Abstract: A three-dimensional, formable constructional element (1) with acoustic properties is provided, having a shell (2) with a low natural bending stiffness to which webs (3) are fixed so as to form a cellular grid. It is important that over the whole extent of the shell (2) the dimensions both of the webs (3) and of the cells (4) that they form together with the shell (2), and also the shape of the shell (2) itself, can be freely chosen. The cells (4) are closed on the outside on the side distant from the shell (2) by a foil system (5) that includes flattened, in particular lens-shaped, air pockets (6). In this way optimum acoustic tuning can be achieved in respect of the incident sound waves on the air-filled cell chambers utilizing frictional damping, so as to achieve maximum absorption of airborne sound.

Abstract: A sound insulation part for surfaces with known source-sink distribution, in particular in passenger spaces of motor vehicles, is provided, which is designed as a mass-spring system with discontinuities incorporated therein for the purpose of converting sources into sinks. In order to achieve a particularly effective sound insulation with low mass or light weight, the sound insulation part contains, over limited parts of its surface, closed cells (1) embedded in the spring (foam 3) and encased in coils (2). These cells (1) can be directed towards the heavy layer (4) or the panel (8) which the part adjoins, or can be wholly or partly in the intermediate region. The cells (1) can be gas- or air-filled. The foils (2) advantageously have masses of about 25 to 150 g/m.sup.2 of surface.