Abstract: A multi-layer product having improved acoustic properties is disclosed. The product contains a multi-wall sheet made of a thermoplastic composition and a first functional layer abutting to said sheet made of a material having shear modulus of 0.5 to 2000 MPa and loss factor tan ? of at least 0.1. An additional embodiment wherein the product further includes a second functional layer containing polymethyl methacrylate or polycarbonate, abutting said first functional layer is also disclosed. The product is especially suitable for making roofing elements.

Abstract: A device for deadening sound in pipelines comprising a chamber (1) positioned on the pipeline (2, 7) with a discontinuous pipeline section (3) projecting inwards at the chamber inlet and a discontinuous section (7) of the pipeline connected at the chamber outlet. Disposed within the chamber (1) opposite the opening of the pipeline section (3) there is a cover cap (4), in the form of a pipe resonator, whose side wall encloses the pipeline section (3) on one part of its length so that an annular channel (5) remains between the side wall and the pipe section (3). This permits the attainment of a very efficient sound deadening under certain geometric conditions.