1.3.4 Seats
Seats with spring cores originally serve only one function, 'cushioning'. The seat with a human occupant forms an oscillatory system, whose natural frequency is in the range of 2.5 – 5 Hz, depending on the spring rigidity of the upholstery, see figure.
The location of the resonance peak between seat and body acceleration of

reduces the suspension comfort significantly, particularly, if the body

natural frequency is high. This is the case in construction machines, agricultural tractors and to some extent in trucks, since body and seat resonances are close to each other.