The works Acusma and Microfônico by the group Chelpa Ferro not only represent an inflexion point in the group's trajectory but also make reference and allow an interpretation which places Chelpa Ferro amongst several other artists who experimented with sound-noise throughout the 20th century. Since the first modernists sound was object of artistic experiments, always informed by technological innovations. Thus the group inserts itself in such context and augments it, appropriating theirselves of everyday objects to produce their sound or by creating their own specially built apparatuses to amplify inexistent sounds, as in the works here discussed.