Frequency-Selective Damping (FSD)
Frequency-selective damping (FSD) is a passive damper principle that uses an internal hydraulic path to respond differently to different patterns and frequencies of suspension motion.
How FSD responds
KONI’s FSD implementation adds a hydraulic control valve alongside the main damper valve. Sustained lower-frequency body motions and shorter, higher-frequency road inputs create different pressure and flow behaviour, allowing the damper characteristic to shift without electronic sensors, a controller, or an external power supply.
“Frequency selective” does not mean that the damper measures frequency as a digital signal or chooses a drive mode. Its mechanical valves react to the timing and pressure history created by damper motion. The result still depends on shaft velocity, stroke, force calibration, temperature, and the vehicle’s springs, tyres, and suspension geometry.
FSD is therefore adaptive in a mechanical sense but remains passive. It cannot command an arbitrary force or predict a road input. It is also distinct from an electronically controlled adaptive damper, whose controller can request a different valve state from sensor and vehicle data.
For passive valve behaviour and comparison with electronic damping, see Suspension Dampers.