ACTIVE ATTENUATORS FOR NOISE
H.G. Leventhall · 2024
The concept of active attenuators for noise is not new.a patent having been taken out over 00 years ago (1).Attempts to produce practical systems (2)-( 5),have not yet led to commercial results.However, recent developments in electronic techniques.feedback and control theory, and the formal theoretical basis for active attenuators make the practical possibilities now look better.The basic principle of active attenuators, as developed by Jessel and his coworkers (6) ( 7) is as follows.Consider a domain (1 nclosed by a surrounding surface 5. 111s primary source produces a pressure P at point Q in the domain.According to Huygen's principle.the primary source can be replaced by anumber cg secondary sources situated on the surrounding surface 5 so that the pressure P at Q due to the secondary sources is identical with that which was produced by the primary source.If new the primary source and secondary sources are operating together.the resultant at Q is the sum of the two.If the phases of the secondary sources are reversed.the pressure at Q is reduced to zero.