Suspension seats are widely used to reduce whole-body
vibration exposure of seated operators. They attenuate vibration
mainly in the vertical z-axis, and are used in a wide variety
of off-road and on-road vehicles. Conventional seats (with
a cushion only) allow only for a small relative displacement
between the floor and the seated subject. For that reason,they are not effective in attenuating low frequency vibrations,
where the associated floor displacements are larger. They
have typically a resonance frequency around 4 Hz, and thus
are effective to reduce whole-body vibration exposure above
about 6 Hz4). On the other hand, suspension seats allow
greater relative displacement between the floor and the seated
subject, resulting in vibration attenuation at lower frequencies.
Suspension seat performances are mainly evaluated by the
SEAT value, representing the overall attenuation of the vibration
by the seat for a given excitation spectra. For a given
direction (mainly vertical zh-axis), the SEAT value is defined
as: