A tractor is the main element of agricultural mechanization. However, the use of tractors has some problems, including noise emissions. The exhaust system in tractors is responsible in addition to the transmission of gases released from combustion into the atmosphere, reducing engine noise. In this study, a combined resistance exhaust system was used to reduce noise emission in two common tractors in Iran (285 and 299 Massey-Ferguson tractors). Noise emission was measured and compared in ordinary and combined resistance exhaust systems. The tests of this study were carried out based on international standards for product noise emissions (ISO 7216 and ISO 5131) taking into account the type of the exhaust system, the position of the microphone, engine speed (rpm) and gear position. The number of tests for each tractor reached 72, which consisted of 24 treatments replicated three times. The data obtained were analyzed in the form of a factorial test which was based on a completely randomized design. The results showed that the effect of the main factors of engine speed, gear position, type of exhaust and microphone position on the noise emitted from the tractors was significant at 1% probability level. In all treatments, the combined resistance exhaust system reduced the sound pressure level and increased allowable driver exposure time compared to the ordinary exhaust system.
