Tackling outdoor noise pollution
Silence Light, is the name coined for a project that aims to address the growing demands of local communities that are close to noise sources, for effective reduction of the high noise levels they are exposed to. Until now, standard auto adaptive approaches have been employed for efficient noise control. These approaches are generally used for confined closed spaces. The problem at hand though, concerns open spaces, large residential areas, and moving sources, particularly aircrafts. The technique proposed by the Silent Light project is an auto adaptive technique designed to perform well in such conditions. Project partners, industries and university research institutes, have developed a full theoretical approach based on an intuitive idea, where a counter source system can reproduce a wave identical to the incident wave in a simple plane wave representation. From the theoretical solution, project partners have moved on to construct such counter sources necessary for their operation both in mechanical, electro-acoustical, computing and electronic equipment. The screening effect is obtained when the two waves, incident and rebuild, have the same space time characteristics. If there is a difference between them then performance is reduced. The operation of the necessary loud speakers requires an acoustical flow rate that is double the incident flow rate. Building two counter sources with two loudspeaker sources results either in a screen that reflects noise or may result in a screen that dissipates noise-depending on their configuration. A computational program “OMBRE ECRAN” has also been developed that simulates the performance of such screens. A full-scale prototype has been constructed with 15 counter sources designed in the form of street lamps at 1,2 meters distance apart. The prototype has proven the feasibility of the proposed technology. Difficulties with the electronic units have prevented until recently, a full-scale validation, but it is expected that such problems will be resolved in the immediate future. Project partners are seeking collaboration with local authorities in areas near European airports to construct a pilot active noise screen system with different configurations. The proposed technology will also be applied to other noise sources like motorways and railways.
