Passive dampers have a fixed amount of oil flow restriction, thus a fixed amount of damping (stifness)
An active damper can vary it's damping forced, to react to different driving/road conditions. They do this in 2 ways.
The older F45 system used a variable orifice, which is adjusted by a small actuator on the side of the amped.
The newer F55/MagneRide/MRC system is mechanically simpler, more reliable, and faster. It uses a fixed orifice, and magneto theological fluid. The fluid is full of microscopic metallic flakes. When an electromagnetic field is applied, the fluid thickens/becomes more viscous. The more electricity applied, the more viscous the fluid becomes, the former the damper becomes.
An active damper can vary it's damping forced, to react to different driving/road conditions. They do this in 2 ways.
The older F45 system used a variable orifice, which is adjusted by a small actuator on the side of the amped.
The newer F55/MagneRide/MRC system is mechanically simpler, more reliable, and faster. It uses a fixed orifice, and magneto theological fluid. The fluid is full of microscopic metallic flakes. When an electromagnetic field is applied, the fluid thickens/becomes more viscous. The more electricity applied, the more viscous the fluid becomes, the former the damper becomes.