Mufflers

By Michael Anthony (張銘元)、Ming-Han Ho (何明翰)

Mechanical mufflers are commonly used in automotive vehicles for reducing engine noise. These mufflers use passive methods such as sound absorbing materials, which are effective to reduce high frequency noise; however, the engine noise usually has dominant power at low frequencies. In addition, the sound absorbing material inside the muffler creating back pressure to the engine, degrading engine power delivery and thus increasing fuel consumption. We built an electronic muffler without any sound absorbing material using the ANC techniques. Two loudspeakers are installed inside the acrylic muffler as the secondary loudspeakers to generate the anti-noises for canceling the engine noise. The frequency mismatch problem resulting from acceleration or deceleration of engine speed is also resolved. Active noise equalization (ANE) function to change the amplitude of every harmonic is also developed and tested.