For some years, a noise prevention concept for the protection of marine animals exists in Germany. Based on that, the underwater sound exposure level (SEL) due to pile driving at offshore wind farms (OWF) is required to be less than 160 dB re 1 µPa²s at a distance of 750 m. This value, however, is often exceeded so that the use of a soundproofing system is necessary. The Hydro Sound Damper (HSD) is a new, versatile method to reduce noise levels during offshore pile driving. To achieve this, elements of different sizes and materials which are fixed to fishing nets are used. The principle of operation and the effectiveness of these HSD elements were investigated in the laboratory and in situ under offshore conditions during different pile installations. During these offshore applications thorough measurements were performed which metered the propagation of the hydro sound and the vibrations of the sea floor at various distances and directions from the source. The evaluation of these data led to very promising results concerning underwater noise reduction. This article describes the theory and implementation of the HSD and focuses on the interpretation of the data from the hydro sound and vibration measurements.