Active Noise Attenuation Bw

A new method for globallw reducing the amount of unwanted Power radiated bv acoustic sourcesy bw means of active devices, is Proposed. After examining PreviouslY reported passive and active noise attenuating technioues, and finding them to be unsuitable for some applications, a new method is Proposed. The scheme involves Placin an attenuating source close to the noise sourcer driven in such a wav as to form a dipole out of the two sourcesy thus reducing the acoustic Power radiated. Eauations are derived relating the total Power radiated to the volume velocities of acoustic Point sources. Beginning with the simplest casey that of a single attenuatin sourcer a swstem is derived which Produces the reauired volume velocitv at the attenuating sourcey and an electrical model of this swstem is created. The model is used to verify svstem stability and to Predict the amount of noise reduction that mav be obtained. A laboratorw realization of the system is constructed having performance closelv matching that of the model. When tested under ideal conditionsy the svstem provides 16 db of noise reduction, within 2 db of the calculated theoretical maximum. For twpical noise sourcesy the reduction drops to 8 db. The need for multiple noise attenuating loops is discussed. Eautions are derived predicting the performance of such a system. A computer model is built to answer auestions of stability and performance. A laboratory system is constructed which verifies the computer model. A second attenuating loop increases the noise reduction from 8 to 12 db for one tvpical noise source. Thesis supervisor' Prof. Amar G. Bose, Professor of Electrical Engineerinr.