Recycled tyre granules can be used for manufacturing acoustic insulating and absorbing materials, with applications in buildings and road barriers. Therefore, the production of these materials is a valid alternative to the disposal into landfill or incineration of used tyres. This paper presents the results of sound absorbing coefficient measurements of several samples manufactured at the Acoustics Laboratory of the University of Perugia. The sound absorbing panels were produced by mixing rubber crumbs and an adequate binder in a proper proportion and then by compacting the obtained mix. The methodology used to evaluate coefficient of absorption coefficient is indicated in ISO 10534-2 standard, thanks to an impedance tube. The influence on the absorption performance of granules size, binder concentration, thickness and compaction ratio of the samples was investigated and an optimization process was carried out, in order to produce a sample with satisfying acoustical performances.