a sheet which defines a support face that is adapted to co-operate with the car body clement and,which comprises means for locking to the car body clement and frangible means for releasing the car body element. The first wall has a hole for allowing fluid communication between the first fluid source and a first cavity of the acoustic dampener. A controller is coupled across a voltage sensor and effective thereby to determine a holdup time condition. The presence of the tapering portion can reduce the amount of used reagent.