In the last years, a lot of papers have reported the results of researchers on metamaterials. The study of metamaterials represents a new research field in noise control. Metamaterials are artificial structures with periodical elements, made by the arrangement of scatterers in a square or triangular lattice configuration. The reason for such sound attenuation is due to the destructive interference of waves in the band of frequencies and the propagating wave has a decaying amplitude, which causes the sound attenuation to take place in the "band gap" region. Metamaterials are structures designed and built to control the propagation of the waves. So the metamaterials are new materials obtained by the interaction of artificial objects and geometric structures of regular shape. The term metamaterials was coined nearly a decade, the word metamaterial is made of two words: meta and material. The word meta, from ?metamorfosi? means a change in conditions, in this context it means later. The prefix ?meta? originates from the Greek word for ?after? or ?beyond". The latest applications are in the room acoustics, noise barriers. This paper describes the state of art of the applications of the metamaterials in the acoustics field and the applications of metamaterials for the sound attenuation of an acoustic barrier are reported. The acoustic measurements were done in a scale model (1:10). The sound attenuation is shown in particular frequencies range, in the function of the distance of the barrier elements.