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wave, its effect is little. This trend fits well with the monolithic muffler
characteristics.(2)The change trend of the simulation results and test results of sound
deadening capacity under each frequency are basically identical, which indicates that the
software SYSNOISE can play a better guiding role in analysis and design of the muffler.
But numerical simulation is different form measured value under specific frequency.
Fig. 3. Test values of transmission loss compared with the simulation value
The measured value is higher than the simulation under the same frequency. It is
mainly due to the following reasons:(1) .simplification is too idealized in the simulation
calculation, for example, take the exit of the muffler as the full absorption surface, but in
the actual testing process, because the muffler connect the duct directly, so it will produce
a certain disturbance to the sound wave transmission at the variable cross-section, and
inevitably have some impact on the sound deadening capacity of the muffler;
furthermore, take the muffler wall as the rigid wall in the calculation and overlook the
transmission effect of the muffler wall in the practice.(2) In the actual test, background
noise will be inevitably affected by the surrounding environment.
4 Analysis of Simulation Results of the Muffler Sound Field
Fig. 4 shows the sound deadening capacity of the muffler under each frequency. It can
be seen from the figure that the monolithic muffler is weak for the noise under the
medium and low frequency, size of the sound deadening capacity is 8dB-12dB. But to
the high frequency, the muffler have a greater impact, the peak volume of the sound
deadening capacity is 2400Hz, 3700Hz and 4100Hz. In general, to the frequency of
600Hz - 2200Hz, the sound deadening capacity is 15dB, to the frequency of 2200Hz-
4300Hz, the sound deadening capacity is 20dB around.
Fig.5 shows the internal sound pressure nephogram of the muffler under the frequency
of 1000Hz.It can be seen from the figure, with the acoustic transmission in the muffler,
due to itself attenuation and the effect of the sound-absorbing material. The sound
pressure of the sound wave show a step decrease, and the reduction in the
sound-absorbing material is significantly greater than in the air, which indicates that
sound-absorbing material play a very important role in the silencing effect of the muffler.
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