Study On The Acoustic Performance Of Hybrid Silencers

The noise of large power equipments does great harm to staff. Due to the strong noise,hybrid silencers with better sound attenuation ability are demand, therefore, it is ofsignificance to master the design principles of silencers. The paper, aiming to how to fillsound-absorbing material to hybrid silencers reasonably, has studied the acoustic performanceof hybrid silencers by two aspects, such as sound-absorbing outer walls and air gap.The sound-absorbing outer walls are the most commonly structure form of hybridsilencers. For study the effects of the sound-absorbing outer walls on the acousticperformance of hybrid silencers, the transmission loss of hybrid silencers is calculated byanalytical approach in the paper. In the analytical process, the analytical expressions of thewave propagation in the dissipative chamber and the dissipative extension are described andthe sound boundary conditions of dissipative silencer full-packed housing are derived. Thetransmission loss results of the silencers are obtained by using mode match methods.Subsequent studies show the effects of the sound-absorbing material resistance, perforatedplate perforation and the silencer geometry dimension on the acoustic performance ofsilencers. In addition, the design principles of the sound-absorbing outer wall are alsoobtained.Air gap is widely used in room acoustic design due to its improvement of low frequencyperformance for sound-absorbing material. In order to improve the low frequencyperformance of silencers, this design is introduced into silencers as a new attempt in recentyears. The effects of air gap on the acoustic performance of hybrid silencers are studied byanalytical approach in the paper. In the analytical process, the characteristic equation of theduct is re-derived for study on the effects of perforation impedance parameter. Throughcalculation and analysis of the silencers transmission loss results, the effects of porosity, thethickness of air gap and the length of chamber on the acoustic performance of silencers arestudied.In order to verify the correctness of the air gap analytical theory, the air gap silencermodel and measuring ducts are processed completely. The sound characteristic of super fineglass fiber¢rifugal glass fiber and the transmission loss of the air gap silencers aremeasured. Through comparison between the experiment and theoretical results, the analyticaltheory of the air gap is proved to be correct.After obtained the effects of sound-absorbing outer walls and air gap on the acoustic performance of silencers, the acoustic performance of a complex hybrid silencer is optimizedby the finite element method. The hybrid silencer is optimized from the three aspects of airgap, sound-absorbing outer walls and inlet extension. The calculation show that the acousticperformance of the silencer is improved5dB-10dB after optimized.