Communication presented at the 17th International Congress on Acoustics, Rome, 2-7 September 2001.Some basic properties of the impulse response (IR) of noise barriers are presented regarding the derivation of a global rating related to transmission loss of such devices. The possibility of representing every barrier by a unique IR is envisaged and some theoretical results derived from theories of Maekawa and Pierce are compared with experimental results in scale models.This study has been supported by the project AMB98-1029-C04-01, of the Spanish Plan Nacional de Investigacion Científica y Técnica (I+D).Peer reviewed