THE CALCULATION OF ACTIVELY ABSORBING SILENCERS IN RECTANGULAR DUCTS

Active silencers can provide effective solutions especially for the control of low-frequency noise in ducts. To evaluate the performance of this technology in the early design stages it is necessary to predict the insertion loss and adjust the silencer sufficiently precisely to the specific requirements of an application. This paper describes different models for the calculation of actively absorbing wall linings with proportional feedback control applied in splitter silencers as used in rectangular air-conditioning ducts. On the basis of well-established theories for the calculation of passive splitter silencers and a network model of electro-acoustic lumped elements for the wall impedance of each active cassette, it is conceivable to determine their insertion loss. Starting with a rather basic approach, the computational model is refined to increase its modelling accuracy. It is shown that a combination of active wall linings with passive linings yields a high attenuation for a wide frequency band. The theoretical findings compare well with experimental results from a laboratory set-up.