acoustical performance of a double-expansion chamber muffler: design and evaluation

Background: exhaust noise is known to be a major pollutant in the environment and workplaces due to the development of industry and transportation. exhaust noise can be reduced to normal levels by mufflers or silencers. a reactive muffler efficiently dampens noise at low frequencies by reflecting sound waves. therefore, muffler design is of great importance in exhaust noise reduction. transmission loss (tl) is an essential characteristic of mufflers, demonstrating their acoustical properties. any acoustical appliance is selected based on its damping performance and reliability. predicting tl through experimentation is different from theoretical calculations. methods: in the present study, a double-expansion chamber muffler was designed as a reflective muffler on a laboratory scale by equations. next, tl was evaluated by an impedance tube applying a 4-microphone technique to determine the acoustical performance of the designed muffler. results: findings revealed that the tl of the muffler at 312 hz frequency obtained 27.5 db agreement with the required tl of the muffler of 25 db. in addition, the tl of the muffler against frequency attenuates noise in broadband frequencies. conclusions: these results indicated that the built muffler provides desired tl for exhaust chambers. therefore, equations can be used as a precise method for muffler design. furthermore, multi-expansion chamber mufflers are useful for reducing noise at a wide range of frequencies.