| Summary: | 碩士 === 逢甲大學 === 機械工程學所 === 94 === Traditionally, the analytical solutions of the transmission loss (TL) of mufflers can be found if the acoustic mode of (0,1,0) is not excited. The acoustic waves in the expansion chamber before the cut-on frequency thus can be regarded as 1-D plane waves, and the results from theoretical, numerical and experimental solutions of the transmission loss agree well. For mufflers with extended tubes that in close propinquity, traditional research assumes a 1-D plane acoustic wave to occur, but this is an
irrational hypothesis due to the fact that acoustic waves propagate in 3-D form even at low frequencies. In this case, the peak of the transmission loss can occur at low frequencies around 700 Hz and the quantity of the TL is about 60 dB ~ 80 dB. When the extended tubes in mufflers are in close proximity and are the same distance apart, the effects of the resonators are identical regardless of any geometrical condition shifts. These effects also make a peak TL occur at low frequencies. The alteration of geometrical values only affects the peak frequency.
Therefore, engineers can use this phenomenon to attenuate sound energy at certain frequencies.
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