Fore-and-aft transmissibility of backrests: Effect of backrest inclination, seat-pan inclination, and measurement location

Abstract

Car seats have inclined backrests and inclined seat-pans, but there has been little study of how the inclinations of the surfaces of a seat influence the transmission of fore-and-aft vibration through the backrest. The effects of backrest inclination and seat-pan inclination on the fore-and-aft transmissibilities of two seats (a car seat and a rigid seat with solid foam backrest) have been investigated in the laboratory. With 12 subjects, each seat was exposed to random fore-and-aft vibration in the frequency range 0.25–20 Hz with a vibration magnitude of 0.4 ms −2 rms. At six vertical locations on each backrest, the fore-and-aft transmissibilities of the backrests were measured with four backrest inclinations (90° (i.e. vertical), 105°, 100°, and 105°) and up to four seat-pan inclinations (0° (i.e. horizontal), 5°, 10°, and 15°). At all six measurement locations, there was a resonance of both backrests at about 4 Hz, which increased in frequency with increasing backrest inclination for the car seat but showed little change with inclination for the foam backrest. The inclination of the backrest had more influence at the bottom that at the top of the backrest of the car seat, but showed little variation with position on the foam backrest. Variations in seat-pan inclination had little influence on the resonance frequencies of either backrest at any location. Inclining the backrest and the seat-pan increased the transmissibility at resonance with the car seat, but produced little change with the foam backrest. It is concluded that both the backrest inclination and the seat inclination can affect the fore-and-aft transmissibility of backrests but, with moderate changes of inclination, the effects are not large.