Noise causes corruption of communication, discomfort and reduction in physical and mental performance of men particularly those who are frequently exposed to high noise like that of farm tractors and machinery. Physically sound is made up of the oscillating waves of different frequencies and amplitudes. Frequencies can be expressed in Hertz (Hz) and amplitudes in decibels (dB). The experiment was carried out to examine the frequency and amplitudes of the sound of tractor noise as influenced by

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... esign of the exhaust mufflers. Two muffler designs were conceptualized based on the principle of reactive/reflective kind of muffling technique being low cost and widely used method of suppressing sound of the exhaust of tractor engine. The changes in diverse frequency contents and corresponding amplitude levels as affected by alteration in the exhaust muffler mountings were observed and analyzed in addition to the resulting sound pressure levels (SPLs). Audio spectrum analyzer (Spectrumview) and an acoustic spectrum analyzer (Spek) were employed for analysis of the sound clips to observe the periodical peak amplitude frequency observations, generation of frequency spectra and spectrograms of the tractor noise recorded at different engine speeds (RPM) under different muffler mountings. Frequency spectra indicated presence of higher frequencies in the noise (SPL) recorded at operator's ear level while at 10 m distance away from tractor, higher frequencies reduced considerably. The mean value of the peak amplitude frequencies observed at operator's ear level under no muffler mounted on exhaust outlet of the tractor was found 1502.6 Hz. The mean peak amplitude frequency under standard muffler was found lowest (i.e. 930.6 Hz) while under altered design of muffler (muffler-C), mean of the peak amplitude frequencies was found moderate (i.e. 1134.9 Hz). Statistical analysis of peak amplitude frequency observations under different muffler installation at different engine speed (RPM) revealed minimum values of standard deviation (Hz) and coefficient of variation (%) under muffler-C among peak amplitude frequency observations recorded under all mufflers at each RPM level. Standard deviation (Hz) and coefficient of variation (%) observed under muffler-C, muffler-S and under no muffler mounting were 232.2 Hz & 20.5%, 261.3 Hz & 28.1% and 453.4 Hz & 30.2% respectively. Spectrograms of the tractor noise recorded under no muffler exhibited erratic pattern of different frequency amplitudes over full length recorded sound of tractor noise and also showed presence of higher frequencies in greater amount particularly at higher engine speeds as compared to that of standard muffler and muffler-C viz. at 1000 RPM, higher frequency range such as 7.5-10.0 had respective percent amplitudes of 7.7, 5.1 & 0.4 percent under no muffler, muffler-S and muffler-C. At 1500 RPM, higher frequency range such as 7.5-10.0 had respective percent amplitudes of 10.4, 4.5 & 1.2 percent under no muffler, muffler-S and muffler-C. At 2000 RPM, higher frequency range such as 10-12.5 Hz had respective percent amplitudes of 4.5, 0.4 & 1.1 percent under no muffler, muffler-S and muffler-C. Thus, presence of higher frequencies were noticed in lesser amount under altered design of muffler (muffler-C) in comparison to standard & no muffler mountings.