THE EFFICIENCY AND STABILITY OF A NOVEL ACTIVE SILENCER

The main feature of actively absorbing silencers is the continuous pre ssure loss along the whole length of its local reacting lining. In con trast to the principle of hybrid silencers where the wall impedance is tried to be optimised the feedback resonators described herein decrea se it. So especially a low frequency noise reduction in HVAC-duct syst ems is attained. Its high efficiency is strongly coupled to the stabil ity of the electro-acoustic control loop which depends on the paramete rs of its elements as well as on the surrounding ductwork. By means of a model consisting of lumped elements and wave impedances the electro -acoustic behaviour could be determined and measures for the stabilisa tion of the system could be developed. On a resulting exemplary silenc er of 1 m length the theoretically predicted insertion loss was experi mentally verified. Besides a peak of nearly 40 dB a broad band attenua tion of minimal 10 dB in the range of 63 Hz up to 200 Hz was achieved. Additionally the calculation and measurement of the reflection loss o f about 3 dB underlines the difference to the well known conventional active noise control with destructive interference. The research repor ted herein was supported by the Volkswagen-Stiftung and was carried ou t in co-operation with the Institute of Technical Acoustics and the In stitute of Telecommunication at the TU Dresden.