The Effect Of The Internal Design Of An Absorptive Muffler On Car Exhaust Sound Levels /

Noise pollution in large urban or suburban areas can be associated with causing various health problems, such as hypertension, general worsened cardiovascular and mental health, and increased stress levels. Large amounts of this noise pollution can be attributed to the exhaust systems of cars. In this experiment, it was thought that comparing different designs for an absorptive muffler would yield noticeable differences in the exhaust’s loudness. The inside tubes of the absorptive muffler were 1.5 inches in outer diameter and 9 inches long, and were wrapped with ¼ inch of wool to act as the sound absorbing component. The first muffler design consisted of 11 rows of 7 evenly spaced holes, each with a diameter of 9 mm. The second muffler design contained 14 9 mm x 25 mm channels , arranged in 7 rows of 2 channels. Each channel row had one 9 mm hole, also evenly spaced. In between each row of channels on this design was a row of 7 evenly spaced holes, totaling 42 holes. These two designs were tested against the stock exhaust system. Sound level measuring points were set up at two locations, point A being 6 inches from the tip of the exhaust, at a 45 degree angle, and point B being 10 feet behind the exhaust in a garage, to mimic the reflective effect of buildings in a city. The car’s engine was revved to intervals of 500 rpm from Idle (1000 rpm) to 4000 rpm, with data measurements being taken from each location. The tubes were switched out, and the same processes was repeated a total of 30 times. ANOVAs and Tukey HSD tests were conducted with alpha=0.05 for each RPM interval of the testing groups at points A and B. It was found that both experimental pipes had significantly lower sound levels than the stock exhaust, but Pipe 2 was only marginally quieter than Pipe 1, and not significantly so in most cases. Because of this, more testing is necessary to determine the most effective design of an absorptive muffler