Improvement of sound barriers using headpieces with finite acoustic impedance

The paper deals with the reduction of the sound energy in the shadow region behind barriers by means of an attached body at the edge of the screen. The reflecting attributes of the barrier’s headpiece are described by a locally reacting impedance. Diffraction at ideal soft and hard bodies demonstrates the basic principle of tangential power transport parallel to their surface: the impedance must be chosen so that the tangential intensity near the edge is lowered, turning the incoming power in harmless directions. The differences due to finite impedances are then discussed. The physical principles are demonstrated in frozen pictures of the sound field for the different cases. Theoretical computations show considerably improved levels in the shadow zone for larger angles of diffraction. These are compared with empirical results, and practical applications are discussed.