Optimum control of broadband noise by arrays of cylindrical units made of a recycled material

We report acoustic barriers that are designed to attenuate efficiently broadband noise. The barriers are structures consisting of only three layers of cylindrical units containing rubber crumb, a sound absorbing material obtained from recycling used tires. An optimization algorithm is developed to obtain the material distribution and dimensions of the building units giving the best attenuation properties for traffic noise, which is here chosen as an example in which the design procedure is applied. A good agreement is found between predictions and measurements for a 3 m height barrier that has been characterized in a transmission room.