analysis of combine harvester sound pressure level in one-third octave band frequency

workplace factors such as sound must have the minimum impact on the operators of combine harvester, so that they can guide and control many functions of the combine. in this study, some factors affecting the noise generated by two combine harvesters john deere 1055 and sampo 3065 were evaluated. research factors were engine speed, gear ratios, type of operation and microphone distance. the results of this study indicated that sound pressure level decreased with increasing center frequencies. the sound pressure level of john deere and sampo combine at center frequency of 4000 hz were 87.96 and 84.73 db, respectively. the results showed also that the maximum sound pressure of john deere and sampo combines were116db at frequency of 250 hz and 111.1db at frequency of 40 hz, respectively.