Abstract: An electro-acoustical transducer arrangement for underwater antennas comprised of a plurality of hydrophones (10) which are arranged at equal distances in a linear array, and are to be disposed vertically above each other on a support. For reasons of a simplified assembly along with good receiving properties, the hydrophones (10), together with a reflector (11) disposed behind them in the direction of incoming sound, are embedded in an acoustically transparent rigid cast enclosure (20) of an elastomer, preferably polyurethane, which can be worked in a casting process. The connecting lines (12) of the hydrophones (10) of the enclosure 20 are combined in a common plug (13), which is accessible on a front end of the rigid cast enclosure (20). The rigid cast enclosure (20) is provided with devices for fastening the enclosure to the support.

Abstract: A method is provided for leak checking pipes or pipe networks wherein the leak check is effected by means of liquid under pressure in that a pressure change is determined. To improve the leak check by excluding temperature caused pressure changes, the liquid pressure in the pipes, pipe networks or pipe sections thereof is set to at least two different pressure levels as initial pressure for at least one respective pressure change determination. From the time standardized pressure changes associated with different initial pressures, a time standardized pressure change difference is formed and is compared with an allowed value with reference to the unit of time. A leak is determined to exist if the pressure change difference is greater than the allowed value.

Abstract: In apparatus for determining the direction of impinging sound waves according to the sum/difference principle, by forming a sum signal and two difference signals in a gradient ranging system composed of four omnidirectional piezoelectric hydrophones arranged in two pairs oriented orthogonally to each other, the hydrophones of each pair are conductively connected together to form a loop in which each terminal of each hydrophone is connected by a short circuit connection to a respective terminal of the other hydrophone of the same pair and the sum signal is derived by producing a signal proportional to the sum of the currents in the two loops and integrating such signal with respect to time.